CN109639151A

CN109639151A - Constant-current control circuit and constant current control method for LLC resonant converter

Info

Publication number: CN109639151A
Application number: CN201910054905.XA
Authority: CN
Inventors: 汤仙明; 谢小高; 姚云龙; 陈华捷; 吴建兴
Original assignee: Hangzhou Silan Microelectronics Co Ltd
Current assignee: Hangzhou Silan Microelectronics Co Ltd
Priority date: 2019-01-21
Filing date: 2019-01-21
Publication date: 2019-04-16
Anticipated expiration: 2039-01-21
Also published as: CN109639151B

Abstract

This application discloses a kind of constant-current control circuits and constant current control method for LLC resonant converter.The LLC resonant converter includes the first bipolar junction transistor and the second bipolar junction transistor to be worked using self-oscillation mode, the constant-current control circuit includes: switch element, for being shorted the driving current of at least one first bipolar junction transistor and second bipolar junction transistor；And drive module, including exporting current calculation module, for calculate the difference of resonance current signal and the first transformer magnetizing current signal absolute value average value as thermal compensation signal, and the on state of the switch element according to compensation signal control, to realize current constant control.In the complicated circuit for constituting charge pump PFC module and LLC resonant transformation combined application, which still can be improved constant-current control accuracy.

Description

Constant-current control circuit and constant current control method for LLC resonant converter

Technical field

The present invention relates to power technique fields, more particularly, to for LLC resonant converter constant-current control circuit and Constant current control method.

Background technique

LED drive circuit is used to provide average anode current to LED light, shines so that LED light is lighted to as illumination Light source.The Specifeca tion speeification of LED drive circuit includes power factor (PF) and output current ripple.Power factor characterization is active The ratio of power and reactive power.The AC compounent of output current ripple characterization average anode current.For example, the AC compounent is Power frequency component, it will the stroboscopic for leading to LED light not only influences illuminating effect, but also influences the service life of LED light.LED drive circuit High Power Factor utilization rate of electrical can be improved, low output current ripple can reduce stroboscopic.

High Power Factor and low output current ripple in order to balance, LED drive circuit can use a variety of cascade circuits Scheme, comprising: the first kind concatenated schemes of single-stage inverse-excitation type primary-side-control constant-current system framework and the ripple circuit composition that disappears；It rises The Second Type concatenated schemes of pressure topology and inverse-excitation type primary-side-control constant current topology composition；Boost topology and resonance oscillation semi-bridge LLC knot The third type concatenated schemes of structure composition；4th type cascade side of charge pump PFC module and resonance oscillation semi-bridge LLC structure composition Case.

The circuit arrangement of four seed types can realize High Power Factor (PF) and low output current ripple (nothing simultaneously above Stroboscopic).However, the shortcomings that first kind concatenated schemes be disappear ripple circuit on system effectiveness influence it is very big, especially when resonance is defeated When voltage is relatively low out.The shortcomings that Second Type concatenated schemes is that two-step scheme systematic comparison is complicated, and system cost is higher, In addition EMI debugging is relatively difficult, and efficiency is not also high.The efficiency of third type concatenated schemes and the 4th type concatenated schemes is than second Type concatenated schemes it is high-efficient, but system is more complicated and cost is higher.

In the concatenated schemes of the 4th type, mode of resonance switch converters are to obtain square-wave voltage using switching tube and adopt Resonance is carried out with resonant tank to realize the power inverter of energy transmission.LLC resonant converter has higher power density And less electronic component quantity, while possessing smooth current waveform, be conducive to improve electromagnetic interference, and can be whole The zero voltage switching (Zero Voltage Switching, ZVS) and zero current switching of switching tube are realized in a range of operation (Zero Current Switching, ZCS), helps to obtain high efficiency.Further, on LLC half-bridge driven Increase the passive PFC of current-type charge pump and the passive PFC combination of voltage-type charge pump, can obtain very high power factor (PF) and Very low total harmonic distortion (THD).Therefore, the concatenated schemes of the 4th type have apparent advantage in terms of circuit efficiency.

Further, expect to take into account the raising of circuit efficiency and the drop of circuit cost in the concatenated schemes of the 4th type It is low.

Summary of the invention

In view of the above problems, the application provides the constant-current control circuit and constant current control method for being used for LLC resonant converter, Wherein, the thermal compensation signal that constant-current control circuit obtains includes resonance current signal and the first transformer magnetizing current signal, thus Constant-current control accuracy can be improved.

According to an aspect of the present invention, a kind of constant-current control circuit for LLC resonant converter is provided, the LLC is humorous The converter that shakes includes the first transformer, the first bipolar junction transistor and the second bipolar junction transistor, first bipolar transistor Pipe and second bipolar junction transistor are worked using self-oscillation mode, so that resonance current and exciting current flow through described the The primary side winding of one transformer, the constant-current control circuit include: switch element, for being shorted first bipolar junction transistor With the driving current of at least one second bipolar junction transistor；And drive module, including output current calculation module, it uses In the difference for calculating resonance current signal and the first transformer magnetizing current signal absolute value average value as thermal compensation signal, And the on state of the switch element according to compensation signal control is to realize the control of resonance frequency, to realize constant current control System.

Preferably, the LLC resonant converter further includes the second transformer, and second transformer has load winding, And the first driving winding and the second driving winding, the load winding of second transformer coupled with the load winding connects It connects on resonant tank to obtain resonance current, the different name of the Same Name of Ends of the first driving winding and the second driving winding End is respectively connected to the base stage of first bipolar junction transistor and second bipolar junction transistor, to provide according to The respective drive electric current that the induced current of resonance current generates.

Preferably, the switch element is when being shorted the driving current by the first driving Same Name of Ends of winding and different Name end is connected to each other.

Preferably, second transformer further includes control winding, and the switch element is when being shorted the driving current The Same Name of Ends of the control winding and different name end are connected to each other.

Preferably, the switch element includes: the first transistor and second transistor, and the first transistor is connected to institute It states between the different name end and ground terminal of the first driving winding, the second transistor is connected to the of the same name of the first driving winding Between end and ground terminal, the ground terminal is connected in first bipolar junction transistor and second bipolar junction transistor Intermediate node.

Preferably, further includes: the first operational amplifier and second operational amplifier are connected respectively to the first transistor It is connected with the control terminal of second transistor, wherein the drive module provides open signal, first operational amplifier and institute It states second operational amplifier and cut-off signals is provided, the switch control signal of the first transistor and second transistor is described opens The superposed signal of messenger and the cut-off signals.

Preferably, first operational amplifier and the respective non-inverting input terminal of the second operational amplifier receive negative electricity Position reference voltage, inverting input terminal is each connected to output end, to realize the Same Name of Ends of the corresponding windings of second transformer With the negative voltage clamper at different name end.

Preferably, the switch element includes: the first transistor and second transistor, and differential concatenation is connected to described second Between the Same Name of Ends and ground terminal of the corresponding windings of transformer, the different name end of the corresponding windings of second transformer and described connect Ground terminal is connected to the intermediate node of first bipolar junction transistor and second bipolar junction transistor.

Preferably, the drive module is connect with the control terminal of the first transistor and second transistor to provide switch Control signal.

Preferably, first transformer includes primary side winding and vice-side winding, and the primary side winding is as resonant tank A part, the vice-side winding couples with the primary side winding to provide resonance output voltage, wherein the output galvanometer It calculates module and institute is obtained according to the current sampling signal of the resonance current and the voltage feedback signal of the resonance output voltage State thermal compensation signal.

Preferably, the output current calculation module includes: the third crystalline substance that third operational amplifier and output end are connected Body pipe, for generating the first electric current；The 4th transistor that four-operational amplifier and output end are connected, for generating the second electricity Stream；Multiple current mirrors, for by first electric current and second current subtraction to generate equivalent charging current；And electricity Hold, for being integrated to equivalent charging current to generate the thermal compensation signal, wherein the third operational amplifier and described The non-inverting input terminal of four-operational amplifier receives the first reference voltage and the second reference voltage, the third operation amplifier respectively The inverting input terminal of one of device and the four-operational amplifier receives the current sampling signal, another inverting input terminal Ground connection.

