CN101841242B - Switch power supply and method for adjusting output current thereof - Google Patents

Abstract

The invention relates to a switch power supply and a method for adjusting output current thereof. The switch power supply comprises a transformer, a pulse frequency modulation controller and a switch transistor; wherein the pulse frequency modulation controller inputs a feedback voltage and a sampling voltage, the feedback voltage is associated with the voltage output by the assistant coil, the sampling voltage is associated with the voltage of a second terminal of the switch transistor, the pulse frequency modulation controller also inputs a control signal, the pulse frequency modulation controller generates the driving voltage according to the feedback voltage, the sampling voltage and the control signal, so as to control the switch transistor to switch on or off of the primary coil, thus adjusting the on time and off time of the secondary coil. The invention improves output current regulating flexibility ratio of switch power supply.

Description

Switching Power Supply and output current regulating method thereof

Technical field

The present invention relates to field of power supplies, relate in particular to a kind of Switching Power Supply and output current regulating method thereof.

Background technology

Switching Power Supply receives extensive use owing to can produce stable output voltage and have high conversion rate.Switching Power Supply mainly is made up of pulse frequency modulated (PFM, Pulse Frequency Modulation) controller and power transistor, produces stable output voltage through transistorized the turning on and off of power controlling.

Referring to Fig. 1, this figure is a kind of typical constant current output inverse-excitation type switch power-supply in the prior art.

Switching Power Supply 100 comprises that mainly PFM controller 101, power transistor 102, sampling resistor 103, secondary coil current over-zero detect resistance 109 and 110 and transformer 115.Wherein, transformer 115 comprises primary coil 104, secondary coil 105 and ancillary coil 106.

AC-input voltage Vac inputs to first filter capacitor 114 after rectifier bridge 108 rectifications, the first direct voltage Vin on said first filter capacitor 114 is entire circuit work power supply.The first direct voltage Vin on said first filter capacitor 114 inputs to the feeder ear VCC of PFM controller 101 through starting resistance 112, and electric capacity 116 is the filter capacitor between said feeder ear VCC and the ground end GND.After electric capacity 116 was activated resistance 112 and charges to starting resistor, PFM controller 101 was started working.In addition, the voltage on the ancillary coil 106 is through said electric capacity 116 chargings of 113 pairs of rectifier diodes, thus required voltage when keeping said PFM controller 101 work.When said Switching Power Supply 100 is worked; Voltage on the secondary coil 105 charges to second filter capacitor 117 after diode 107 rectifications; The second direct voltage Vout on said second filter capacitor 117 is that external load provides required voltage; Wherein, resistance 111 is connected in parallel on said second filter capacitor 117 two ends as bleeder resistance.

The drive end OUT of said PFM controller 101 is connected to the control end of power transistor 102, makes power transistor 102 do high-frequency switch motion.The sampling resistor 103 back ground connection of connecting with power transistor 102, the sampling of the primary current that is used for primary coil 104 is flow through, and the sampled voltage that obtains after the sample conversion transferred to the peak current detection end Vcs of PFM controller 101.

The voltage at said secondary coil 105 two ends is reflected on the ancillary coil 106 according to turn ratio.Voltage on the ancillary coil 106 obtains feedback voltage after through zero passage detection resistance 109 and 110 dividing potential drops, and said feedback voltage transfers to the secondary current zero passage detection end Vfb of PFM controller 101.

Signal waveform when Fig. 2 is 100 work of constant current shown in Figure 1 output inverse-excitation type switch power-supply; Wherein, Vfb representes the feedback voltage that said secondary current zero passage detection end Vfb receives, and Ip representes the primary current that passes through in the said primary coil 104; Is representes the secondary current that passes through in the said secondary coil 105; Vcs representes the sampled voltage that said peak current detection end Vcs receives, and OUT representes the driving voltage of said drive end OUT output, is elaborated below in conjunction with Fig. 1 and Fig. 2.

End relation of the same name according to each coil in the transformer 115; The voltage waveform of the feedback voltage that current over-zero test side Vfb receives is similar with the voltage waveform at secondary coil 105 two ends, and its voltage magnitude is by the resistance value ratio decision of ancillary coil 106 and secondary coil 105 turn ratios and zero passage detection resistance 109 and 110.When secondary coil 105 conductings, secondary current Is flows through secondary coil 105, and this moment, feedback voltage was a positive voltage, and PFM controller 101 record feedback voltages are that the duration of positive voltage is ON time Ton, represent the length of secondary coil 105 ON times.During ON time Ton, secondary current Is descends with certain slope, and when secondary current Is dropped to zero, feedback voltage descended and zero crossing with free-running mode, like the time point A among Fig. 2.When PFM controller 101 detects the feedback voltage zero passage that inputs to current over-zero test side Vfb; PFM controller 101 stops the recording process of ON time Ton; Open the record of turn-off time Toff simultaneously, the duration length that on behalf of secondary coil 105, turn-off time Toff turn-off.Wherein, the conducting of secondary coil 105 is meant wherein has electric current to pass through (being that secondary current Is is not 0), and its shutoff is meant wherein do not have electric current to pass through (being that secondary current Is is 0).Time point B during turn-off time Toff, the driving voltage that the drive end OUT of PFM controller 101 produces is a high level, makes power transistor 102 conductings.In 102 conduction periods of power transistor, the primary current Ip that flows through primary coil 104 rises with certain slope.Primary current Ip flows through sampling resistor 103, thereby on sampling resistor 103, produces corresponding sampled voltage, and said sampled voltage transfers to the peak current detection end Vcs of PFM controller 101.When the sampled voltage of linearity rising surpasses the threshold voltage vt h of PFM controller 101 inner settings; The driving voltage that the drive end OUT of PFM controller 101 produces changes low level into; Power transistor 102 is turn-offed; The recording process of turn-off time Toff stops simultaneously, and the recording process of ON time Ton is opened again.Thus, the energy of turn-off time Toff storage in primary coil 104 is released in the secondary coil 105 during the ON time Ton of next switch periods, and Switching Power Supply gets into next switch periods.

Shown in the signal waveform among Fig. 2; The switch periods of Switching Power Supply 100 is above-mentioned ON time Ton and turn-off time Toff sum, and the average current Iavg that 100 of Switching Power Supplies output to load is the mean value of secondary coil 105 conducting electric current I s in Switching Power Supply 100 switch periods; The mean value of secondary current Is is relevant with the peak current Isk of the ON time Ton zero hour; The peak current Isk of secondary coil 105 is by the turn ratio decision of peak current Ipk and the primary coil 104 and the secondary coil 105 of the turn-off time Toff primary coil finish time 104, and the peak current Ipk of primary coil 104 is determined by PFM controller 101 inner threshold voltage vt h and sampling resistors 103.

H fixes when threshold voltage vt, and the resistance Rcs of sampling resistor 103 fixes, and the number of turn Ns of the number of turn Np of primary coil 104 and secondary coil 105 is fixedly the time, and the average current Iavg of Switching Power Supply 100 outputs can use formula (1) to be expressed as:

$\mathrm{Iavg}=\frac{1}{2}\·\mathrm{Ipk}\·\frac{\mathrm{Np}}{\mathrm{Ns}}\·\frac{\mathrm{Ton}}{\mathrm{Ton}+\mathrm{Toff}}=\frac{1}{2}\·\frac{\mathrm{Vth}}{\mathrm{Rcs}}\·\frac{\mathrm{Np}}{\mathrm{Ns}}\·\frac{1}{1+\frac{\mathrm{Toff}}{\mathrm{Ton}}}---\left(1\right)$

In the prior art; The internal control circuit of PFM controller 101 makes that the ratio of ON time Ton and turn-off time Toff is fixed value; Thereby according to formula (1), the value of average current Iavg also is a fixed value, makes the electric current of Switching Power Supply 100 outputs keep constant thus.

The control of the constant current of Switching Power Supply 100 output is to realize through the signal of telecommunication that detects primary coil 104 in the technique scheme, and need not the output current of Switching Power Supply 100 is sampled, thereby is called as former limit control technology.This technological advantage is: need not output current (being the electric current in the secondary coil 105) to Switching Power Supply 100 thus sample and save isolation feedback circuit based on photoelectrical coupler.This technological shortcoming is: after the internal circuit of PFM controller 101 was confirmed, fixing ON time Ton and turn-off time Toff ratio made that the output current that produces is a steady state value, can not regulate according to the actual requirements.

Also comprise another kind of Switching Power Supply in the prior art; Input to the PFM controller through the sampling output current and via photoelectric coupler isolation feedback generation feedback signal; The PFM controller changes the duty ratio of drive voltage signal according to external control signal and feedback signal, thereby realizes the output current adjusting.This technological shortcoming is: must the sampling output current and by photoelectric coupler isolation feedback, and cause complicated circuit and cost to increase thus; The sampling resistor of output current causes the decrease in efficiency of power-supply system; The signal to noise ratio of output current sampled signal is deterioration when little electric current, control deterioration in accuracy when causing output current less.

Summary of the invention

The problem that the present invention solves provides a kind of Switching Power Supply and output current regulating method thereof, improves the output current regulating flexibility ratio of Switching Power Supply.

For addressing the above problem, the invention provides a kind of Switching Power Supply, comprise transformer, pulse frequency modulated controller and switching transistor, wherein,

Said transformer comprises primary coil, secondary coil and ancillary coil, said secondary coil and the coupling of said primary coil, said ancillary coil and the coupling of said secondary coil;

Said switching transistor comprises control end, first end and second end, said control end input driving voltage, and first end connects the output of said primary coil;

Said pulse frequency modulated controller input feedback voltage and sampled voltage; Said feedback voltage is related with the voltage of said ancillary coil output; Said sampled voltage is related with the voltage of second end of said switching transistor; Said pulse frequency modulated controller is input control signal also; Said pulse frequency modulated controller produces said driving voltage according to said feedback voltage, sampled voltage and control signal, is used for conducting or shutoff that the control switch transistor switches said primary coil, with ON time and the turn-off time of adjusting said secondary coil.

