CN100514824C - Switch type power converter and control circuit for pulse-width modulation - Google Patents

Abstract

The present invention relates to a pulse width modulation control circuit which is applied on a switching electric power converter that is feedback-controlled by the primary side. The switching electric power converter comprises a transformer, a power switch, a current sensing resistor and the pulse width modulation control circuit. The transformer is provided with a primary winding, a secondary winding and an auxiliary winding. The pulse width modulation control circuit comprises a sampling hold circuit, a transconductance circuit, an error amplifier and a pulse width modulation generator.

Description

A kind of switch type power converter and control circuit for pulse-width modulation

Technical field

The present invention relates to a kind of suitching type (switching-mode) power supply changeover device and pulse-width modulation (pulsewidth modulation; PWM) control circuit, particularly a kind of switch type power converter and control circuit for pulse-width modulation that is applied to primary side (primary-side) FEEDBACK CONTROL.

Background technology

Fig. 1 is an existing inverse excitation type converter (flyback converter) 100, the alternating voltage V that alternating-current voltage source 101 is provided _ACThrough electromagnetic interference (Electro-Magnetic Interference; EMI) after (bridge rectifier) 104 filtering of filter 102 and bridge rectifier and the rectification, obtain having the DC input voitage Vi of ripple, be coupled to first side winding (primary-side winding) Lp of transformer TX, power switch SW connects with the first side winding Lp of transformer TX, controller 106 output pulse width modulation signal Vpwm power switched switch SW are with secondary side (secondary-side) the generation output voltage V o of conversion input voltage Vi to transformer TX.Resistance R 3 is connected with the first side winding Lp of transformer TX, in order to detect first side winding electric current I p.In order to regulate (regulate) output voltage V o, voltage stabilizing adjuster 110 and optical coupler (optical coupler) 108 gives controller 106 from the feedback signal Vfb that the secondary side-draw one of transformer TX is directly proportional with output voltage, controller 106 is controlled the duty ratio (duty cycle) of pulse-width signal Vpwm according to feedback signal Vfb and first side winding electric current I p, thus regulated output voltage Vo.

Inverse excitation type converter 100 can provide output voltage adjusting accurately, but owing to need the relevant circuit of secondary side feedback, thereby the cost of control system is higher.

Summary of the invention

Purpose of the present invention is to propose a kind of low-cost advantage that has, and is applied to the switch type power converter and the control circuit for pulse-width modulation of primary side FEEDBACK CONTROL.

Control circuit for pulse-width modulation of the present invention, be applied to the switch type power converter of primary side FEEDBACK CONTROL, this switch type power converter comprises a transformer, a power switch, a current sense (currentsensing) resistance and a control circuit for pulse-width modulation.This transformer has first side winding, secondary side winding and an auxiliary winding, and wherein the voltage that should assist winding is exported the feedback voltage of a direct current behind over commutation; This power switch of connecting with this first side winding, the pulse-width signal that produced by this control circuit for pulse-width modulation switches, and this current sense resistance configuration is a sensing voltage with the current conversion of this first side winding between this power switch and ground connection.

The control circuit for pulse-width modulation of first embodiment of the invention comprises a sampling and keeps (sample and hold) circuit, a mutual conductance (transconductor) circuit, an error (error) amplifier and a pwm generator.Wherein, after this sample-and-hold circuit was made peak sample to this sensing voltage, the peak value with sensing voltage remained on output again; This transconductance circuit is coupled to the output of this sample-and-hold circuit, and the peak value of sensing voltage is converted to a current signal; This error amplifier has two inputs, and an input couples this current signal and this feedback voltage, and another input is coupled to a fixed reference potential, and this error amplifier produces an error signal; This pwm generator determines the duty ratio of this pulse-width signal according to this error signal.