Preferably, the output current calculation module further include: first switch, for by the third operational amplifier Inverting input terminal selectively grounded or receives the current sampling signal；Second switch is used for the 4th operation amplifier The inverting input terminal of device selectively grounded or receives the current sampling signal；Comparator, by the voltage feedback signal with Third reference voltage compares, to generate the control signal of the first switch and the second switch.

Preferably, second reference voltage is greater than first reference voltage.

Preferably, the drive module further include: oscillator generates clock letter according to ramp signal and the thermal compensation signal Number；And logic module, open signal or switch control signal are generated according to the clock signal.

According to another aspect of the present invention, a kind of constant current control method for LLC resonant converter, the LLC are provided Controlled resonant converter includes the first transformer, the first bipolar junction transistor and the second bipolar junction transistor, the first ambipolar crystalline substance Body pipe and second bipolar junction transistor are worked using self-oscillation mode so that resonance current and exciting current flow through it is described The primary side winding of first transformer, the constant current control method include: to calculate resonance current signal and the first static exciter electricity The average value of the absolute value of the difference of signal is flowed, thermal compensation signal is obtained；According to the conducting of the compensation signal control switch element State is to realize the control of resonance frequency, to realize current constant control, wherein be shorted described first pair in switching elements conductive The driving current of at least one bipolar transistor and second bipolar junction transistor.

Preferably, the step of obtaining thermal compensation signal includes: to refer to the current sampling signal of resonance current signal and first Voltage compares, to generate the first electric current；Second electric current is generated using the second reference voltage；By first electric current and described Two current subtractions are to generate equivalent charging current；And equivalent charging current is integrated to generate the thermal compensation signal, In, second reference voltage is greater than first reference voltage.

It preferably, further include switching the path of the current sampling signal, according to the resonance output voltage signal to obtain Obtain the average value of the absolute value of the difference of the resonance current signal and the first transformer magnetizing current signal.

Preferably, the resonance output voltage signal is compared with third reference voltage to obtain the circuit sampling letter Number path switching signal.

It preferably, further include being carried out to the control terminal of first bipolar junction transistor and second bipolar junction transistor Negative voltage clamper.

Constant-current control circuit according to an embodiment of the present invention is shorted the first bipolar junction transistor and second using switch element The driving current of bipolar junction transistor, so that the switch of first bipolar junction transistor and second bipolar junction transistor is all Phase follows switch control signal, to realize the control of resonance frequency.The thermal compensation signal characterization that the constant-current control circuit obtains is humorous The average value of the absolute value for electric current and the first transformer magnetizing current difference of shaking, according to the negative feedback control switch control of average value The frequency of signal, so as in the output electric current constant current control of the secondary side of the first transformer of the primary side side of the first transformer realization System.In the complicated circuit for constituting charge pump PFC module and LLC resonant converter combined application, the constant-current control circuit is still Constant-current control accuracy so can be improved.

In a preferred embodiment, the control circuit in constant-current control circuit can directly control the first bipolar junction transistor It is ambipolar to be indirectly controlled second using the coupling between the first driving winding and the second driving winding for the driving current of base stage The driving current of transistor base.The constant-current control circuit is not necessarily to provide additional control circuit for the second bipolar junction transistor, So as to be further simplified the circuit structure of control circuit and reduce circuit cost.

In a preferred embodiment, control circuit includes being connected between the different name end and Same Name of Ends of the first driving winding The first transistor and second transistor control the driving electricity of the first bipolar junction transistor base stage for being shorted the first driving winding Stream.Ground terminal (floating ground) of the intermediate node of first bipolar junction transistor and the second bipolar junction transistor as control circuit.The One transistor and second transistor are as switch element, for being shorted the first driving winding, because without practical ground connection.The control Control electric current needed for circuit generates control winding without power supply circuit, thus the power consumption of circuit can be reduced and reduce electricity Road cost.

Detailed description of the invention

By referring to the drawings to the description of the embodiment of the present invention, above-mentioned and other purposes of the invention, feature and Advantage will be apparent from, in the accompanying drawings:

Fig. 1 shows the schematic circuit of power supply device according to prior art.

Fig. 2 shows the schematic circuits of LED drive circuit according to a first embodiment of the present invention.

Fig. 3 shows the schematic circuit of LED drive circuit according to a second embodiment of the present invention.

Fig. 4 shows the schematic circuit of control circuit in LED drive circuit shown in Fig. 3.

Fig. 5 shows the working waveform figure of LED drive circuit shown in Fig. 3.

Fig. 6 a to 6c shows the equivalent circuit diagram of LED drive circuit shown in Fig. 3 in the first stage.

Fig. 7 a to 7b shows LED drive circuit shown in Fig. 3 in the equivalent circuit diagram of second stage.

Fig. 8 a to 8c shows LED drive circuit shown in Fig. 3 in the equivalent circuit diagram of phase III.

Fig. 9 a to 9b shows LED drive circuit shown in Fig. 3 in the equivalent circuit diagram of fourth stage.

Figure 10 shows the schematic circuit of control circuit in LED drive circuit according to a third embodiment of the present invention.

Figure 11 shows the working waveform figure of control circuit shown in Figure 10.

Figure 12 shows the detailed circuit block diagram of control circuit shown in Fig. 4.

Figure 13 shows the schematic circuit that current calculation module is exported in control circuit shown in Figure 12.

Figure 14 shows the schematic illustration that control circuit shown in Figure 12 carries out current regulation.

Specific embodiment

The various embodiments that the present invention will be described in more detail that hereinafter reference will be made to the drawings.In various figures, identical element It is indicated using same or similar appended drawing reference.For the sake of clarity, the various pieces in attached drawing are not necessarily to scale.

Fig. 1 shows the schematic circuit of power supply device according to prior art.Power supply device 100 include rectifier bridge DB, Filter condenser Ce, charge pump PFC module 110, controlled resonant converter 120.Rectifier bridge DB is for converting AC-input voltage AC At rectified input voltage.Charge pump PFC module 110 is folded using the resonance output voltage and resonance current obtained from resonant tank The input terminal of LLC resonant converter 120 is added in realize PFC.Filter condenser Ce converts rectified input voltage At smooth DC input voitage.DC input voitage is converted into resonance output voltage by controlled resonant converter 120, thus to load LD power supply.

Charge pump PFC module 110 includes diode DX1 and DX2, diode Di1 and Di2, boost capacitor Ci1 and Ci2. Current source electric charge pump module includes boost capacitor Ci2 and diode Di2, utilizes resonant inductor Lr and resonant capacitor Cr group At resonant tank generate resonance current as current source.Voltage source electric charge pump module includes boost capacitor Ci1 and two poles Pipe Di1, using the end voltage of resonant capacitor Cr as voltage source.

Controlled resonant converter 120 includes control circuit 121, switch element M1 and M2, coupling capacitor Cc, resonant inductor Lr With resonant capacitor Cr.The on state of control circuit 121 control switch element M1 and M2 generate square-wave voltage.Square wave electricity Pressure input resonant tank, to generate resonance.The end voltage of resonant capacitor Cr powers to the load.

In the power supply device 100, electric current source charge pump utilizes the conducting of switch element and disconnects the high-frequency current generated Ring obtains the electric energy of AC-input voltage, the high frequency node electricity that voltage source charge pump is generated using the conducting and disconnection of switch element Pressure obtains the electric energy of AC-input voltage, to promote the voltage and current of DC input voitage.Switch element M1 and M2 pass through Switched conductive and off-state are to generate high frequency voltage and electric current.It is formed due to resonant inductor Lr and resonant capacitor Cr Load of the resonant tank as switch element M1 and M2, therefore, high frequency output electric current are the resonance current under resonance frequency.

In the LED drive circuit, switch element M1 and M2 used in controlled resonant converter are respectively metal oxide half Conductor field effect transistor (MOSFET) is used as switching tube.Although MOSFET has outstanding switch performance, complexity is needed Control circuit provides control signal for switching tube, therefore, leads to mentioning for LED drive circuit cost as switching tube using MOSFET It is high.