Optional; Said Switching Power Supply also comprises rectifier diode and filter capacitor; The input of said rectifier diode connects an end of said secondary coil; The output of said rectifier diode and the other end of said secondary coil are connected the two ends of said filter capacitor respectively, are used for the electric current of said secondary coil is carried out rectification.

Optional; Said pulse frequency modulated controller comprises timing capacitor and control unit; Be used for realizing producing said driving voltage according to said feedback voltage, sampled voltage and control signal; Wherein, said timing capacitor is used for the ON time of said secondary coil and turn-off time are carried out timing, and the timing voltage at its two ends is used to produce said driving voltage; Said control unit produces the charging current of the said timing capacitor charging of confession and the discharging current of discharge according to said control signal, feedback voltage and sampled voltage; The duration of said charging current is the turn-off time of said secondary coil, and the duration of said discharging current is the ON time of said secondary coil.

Optional, said control unit comprises:

Discharge and recharge control unit; Discharge and recharge control signal and said driving voltage according to said feedback voltage, sampled voltage and timing voltage generation; The said control signal that discharges and recharges comprises first voltage and second voltage alternately; The duration of said first voltage is the duration of said charging current, and the duration of said second voltage is the duration of said discharging current;

Current generating unit, according to said control signal with discharge and recharge control signal and produce said charging current and discharging current.

Optional, said current generating unit comprises:

The charging current generation unit produces first charging current according to said control signal, said first charging current is exported as charging current when being first voltage in the said control signal that discharges and recharges;

The discharging current generation unit produces first discharging current according to said control signal, said first discharging current is exported as discharging current when being second voltage in the said control signal that discharges and recharges.

Optional, also comprising first resistance setting end, said current generating unit also comprises:

First current generator, the signal of setting end according to said first resistance of input produces first reference current;

Second current generator produces second reference current according to said control signal;

Said charging current generation unit comprises:

The first current mirror device is to producing first electric current behind the said first reference current mirror image;

The second current mirror device is to producing second electric current behind the said second reference current mirror image;

Wherein, said first electric current and second electric current carry out producing said first charging current behind the subtraction;

Said discharging current generation unit comprises:

The 3rd current mirror device is to producing the 3rd electric current behind the said first reference current mirror image;

The 4th current mirror device is to producing the 4th electric current behind the said second reference current mirror image;

Wherein, said the 3rd electric current and the 4th electric current carry out producing said first discharging current after the add operation.

Optional, the said control unit that discharges and recharges comprises:

First comparator compares the said feedback voltage and second reference voltage, produces the feedback comparison signal;

Second comparator compares said sampled voltage and the 3rd reference voltage, produces the sampling comparison signal;

Secondary current on-off timing device receives said timing voltage, feedback comparison signal and sampling comparison signal, produces said driving voltage and discharges and recharges control signal.

Optional, also comprise bias current sources, produce bias current according to said control signal, said bias current is imported said biasing resistor and sampling resistor, and said sampled voltage is regulated.

For addressing the above problem; The invention provides a kind of control method of switch power supply output current; Said Switching Power Supply comprise have primary coil, the transformer of secondary coil and ancillary coil, said secondary coil and the coupling of said primary coil, said ancillary coil is coupled with said secondary coil; The output current of said secondary coil is the output current of said Switching Power Supply; Comprise: the conducting or the shutoff of switching said primary coil according to feedback voltage, sampled voltage and control signal, with ON time and the turn-off time of adjusting said secondary coil, wherein; Said feedback voltage is related with the voltage of said ancillary coil output, and said sampled voltage is related with the electric current of said primary coil output.

Optional, the conducting or the shutoff of switching said primary coil according to feedback voltage, sampled voltage and control signal comprise: use the charge and discharge process of timing capacitor that the ON time and the turn-off time of said secondary coil are carried out timing; Charging interval and discharge time that charging current through adjusting said timing capacitor and discharging current are controlled said timing capacitor; The duration of said charging current is the turn-off time of said secondary coil, and the duration of said discharging current is the ON time of said secondary coil.

Optional, also comprise: the magnitude of voltage to said sampled voltage is adjusted, with the peak value of the electric current of adjusting said primary coil output.

Optional, the magnitude of voltage adjustment of said sampled voltage is comprised: produce bias current according to said control signal; Convert said bias current to bias voltage; With said bias voltage and the stack of said sampled voltage.

Compared with prior art, present technique has the following advantages:

The Switching Power Supply of present technique scheme and output current regulating method thereof are adjusted the ON time and the turn-off time of secondary coil through control signal; Thereby changed ON time and the ratio between the turn-off time, therefore improved the output current regulating flexibility ratio of Switching Power Supply.

In addition, the present technique scheme is also passed through the peak current of the magnitude of voltage of adjustment sampled voltage with the adjustment primary coil, and then the peak current of adjustment secondary coil, thereby has improved the output current regulating flexibility ratio of Switching Power Supply.

Description of drawings

Fig. 1 is the structural representation of a kind of Switching Power Supply of prior art;

Fig. 2 is the signal waveform sketch map of Switching Power Supply shown in Figure 1;

Fig. 3 is the structural representation of the Switching Power Supply of the embodiment of the invention;

Fig. 4 is a kind of structural representation of the PFM controller in the structure shown in Figure 3;

Fig. 5 is the circuit structure diagram of the module 301 in the structure shown in Figure 4;

Fig. 6 is the circuit structure diagram of the module 302 in the structure shown in Figure 4;

Fig. 7 is the signal waveform sketch map of the Switching Power Supply of the embodiment of the invention;

Fig. 8 is the control signal-output current characteristic curve chart of the Switching Power Supply of the embodiment of the invention;

Fig. 9 is the structural representation of another embodiment of the PFM controller in the structure shown in Figure 3.

Embodiment

For make above-mentioned purpose of the present invention, feature and advantage can be more obviously understandable, does detailed explanation below in conjunction with accompanying drawing and embodiment specific embodiments of the invention.

In the Switching Power Supply of prior art; Because make that the ON time of secondary coil and the ratio of turn-off time are fixed value after its circuit structure is fixing, according to formula (1), the mean value of its output current also is fixed value; Can't regulate according to the demand of practical application, flexibility ratio is lower.Though and adopt the photoelectric coupler isolation feedback arrangement can regulate output current, its complicated circuit, be difficult to integrated, and output current when less control precision relatively poor.

The Switching Power Supply of embodiment of the present invention comprises: transformer, pulse frequency modulated controller and switching transistor, wherein,

Said transformer comprises primary coil, secondary coil and ancillary coil, said secondary coil and the coupling of said primary coil, said ancillary coil and the coupling of said secondary coil;

Said switching transistor comprises control end, first end and second end, said control end input driving voltage, and first end connects the output of said primary coil;

The said input of pulse frequency modulated controller feedback voltage, sampled voltage and control signal; Said feedback voltage is related with the voltage of said ancillary coil output; Said sampled voltage is related with the voltage of second end of said switching transistor; Said pulse frequency modulated controller produces said driving voltage according to said feedback voltage, sampled voltage and control signal; Be used for conducting or shutoff that the control switch transistor switches said primary coil, with ON time and the turn-off time of adjusting said secondary coil.

The conducting of said secondary coil is meant has electric current output on the secondary coil, the shutoff of secondary coil is meant does not have electric current output on the secondary coil, and the mean value of the output current of said secondary coil (can be referred to as secondary current) is the output current of Switching Power Supply.

In the Switching Power Supply of technical scheme of the present invention; Combine feedback voltage and sampled voltage to produce driving voltage through external control signal; Said driving voltage is used to control the conducting or the shutoff of primary coil, with the ON time and the turn-off time of adjustment secondary coil, thereby has changed the ON time of secondary coil and the ratio of turn-off time; Improved the adjusting flexibility ratio of the output current (being the output current of secondary coil) of Switching Power Supply thus, and simple in structure be easy to integrated.

With reference to figure 3, this figure is the structural representation of the Switching Power Supply of the embodiment of the invention.

The Switching Power Supply 200 of present embodiment mainly comprises input rectifying unit 200a, output rectification unit 200b, transformer 215, switching transistor 202 and PFM controller 201.

Said input rectifying unit 200a comprises the rectifier bridge 208 and input filter capacitor 214 that is made up of four diodes, and the alternating voltage Vac that imports is carried out rectification, produces input voltage vin, and said input voltage vin is a direct voltage.

Said transformer 215 is an inverse-excitation type transformer; Comprise primary coil 204, secondary coil 205 and ancillary coil 206; The input of said primary coil 204 receives said input voltage vin; Said secondary coil 205 and said primary coil 204 couplings, said ancillary coil 206 and said secondary coil 205 couplings.

Said switching transistor 202 comprises control end, first end and second end; Switching transistor can be field-effect transistor; Its first end (being the drain electrode of field-effect transistor in the present embodiment) connects the output of said primary coil 204, the driving voltage that the said PFM controller 201 of its control end (being the grid of field-effect transistor in the present embodiment) input produces.In addition, in other embodiments of the invention, said switching transistor 202 can also be bipolar transistor, and its base stage is said control end, very said first end of its current collection, and it launches very said second end.