The control circuit for pulse-width modulation of second embodiment of the invention comprises one first sample-and-hold circuit, one second sample-and-hold circuit, an operation processing unit, a transconductance circuit, an error amplifier and a pwm generator.Wherein, after this first sample-and-hold circuit is made peak sample to this sensing voltage, the peak value of this sensing voltage is remained on output; After this second sample-and-hold circuit is done initial value sampling to this sensing voltage, the initial value of this sensing voltage is remained on output; This operation processing unit deducts this initial value with the peak value of this sensing voltage, produces a sensing voltage variable quantity; This transconductance circuit is coupled to the output of this operation processing unit, and this sensing voltage variable quantity is converted to a current signal; This error amplifier has two inputs, and an input couples this current signal and this feedback voltage, and another input is coupled to a fixed reference potential, and this error amplifier produces an error signal; This pwm generator determines the duty ratio of this pulse-width signal according to this error signal.

Describe the present invention below in conjunction with the drawings and specific embodiments, but not as a limitation of the invention.

Description of drawings

Fig. 1 is existing inverse excitation type converter;

Fig. 2 (a) is the switch type power converter of the first embodiment of the present invention;

Fig. 2 (b) is that pulse-width signal, first side winding electric current and secondary side winding electric current among Fig. 2 (a) is in the oscillogram of DCM;

Fig. 3 (a) is the switch type power converter of the second embodiment of the present invention;

Fig. 3 (b) is that pulse-width signal, first side winding electric current and secondary side winding electric current among Fig. 3 (a) is in the oscillogram of continuous conduction mode.

Wherein, Reference numeral:

100-inverse excitation type converter

101,202-alternating-current voltage source

102,204-electromagnetic interface filter

104,206-bridge rectifier

106-controller

108-optical coupler

110-voltage stabilizing adjuster

The waveform of 200b, 300b-pulse-width signal

The waveform of 202b, 302b-first side winding electric current

The waveform of 204b, 304b-secondary side winding electric current

20,30-switch type power converter

200,300-control circuit for pulse-width modulation

212-error amplifier

214-PWM generator

220,330-sample-and-hold circuit

221,224-transistor

222,225-electric capacity

223-buffer

240-transconductance circuit

331-pulse produces circuit

350-operation processing unit

Embodiment

Fig. 2 (a) is the switch type power converter 20 of the first embodiment of the present invention, the alternating voltage V that alternating-current voltage source 202 is provided _ACAfter electromagnetic interface filter 204 and bridge rectifier 206 filtering and rectification, produce DC input voitage Vi, be coupled to the first side winding Lp of transformer TX, power switch SW connects with the first side winding Lp of transformer TX, PWM generator 214 produces pulse-width signal Vpwm and comes the power switched switch SW, and input voltage Vi is converted to output voltage V o.

Fig. 2 (b) is that pulse-width signal Vpwm, first side winding electric current I p among Fig. 2 (a) and secondary side winding electric current I s are at DCM (Discontinuous Conduction Mode; DCM) oscillogram.

In Fig. 2 (b), waveform 200b represents pulse-width signal Vpwm, and waveform 202b represents first side winding electric current I p, and waveform 204b represents secondary side winding electric current I s.(on-duty period) Ton during the responsibility of pulse-width signal Vpwm, power switch SW conducting, first side winding electric current I p increases to peak value (peak value) I gradually from 0 _PK, first side winding Lp so storage power

$\frac{1}{2}\mathrm{Lp}\&times;{I_{\mathrm{PK}}}^2=\frac{1}{2}\mathrm{Lp}{(\frac{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C200710088804E00141.png,C200710088804E00151.png"\; state="\{\{state\}\}">V</figure-callout>}1}{\mathrm{Lp}}\&times;\mathrm{Ton})}^2=\frac{1}{2}\&times;\frac{{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C200710088804E00141.png,C200710088804E00151.png"\; state="\{\{state\}\}">V</figure-callout>}1}^2}{\mathrm{Lp}}\&times;{\mathrm{Ton}}^2$ [formula 1]

Wherein V1 is the cross-pressure on the first side winding Lp.(off-duty period) Toff during the non-responsibility of pulse-width signal Vpwm, power switch SW closes, and the energy delivery that is stored in first side winding Lp is to secondary side winding Ls, and s is from peak I for the secondary side winding electric current I _SKReduce to 0 gradually.The diode D1 that is connected with secondary side winding is used for rectification, and its forward voltage (forward voltage) is Vf, and Ro is the output impedance of secondary side, and Io is the mean value of secondary side winding electric current I s, and the voltage at output capacitance Co two ends is output voltage V o.Toff during non-responsibility, the secondary side consumed energy of transformer TX is