Fig. 2 shows the schematic circuits of LED drive circuit according to a first embodiment of the present invention.Power supply device 200 wraps Include rectifier bridge DB, filter condenser Cht, charge pump PFC module 210, LLC resonant converter 220.

Rectifier bridge DB is used to AC-input voltage AC being converted into rectified input voltage.

Charge pump PFC module 210 includes diode D1 and boost capacitor Cboost.Diode D1 is connected to rectifier bridge DB Positive output end and LLC resonant converter 220 positive input terminal between, to form rectifier bridge DB to LLC resonant converter 220 Unilateal conduction path.The cathode of diode D1 is connected to the first end of the resonant capacitor Cr in LLC resonant converter 220. Boost capacitor Cboost is connected between the positive output end and negative output terminal of rectifier bridge DB.Charge pump PFC module 210 using from The resonance current that resonant tank obtains extracts electric current from rectified input voltage to realize PFC, and gives filtered electrical Container Cht provides electric current, to realize the function of boosting.

Filter condenser Cht is connected between the output end of charge pump PFC module 210 and the negative output terminal of rectifier bridge DB. Rectified input voltage is converted into smooth DC input voitage by filter condenser Cht.

LLC resonant converter 220 includes the first transformer T1, the second transformer T2, bipolar junction transistor Q1 and Q2, two poles Pipe D2 and D3, capacitor Cmid, resonant capacitor Cr and resonant inductor Lr.Diode D2 and D3 respectively with bipolar junction transistor Q1 and Q2 are connected in inverse parallel, and capacitor Cmid is connected in parallel with bipolar junction transistor Q2.

In the primary side of the first transformer T1, primary side winding Lp, resonant capacitor Cr and the resonant inductance of the first transformer T1 Device Lr forms resonant tank.Between the positive input terminal and negative input end of LLC resonant converter 220, bipolar junction transistor Q1 and Q2 is connected in series, and the intermediate node of the two is connected to resonant tank.In resonant tank, sampling resistor Rs and primary side winding Lp are gone here and there Connection connection, it is hereby achieved that the sampled signal for characterizing the inductive current for flowing through primary side winding Lp.Second transformer T2 packet Include four windings around same iron core, i.e. load winding W1, driving winding W2 and W3, control winding W4.In resonant tank, Load winding W1 and primary side winding Lp is connected in series.Meanwhile drive winding W2 and W3 respectively with bipolar junction transistor Q1 and Q2 Base stage coupling, but it is contrary.That is, the Same Name of Ends of driving winding W2 is connected to the base stage of bipolar junction transistor Q1, driving around The different name end of group W3 is connected to the base stage of bipolar junction transistor Q2.These windings are for providing necessary electric current to drive ambipolar crystalline substance The base stage of body pipe Q1 and Q2, to realize that self-oscillation drives (SOC, Self-Oscillating Converter).From exciting It swings under the control of driving signal, DC input voitage is converted into square wave by bipolar junction transistor Q1 and Q2 alternate conduction and shutdown Voltage.The square-wave voltage inputs resonant tank, to generate the resonance current under resonance frequency.Therefore, pass through resonant tank, electric energy The secondary side of the first transformer T1 is transferred to from the primary side of the first transformer T1.

On the secondary side of the first transformer T1, diode D4 and D5 form rectification circuit.The both ends of vice-side winding are separately connected The anode of diode D4 and D5, the centre tap ground connection of vice-side winding.Output capacitance C1 is connected to the cathode of diode D4 and D5 Between ground, process resonance output voltage is provided at its both ends.

LLC resonant converter 220 further includes constant-current control circuit 221.The constant-current control circuit 221 is from controlled resonant converter The current sampling signal CS that resonance current is obtained on 220 sampling resistor Rs, from the first transformer T1's of controlled resonant converter 220 The voltage feedback signal FB of auxiliary winding Lf acquisition resonance output voltage.The constant-current control circuit 221 includes being respectively connected to the The different name end of the control winding W4 of two transformer T2 and the driving end DR1 and DR2 of Same Name of Ends.The constant-current control circuit 221 passes through The connection relationship of control driving end DR1 and DR2, so that resonance frequency is controlled, to control resonance current.

During operation, DC input voitage is converted into resonance output voltage by LLC resonant converter 220, thus to LED Load supplying.The switch commutation of bipolar junction transistor Q1 and Q2 are spontaneous in LLC resonant converter 220, are intrinsic SOC frequency of oscillation.However, when LLC resonant converter 220 works, it is also necessary to adjust its switching frequency, the frequency is general Higher than intrinsic SOC frequency of oscillation.

LED drive circuit is real using the concatenated schemes of charge pump PFC module and LLC resonant converter according to this embodiment Existing AC-DC voltage transformation, powers to LED load, it is hereby achieved that very high power factor (PF) and very low total harmonic wave lose Very (THD).Using bipolar junction transistor as switching tube in LLC resonant converter, using self-oscillation control switch pipe Conducting and off-state, and control the short circuit of control winding and discharge short-circuit condition in the suitable time, carry out control switch Pipe alternate conduction, thus to control resonance frequency, thus realize current constant control and simplified control circuit and reduce circuit at This.

Fig. 3 shows the schematic circuit of LED drive circuit according to a second embodiment of the present invention.Power supply device 300 wraps Include rectifier bridge DB, filter condenser Cht, charge pump PFC module 310, LLC resonant converter 320.

Charge pump PFC module 310 includes diode D1 and boost capacitor Cboost.Diode D1 is connected to rectifier bridge DB Positive output end and LLC resonant converter 320 positive input terminal between, to form rectifier bridge DB to LLC resonant converter 320 Unilateal conduction path.The anode of diode D1 is connected to the first end of the resonant capacitor Cr in LLC resonant converter 320. Boost capacitor Cboost is connected between the positive output end and negative output terminal of rectifier bridge DB.Charge pump PFC module 310 using from The resonance current that resonant tank obtains extracts electric current from rectified input voltage to realize PFC, and gives filtered electrical Container Cht provides electric current, to realize the function of boosting.

Filter condenser Cht is connected between the output end of charge pump PFC module 310 and the negative output terminal of rectifier bridge DB. Rectified input voltage is converted into smooth DC input voitage by filter condenser Cht.

LLC resonant converter 320 includes the first transformer T1, the second transformer T2, bipolar junction transistor Q1 and Q2, two poles Pipe D2 and D3, capacitor Cmid, resonant capacitor Cr and resonant inductor Lr.Diode D2 and D3 respectively with bipolar junction transistor Q1 and Q2 are connected in inverse parallel, and capacitor Cmid is connected in parallel with bipolar junction transistor Q2.

In the primary side of the first transformer T1, primary side winding Lp, resonant capacitor Cr and the resonant inductance of the first transformer T1 Device Lr forms resonant tank.Between the positive input terminal and negative input end of LLC resonant converter 320, bipolar junction transistor Q1 and Q2 is connected in series, and the intermediate node of the two is connected to resonant tank.In resonant tank, sampling resistor Rs and primary side winding Lp are gone here and there Connection connection, it is hereby achieved that the sampled signal for characterizing the inductive current for flowing through primary side winding Lp.Second transformer T2 packet Include three windings around same iron core, i.e. load winding W1, driving winding W2 and W3.In resonant tank, load winding W1 It is connected in series with primary side winding Lp.Meanwhile winding W2 and W3 being driven to couple respectively with the base stage of bipolar junction transistor Q1 and Q2, but It is contrary.That is, the Same Name of Ends of driving winding W2 is connected to the base stage of bipolar junction transistor Q1, the different name end of winding W3 is driven It is connected to the base stage of bipolar junction transistor Q2.These windings are for providing necessary electric current to drive bipolar junction transistor Q1 and Q2 Base stage, to realize that self-oscillation drives (SOC, Self-Oscillating Converter).In self-oscillation driving signal Under control, DC input voitage is converted into square-wave voltage by bipolar junction transistor Q1 and Q2 alternate conduction and shutdown.Square wave electricity Pressure input resonant tank, to generate the resonance current under resonance frequency.Therefore, by resonant tank, electric energy is from the first transformer The primary side of T1 is transferred to the secondary side of the first transformer T1.