Said PFM controller 201 input feedback voltage, sampled voltage and control signals; Said feedback voltage is related with the voltage of said ancillary coil 206 outputs; Wherein said sampled voltage is related with the voltage of second end of said switching transistor 202; Said PFM controller 201 produces said driving voltage according to said feedback voltage, sampled voltage and control signal; Be used for conducting or shutoff that control switch transistor 202 switches said primary coil 204, with ON time Ton and the turn-off time Toff that adjusts said secondary coil 205, thus the ratio of adjustment ON time Ton and turn-off time Toff.

Said output rectification unit 200b carries out rectification to the secondary current that flows through in the said secondary coil 205; Specifically comprise: rectifier diode 207, filter capacitor 217 and resistance 211; The input of said rectifier diode 207 connects an end of said secondary coil 205; The output of said rectifier diode 207 and the other end of said secondary coil 205 are connected the two ends of said filter capacitor 217 respectively, are used for the electric current of said secondary coil 205 is carried out rectification.Said resistance 211 is connected in parallel on the two ends of filter capacitor 217, as bleeder resistance, does not carry out current drain when the output end vo ut of Switching Power Supply 200 connects load (when promptly opening a way).

Need to prove that the end that secondary coil described in the present embodiment 205 connects rectifier diode 217 is connected an end of switching transistor 202 with primary coil 204, and the voltage output end of said ancillary coil 206 is an end of the same name.

Said sampled voltage is related with the voltage of second end of said switching transistor 202 through sampling resistor 203.One end of said sampling resistor 203 connects second end (in this enforcement be source electrode for the example of field-effect transistor) of said switching transistor 202, and other end ground connection is sampled to the primary current Ip that flows through said primary coil 204, produces said sampled voltage.

In addition, said input voltage vin is via the power end VCC and ground end GND that input to said PFM controller 201 behind resistance 212 and the electric capacity 216.Also input to said power end VCC after signal of telecommunication process rectifier diode 213 rectifications that the voltage output end of said ancillary coil 206 produces, in order to stable supply power voltage to be provided.

The drive end OUT of said PFM controller 201 is connected to the control end of switching transistor 202, exports the switch motion that said driving voltage makes it to do high frequency.Connect with switching transistor 202 detection of the primary current Ip that is used for primary coil 204 of said sampling resistor 203 produces the peak current detection end Vcs that inputs to PFM controller 201 behind the sampled voltage.Sampled voltage described in the present embodiment is also related with the voltage of second end of said switching transistor 202 through biasing resistor 220, and concrete association process will be elaborated hereinafter.

Said feedback voltage is related with the voltage of the voltage output end of said ancillary coil 206 through partial pressure unit (comprising zero passage detection divider resistance 209 and 210 in the present embodiment), and the voltage on the said ancillary coil 206 feeds back to the secondary current zero passage detection end Vfb of PFM controller 201 after through said zero passage detection divider resistance 209 and 210 dividing potential drops.

Said PFM controller 201 also comprises signal input end DIM, is used for receiving control signal (being provided by variable voltage source 221 like Fig. 3).PFM controller 201 in the present embodiment comprises that also first resistance is set end RS1 and second resistance is set end RS2; Wherein first resistance is set the end that end RS 1 connects first resistance 218; The other end ground connection of said first resistance 218; Second resistance is set the end that end RS2 connects second resistance 219, the other end ground connection of said second resistance 219.

Need to prove; Also be integrated with the bias current sources (not shown) in the controller of PFM described in the present embodiment 201; The control signal that receives according to said signal input end DIM produces bias current; Said bias current is imported said biasing resistor 220 and sampling resistor 203, and the sampled voltage that said peak current detection end Vcs receives is regulated, and concrete adjustment process will be described in further detail below.

In the present embodiment; Said PFM controller 201 comes the ON time Ton and the turn-off time Toff of the secondary coil 205 of by-pass cock power supply 200 according to said control signal; Thereby the ratio of adjustment ON time Ton and turn-off time Toff; And change the peak value of the primary current Ip that flows through in the primary coil 204 and then the peak value of the secondary current Is that flows through in the adjustment secondary coil 205 through magnitude of voltage adjustment to the sampled voltage of said peak current detection end Vcs.Concrete adjusting gain is decided by the internal circuit configuration of said first resistance 218, second resistance 219, biasing resistor 220, sampling resistor 203 and PFM controller 201.Thus, the mean value Iavg of Switching Power Supply 200 output currents can be adjusted to the pairing fixed value of control signal, and the output voltage V out of this fixed value and load end and input voltage vin are irrelevant.

Fig. 4 is the internal circuit configuration sketch map of PFM controller 201 shown in Fig. 3, and Fig. 5 is the internal circuit configuration sketch map of module 301 shown in Figure 4, and Fig. 6 is the internal circuit configuration sketch map of module 302 shown in Figure 4, is elaborated below in conjunction with Fig. 3 to Fig. 6.

Said PFM controller 201 comprises timing capacitor and control unit, and said timing capacitor is used for the ON time Ton of secondary coil 205 and turn-off time Toff are carried out timing, and the timing voltage at its two ends is used to produce said driving voltage; Said control unit produces the charging current of the said timing capacitor charging of confession and the discharging current of discharge according to said control signal, feedback voltage and sampled voltage; The duration of said charging current is the turn-off time Toff of said secondary coil 205, and the duration of said discharging current is the ON time Ton of said secondary coil 205.

Control unit in the said PFM controller 201 comprises: discharge and recharge control unit (comprising module 520b shown in Figure 6,321 and 322); Discharge and recharge control signal Tons and said driving voltage according to said feedback voltage, sampled voltage and timing voltage generation; The said control signal Tons that discharges and recharges comprises first voltage and second voltage alternately; The duration of said first voltage equals the duration of said charging current, and the duration of said second voltage equals the duration of said discharging current; Current generating unit (comprise module shown in Figure 4 301 with module 520a shown in Figure 6), according to said control signal with discharge and recharge control signal Tons and produce said charging current and discharging current.

Said current generating unit comprises: charging current generation unit (comprising shown in Figure 4 313,314,318 and shown in Figure 6 505,503); Produce the first charging current Ich according to said control signal, the said first charging current Ich is exported as charging current when being first voltage at the said control signal Tons that discharges and recharges; Discharging current generation unit (comprising shown in Figure 4 315,316,319 and shown in Figure 6 506); Produce the first discharging current Idis according to said control signal, the said first discharging current Idis is exported as discharging current when being second voltage at the said control signal Tons that discharges and recharges.

Driving voltage described in the present embodiment is transferred to the output OUT that exports said PFM controller 201 after a driver 304 amplifies to by output PFM.In addition, also comprise power supply bias unit 303 in the said PFM controller 201, be used for the power supply signal between said feeder ear VCC and the ground end GND is handled, produce required power supply signal, reference voltage (like V1, V2, V3 among Fig. 4) etc.

Do further detailed description with reference to current generating unit described in figure 4 present embodiments below.Module 301 among Fig. 4 comprises four signal input parts (first input end, second input, the 3rd input and four-input terminal) and three signal output parts (first output, second output and the 3rd output).

Said first input end receives first reference voltage V 1; Second input connects said first resistance and sets end RS 1; The 3rd input connects said signal input end DIM; Four-input terminal connects said second resistance and sets end RS2.

The input Ch of the said first output link block 302; The input Dis of the second output link block 302; The 3rd output connects said peak current detection end Vcs.

Said current generating unit comprises in the module 301: first current generator 310, and the signal (through said first resistance 218) and first reference voltage V 1 of setting end RS1 according to said first resistance of input produce the first reference current Ia; Second current generator 312 is according to signal (through said second resistance 219) the generation second reference current Ib of control signal Vdim that inputs to said signal input end DIM and the said second resistance terminal RS2 of input; The charging current generation unit is according to the said charging current that discharges and recharges control signal Tons generation timing capacitor; The discharging current generation unit is according to the said discharging current that discharges and recharges control signal Tons generation timing capacitor.

Wherein, said charging current generation unit comprises: the first current mirror device 313, to producing the first electric current m1*Ia behind the said first reference current Ia mirror image; The second current mirror device 314, to producing the second electric current m2*Ib behind the said second reference current mirror Ib picture, the wherein said first electric current m1*Ia and the second electric current m2*Ib carry out producing the said first charging current Ich behind the subtraction through current subtraction device 318.

Said discharging current generation unit comprises: the 3rd current mirror device 315, to producing the 3rd electric current m3*Ia behind the said first reference current Ia mirror image; The 4th current mirror device 316 is to producing the 4th electric current m4*Ib behind the said second reference current Ib mirror image; Wherein, said the 3rd electric current m3*Ia and the 4th electric current m4*Ib carry out producing the said first discharging current Idis after the add operation through current adder 319.

In addition, said current generating unit also comprises the inverting amplifier 311 in the module 301, is used for that control signal Vdim is carried out anti-phase and amplifies back generation anti-phase control signal.Therefore, the input signal of second current generator 312 described in the present embodiment is said anti-phase control signal but not control signal Vdim itself.

Also comprise the 5th current mirror device 317 in the current generating unit in the present embodiment; As said bias current sources; The said second reference current Ib is carried out generating the 5th electric current m5*Ib (being bias current Ivcs) behind the mirror image; Input to said biasing resistor 220 and sampling resistor 203 after transferring to said peak current detection end Vcs; On said biasing resistor 220, produce bias voltage, after the stack of sampled voltage on the said sampling resistor 203, the voltage that inputs to said peak current detection end Vcs is adjusted.Need to prove; Said bias current Ivcs also flows into said sampling resistor 203 simultaneously; Make that the electric current that passes through in the sampling resistor 203 is the primary current Ip sum in bias current Ivcs and the primary coil 204, still, in a preferred embodiment; The resistance value of said biasing resistor 220 (being generally hundreds of ohm to thousands of ohms) is much larger than the resistance value (being generally several ohm) of sampling resistor 203, and therefore the said bias current Ivcs voltage that sampling resistor 203 produces of flowing through is ignored at this.