Vo * Io * Toff+Io ²* Ro * Toff+Io * Vf * Toff [formula 2]

In fact, first side winding Lp energy stored not only passes to secondary side winding Ls, also passes to the auxiliary winding L aux of primary side, and still, the energy that auxiliary winding L aux consumes is very little, so can ignore.Therefore, formula 1 equals formula 2, all can get divided by Toff

$\mathrm{Vo}\&times;\mathrm{Io}+{\mathrm{Io}}^2\&times;\mathrm{Ro}+\mathrm{Io}\&times;\mathrm{Vf}=\frac{1}{2}\&times;\frac{{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C200710088804E00141.png,C200710088804E00151.png"\; state="\{\{state\}\}">V</figure-callout>}1}^2}{\mathrm{Lp}}\&times;\frac{{\mathrm{Ton}}^2}{\mathrm{Toff}}$ [formula 3]

Again because the cross-pressure on the secondary side winding Ls

V2=Vo+Io * Ro+Vf [formula 4]

Formula 3 is divided by Io, and substitution formula 4 can get

$V2=\mathrm{Vo}+\mathrm{Io}\&times;\mathrm{Ro}+\mathrm{Vf}=\frac{1}{2}\&times;\frac{{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C200710088804E00141.png,C200710088804E00151.png"\; state="\{\{state\}\}">V</figure-callout>}1}^2}{\mathrm{Lp}}\&times;\frac{{\mathrm{Ton}}^2}{\mathrm{Toff}}\&times;\frac{1}{\mathrm{Io}}$ [formula 5]

By formula 5 as can be known, when secondary side average current Io increases because load increases, cross-pressure V2 on the secondary side winding Ls and output voltage V o will descend, otherwise then rise.

Auxiliary winding L aux is at the primary side of transformer TX, and its winding current Iaux is through diode D2 rectification, and 1 charging produces the feedback voltage Vfb of direct current, the cross-pressure on the auxiliary winding L aux to capacitor C

V3=Vf2+Vfb [formula 6]

Wherein, voltage Vf2 is the forward voltage of diode D2.The turn ratio of supposing winding L p, Ls and Laux is n1:n2:n3, then secondary side winding voltage

V2=(n2/n3) * V3=N * V3 [formula 7]

Wherein, N is the turn ratio of secondary side winding Ls to auxiliary winding L aux.

Resistance R 1 and R2 series connection can be considered resitstance voltage divider, and the voltage at resistance R 2 two ends is Vfb1, Vfb1=Vfb * [R2/ (R1+R2)]

The current sense resistance R _CSLp connects with first side winding, first side winding electric current I p can be converted to sensing voltage V _CS

Control circuit for pulse-width modulation 200 comprises a sample-and-hold circuit 220, a transconductance circuit 240, an error amplifier 212 and a pwm generator 214.This sample-and-hold circuit 220 comprises MOS transistor 221 and 224, electric capacity 222 and 225, a buffer (buffer) 223 and an inverter 226.

When pulse-width signal Vpwm is the logic high levle (as the Ton of Fig. 2 (b)), since transistor 221 conductings, sensing voltage V _CSBe passed to electric capacity 222 chargings, when pulse-width signal Vpwm transfers the logic low level to (as the Toff of Fig. 2 (b)), transistor 221 is closed, and makes that the sampling voltage of electric capacity 222 is the peak I of first side winding electric current _PK(shown in Fig. 2 (b)) is multiplied by the current sense resistance R _CS, i.e. sensing voltage V _CSPeak value V _PK, transistor 224 conductings this moment charge to the sensing voltage peak value V of electric capacity 222 _PKBe passed to electric capacity 225 and maintain sensing voltage peak value V by buffer 223 _PKBehind the transconductance circuit 240 by a voltage transitions electric current, can obtain an electric current I x,

Ix=V _PK/ Rx [formula 8]

Error amplifier 212 has two inputs, and its inverting input couples being connected in series a little of this sense current Ix and resistance R 1 and R2, and this serial connection point voltage Vfb1 is proportional to feedback voltage Vfb; The non-inverting input of error amplifier 212 is coupled to a fixed reference potential Vref.