LLC resonant converter 320 further includes constant-current control circuit 321.The constant-current control circuit 221 is from controlled resonant converter The current sampling signal CS that resonance current is obtained on 220 sampling resistor Rs, from the first transformer T1's of controlled resonant converter 220 The voltage feedback signal FB of auxiliary winding Lf acquisition resonance output voltage.The constant-current control circuit 321 includes being respectively connected to the The different name end of the driving winding W2 of two transformer T2 and the driving end DR1 and DR2 of Same Name of Ends, and it is connected to bipolar junction transistor The ground terminal GND of the intermediate node of Q1 and Q2.The constant-current control circuit 321 passes through control driving end DR1 and DR2 and ground terminal The connection relationship of GND, so that resonance frequency is controlled, to control resonance current.

During operation, DC input voitage is converted into resonance output voltage by LLC resonant converter 320, thus to LED Load supplying.The switch commutation of bipolar junction transistor Q1 and Q2 are spontaneous in LLC resonant converter 320, are intrinsic SOC frequency of oscillation.However, when LLC resonant converter 320 works, it is also necessary to adjust its switching frequency, the frequency is general Higher than intrinsic SOC frequency of oscillation.

LED drive circuit is real using the concatenated schemes of charge pump PFC module and LLC resonant converter according to this embodiment Existing AC-DC voltage transformation, powers to LED load, it is hereby achieved that very high power factor (PF) and very low total harmonic wave lose Very (THD).Using bipolar junction transistor as switching tube in LLC resonant converter, using self-oscillation control switch pipe Conducting and off-state, and control the short circuit of at least one driving winding and discharge short-circuit condition in the suitable time, come Control switch pipe alternate conduction, thus to control resonance frequency, to realize current constant control and simplified control circuit and reduction Circuit cost.

Constant-current control circuit 321 includes transistor M1 and M2, operational amplifier U1 and U2, drive module 3211.In the reality It applies in example, transistor M1 and M2 are, for example, MOSFET.Further, the first end and second end of transistor M1 is connected to drive Between moved end DR1 and ground terminal GND, the first end and second end of transistor M2 is connected to driving end DR2 and ground terminal GND Between.

Drive module 3211 obtains the current sampling signal of resonance current from the sampling resistor Rs of controlled resonant converter 320 CS obtains the voltage feedback signal FB of resonance output voltage from the auxiliary winding Lf of the first transformer T1 of controlled resonant converter 320, And thermal compensation signal Vcomp is generated according to current sampling signal CS and voltage feedback signal FB.Drive module 3211 and transistor M1 is connected with the control terminal of M2, for providing open signal VG1 and VG2, operational amplifier U1 to transistor M1 and M2 respectively Cut-off signals are provided to transistor M1 and M2 with U2, therefore, the switch control signal of transistor M1 and M2 are open signal and pass The superposed signal of break signal.The non-inverting input terminal of operational amplifier U1 receives negative potential reference voltage-Vref, preferably -0.1V, Inverting input terminal is connected with output end, and further, the output end of operational amplifier U1 is connected with the control terminal of transistor M1 It connects, operational amplifier U1 is other than it can control M1 shutdown, and when negative pressure occurs in the end DR1, operational amplifier U1 is controlled at M1 In magnifying state, it is ensured that the end DR1 voltage is not less than -0.1V.The non-inverting input terminal of operational amplifier U2 receives negative potential with reference to electricity Pressure, preferably -0.1V, inverting input terminal are connected with output end, further, the output end and transistor of operational amplifier U2 The control terminal of M2 is connected, and operational amplifier U2 is other than it can control M2 shutdown, and when negative pressure occurs in the end DR2, operation is put Big device U2 control M2 is in magnifying state, it is ensured that the end DR2 voltage is not less than -0.1V.

Fig. 5 shows the working waveform figure of LED drive circuit shown in Fig. 3.It is shown in figure the humorous of the acquisition of drive module 3211 Shake the exciting current CT1 of current sampling signal CS, voltage feedback signal FB, clock signal clk and the first transformer T1, the second change The exciting current CT2 of depressor T2 changes with time relationship.

The exciting current CT2 of resonance current sampled signal CS and the second transformer T2 intersect at A, B, C point.Clock signal CLK has a level of high and low (1,0) two states, and resonance current sampled signal CS also has the electricity of positive and negative (>0,<0) two states Flat, combination of two, there are four types of different states altogether, to generate the different circuit stages.

It is open-minded that drive module 3211 in the low level state of clock signal clk, constant-current control circuit 321 generates first Signal VG1, so that transistor M1 is connected, transistor M2 then has operational amplifier U2 control, and can be there are two state: one be off shape State；Second is that negative voltage clamping state.Drive module in the high level state of clock signal clk, constant-current control circuit 321 3211 generate the second open signal VG2, so that transistor M2 is connected, transistor M1 then has operational amplifier U1 control, have two A state: first is that off state；Second is that negative voltage clamping state.

It is converted into just in the current sampling signal CS of the low level time section of clock signal clk, resonance current from negative current Electric current.Negative electricity is converted into from positive current in the current sampling signal CS of the high level time section of clock signal clk, resonance current Stream.

Therefore, the first stage of LED drive circuit corresponds to the time period t 0 in figure to t1, and second stage corresponds in figure Time period t 1 to t2, the phase III corresponds to the time period t 2 in figure to t3, and fourth stage corresponds to the time period t 3 in figure To t4.

Fig. 6 a to 6c shows the equivalent circuit diagram of LED drive circuit shown in Fig. 3 in the first stage.As shown, clock Signal CLK is low level, is the first stage of circuit when resonance current is negative current.In the first phase, constant-current control circuit Transistor M1 conducting in 321, transistor M2 negative voltage clamper.The current path of LED drive circuit 300 is sampled because of resonance current The change of the charged state of the variation and capacitor Cmid of the difference of the exciting current CT2 of signal CS and the second transformer T2 And it changes.

Rectifier bridge DB includes four diode D11 to D14 for forming bridge, in the positive output end and negative output of rectifier bridge DB Rectified input voltage is provided between end.

In moment t0, bipolar junction transistor Q1 and Q2 are off state.AC-input voltage is via resonant tank to electricity Container Cmid charging.During the charging of capacitor Cmid, the end voltage Vmid of capacitor Cmid is gradually risen.Resonance current is anti- To the load winding W1 of the primary side winding Lp for flowing through the first transformer T1 and the second transformer T2, that is, in the inside of corresponding windings Same Name of Ends is flowed to from different name end, can judge to drive according to the difference of the exciting current CT2 of resonance current CS and the second transformer T2 The current internal of dynamic winding W2 and W3 are that different name end is flowed to from Same Name of Ends, since the voltage difference of the two ends of driving winding W2 only has 0.1V, therefore may determine that inside driving winding W3 be not no electric current flowing.

As shown in Figure 6 a, the resonance current path in LED drive circuit 300 are as follows: from the positive output end of rectifier bridge DB, via Resonant capacitor Cr, resonant inductor Lr, the primary side winding Lp of the first transformer T1, the second transformer T2 load winding W1, Sampling resistor Rs, capacitor Cmid return to the negative output terminal of rectifier bridge DB.Further, since the crystal in constant-current control circuit 321 Pipe M2 negative voltage clamper, effect are similar to the electricity between the driving end DR2 and ground terminal GND for being connected to constant-current control circuit 321 Potential source, therefore, the driving current path of bipolar junction transistor Q1 are as follows: from the driving end DR2 of constant-current control circuit 321, via The driving end DR1 of driving the winding W2 and constant-current control circuit 321 of two transformer T2, return to the ground connection of constant-current control circuit 321 GND is held, current loop is formed.The driving current path of bipolar junction transistor Q2 disconnects.