In conjunction with Fig. 6, said current generating unit also comprises first switch 505 and second switch 506.The input of said first switch 505 receives the said first charging current Ich; Control end receives the said inversion signal (via not gate 503) that discharges and recharges control signal Tons; The said first charging current Ich being exported as charging current when being first voltage (being specially low level) at the said control signal Tons that discharges and recharges, is said timing capacitor Ct charging; The output of said second switch 506 receives the said first discharging current Idis; Control end receives the said control signal Tons that discharges and recharges; The said first discharging current Idis being exported as discharging current when being second voltage (being specially high level) at the said control signal Tons that discharges and recharges, is said timing capacitor Ct discharge.First end of said timing capacitor Ct connects the output of said first switch 505 and the input of said second switch 506; The second end ground connection of said timing capacitor Ct; Through the charging process of said charging current and the discharge process of discharging current, make first end of said timing capacitor Ct produce said timing voltage.

The course of work in the face of said current generating unit is elaborated down.

In conjunction with Fig. 3 and Fig. 4; Said first current generator 310 is set end first resistance 218 that RS1 connect according to first reference voltage V 1 and first resistance and is produced the first reference current Ia, and the current value of the said first reference current Ia is definite with the ratio of the resistance value of first resistance 218 by the magnitude of voltage of first reference voltage V 1.The said first reference current electric current I a while is as the input of the first current mirror device 313 and the 3rd current mirror device 315; The current gain of the first current mirror device 313 and the 3rd current mirror device 315 is respectively m1 and m3; Thus; First electric current of the first current mirror device, 313 outputs is m1*Ia, and the 3rd electric current of the 3rd current mirror device 315 outputs is m3*Ia.

The control signal Vdim that 311 couples of signal input end DIM of said inverting amplifier go up input transfers to second current generator 312 after carrying out amplifying after the anti-phase.The gain of said inverting amplifier 311 is the negative slope characteristic, that is when said control signal Vdim increased, the anti-phase control signal that inverting amplifier 311 produces reduced thereupon; When said control signal Vdim reduced, the anti-phase control signal of the generation of inverting amplifier 311 increased thereupon.

Said second current generator 312 is set end second resistance 219 that RS2 connect according to the anti-phase control signal of said inverting amplifier 311 outputs and second resistance and is produced the second reference current Ib, and the ratio that the current value of the said second reference current Ib is set by the magnitude of voltage of the anti-phase control signal of inverting amplifier 311 outputs and second resistance between the resistance value of end second resistance 219 that RS2 was connected is definite.In other words, the current value of the said second reference current Ib is confirmed by the gain of said control signal Vdim, inverting amplifier 311 and the resistance value of second resistance 219.The said second reference current Ib is simultaneously as the input of the said second current mirror device 314, the 4th current mirror device 316 and the 5th current mirror device 317.The current gain of the second current mirror device 314, the 4th current mirror device 316 and the 5th current mirror device 317 is respectively m2, m4 and m5; Thus; The current value of second electric current of the said second current mirror device, 314 outputs is m2*Ib; The current value of the 4th electric current of the 4th current mirror device 316 outputs is m4*Ib, and the current value of the 5th electric current of the 5th current mirror device 317 outputs is m5*Ib.

Need to prove that current gain m1, m2, m3, m4 and the m5 of the said first current mirror device 313, the second current mirror device 314, the 3rd current mirror device 315, the 4th current mirror device 316 and the 5th current mirror device 317 is respectively by the internal components parameter determining of each current mirror device.

After doing subtraction, the second electric current m2*Ib that the first electric current m1*Ia that 318 pairs of said first current mirror devices 313 of said current subtraction device produce and the second current mirror device 314 produce produces the said first charging current Ich.After doing add operation, the 4th electric current m4*Ib that the 3rd electric current m3*Ia that 319 pairs the 3rd current mirror devices of said current adder 315 produce and the 4th current mirror device 316 produce produces the said first discharging current Idis.The said first charging current Ich inputs to the input of said first switch 505 via the input Ch of module 302, and the said first discharging current Idis inputs to the output of said second switch 506 via another input Dis of module 302.

From the above mentioned; Said current generating unit is according to the control signal Vdim that applies on the said signal input end DIM; Simultaneously the said first charging current Ich, the first discharging current Idis and bias current Ivcs are regulated, resistance value, second resistance that its concrete adjustment factor is set first resistance 218 of end RS1 by first resistance is set the gain m1, m2, m3, m4, m5 of gain, each current mirror device of resistance value, the inverting amplifier 311 of second resistance 219 of end RS2 end and is confirmed.

According to the above, the said first charging current Ich is expressed as:

Ich＝m1*Ia-m2*Ib (2)

The said first discharging current Idis is expressed as:

Idis＝m3*Ia+m4*Ib (3)

Said bias current Ivcs is expressed as:

Ivcs＝m5*Ib (4)

The said first charging current Ich and the first discharging current Idis charge to said timing capacitor Ct as charging current and discharging current respectively under the said control that discharges and recharges control signal Tons and discharge; With turn-off time Toff and the ON time Ton that adjusts said secondary coil 205, and then the ratio of adjustment ON time Ton and turn-off time Toff.

Do further detailed description in the face of the module 302 among Fig. 4 down.Said module 302 comprises four signal input parts and a signal output part;

The first input end Ch of said module 302 connects the output of said current subtraction device 318; The second input Dis connects the output of said current adder 319; The 3rd input connects said secondary current zero passage detection end Vfb; Four-input terminal connects said peak current detection end Vcs.The output signal of the output PFM of said module 302 amplifies the back via driver 304 and is exported by output OUT.

The four-input terminal of said module 302 connects an end of said biasing resistor 220 through said peak current detection end Vcs; The other end of biasing resistor 220 connects the end that said sampling resistor 203 links to each other with switching transistor 202, the other end ground connection of sampling resistor 203.

Said module 302 comprises: first comparator 321, second comparator 322 and module 320.

The input Ch of the first input end link block 302 of module 320; The input Dis of the second input link block 302 of module 320; The 3rd input Demag of module 320 connects the output of said first comparator 321; The four-input terminal Peak of module 320 connects the output of second comparator 322, and the output signal of module 320 is by the output PFM output of said module 302.

The positive input terminal of said first comparator 321 connects second reference voltage V 2, and negative input end connects secondary current over-zero test side Vfb, the 3rd input Demag of output link block 320.

The negative input end of said second comparator 322 connects the 3rd reference voltage V 3, and positive input terminal connects peak current detection end Vcs, the four-input terminal Peak of output link block 320.

Specify the course of work that discharges and recharges control unit in the present embodiment below in conjunction with module 302; The said control unit that discharges and recharges comprises said first comparator 321, second comparator 322 and secondary current on-off timing device (520b among Fig. 6 is integrated in the module 320).Need to prove,, comprised said timing capacitor Ct, first switch 505, second switch 506, not gate 503 in the said module 320 and discharged and recharged the secondary current on-off timing device 520b in the control unit with reference to figure 6.

Said secondary current on-off timing device 520b produces the said control signal Tons that discharges and recharges; The said first charging current Ich is charged to timing capacitor Ct as charging current when being first voltage at the said control signal Tons that discharges and recharges, the charging interval of timing capacitor Ct is corresponding to the turn-off time Toff of said secondary coil 205; The said first discharging current Idis is discharged to said timing capacitor Ct as discharging current when being second voltage at the said control signal Tons that discharges and recharges, the discharge time of timing capacitor Ct is corresponding to the ON time Ton of said secondary coil 205.

As the said control signal Tons that discharges and recharges when being first voltage (being specially low level); Certain time point during turn-off time Toff begins; The output PFM output high level of module 320; Behind driver 304, make said switching transistor 202 conductings, produce the primary current Ip of flow through primary coil 204 and switching transistor 202.

The said primary current Ip sampling resistor 203 of flowing through; On said sampling resistor 203, produce sampled voltage Vrcs; Meanwhile, flow through biasing resistor 220 (its resistance value is Rpk) and sampling resistor 203 (its resistance value is Rcs) back generation bias voltage Vrpk on said biasing resistor 220 of the bias current Ivcs that produces of said the 5th current mirror device 317.Said sampled voltage Vrcs and bias voltage Vrpk are superimposed after transfer to second comparator 322 by peak current detection end Vcs; Compare with the 3rd reference voltage V 3; Second comparator, 322 output high level when surpassing said the 3rd reference voltage V 3; The signal that makes four-input terminal Peak is a high level; Four-input terminal Peak is that second voltage (being specially high level) stops the charging to timing capacitor Ct for the high control signal Tons that discharges and recharges that makes said secondary current on-off timing device 520b produce, and the turn-off time Toff of secondary coil 205 regularly finishes, the output of secondary current on-off timing device 520b (being the output PFM of module 320) output low level; Behind driver 304, produce said driving voltage; Thereby switching transistor 202 is turn-offed, and secondary coil 205 begins to produce secondary current Is, via output rectification unit 200b output.