Can find out that by Fig. 2 (a) electric current I 1 of the resistance R of flowing through 1 is the summation of the electric current I x of the flow through electric current I 2 of resistance R 2 and the resistance R x that flows through, promptly

I1=I2+Ix [formula 9]

The flow through pressure drop of resistance R 1 of feedback voltage Vfb deduction electric current is the inverting input voltage Vfb1 of error amplifier 212,

Vfb-I1 * R1=Vfb1 [formula 10]

Because after whole reponse system is stable, the inverting input voltage Vfb1 of error amplifier 212 will equal the in-phase input end voltage Vref of error amplifier 212, promptly

Vfb1=Vref [formula 11]

With formula 11 and formula 9 substitution formula 10,, can obtain again because of I2=Vfb1/R2

Vfb=Vref * [1+ (R1/R2)]+Ix * R1 [formula 12]

Suppose that diode D1 and D2 have identical forward voltage, promptly Vf=Vf2 can get according to formula 4, formula 6 and formula 7

Vo=Vfb * N+ (N-1) Vf-Io * Ro [formula 13]

Can know by inference by formula 13, as secondary side average current Io because load increases the added-time of uprushing, output voltage V o will descend; By formula 5 as can be known, as secondary side average current Io because load increases the added-time of uprushing, cross-pressure V2 on the secondary side winding Ls will descend, can derive feedback voltage Vfb by formula 6 and formula 7 also descends thereupon, can derive the also decline thereupon of inverting input voltage Vfb1 of error amplifier 212 again by formula 10, thereby make the wrong difference DELTA Ve of the error signal Ve of output of error amplifier 212 produce, after pwm generator 214 detects this error amount Δ Ve, then improve the duty ratio of this pulse-width signal Vpwm, electric current I p on the first side winding Lp also raises sensing voltage V at this moment _CSAlso raise, electric current I x also raises, and can learn that by formula 12 Vfb also raises.

Can derive output voltage V o by formula 13 again and also will raise and rise with Vfb, can offset because of secondary side average current Io increases the decline that is caused.

Fig. 3 (a) is the switch type power converter 30 of second embodiment of the invention, and Fig. 3 (b) is that pulse-width signal Vpwm, first side winding electric current I p among Fig. 3 (a) and secondary side winding electric current I s are at continuous conduction mode (Continuous Conduction Mode; CCM) oscillogram.In Fig. 3 (b), waveform 300b represents pulse-width signal Vpwm, and waveform 302b represents first side winding electric current I p, and waveform 304b represents secondary side winding electric current I s.Ton during the responsibility of pulse-width signal Vpwm, power switch SW conducting, first side winding electric current I p is from initial value I _POIncrease to peak I gradually _PK, Toff during the non-responsibility of pulse-width signal Vpwm, power switch SW closes, and the energy delivery that is stored in first side winding Lp is to secondary side winding Ls, so secondary side winding electric current I s is from peak I _SKReduce to I gradually _SO

Compare with the first embodiment of the present invention, the control circuit for pulse-width modulation 300 of second embodiment increases a sample-and-hold circuit 330 and an operation processing unit 350.Sample-and-hold circuit 330 is compared with sample-and-hold circuit 220, and sample-and-hold circuit 330 increases by single (one shot) pulse-generating circuit 331; When this pulse-width signal Vpwm transferred the logic high levle to by the logic low level, this pulse produced circuit 331 and makes a short pulse, and this sample-and-hold circuit 330 utilizes this short pulse to sensing voltage V _CSAfter doing the initial value sampling, with the initial value V of sensing voltage _PORemain on output, this sensing voltage initial value V _POBe proportional to the initial current I among Fig. 3 (b) _POSample-and-hold circuit 220 is the same with the first embodiment of the present invention, at output output sensing voltage V _CSPeak value V _PKThis operation processing unit 350 is with the peak value V of this sensing voltage _PKDeduct this initial value V _PO, produce a sensing voltage variable quantity; Transconductance circuit 240 is coupled to the output of this operation processing unit 350 in a second embodiment, and this sensing voltage variable quantity is converted to electric current I x.