Then, when voltage Vmid is greater than the end voltage of filter condenser Cht, resonance current path changes.At this point, The base-collector junction afterflow of bipolar junction transistor Q1, so that work is connected in reverse phase.Resonance current is no longer to capacitor Cmid Charging, but charge via bipolar junction transistor Q1 to filter condenser Cht.

As shown in Figure 6 b, the resonance current path in LED drive circuit 300 are as follows: from the positive output end of rectifier bridge DB, via Resonant capacitor Cr, resonant inductor Lr, the primary side winding Lp of the first transformer T1, the second transformer T2 load winding W1, Sampling resistor Rs, bipolar junction transistor Q1, filter condenser Cht return to the negative output terminal of rectifier bridge DB.In addition, ambipolar crystalline substance The driving current path of body pipe Q1 remains unchanged, and the driving current path of bipolar junction transistor Q2 disconnects.

Then, in Fig. 5 after A point, occur in the exciting current difference of resonance current CS and the second transformer T2 by bearing Become timing, the current direction of driving the winding W2 and W3 of the second transformer T2 will also change, and flow direction is same from internal different name end Name end, at this point, transistor M2's constant-current control circuit 321 inside becomes off state by negative voltage clamping state, resonance is electric The one part of current of stream reversely flows through the driving winding W2 of the second transformer T2, i.e., flows in the inside of corresponding windings from different name end Same Name of Ends, and the base-collector junction of bipolar junction transistor Q1 is flowed through, so that bipolar junction transistor Q1 is completely reversed conducting.It is humorous Another part of vibration electric current charges to filter condenser Cht via bipolar junction transistor Q1.

As fig. 6 c, the resonance current path in LED drive circuit 300 are as follows: from the positive output end of rectifier bridge DB, via Resonant capacitor Cr, resonant inductor Lr, the primary side winding Lp of the first transformer T1, the second transformer T2 load winding W1, Sampling resistor Rs, bipolar junction transistor Q1, filter condenser Cht return to the negative output terminal of rectifier bridge DB.In addition, ambipolar crystalline substance The driving current path of body pipe Q1 via the second transformer T2 driving winding W2 and bipolar junction transistor Q1 base collector The driving current path of knot, bipolar junction transistor Q2 disconnects.

Terminate in the negative current stage of moment t1, resonance current, the first stage of LED drive circuit 300 terminates.

Fig. 7 a to 7b shows LED drive circuit shown in Fig. 3 in the equivalent circuit diagram of second stage.As shown, clock Signal CLK is low level, is the second stage of circuit when resonance current is positive current.In second stage, constant-current control circuit Transistor M1 conducting, transistor M2 shutdown in 321.The current path of LED drive circuit 300 is because of resonance current sampled signal CS With the variation of the difference of the exciting current CT2 of the second transformer T2.

In moment t1, resonance current CS is positive, and the driving winding W2 of the second transformer T2 obtains reversed driving current, makes Obtaining bipolar junction transistor Q1 is on state.Bipolar junction transistor Q2 is maintained off state.Resonance current is via diode D1 It charges to boost capacitor Cboost.During the charging of capacitor Cboost, the end voltage of boost capacitor Cboost Vboost gradually rises.Resonance current forward direction flow through the load of the primary side winding Lp and the second transformer T2 of the first transformer T1 around Group W1, that is, different name end is flowed to from Same Name of Ends in the inside of corresponding windings, it can be according to resonance current CS's and the second transformer T2 The current internal of difference judgement driving the winding W2 and W3 of exciting current CT2 are to flow to Same Name of Ends from different name end.

As shown in Figure 7a, the resonance current path in LED drive circuit 300 are as follows: from the first end of resonant inductor Lr, warp By resonant capacitor Cr, boost capacitor Cboost, filter condenser Cht, bipolar junction transistor Q1, sampling resistor Rs, second The primary side winding Lp of the load winding W1 of transformer T2, the first transformer T1 return to the second end of resonant inductor Lr.In addition, Since the driving winding W2 of the second transformer T2 obtains reversed driving current, the driving current of bipolar junction transistor Q1 Path are as follows: returned from the Same Name of Ends of the driving winding W2 of the second transformer T2 via the base emitter junction of bipolar junction transistor Q1 Go back to the different name end of the driving winding W2 of the second transformer T2.The driving current path of bipolar junction transistor Q2 disconnects.

Then, when the end voltage Vboost of boost capacitor Cboost is greater than the end voltage Vht of filter condenser Cht, Resonance current path changes.At this point, diode D1 is connected.Resonance current no longer charges to boost capacitor Cboost, and It is the collector that bipolar junction transistor Q1 is flowed to via diode D1.

As shown in Figure 7b, the resonance current path in LED drive circuit 300 are as follows: from the first end of resonant inductor Lr, warp By resonant capacitor Cr, diode D1, bipolar junction transistor Q1, sampling resistor Rs, the load winding W1 of the second transformer T2, The primary side winding Lp of one transformer T1 returns to the second end of resonant inductor Lr.Further, since the driving of the second transformer T2 around Group W2 obtains reversed driving current, and therefore, the driving current path of bipolar junction transistor Q1 remains unchanged.Bipolar junction transistor The driving current path of Q2 disconnects.

Terminate in the low level stage of moment t2, clock signal clk, the second stage of LED drive circuit 300 terminates.

Fig. 8 a to 8c shows LED drive circuit shown in Fig. 3 in the equivalent circuit diagram of phase III.As shown, clock Signal CLK is high level, and resonance current CS is the phase III of circuit when being positive current.In the phase III, current constant control electricity Transistor M1 negative voltage clamper, transistor M2 conducting in road 321.The conducting of transistor M2 so that bipolar junction transistor Q1 base Pole emitter is shorted, and therefore, bipolar junction transistor Q1 is in off state always.The current path of LED drive circuit 300 is because of electricity Flow the variation of the difference of the exciting current CT2 of sampled signal CS and the second transformer T2 and the charged state of capacitor Cmid Change and change.

In moment t2, clock signal clk is turned into high level from low level, and bipolar junction transistor Q1 and Q2 are cut-off shape State.Capacitor Cmid discharges via resonant tank.During the electric discharge of capacitor Cmid, the end voltage Vmid of capacitor Cmid is gradually It reduces.Resonance current forward direction flows through the load winding W1 of the primary side winding Lp and the second transformer T2 of the first transformer T1, that is, The inside of corresponding windings flows to different name end from Same Name of Ends, can be according to the exciting current of resonance current CS and the second transformer T2 The current internal of difference judgement driving the winding W2 and W3 of CT2 are to flow to Same Name of Ends from different name end, due to the voltage difference of the two ends of W2 Only 0.1V, therefore may determine that inside W3 it is not no electric current flowing.

As shown in Figure 8 a, the resonance current path in LED drive circuit 300 are as follows: from the first end of resonant inductor Lr, warp By resonant capacitor Cr, diode D1, filter condenser Cht, capacitor Cmid, sampling resistor Rs, the second transformer T2 it is negative The primary side winding Lp of winding W1, the first transformer T1 are carried, the second end of resonant inductor Lr is returned.Further, since current constant control Transistor M1 negative voltage clamper in circuit 321, effect are similar to connecing for the driving end DR1 for being connected to constant-current control circuit 321 Voltage source between ground terminal GND, therefore, the driving current path of bipolar junction transistor Q1 are as follows: from the drive of constant-current control circuit 321 Moved end DR1 returns to current constant control via the driving end DR2 of driving the winding W2 and constant-current control circuit 321 of the second transformer T2 The ground terminal GND of circuit 321 forms current loop.The driving current path of bipolar junction transistor Q2 disconnects.

Then, when being less than the voltage of ground terminal GND of constant-current control circuit 321 in voltage Vmid, bipolar junction transistor Q2 Driving current path change.At this point, the base-collector junction afterflow of bipolar junction transistor Q2, so that work is led in reverse phase It is logical.Capacitor Cmid no longer discharges via resonant tank.