In the moment that said turn-off time Toff timing process finishes; The control signal Tons that discharges and recharges that said secondary current on-off timing device 520b produces is second voltage (being specially high level); Use the said first discharging current Idis said timing capacitor Ct to be discharged as discharging current; The ON time Ton of secondary coil 205 regularly begins thus, the ON time Ton of timing capacitor Ct correspondence discharge time secondary coil 205.When the energy of secondary coil 205 has been put; Secondary current Is zero passage constantly; Voltage on the ancillary coil 206 is zero passage also, and this voltage transfers to secondary current zero passage detection end Vfb after said zero passage detection divider resistance 209 and 210 dividing potential drops; And transfer to said first comparator 321, compare with second reference voltage V 2.When secondary current Is zero passage, the output that the feedback voltage of secondary current zero passage detection end Vfb is lower than second reference voltage V, 2, the first comparators 321 is a high level, and this signal transfers to the input Demag of module 320.When said secondary current on-off timing device 520b detects the moment that the Demag signal is a high level; The control signal Tons that discharges and recharges of its generation changes, and makes the discharge process of said timing capacitor Ct be stopped, and is corresponding; The ON time Ton of secondary coil 205 regularly finishes; Meanwhile, timing capacitor Ct restarts to be recharged, and the turn-off time Toff of next cycle begins regularly thus.

From the above mentioned; Secondary current on-off timing device 520b utilizes charging current (being specially the first charging current Ich in the present embodiment) and discharging current (being specially the first discharging current Idis in the present embodiment) that timing capacitor Ct is carried out charge and discharge and carries out timing; The duration of said charging process equals the turn-off time Toff of said secondary coil 205, and the duration of said discharge process equals the ON time Ton of said secondary coil 205.Because the duration (being the charging interval of said timing capacitor Ct) of said turn-off time Toff is by the capacitance decision of current value and the timing capacitor Ct of the first charging current Ich; The duration of ON time Ton (being the discharge time of said timing capacitor Ct) is by the capacitance decision of current value and the timing capacitor Ct of the first discharging current Idis; Therefore; The ratio of ON time Ton and turn-off time Toff is only by the decision of the ratio of the first charging current Ich and the first discharging current Idis, and irrelevant with the capacitance size of timing capacitor Ct.

In sum, according to formula (1), (2), (3), (4), the mean value Iavg of switch power supply output current can be expressed as:

$\mathrm{Iavg}=\frac{1}{2}\·\mathrm{Ipk}\·\frac{\mathrm{Np}}{\mathrm{Ns}}\·\frac{\mathrm{Ton}}{\mathrm{Ton}+\mathrm{Toff}}=\frac{1}{2}\·\frac{V3-\mathrm{Ivcs}.\mathrm{Rpk}}{\mathrm{Rcs}}\·\frac{\mathrm{Np}}{\mathrm{Ns}}\·\frac{1}{1+\frac{\mathrm{Idis}}{\mathrm{Ich}}}---\left(5\right)$

Wherein Np is the number of turn of primary coil 204, and Ns is the number of turn of secondary coil 205.Can know according to formula (5); When the device in the said Switching Power Supply 200 is all confirmed; If the magnitude of voltage of said control signal Vdim is fixed; The said first charging current Ich, the first discharging current Idis and bias current Ivcs are fixed value also, thereby make the mean value Iavg of output current of Switching Power Supply also accordingly for fixed value.

If the magnitude of voltage of said control signal Vdim changes; The current value of the then said first charging current Ich, the first discharging current Idis and bias current Ivcs also all changes thereupon; The peak current Ipk of primary current Ip in the ON time Ton of said thus secondary coil 205 and the ratio of turn-off time Toff and the primary coil 204 also is conditioned accordingly, thereby the output current that makes Switching Power Supply 200 produce changes.Therefore the present technique scheme can be regulated the output current of said Switching Power Supply 200 through regulating control signal Vdim.

Said control signal Vdim can by-pass cock power supply 200 the mean value Iavg of output current, its adjustment process is relevant with following factor: the circuit parameter of first current generator, second current generator and each current mirror device that the turn ratio of second resistance 219 that first resistance 218, second resistance that first resistance sets that end RS1 connects sets that end RS2 connects, biasing resistor 220, sampling resistor 203, primary coil 204 and secondary coil 205 and said PFM controller 201 are inner.

Particular circuit configurations in the face of said current generating unit is elaborated down.

In conjunction with Fig. 4 and Fig. 5; Inverting amplifier 311 in the said current generating unit comprises: the 3rd operational amplifier 408; Its positive input terminal receives said control signal Vdim; Its negative input end connects its output, and this syndeton makes said the 3rd operational amplifier 408 constitute a unity gain amplifier, and the signal of its output is followed said control signal Vdim; Four-operational amplifier 409; Its negative input end connects the output of said the 3rd operational amplifier 408 and connects the output of said four-operational amplifier 409 via the 4th resistance 413 through the 3rd resistance 412, and its positive input terminal connects reference voltage Vref (being generated by said power supply bias unit 303).Through above-mentioned connected mode, make that the gain of said inverting amplifier 311 is a negative slope, when promptly said control signal Vdim increased, the anti-phase control signal of generation reduced; Otherwise when said control signal Vdim reduced, the anti-phase control signal of generation increased.

First current generator 310 in the said current generating unit comprises first operational amplifier 401 and the first transistor 402.The positive input terminal of said first operational amplifier 401 receives first reference voltage V 1 (being generated by said power supply bias unit 303); The negative input end of said first operational amplifier 401 is set the end that end RS1 connects said first resistance 218, the other end ground connection of said first resistance 218 through first resistance.The connected mode of said the first transistor 402 is that source electrode is followed structure; Its grid connects the output of said first operational amplifier 401; Its source electrode is via said first resistance, 218 ground connection; Its drain electrode produces the said first reference current Ia as the current signal output end of said first current generator 310.

The first reference current Ia of the output of said first current generator 310 is expressed as:

$\mathrm{Ia}=\frac{V1}{R218}---\left(6\right)$

V1 representes the magnitude of voltage of said first reference voltage in the formula (6), and R218 representes the resistance value of said first resistance 218.

Second current generator 312 in the said current generating unit comprises second operational amplifier 410 and transistor seconds 411.The positive input terminal of said second operational amplifier 410 connects the output of said four-operational amplifier 409, and the negative input end of second operational amplifier 410 is via said second resistance, 219 ground connection.The connected mode of said transistor seconds 411 is that source electrode is followed structure; Its grid connects the output of said second operational amplifier 410; Source electrode is via said second resistance, 219 ground connection, and draining is the current signal output end of said second current generator 312, produces the said second reference current Ib.The said second reference current Ib is the ratio of resistance value of magnitude of voltage and said second resistance 219 of the anti-phase control signal that produces of inverting amplifier 311.

Need to prove; In the present embodiment; The input signal of said second current generator 312 is the anti-phase control signal that said inverting amplifier 311 produces; In other embodiments of the invention, can also said inverting amplifier 311 be saved, directly use the input of said control signal Vdim as second current generator 312.

The second reference current Ib of said second current generator, 312 outputs is expressed as:

$\mathrm{Ib}=\frac{\mathrm{Vref}+\frac{\mathrm{Vref}-\mathrm{<figure-callout\; id="412"\; label="Vdim\; R"\; filenames="HSA00000076983400041.png"\; state="\{\{state\}\}">Vdim</figure-callout>}}{R}\&CenterDot;R413}{R219}---\left(7\right)$

R413, R412 and R219 in the above-mentioned formula (7) representes the resistance value of said the 4th resistance 413, the 3rd resistance 412 and second resistance 219 respectively, and Vref representes the magnitude of voltage of said reference voltage Vref, and Vdim representes the magnitude of voltage of said control signal Vdim.

The first current mirror device 313 in the said current generating unit comprises a P transistor npn npn 403 and the 2nd P transistor npn npn 405; The source electrode of a said P transistor npn npn 403 connects positive source; Drain electrode connects the grid of a said P transistor npn npn 403 and receives the said first reference current Ia; The source electrode of said the 2nd P transistor npn npn 405 connects positive source, and grid connects the grid of a said P transistor npn npn 403.The current gain m1 of the said first current mirror device 313 is by the breadth length ratio decision of above-mentioned two P transistor npn npns, and the first electric current m1*Ia of its generation is by the drain electrode output of the 2nd P transistor npn npn 405.

The second current mirror device 314 in the said current generating unit comprises the 3rd P transistor npn npn 414, the 4th P transistor npn npn 416, a N transistor npn npn 417 and the 2nd N transistor npn npn 418; The source electrode of said the 3rd P transistor npn npn 414 connects positive source; Drain electrode connects the grid of said the 3rd P transistor npn npn 414 and receives the said second reference current Ib; The source electrode of said the 4th P transistor npn npn 416 connects positive source, and grid connects the grid of said the 3rd P transistor npn npn 414, the source ground of a said N transistor npn npn 417; Drain electrode connects the drain electrode of said the 4th P transistor npn npn 416 and the grid of a said N transistor npn npn 417; The source ground of said the 2nd N transistor npn npn 418, grid connect the grid of a said N transistor npn npn 417, and drain electrode produces the said second electric current m2*Ib.The current gain m2 of the said second current mirror device 314 is confirmed by they above-mentioned 4 transistorized breadth length ratios that comprise.

The 3rd current mirror device 315 in the said current generating unit comprises the 5th P transistor npn npn 404, the 3rd N transistor npn npn 406, the 4th N transistor npn npn 407 and a said P transistor npn npn 403; The source electrode of said the 5th P transistor npn npn 404 connects positive source; Grid connects the grid of a said P transistor npn npn 403; The source ground of said the 3rd N transistor npn npn 406; Drain electrode connects the drain electrode of said the 5th P transistor npn npn 404 and the grid of said the 3rd N transistor npn npn 406, and the source ground of said the 4th N transistor npn npn 407, grid connect the grid of said the 3rd N transistor npn npn 406; Drain electrode produces said the 3rd electric current m3*Ia, and its current gain m3 is confirmed by they above-mentioned 4 transistorized breadth length ratios that comprise.