In the second embodiment of the present invention, this sensing voltage variable quantity is converted to electric current I x, when switch type power converter operates in continuous conduction mode, can reach the effect of carrying out more accurate control.

Certainly; the present invention also can have other various embodiments; under the situation that does not deviate from spirit of the present invention and essence thereof; those of ordinary skill in the art work as can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection range of the appended claim of the present invention.

Claims (14)

1. control circuit for pulse-width modulation is applied to the switch type power converter of primary side FEEDBACK CONTROL, and this switch type power converter comprises a transformer, a power switch, a current sense resistance and this control circuit for pulse-width modulation; This transformer has first side winding, secondary side winding and an auxiliary winding, and wherein, the voltage of this auxiliary winding is exported the feedback voltage of a direct current behind over commutation; This power switch is connected with this first side winding, and a pulse-width signal that produced by this control circuit for pulse-width modulation switches; This current sense resistance configuration is a sensing voltage with the current conversion of this first side winding between this power switch and ground connection, it is characterized in that this control circuit for pulse-width modulation comprises:

One sample-and-hold circuit, this sample-and-hold circuit remain on output with the peak value of this sensing voltage after this sensing voltage is made peak sample;

One transconductance circuit, this transconductance circuit is coupled to the output of this sample-and-hold circuit, and the peak value of this sensing voltage is converted to a current signal;

One error amplifier has two inputs, and an input couples this current signal and this feedback voltage, and another input is coupled to a fixed reference potential, and this error amplifier produces an error signal;

One pwm generator, this pwm generator determine the duty ratio of this pulse-width signal according to this error signal.

2. control circuit for pulse-width modulation according to claim 1, it is characterized in that, this sample-and-hold circuit is made peak sample to this sensing voltage when this pulse-width signal is the logic high levle, again the peak value of sensing voltage is remained on output when this pulsewidth modulation signal converting is the logic low level.

3. control circuit for pulse-width modulation according to claim 1 is characterized in that, this feedback voltage through a resitstance voltage divider dividing potential drop after, be coupled to an input of this error amplifier again.

4. control circuit for pulse-width modulation is applied to the switch type power converter of primary side FEEDBACK CONTROL, it is characterized in that this switch type power converter comprises a transformer, a power switch, a current sense resistance and this control circuit for pulse-width modulation; This transformer has first side winding, secondary side winding and an auxiliary winding, and wherein, the voltage of this auxiliary winding is exported the feedback voltage of a direct current behind over commutation; This power switch is connected with this first side winding, and a pulse-width signal that produced by this control circuit for pulse-width modulation switches; This current sense resistance configuration is a sensing voltage with the current conversion of this first side winding between this power switch and ground connection, and this control circuit for pulse-width modulation comprises:

After one first sample-and-hold circuit, this first sample-and-hold circuit are made peak sample to this sensing voltage, the peak value of sensing voltage is remained on the output of this first sample-and-hold circuit;

After one second sample-and-hold circuit, this second sample-and-hold circuit are done the initial value sampling to this sensing voltage, the initial value of sensing voltage is remained on the output of this second sample-and-hold circuit;

One operation processing unit deducts this initial value with the peak value of this sensing voltage, produces a sensing voltage variable quantity;

One transconductance circuit is coupled to the output of this operation processing unit, and this sensing voltage variable quantity is converted to a current signal;

One error amplifier has two inputs, and an input couples this current signal and this feedback voltage, and another input is coupled to a fixed reference potential, and this error amplifier produces an error signal;

One pwm generator determines the duty ratio of this pulse-width signal according to this error signal.

5. control circuit for pulse-width modulation according to claim 4, it is characterized in that, this first sample-and-hold circuit is made peak sample to this sensing voltage when this pulse-width signal is the logic high levle, the peak value of sensing voltage is remained on the output of this first sample-and-hold circuit when this pulsewidth modulation signal converting is the logic low level again.