As shown in Figure 8 b, the one part of current forward direction of resonance current flows through the driving winding W3 of the second transformer T2, that is, exists The inside of corresponding windings flows to different name end from Same Name of Ends, and flows through the base-collector junction of bipolar junction transistor Q2, so that double Bipolar transistor Q2 is completely reversed conducting.Another part of resonance current flows to resonant tank via bipolar junction transistor Q2.This Outside, the driving current path of bipolar junction transistor Q1 remains unchanged.

Then, in Fig. 5 after B point, occur in the exciting current difference of resonance current and the second transformer T2 by just becoming When negative, the current direction of driving the winding W2 and W3 of the second transformer T2 will also change, at this point, flowing to from internal Same Name of Ends Different name end, transistor M1's inside constant-current control circuit 321 becomes off state by negative voltage clamping state.

As shown in Figure 8 c, the resonance current path in LED drive circuit 300 are as follows: from the first end of resonant inductor Lr, warp By the load of resonant capacitor Cr, diode D1, filter condenser Cht, triode Q2, sampling resistor Rs, the second transformer T2 The primary side winding Lp of winding W1, the first transformer T1 return to the second end of resonant inductor Lr.In addition, bipolar junction transistor Q1 Driving current path disconnect, the driving current path of bipolar junction transistor Q2 via bipolar junction transistor Q2 base collector Knot.

Terminate in the positive current stage of moment t3, resonance current, the phase III of LED drive circuit 300 terminates.

Fig. 9 a to 9b shows LED drive circuit shown in Fig. 3 in the equivalent circuit diagram of fourth stage.As shown, clock Signal CLK is high level, is the fourth stage of circuit when resonance current is negative current.In fourth stage, constant-current control circuit Transistor M1 shutdown in 321, transistor M2 conducting.The conducting of transistor M2 so that bipolar junction transistor Q1 Base-Emitter It is shorted, therefore, bipolar junction transistor Q1 is in off state always.The current path of LED drive circuit 300 is believed because of current sample The variation of the difference of the exciting current CT2 of number CS and the second transformer.

In moment t3, resonance current is reversed, and the driving winding W3 of the second transformer T2 obtains positive driving current, so that Bipolar junction transistor Q2 is on state.Bipolar junction transistor Q1 is maintained off state.Boost capacitor Cboost is via humorous The electric discharge of vibration circuit, the end voltage Vboost of boost capacitor Cboost are gradually decreased.Resonance current reversely flows through the first transformer The load winding W1 of the primary side winding Lp of T1 and the second transformer T2, that is, flow in the inside of corresponding windings from different name end of the same name End can judge the electricity of driving winding W2 and W3 according to the difference of the exciting current CT2 of resonance current CS and the second transformer T2 It is that different name end is flowed to from Same Name of Ends that stream is internal.

As illustrated in fig. 9, the resonance current path in LED drive circuit 300 are as follows: from the first of boost capacitor Cboost End, via the load of resonant capacitor Cr, resonant inductor Lr, the primary side winding Lp of the first transformer T1, the second transformer T2 Winding W1, sampling resistor Rs, bipolar junction transistor Q2 return to the second end of boost capacitor Cboost.Further, since second becomes The driving winding W3 of depressor T2 obtains positive driving current, and the driving current path of bipolar junction transistor Q2 is via ambipolar crystalline substance The driving current path of the base emitter junction of body pipe Q2, bipolar junction transistor Q2 forward conduction, bipolar junction transistor Q1 disconnects.

Then, when the end voltage Vboost of boost capacitor Cboost is less than AC-input voltage, resonance current path It changes.AC-input voltage is powered to resonant tank.

As shown in figure 9b, the resonance current path in LED drive circuit 300 are as follows: from the positive output end of rectifier bridge DB, via Resonant capacitor Cr, resonant inductor Lr, the primary side winding Lp of the first transformer T1, the second transformer T2 load winding W1, Sampling resistor Rs, bipolar junction transistor Q2 return to the negative output terminal of rectifier bridge DB.Further, since the driving of the second transformer T around Group W3 obtains positive driving current, and the driving current path of bipolar junction transistor Q2 is sent out via the base stage of bipolar junction transistor Q2 The driving current path of emitter-base bandgap grading knot, bipolar junction transistor Q2 forward conduction, bipolar junction transistor Q1 disconnects.

Terminate in the high level stage of moment t4, clock signal clk, the fourth stage of LED drive circuit 300 terminates.

Figure 10 shows the illustrative circuitry of constant-current control circuit in LED drive circuit according to a third embodiment of the present invention Figure.LED drive circuit and second embodiment according to a third embodiment of the present invention are the difference is that constant-current control circuit Circuit structure, remaining aspect is then identical as second embodiment, below the difference of both main descriptions.

Constant-current control circuit 421 includes transistor M1 and M2 and drive module 4211.In the embodiment, transistor M1 It is, for example, MOSFET with M2.Further, the driving end DR1 of constant-current control circuit 421 is directly shorted with ground terminal GND, crystal Pipe M1 is connected with M2 differential concatenation, organizes pairs of top switch, is connected to the driving end DR2 and ground terminal GND of constant-current control circuit 421 Between.That is, the first end of transistor M1 is connected to the driving end DR2 of constant-current control circuit 421, the first end of transistor M2 connects It is connected to the ground terminal GND of constant-current control circuit 421, the second end of transistor M1 and M2 are connected to each other.

Drive module 4211 obtains the current sampling signal of resonance current from the sampling resistor Rs of controlled resonant converter 220 CS obtains the voltage feedback signal FB of resonance output voltage from the additional winding Lf of the first transformer T1 of controlled resonant converter 220, And the switch control signal of transistor M1 and M2 are generated according to current sampling signal CS and voltage feedback signal FB.Drive module 4211 are connected with the control terminal of transistor M1 and M2, for providing the same switch control signal VG to transistor M1 and M2.

LED drive circuit according to this embodiment, a driving end and ground terminal in control circuit are shorted, another drive Differential concatenation connection transistor M1 and M2 are used as to top switch, so as to save in control circuit between moved end and ground terminal Negative voltage clamper module (for example, operational amplifier), to simplify circuit structure and reduce circuit cost.

Figure 11 shows the working waveform figure of control circuit shown in Figure 10.It is shown in figure the electric current of the acquisition of drive module 4211 Sampled signal CS, voltage feedback signal FB, clock signal clk and the first transformer T1 exciting current CT1 and the second transformer The exciting current CT2 of T2 changes with time relationship.

The exciting current CT2 of current sampling signal CS and the second transformer T2 intersect at A, B, C point.Clock signal clk has The level of high and low (1,0) two states, current sampling signal CS also have the voltage of positive and negative (>0,<0) two states, two-by-two group It closes, there are four types of different states altogether, to generate the different circuit stages.

Drive module 4211 in the rising edge or failing edge of clock signal clk, constant-current control circuit 421 generates switch Signal VG is controlled, so that transistor M1 and M2 are connected, it will be short between the driving end DR2 and ground terminal GND of constant-current control circuit 421 It connects.Drive module 4211 in the rising edge or failing edge of voltage feedback signal FB, constant-current control circuit 421 generates switch control Signal VG processed, so that transistor M1 and M2 end, by the interruption of the driving end DR2 of constant-current control circuit 421 and ground terminal GND It opens.

Figure 12 shows the detailed circuit block diagram of constant-current control circuit 321 shown in Fig. 4.The constant-current control circuit 321 is, for example, The chip of single package.Referring to fig. 4, constant-current control circuit 321 includes transistor M1 and M2, operational amplifier U1 and U2, driving Module 3211.

Drive module 3211 obtains the current sampling signal of resonance current from the sampling resistor Rs of controlled resonant converter 320 CS obtains the voltage feedback signal FB of DC output voltage from the additional winding Lf of the first transformer T1 of controlled resonant converter 320, And open signal VG1 and VG2 are provided respectively to transistor M1 and M2.

Further, as shown in figure 12, the drive module 3211 of constant-current control circuit 321 includes output current calculation module 11, peak value current-limiting protection module 12, oscillator 13, logic module 14 and driving stage 15, capacitor C12, constant-current source I11.