The 4th current mirror device 316 in the said current generating unit comprises the 5th N transistor npn npn 419 and said the 3rd P transistor npn npn 414, the 4th P transistor npn npn 416 and a N transistor npn npn 417; The source ground of said the 5th N transistor npn npn 419; Grid connects the grid of a said N transistor npn npn 417; Drain electrode produces said the 4th electric current m4*Ib, and its current gain m4 is confirmed by they above-mentioned 4 transistorized breadth length ratios that comprise.

The 5th current mirror device 317 in the said current generating unit comprises the 6th P transistor npn npn 415 and said the 3rd P transistor npn npn 414; The source electrode of said the 6th P transistor npn npn 415 connects positive source; Grid connects the grid of said the 3rd P transistor npn npn 414, and drain electrode produces the 5th electric current m5*Ib (being said bias current Ivcs) and via said biasing resistor 220 and sampling resistor 203 back ground connection.

Current subtraction device 318 in the said current generating unit comprises said the 2nd P transistor npn npn 405 and the 2nd N transistor npn npn 418, and by the continuous subtraction of realizing electric current that fetches of above-mentioned two transistor drain.The electric current of said current subtraction device 318 outputs is the said first charging current Ich, and its value is (m1*Ia-m2*Ib).

Current adder 319 in the said current generating unit comprises said the 4th N transistor npn npn 407 and the 5th N transistor npn npn 419, and by the continuous add operation that fetches the realization electric current of above-mentioned two transistor drain.The electric current of said current adder 319 outputs is the said first discharging current Idis, and its value is (m3*Ia+m4*Ib).

According to the above; Said current generating unit is regulated the said first charging current Ich and the first discharging current Idis according to the control signal Vdim of input; And said bias current Ivcs is also regulated by control signal Vdim simultaneously, and adjustment process that it is concrete and parameter can be with reference to formula (2), (3), (4), (6), (7).Below in conjunction with Fig. 3, Fig. 4 and Fig. 6 the said control unit that discharges and recharges is elaborated.

Fig. 6 shows the structural representation of the module 302 among embodiment of the invention Fig. 4; The wherein said control unit that discharges and recharges comprises: first comparator 321; Feedback voltage and second reference voltage V 2 (being generated by said power supply bias unit 303) that said secondary current zero passage detection end Vfb is received compare, and produce the feedback comparison signal; Second comparator 322, sampled voltage and the 3rd reference voltage V 3 (being generated by said power supply bias unit 303) that said peak current detection end Vcs is received compare, and produce the sampling comparison signal; Secondary current on-off timing device 520b receives the timing voltage that said feedback comparison signal, sampling comparison signal and said timing capacitor Ct produce, and produces said driving voltage and discharges and recharges control signal Tons.Wherein, module 520a is the part of said current generating unit, and it is explained referring to preamble, just repeats no more here.

Said secondary current on-off timing device 520b comprises: d type flip flop 501, and its D input RL high level (" 1 "), input end of clock receives said feedback comparison signal; Rest-set flip-flop 502, its reset terminal connects the positive output end of said d type flip flop 501, and the set termination is received said sampling comparison signal, and its positive output end produces the said control signal Tons that discharges and recharges; The 3rd comparator 507, its positive input terminal is imported said timing voltage, and its negative input end is imported the 4th reference voltage V 4 (being generated by said power supply bias unit 303); NAND gate 509; One input end connects the output of said the 3rd comparator 507; Another input receives the said inversion signal (through not gate 508) that discharges and recharges control signal Tons; Its output connects the reset terminal of said d type flip flop 501, and its output produces said driving voltage via inverter 510 backs.

Said timing capacitor Ct among Fig. 6 carries out timing to the conducting and the turn-off time of said secondary coil 205, and its charge and discharge process is controlled by the said control signal Tons that discharges and recharges.

Specify the course of work that discharges and recharges control unit described in the present embodiment below.

During the ON time Ton of secondary coil 205; The said driving voltage that discharges and recharges control unit output (via output PFM) is a low level; Discharging and recharging control signal Tons signal is high level; Make second switch 506 conductings in the said current generating unit, first switch 505 turn-offs, and said timing capacitor Ct is discharged through second switch 506 by the discharging current (i.e. the first discharging current Idis) of input Dis input; After voltage signal in the secondary coil 205 is coupled through ancillary coil 206; (via the zero passage detection divider resistance among Fig. 3 209,210) transfers to secondary current zero passage detection end Vfb after dividing potential drop again; During secondary current Is decline zero crossing during said secondary coil 205 conductings; The feedback voltage that makes secondary current zero passage detection end Vfb receive is lower than said second reference voltage V 2, thereby makes the level (being said feedback comparison signal) of first comparator, 321 outputs uprise and input to said input Demag; The rising edge of input Demag makes the positive output end output high level of said d type flip flop 501; Positive output end zero clearing with rest-set flip-flop 502; Make that the said control signal Tons signal that discharges and recharges is a low level, promptly ON time Ton regularly finishes, turn-off time Toff time opening; Discharge and recharge control signal Tons and be low level and make 505 conductings of said first switch, second switch 506 turn-offs, and timing capacitor Ct is charged through first switch 505 by said charging current (i.e. the first charging current Ich), produces said timing voltage; When the timing voltage of the positive input terminal of the 3rd comparator 507 that connects as said timing capacitor Ct surpasses said the 4th reference voltage V 4; The 3rd comparator 507 output high level; The driving voltage that corresponding output PFM produces is a high level, and d type flip flop 501 is reset simultaneously; Afterwards, the drive signal of high level makes switching transistor 202 conductings through driver 304 output, and produces primary current Ip; Primary current Ip transfers to said peak current detection end Vcs after the sampled voltage that produces on the sampling resistor 203 is through the bias voltage stack adjustment that produces on the biasing resistor 220; When the voltage that receives as peak current detection end Vcs surpasses said the 3rd reference voltage V 3; The output voltage of second comparator 322 uprises and transfers to input Peak; Make the output of rest-set flip-flop 502 be set, discharge and recharge control signal Tons and be changed to high level once more that the turn-off time, Toff regularly finished; ON time Ton timing process is opened again, and the driving voltage of output PFM is changed to low level again makes switching transistor 202 turn-off; Timing capacitor Ct is discharged through second switch 506 once more, and secondary coil 205 conducting once more produces secondary current Is release energy storage wherein.

From the above mentioned, the ON time Ton of secondary coil 205 and turn-off time Toff correspond respectively to high level and the low duration that discharges and recharges control signal Tons, that is discharge time and the charging interval of the corresponding timing capacitor Ct of difference.And the discharge time of timing capacitor Ct and charging interval are determined by the capacitance size of the first discharging current Idis and the first charging current Ich and timing capacitor Ct respectively; Thereby the ratio of ON time Ton and turn-off time Toff is by the decision of the ratio of the first charging current Ich and the first discharging current Idis, and irrelevant with the capacitance size of timing capacitor Ct.According to formula (2) to formula (7); When the magnitude of voltage of said control signal Vdim fixedly the time; The ratio of the said first charging current Ich and the first discharging current Idis is also fixed; The mean value Iavg of the output current of Switching Power Supply 200 also fixes accordingly thus, therefore can obtain the mean value Iavg of corresponding output current through the magnitude of voltage of adjusting said control signal Vdim.

Fig. 7 is the signal waveform sketch map of the Switching Power Supply 200 of present embodiment, and wherein, Vfb representes the feedback voltage that secondary current over-zero test side Vfb receives; Vcs representes the voltage signal that peak current detection end Vcs receives; Vrcs representes the voltage signal on the sampling resistor 203; Vrpk representes the voltage signal on the biasing resistor 220; Ipk representes the peak value of primary current Ip; Isk representes the peak value of secondary electric current I s; Iavg representes the mean value of secondary electric current I s; Vct representes the timing voltage on the timing capacitor Ct; State 1 is illustrated in the magnitude of voltage of control signal Vdim corresponding waveform when higher; Corresponding waveform when the magnitude of voltage that state 2 is illustrated in control signal Vdim is medium value; State 3 is illustrated in the magnitude of voltage of control signal Vdim corresponding waveform when low.

As shown in Figure 7, the Switching Power Supply 200 in the present embodiment is along with the decline of the magnitude of voltage of said control signal Vdim, and corresponding the reducing of ON time Ton of secondary coil 205 and the corresponding increase of turn-off time Toff make corresponding the reducing of mean value Iavg of output current.In addition; With reference to state among the figure 72 and state 3, along with the increase of said bias current Ivcs, the also corresponding increase of bias voltage Vrpk at said biasing resistor 220 two ends; The voltage signal Vcs that makes peak current detection end Vcs receive rises to said the 3rd reference voltage V3 faster; Thereby said primary coil is comparatively fast turn-offed, cause primary current peak I pk and secondary current peak I sk to reduce accordingly, so the mean value Iavg of output current (being secondary current Is) also reduces accordingly.

Fig. 8 shows the corresponding relation curve chart of mean value Iavg of control signal Vdim and output current of the Switching Power Supply of the embodiment of the invention; What need explanation is that the curve of Fig. 8 is in Switching Power Supply, to obtain under all fixed prerequisite of other device parameters except that said control signal Vdim.Visible by Fig. 8, when said control signal Vdim increased, the also corresponding increase of the mean value Iavg of output current in practical application, can be adjusted the magnitude of voltage of said control signal Vdim according to needed output current.In addition, in other embodiments of the invention, if do not comprise the said inverting amplifier 311 shown in Fig. 4 in the said current generating unit, then the mean value Iavg of output current is along with the increase of control signal Vdim reduces accordingly.