6. control circuit for pulse-width modulation according to claim 4, it is characterized in that, this second sample-and-hold circuit comprises a pulse and produces circuit, when this pulse-width signal transfers the logic high levle to by the logic low level, this pulse produces circuit and makes a pulse, after this second sample-and-hold circuit utilizes this pulse that this sensing voltage is done the initial value sampling, the initial value of sensing voltage is remained on the output of this second sample-and-hold circuit.

7. control circuit for pulse-width modulation according to claim 4 is characterized in that, this feedback voltage through a resitstance voltage divider dividing potential drop after, be coupled to an input of this error amplifier again.

8. the switch type power converter with primary side FEEDBACK CONTROL is characterized in that, comprises:

One transformer has first side winding, secondary side winding and an auxiliary winding, and wherein, the voltage of this auxiliary winding is exported the feedback voltage of a direct current behind over commutation;

One power switch is connected with this first side winding, and this power switch is switched by a pulse-width signal;

One current sense resistance is disposed between this power switch and the ground connection, is a sensing voltage with the current conversion of this first side winding;

After one sample-and-hold circuit, this sample-and-hold circuit are made peak sample to this sensing voltage, the peak value of this sensing voltage is remained on output;

One transconductance circuit is coupled to the output of this sample-and-hold circuit, and the peak value of this sensing voltage is converted to a current signal;

One error amplifier has two inputs, and an input couples this current signal and this feedback voltage, and another input is coupled to a fixed reference potential, and this error amplifier produces an error signal;

One pwm generator determines the duty ratio of this pulse-width signal according to this error signal.

9. switch type power converter according to claim 8 is characterized in that, also comprises a resitstance voltage divider, and wherein this feedback voltage is coupled to an input of this error amplifier again through after this resitstance voltage divider dividing potential drop.

10. switch type power converter according to claim 8, it is characterized in that, this sample-and-hold circuit is made peak sample to this sensing voltage when this pulse-width signal is the logic high levle, again the peak value of sensing voltage is remained on output when this pulsewidth modulation signal converting is the logic low level.

11. the switch type power converter with primary side FEEDBACK CONTROL is characterized in that, comprises:

One transformer has first side winding, secondary side winding and an auxiliary winding, and the voltage that wherein is somebody's turn to do auxiliary winding is exported the feedback voltage of a direct current behind over commutation;

One power switch is connected with this first side winding, and this power switch is switched by a pulse-width signal;

One current sense resistance is disposed between this power switch and the ground connection, is a sensing voltage with the current conversion of this first side winding;

After one first sample-and-hold circuit, this first sample-and-hold circuit are made peak sample to this sensing voltage, again the peak value of sensing voltage is remained on the output of this first sample-and-hold circuit;

After one second sample-and-hold circuit, this second sample-and-hold circuit are done the initial value sampling to this sensing voltage, again the initial value of sensing voltage is remained on the output of this second sample-and-hold circuit;

One operation processing unit deducts this initial value with the peak value of this sensing voltage, produces a sensing voltage variable quantity;

One transconductance circuit is coupled to the output of this operation processing unit, and this sensing voltage variable quantity is converted to a current signal;

One error amplifier has two inputs, and an input couples this current signal and this feedback voltage, and another input is coupled to a fixed reference potential, and this error amplifier produces an error signal;

One pwm generator determines the duty ratio of this pulse-width signal according to this error signal.

12. switch type power converter according to claim 11 is characterized in that, also comprises a resitstance voltage divider, wherein, this feedback voltage is coupled to an input of this error amplifier again through after this resitstance voltage divider dividing potential drop.

13. switch type power converter according to claim 11, it is characterized in that, this first sample-and-hold circuit is made peak sample to this sensing voltage when this pulse-width signal is the logic high levle, the peak value of sensing voltage is remained on the output of this first sample-and-hold circuit when this pulsewidth modulation signal converting is the logic low level again.

14. switch type power converter according to claim 11, it is characterized in that, this second sample-and-hold circuit comprises a pulse and produces circuit, when this pulse-width signal transfers the logic high levle to by the logic low level, this pulse produces circuit and makes a pulse, after this second sample-and-hold circuit utilizes this pulse that this sensing voltage is done the initial value sampling, the initial value of sensing voltage is remained on the output of this second sample-and-hold circuit.

Images