It exports current calculation module 11 and thermal compensation signal is generated according to voltage feedback signal FB and resonance current sampling signal CS Vcomp。

Constant-current source I11 and capacitor C12 are connected in series between feeder ear and ground, are generated slope in the intermediate node of the two and are believed Number.Two input terminals of oscillator 13 receive ramp signal and thermal compensation signal Vcomp respectively, generate clock signal according to the two CLK.Logic module 14 generates open signal VG1 and VG2 according to clock signal clk.

In the constant-current control circuit 321, the frequency and resonance current and the first transformer T1 excitation of switch control signal The average value of the absolute value of electric current CT1 difference is related, that is, according to the frequency of the negative feedback control switch control signal of average value Rate, so as in the output electric current current constant control of the secondary side of the first transformer T1 of the primary side side of the first transformer T1 realization.

Preferably, constant-current control circuit 321 can also include multiple protective modules, the clamper module including pressure feedback port 16, the clamper module 19 of open-circuit-protection module 17, short circuit protection module 18 and feeder ear, under-voltage locking module 22.In addition, Constant-current control circuit 321 can also include overvoltage protective module 20, overheat protector module 21.

Figure 13 shows the schematic circuit that current calculation module is exported in constant-current control circuit 321 shown in Figure 12, Figure 14 The schematic illustration that the output electric current of control circuit shown in Figure 12 calculates is shown.

As shown in figure 13, output current calculation module 11 includes operational amplifier AMP1 and AMP2, comparator COMP1, opens Close K11 and K12, transistor M11 to M16, resistance R11 and R12, capacitor C11.

The non-inverting input terminal of operational amplifier AMP1 receives reference voltage VREF1, and inverting input terminal selectively receives electricity Stream sampled signal CS or ground connection, output end are connected to the grid of transistor M11.Further, the source electrode of transistor M11 is connected to The inverting input terminal of operational amplifier AMP1.Transistor M13 and M14 form the first current mirror, transistor M17 and M18 composition the Two current mirrors, the first current mirror and the second current mirror are coupled to each other.Transistor M11 and transistor M13 is connected in series, and passes through The electric current of transistor M11 generates the first electric current I11 for flowing through transistor M18 through current mirror coupled.

The non-inverting input terminal of operational amplifier AMP2 receives reference voltage VREF2, and inverting input terminal selectively receives electricity Stream sampled signal CS or ground connection, output end are connected to the grid of transistor M12.Further, the source electrode of transistor M12 is connected to The inverting input terminal of operational amplifier AMP2.Transistor M15 and M16 form third current mirror.Transistor M12 and transistor M15 It is connected in series, passes through the electric current of transistor M12 through current mirror coupled, generate the second electric current I12 for flowing through transistor M16.

Transistor M16 and M18 are connected in series, so that the second current mirror and third current mirror are connected in series.Further, electric Hold C11 to be connected between the intermediate node and ground of transistor M16 and M18, to provide thermal compensation signal at the both ends of capacitor C11 Vcomp。

The non-inverting input terminal and inverting input terminal of comparator COMP1 receives voltage feedback signal FB and reference voltage respectively VREF3.Switch K11 and K12 are single-pole double-throw switch (SPDT) respectively.The output end of comparator COMP1 is connected to switch K11's and K12 Control terminal, so that switch K11 and K12 switch simultaneously, thus by the inverting input terminal of operational amplifier AMP1 and AMP2 with complementation Mode is grounded, or be connected to current sampling signal CS via resistance R12 via resistance R11.

In order to be further described, the amplification factor of current mirror is assumed to 1 in following analysis, above-mentioned reference voltage VREF1, VREF2 and VREF3 are respectively set to 0.85,0.95V, 0.2V.However, the invention is not limited thereto, reference voltage VREF2 It greater than VREF1, and can be any appropriate numerical value respectively.Further, reference voltage signal Vcscc=VREF2- is defined VREF1。

First stage T1: voltage feedback signal FB is greater than reference voltage VREF3

In the first stage, switch K11 and K12 are switched to the end A by the switch control signal that comparator COMP1 is generated respectively. The inverting input terminal of operational amplifier AMP2 receives current sampling signal CS, the reverse phase of operational amplifier AMP1 via resistance R12 End is grounded via resistance R11.When current sampling signal CS is zero, operational amplifier AMP2 intermediate node generate second electricity Flow I12=VREF2/R, wherein the resistance value of R expression resistance R11 and R12.Operational amplifier AMP1 is generated in intermediate node First electric current I11=VREF1/R, wherein R indicates the resistance value of resistance R11 and R12, therefore, the received electric current of capacitor C11 IDIFF=I12-I11=(VREF2-VREF1)/R=Vcscc/R > 0, charges to capacitor C11.In current sampling signal CS When less than zero (note represents part of the first stage CS electric current less than 0 at CS1), operational amplifier AMP2 is generated in intermediate node The second electric current I12=VREF2/R+ | CS1 | Rs/R > 0 *.The first electric current I11 that operational amplifier AMP1 is generated in intermediate node =VREF1/R, wherein the resistance value of R expression resistance R11 and R12.Therefore, the received electric current IDIFF=I12-I11 of capacitor C11 =(VREF2-VREF1)/R+ | CS1 | * Rs/R=Vcscc/R+ | CS1 | Rs/R > 0 * charges to capacitor C11.

(note represents the part that first stage CS electric current is greater than 0 at CS2), operation when current sampling signal CS is greater than zero The second electric current I12=VREF2/R-CS2*Rs/R that amplifier AMP2 is generated in intermediate node.Operational amplifier AMP1 is in centre The I11=VREF1/R that node generates, wherein the resistance value of R expression resistance R11 and R12.Therefore, the received electric current of capacitor C11 IDIFF=I12-I11=(VREF2-VREF1)/R-CS2*Rs/R=Vcscc/R-CS2*Rs/R is in Vcscc/R > CS2*Rs/R When, received electric current IDIFF=Vcscc/R-CS2*Rs/R > 0 capacitor C11 charges to capacitor C11.Vcscc/R < When CS2*Rs/R, received electric current IDIFF=Vcscc/R-CS2*Rs/R < 0 capacitor C11 discharges to capacitor C11.

Therefore in the first stage: the average value that capacitor C11 receives electric current IDIFF is equal to:

Since reference voltage signal is DC voltage,

It is the area of S (c) inside Figure 14

It is that the area of S (b) inside Figure 14 is gained knowledge according to geometry it is found that the region area S (a)=S (b)-S (c).And S (a) is exactly resonance current CS and the first transformer magnetizing current CT1 area defined area, therefore:

Therefore formula (1) becomes:

Definition is Isource to capacitor C11 average eguivalent charging current；Average eguivalent discharge current is Isink

In the first stage, average eguivalent charging current Isource=Vcscc/R.

In the first stage, average eguivalent discharge current Isink is equal to the exciting current of resonance current and the first transformer T1 The average value of the absolute value of CT1 difference:

Wherein, Rs indicates the resistance value of sampling resistor Rs, and R indicates resistance R11 and R12 Resistance value, CS indicates that relevant to resonance current current sampling signal, CT1 indicate that current sample relevant to exciting current is believed Number.

Second stage T2: voltage feedback signal FB is less than reference voltage VREF3

In the switch control signal that second stage, comparator COMP1 generate, switch K11 and K12 are switched into the end B respectively. The inverting input terminal of operational amplifier AMP2 is grounded via resistance R11, and the reverse side of operational amplifier AMP1 connects via resistance R12 Receive current sampling signal CS.

When current sampling signal CS is zero, the second electric current I12=that operational amplifier AMP2 is generated in intermediate node VREF2/R, wherein the resistance value of R expression resistance R11 and R12.The first electric current that operational amplifier AMP1 is generated in intermediate node I11=VREF1/R, wherein R indicates the resistance value of resistance R11 and R12, therefore, the received electric current IDIFF=I12- of capacitor C11 I11=

(VREF2-VREF1)/R=Vcscc/R > 0 charges to capacitor C11.