Need to prove that with reference to figure 3 and Fig. 4, the 5th current mirror device 317 is used for said sampled voltage is adjusted with biasing resistor 220 described in the present embodiment.The bias current Ivcs that said the 5th current mirror device 317 produces flow through said biasing resistor 220 and sampling resistor 203 produce bias voltage the sampled voltage that said peak current detection end Vcs receives are adjusted.Wherein, the size of said bias current Ivcs receives the control of said control signal Vdim.In addition; Can also adopt among other embodiment of the present invention one be independent of said control signal Vdim bias current sources produce said bias current Ivcs; So that said sampled voltage is adjusted; Adjusting the peak current of said primary coil 204, and then realize adjustment to the peak current of said secondary coil 205.

PFM controller 201 in the foregoing description is integrated in the single chip; Said first resistance 218 and second resistance 219 are connected to said PFM controller 201 through chip pin; In other embodiments, said first resistance 218 and second resistance 219 also can be integrated in said chip internal.Its difference is; Because the restriction of semiconductor process technology, the resistance value that is integrated in the resistance of chip internal has certain deviation, so the scheme of the employing outer meeting resistance of present embodiment; Make its resistance value more accurate, the variation relation of corresponding input and output is control more easily also.

Fig. 9 shows the electrical block diagram of another embodiment of the PFM controller 201 shown in Fig. 3.Its overall structure is with said embodiment is similar before; Comprise timing capacitor 612 and control unit; Wherein control unit comprises current generating unit (comprising that 601 among Fig. 9 is to 608,610,611,613 to 617) and discharges and recharges control unit (comprising 640 among Fig. 9 and 623,625).

As shown in Figure 9; Said current generating unit comprises: timing current generating unit (comprising that 601 among Fig. 9 is to 608,610,611) receives said control signal Vdim; Produce regularly electric current I ct, the current value of said timing electric current I ct is regulated by the magnitude of voltage of said control signal Vdim; First reference current source 613; Export the first reference current Id; Said first reference current Id and said timing electric current I ct carry out producing behind the subtraction second charging current, said second charging current are exported as charging current when being first voltage (being specially low level) at the said control signal Tons that discharges and recharges; Second reference current source 616; Export the second reference current k*Id; Said second reference current k*Id and said timing electric current I ct carry out producing after the add operation second discharging current, said second discharging current are exported as discharging current when being second voltage (being specially high level) at the said control signal Tons that discharges and recharges.

Need to prove; First reference current source 613 is a reference current source common in the prior art described in the present embodiment; Said second reference current source 616 can be a current mirror device (gain is k); To producing the said second reference current k*Id behind the said first reference current mirror image, also can be a current source independently.

Wherein, said timing current generating unit comprises the 3rd current generator, produces the 3rd reference current Ic according to said control signal Vdim; Timing current mirror device is to producing said timing electric current I ct behind said the 3rd reference current Ic mirror image.The Vdim of control signal described in the present embodiment inputs to said the 3rd current generator after amplifying through the inverting amplifier anti-phase.

Wherein, said inverting amplifier comprises: the 6th operational amplifier 601, and positive input terminal receives said control signal Vdim, and negative input end connects its output; The 7th operational amplifier 602; Negative input end connects the output of said the 6th operational amplifier 601 and passes through the output that the 6th resistance 605 connects said the 7th operational amplifier 602 through the 5th resistance 604; Positive input terminal connects reference voltage, and output produces the anti-phase control signal.

Said the 3rd current generator comprises: the 5th operational amplifier 603, positive input terminal receive said anti-phase control signal, and negative input end connects said second resistance and sets end RS2; The 3rd transistor 606, grid connects the output of said the 5th operational amplifier 603, and source electrode connects said second resistance and sets end RS2, and drain electrode produces said the 3rd reference current Ic.

Said timing current mirror device comprises P transistor npn npn 607,608 and N transistor npn npn 610,611, to producing said timing electric current I ct behind said the 3rd reference current Ic mirror image.

In addition, also comprise another current mirror device in the present embodiment, constitute by P transistor npn npn 607 and 609; Be used for producing bias current Ivcs behind said the 3rd reference current Ic mirror image; Be used for said sampled voltage is adjusted, its adjustment process just repeats no more referring to preamble here.

The said control unit that discharges and recharges receives said feedback voltage, sampled voltage and timing voltage, produces said driving voltage and discharges and recharges control signal Tons.

Said structure and the previous embodiment that discharges and recharges control unit is similar, comprising: the 4th comparator 625, said feedback voltage and said second reference voltage V 2 are compared, and produce the feedback comparison signal; The 5th comparator 623 compares said sampled voltage and said the 3rd reference voltage V 3, produces the sampling comparison signal; Secondary current on-off timing device 640 receives said timing voltage, feedback comparison signal and sampling comparison signal, produces said driving voltage and discharges and recharges control signal Tons.

Said secondary current on-off timing device 640 is similar with previous embodiment, comprising: d type flip flop 622, and its D input RL high level, input end of clock receives said feedback comparison signal; Rest-set flip-flop 621, its reset terminal connects the positive output end of said d type flip flop 622, and the set termination is received said sampling comparison signal, and its positive output end produces the said control signal Tons that discharges and recharges; The 6th comparator 618, its positive input terminal receives said timing voltage, and its negative input end receives the 4th reference voltage V 4; NAND gate 620; One input end connects the output of said comparator 618; Another input receives the said inversion signal (producing via not gate 619) that discharges and recharges control signal Tons; Its output connects the reset terminal of said d type flip flop 622, and its output produces said driving voltage via inverter 624 backs.

Saidly discharge and recharge control signal Tons controls said timing capacitor 612 through the 3rd switch 614 and the 4th switch 615 charge and discharge process.The input of said the 3rd switch 614 is imported the said first reference current Id, and its control end receives the said inversion signal (producing via not gate 617) that discharges and recharges control signal Tons, and its output receives said timing electric current I ct.The input of said the 4th switch 615 receives said timing electric current I ct, and its control end is received the said control signal Tons that discharges and recharges, and its output receives the said second reference current k*Id; First end of timing capacitor 612 connects the output of said the 3rd switch 614 and the input of said the 4th switch 615, its second end ground connection, and its first end produces said timing voltage.

The embodiment of the invention also provides a kind of output current regulating method of Switching Power Supply; With reference to figure 3 and Fig. 4; Through adjusting the magnitude of voltage of said control signal Vdim, thereby adjust the charging current of said timing capacitor Ct and the current value of discharging current, made the ON time Ton of said secondary coil 205 and turn-off time Toff change; And then the ratio of said ON time Ton and turn-off time Toff regulated, thereby changed the mean value of switch power supply output current.In addition; Through regulating the magnitude of voltage of said control signal Vdim; Produce corresponding bias current Ivcs, said bias current is inputed in biasing resistor 220 and the sampling resistor 203 convert bias voltage into, with said bias voltage and sampled voltage stack; To adjust the size of the voltage that said peak current detection end Vcs receives; And then adjust the peak current of said primary coil 204, thus realized adjustment to the peak current of said secondary coil 205, therefore changed the mean value of the output current of Switching Power Supply 200.

To sum up; Switching Power Supply that technique scheme provides and output current regulating method thereof; Regulate the ON time and the turn-off time of secondary coil through control signal, thereby changed ON time and the ratio between the turn-off time, therefore improved output current regulating flexibility ratio.

In addition, also regulate the sampled voltage of primary current through obtaining behind the sampling resistor through control signal, and then the peak current of adjustment primary coil, thereby the peak current of change secondary coil has further been realized the flexible to output current.

Though the present invention with preferred embodiment openly as above; But it is not to be used for limiting the present invention; Any those skilled in the art are not breaking away from the spirit and scope of the present invention; Can utilize the method and the technology contents of above-mentioned announcement that technical scheme of the present invention is made possible change and modification, therefore, every content that does not break away from technical scheme of the present invention; To any simple modification, equivalent variations and modification that above embodiment did, all belong to the protection range of technical scheme of the present invention according to technical spirit of the present invention.

Claims (26)

1. a Switching Power Supply comprises transformer, pulse frequency modulated controller and switching transistor, wherein,

Said transformer comprises primary coil, secondary coil and ancillary coil, said secondary coil and the coupling of said primary coil, said ancillary coil and the coupling of said secondary coil;

Said switching transistor comprises control end, first end and second end, said control end input driving voltage, and first end connects the output of said primary coil;

Said pulse frequency modulated controller input feedback voltage and sampled voltage, said feedback voltage is related with the voltage of said ancillary coil output, and said sampled voltage is related with the voltage of second end of said switching transistor,

It is characterized in that,

Said pulse frequency modulated controller is input control signal also; Said pulse frequency modulated controller produces said driving voltage according to said feedback voltage, sampled voltage and control signal; Be used for conducting or shutoff that the control switch transistor switches said primary coil, with ON time and the turn-off time of adjusting said secondary coil; Wherein, said control signal is provided by variable voltage source;

Said pulse frequency modulated controller comprises timing capacitor and control unit; Be used for realizing producing said driving voltage according to said feedback voltage, sampled voltage and control signal; Wherein, Said timing capacitor is used for the ON time of said secondary coil and turn-off time are carried out timing, and the timing voltage at its two ends is used to produce said driving voltage; Said control unit produces the charging current of the said timing capacitor charging of confession and the discharging current of discharge according to said control signal, feedback voltage and sampled voltage; The duration of said charging current is the turn-off time of said secondary coil, and the duration of said discharging current is the ON time of said secondary coil.

2. Switching Power Supply according to claim 1; It is characterized in that; Said Switching Power Supply also comprises rectifier diode and filter capacitor; The input of said rectifier diode connects an end of said secondary coil, and the output of said rectifier diode and the other end of said secondary coil are connected the two ends of said filter capacitor respectively, are used for the electric current of said secondary coil is carried out rectification.

3. Switching Power Supply according to claim 1 and 2 is characterized in that, said control unit comprises:

Discharge and recharge control unit; Discharge and recharge control signal and said driving voltage according to said feedback voltage, sampled voltage and timing voltage generation; The said control signal that discharges and recharges comprises first voltage and second voltage alternately; The duration of said first voltage is the duration of said charging current, and the duration of said second voltage is the duration of said discharging current;

Current generating unit, according to said control signal with discharge and recharge control signal and produce said charging current and discharging current.

4. Switching Power Supply according to claim 3 is characterized in that, said current generating unit comprises:

The charging current generation unit produces first charging current according to the said control signal of the said pulse frequency modulated controller of input, said first charging current is exported as charging current when being first voltage in the said control signal that discharges and recharges;

The discharging current generation unit produces first discharging current according to said control signal, said first discharging current is exported as discharging current when being second voltage in the said control signal that discharges and recharges.

5. Switching Power Supply according to claim 4 is characterized in that, also comprises first resistance setting end, and said current generating unit also comprises:

First current generator, the signal of setting end according to said first resistance of input produces first reference current;

Second current generator produces second reference current according to the said control signal of importing said pulse frequency modulated controller;

Said charging current generation unit comprises:

The first current mirror device is to producing first electric current behind the said first reference current mirror image;

The second current mirror device is to producing second electric current behind the said second reference current mirror image;

Wherein, said first electric current and second electric current carry out producing said first charging current behind the subtraction;

Said discharging current generation unit comprises:

The 3rd current mirror device is to producing the 3rd electric current behind the said first reference current mirror image;

The 4th current mirror device is to producing the 4th electric current behind the said second reference current mirror image;

Wherein, said the 3rd electric current and the 4th electric current carry out producing said first discharging current after the add operation.

6. Switching Power Supply according to claim 5 is characterized in that, said first resistance is set end and is connected to ground through first resistance.

7. Switching Power Supply according to claim 5 is characterized in that, said first current generator comprises:

First operational amplifier, positive input terminal receive first reference voltage, and negative input end connects said first resistance and sets end;

The first transistor, grid connect the output of said first operational amplifier, and source electrode connects said first resistance and sets end, and drain electrode produces said first reference current.

8. Switching Power Supply according to claim 5 is characterized in that, also comprises second resistance setting end, and said second current generator comprises:

Second operational amplifier, positive input terminal receives the said control signal of the said pulse frequency modulated controller of input, and negative input end connects said second resistance and sets end;

Transistor seconds, grid connect the output of said second operational amplifier, and source electrode connects said second resistance and sets end, and drain electrode produces said second reference current.

9. Switching Power Supply according to claim 8 is characterized in that, said second resistance is set end and is connected to ground through second resistance.

10. Switching Power Supply according to claim 8 is characterized in that, also comprises inverting amplifier, the said control signal of importing said pulse frequency modulated controller is carried out inputing to after anti-phase is amplified the positive input terminal of said second operational amplifier.

11. Switching Power Supply according to claim 10 is characterized in that, said inverting amplifier comprises:

The 3rd operational amplifier, positive input terminal receives the said control signal of the said pulse frequency modulated controller of input, and negative input end connects its output;

Four-operational amplifier; Negative input end connects the output of said the 3rd operational amplifier through the 3rd resistance and connects the output of said four-operational amplifier through the 4th resistance; Positive input terminal connects reference voltage, and output connects the positive input terminal of said second operational amplifier.

12. Switching Power Supply according to claim 3 is characterized in that, said current generating unit comprises:

Regularly current generating unit produces regularly electric current according to the said control signal of importing said pulse frequency modulated controller;

First reference current source; Export first reference current; Said first reference current and said timing electric current carry out producing behind the subtraction second charging current, said second charging current are exported as charging current when being first voltage in the said control signal that discharges and recharges;

Second reference current source; Export second reference current; Said second reference current and said timing electric current carry out producing after the add operation second discharging current, said second discharging current are exported as discharging current when being second voltage in the said control signal that discharges and recharges.

13. Switching Power Supply according to claim 12 is characterized in that, said timing current generating unit comprises:

The 3rd current generator produces the 3rd reference current according to the said control signal of importing said pulse frequency modulated controller;

Timing current mirror device is to producing said timing electric current behind said the 3rd reference current mirror image.

14. Switching Power Supply according to claim 13 is characterized in that, also comprises second resistance setting end, said the 3rd current generator comprises:

The 5th operational amplifier, positive input terminal receives the anti-phase control signal, and negative input end connects said second resistance and sets end; Wherein, said anti-phase control signal is to obtain after being amplified via the inverting amplifier anti-phase by the control signal of the said pulse frequency modulated controller of input;

The 3rd transistor, grid connect the output of said the 5th operational amplifier, and source electrode connects said second resistance and sets end, and drain electrode produces said the 3rd reference current.

15. Switching Power Supply according to claim 14 is characterized in that, also comprises inverting amplifier, the said control signal of importing said pulse frequency modulated controller is carried out inputing to after anti-phase is amplified the positive input terminal of said the 5th operational amplifier.

16. Switching Power Supply according to claim 15 is characterized in that, said inverting amplifier comprises:

The 6th operational amplifier, positive input terminal receives the said control signal of the said pulse frequency modulated controller of input, and negative input end connects its output;

The 7th operational amplifier; Negative input end connects the output of said the 6th operational amplifier through the 5th resistance and connects the output of said the 7th operational amplifier through the 6th resistance; Positive input terminal connects reference voltage, and output connects the positive input terminal of said the 5th operational amplifier.

17. Switching Power Supply according to claim 3 is characterized in that, the said control unit that discharges and recharges comprises:

First comparator compares the said feedback voltage and second reference voltage, produces the feedback comparison signal;

Second comparator compares said sampled voltage and the 3rd reference voltage, produces the sampling comparison signal;

Secondary current on-off timing device receives said timing voltage, feedback comparison signal and sampling comparison signal, produces said driving voltage and discharges and recharges control signal.

18. Switching Power Supply according to claim 17 is characterized in that, said secondary current on-off timing device comprises:

D type flip flop, its D input RL high level, input end of clock receives said feedback comparison signal;

Rest-set flip-flop, its reset terminal connects the positive output end of said d type flip flop, and the set termination is received said sampling comparison signal, and its positive output end produces the said control signal that discharges and recharges;

The 3rd comparator, its positive input terminal is imported said timing voltage, and its negative input end is imported the 4th reference voltage;

NAND gate, one input end connect the output of said the 3rd comparator, and another input receives the said inversion signal that discharges and recharges control signal, and its output connects the reset terminal of said d type flip flop, and its output produces said driving voltage after via an inverter.

19. Switching Power Supply according to claim 1 is characterized in that, said feedback voltage is related with the voltage of said ancillary coil output through partial pressure unit.

20. Switching Power Supply according to claim 1 is characterized in that, said sampled voltage is related with the voltage of second end of said switching transistor through sampling resistor.

21. Switching Power Supply according to claim 1 is characterized in that, said sampled voltage is related with the voltage of second end of said switching transistor through sampling resistor, biasing resistor.

22. Switching Power Supply according to claim 21 is characterized in that, also comprises bias current sources, produces bias current according to said control signal, said bias current is imported said biasing resistor and sampling resistor, and said sampled voltage is regulated.

23. Switching Power Supply according to claim 1 is characterized in that, also comprises the input rectifying unit, and alternating voltage is carried out rectification, produces the input voltage of direct current and inputs to the input of said primary coil.

24. the output current regulating method of a Switching Power Supply; Said Switching Power Supply comprise have primary coil, the transformer of secondary coil and ancillary coil, said secondary coil and the coupling of said primary coil, said ancillary coil is coupled with said secondary coil; The output current of said secondary coil is the output current of said Switching Power Supply; It is characterized in that, comprising: the conducting or the shutoff of switching said primary coil according to feedback voltage, sampled voltage and control signal, with ON time and the turn-off time of adjusting said secondary coil; Wherein, Said feedback voltage is related with the voltage of said ancillary coil output, and said sampled voltage is related with the electric current of said primary coil output, and said control signal is provided by variable voltage source;

Said conducting or shutoff of switching said primary coil according to feedback voltage, sampled voltage and control signal comprises: use the charge and discharge process of timing capacitor that the ON time and the turn-off time of said secondary coil are carried out timing; Charging interval and discharge time that charging current through adjusting said timing capacitor and discharging current are controlled said timing capacitor; The duration of said charging current is the turn-off time of said secondary coil, and the duration of said discharging current is the ON time of said secondary coil.

25. the output current regulating method of Switching Power Supply according to claim 24 is characterized in that, also comprises: the magnitude of voltage to said sampled voltage is adjusted, with the peak value of the electric current of adjusting the output of said primary coil.

26. the output current regulating method of Switching Power Supply according to claim 25 is characterized in that, the magnitude of voltage adjustment of said sampled voltage is comprised: produce bias current according to said control signal; Convert said bias current to bias voltage; With said bias voltage and the stack of said sampled voltage.

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