(note represents the part that second stage CS electric current is greater than 0 at CS3), operation when current sampling signal CS is greater than zero The second electric current I12=VREF2/R that amplifier AMP2 is generated in intermediate node.Operational amplifier AMP1 is generated in intermediate node I11=VREF1-CS3*Rs/R, wherein the resistance value of R expression resistance R11 and R12.Therefore, the received electric current of capacitor C11 IDIFF=I12-I11=(VREF2-VREF1)/R+ | CS | capacitor C11 is filled in Rs/R=Vcscc/R+CS3*Rs/R > 0 * Electricity.

(note represents part of the second stage CS electric current less than 0 at CS4), operation when current sampling signal CS is less than zero The second electric current I12=VREF2/R that amplifier AMP2 is generated in intermediate node.Operational amplifier AMP1 is generated in intermediate node First electric current I11=VREF1/R+ | CS4 | * Rs

/ R > 0, wherein the resistance value of R expression resistance R11 and R12.Therefore, the received electric current IDIFF=of capacitor C11 (VREF2-VREF1)/R- | CS4 | * Rs/R=Vcscc/R- | CS4 | Rs/R > 0 * Vcscc/R > | CS4 | when * Rs/R, capacitor The received electric current IDIFF of C11

=Vcscc/R- | CS4 | Rs/R > 0 * charges to capacitor C11.

Vcscc/R < | CS4 | when * Rs/R, the received electric current IDIFF of capacitor C11

=Vcscc/R- | CS4 | Rs/R < 0 * discharges to capacitor C11.

Therefore in second stage: the average value that capacitor C11 receives electric current IDIFF is equal to:

Since reference voltage signal is DC voltage,It is similarly available

Therefore formula (3) equally becomes:

In second stage, average eguivalent charging current Isource=Vcscc/R.

In second stage, average eguivalent discharge current Isink is equally equal to the excitation of resonance current and the first transformer T1 The average value of the absolute value of electric current CT1 difference:

Wherein, Rs indicates the resistance value of sampling resistor Rs, and R indicates the resistance value of resistance R11 and R12, and CS is indicated and resonance The relevant current sampling signal of electric current, CT1 indicate current sampling signal relevant to exciting current.

In output current calculation module 11, the effect of capacitor C11 is in harmonic period to equivalent mean charging current Isource and average eguivalent discharge current Isink are integrated, to generate thermal compensation signal Vcomp.WhenGreatly When reference voltage signal Vcscc, at this moment the average value of average eguivalent discharge current Isink is greater than average eguivalent charging current The average value of Isource, thermal compensation signal Vcomp reduces, so that the frequency of switch control signal reduces, to reduce

WhenWhen less than reference voltage signal Vcscc, at this moment average eguivalent discharge current Isink is averaged Value is less than the average value of average eguivalent charging current Isource, and thermal compensation signal Vcomp increases, so that the frequency of switch control signal Rate increases, to increase

WhenWhen equal to reference voltage signal Vcscc, at this moment average eguivalent discharge current Isink is averaged Value is equal to the average value of average eguivalent charging current Isource, and thermal compensation signal Vcomp remains unchanged.

As shown in figure 14, output current calculation module 11 is according to resonance current signal and the first transformer magnetizing current signal The average value of absolute value of difference obtain thermal compensation signal, the numerical value of the thermal compensation signal corresponds to resonance current CS and the first transformation Device exciting current CT1 area defined area S (a)=S (b)-S (c), according to LLC half-bridge principle it is found that the region area with Export the proportional relationship of electric current.Specifically, switch control signal is generated according to thermal compensation signal, to be shorted the described first ambipolar crystalline substance The driving current of at least one body pipe and second bipolar junction transistor, to realize the control of resonance frequency.In constant current control In feedback loop processed, above-mentioned thermal compensation signal Vcomp remains unchanged, that is, maintains corresponding region area to remain unchanged, so that resonance Frequency maintains constant value corresponding with the output of desired electric current, to realize current constant control.

In the above-described embodiment, the LED drive circuit including charge pump PFC module and LLC resonant converter is described. It is appreciated that LLC resonant converter can be used alone, and still may be implemented identical based on similar working principle Technical effect.

In the above-described embodiment, the drive by control upside bipolar junction transistor in LLC resonant converter is described It moves the short circuit of winding and discharges short-circuit condition in the suitable time, carry out control switch pipe alternate conduction, so that ambipolar The switch periods of transistor follow the period of circuit internal switch control signal, further according to the negative feedback control of resonance current Switch control signal obtains frequency, so that resonance frequency maintains constant value corresponding with the output of desired electric current, to realize Current constant control.However, the invention is not limited thereto.It is appreciated that based on similar working principle, under LLC resonant converter Identical technical effect also may be implemented in the circuit paths control of the driving winding of side bipolar junction transistor.

It is as described above according to the embodiment of the present invention, these embodiments details all there is no detailed descriptionthe, also not Limiting the invention is only the specific embodiment.Obviously, as described above, can make many modifications and variations.This explanation These embodiments are chosen and specifically described to book, is principle and practical application in order to better explain the present invention, thus belonging to making Technical field technical staff can be used using modification of the invention and on the basis of the present invention well.The present invention is only by right The limitation of claim and its full scope and equivalent.

Claims

1. A constant current control circuit for an LLC resonant converter, the LLC resonant converter comprising a first transformer, a first bipolar transistor and a second bipolar transistor, the first bipolar transistor and The second bipolar transistor works in a self-excited oscillation mode, so that the resonant current and the excitation current flow through the primary winding of the first transformer, and the constant current control circuit includes:

a switching element for short-circuiting the drive current of at least one of the first bipolar transistor and the second bipolar transistor; and

The drive module includes an output current calculation module for calculating the average value of the absolute value of the difference between the resonant current signal and the first transformer excitation current signal as a compensation signal, and controlling the conduction state of the switching element according to the compensation signal to achieve Resonant frequency control to achieve constant current control.

2. The constant current control circuit of claim 1, wherein the LLC resonant converter further comprises a second transformer having a load winding, and a first drive winding coupled to the load winding and the second drive winding, the load winding of the second transformer is connected to the resonant tank to obtain the resonant current, the same name terminal of the first drive winding and the different name terminal of the second drive winding are respectively connected to the first drive winding The bipolar transistors and the bases of the second bipolar transistors provide corresponding drive currents generated according to the induced currents of the resonant currents.

3 . The constant current control circuit according to claim 2 , wherein the switching element connects the same-named terminal and the different-named terminal of the first driving winding to each other when the driving current is short-circuited. 4 .

4 . The constant current control circuit according to claim 2 , wherein the second transformer further comprises a control winding, and the switching element switches the same name terminal and the different name terminal of the control winding when the driving current is short-circuited. 5 . connected to each other.

5. The constant current control circuit according to claim 3 or 4, wherein the switching element comprises:

a first transistor and a second transistor, the first transistor is connected between the synonym terminal and the ground terminal of the first drive winding, and the second transistor is connected between the synonym terminal and the ground terminal of the first drive winding In between, the ground terminal is connected to the intermediate node of the first bipolar transistor and the second bipolar transistor.

6. The constant current control circuit according to claim 5, further comprising:

The first operational amplifier and the second operational amplifier are respectively connected to the control terminals of the first transistor and the second transistor,

Wherein, the driving module provides a turn-on signal, the first operational amplifier and the second operational amplifier provide a turn-off signal, and the switch control signals of the first transistor and the second transistor are the turn-on signal and the turn-off signal. The superimposed signal of the off signal.

7. The constant current control circuit according to claim 6, wherein the respective non-inverting input terminals of the first operational amplifier and the second operational amplifier receive a negative potential reference voltage, and the inverting input terminals are connected to the respective output terminals, In order to realize the negative voltage clamping of the same name terminal and the different name terminal of the corresponding winding of the second transformer.

8. The constant current control circuit according to claim 3 or 4, wherein the switching element comprises:

The first transistor and the second transistor are connected in reverse series between the same name terminal and the ground terminal of the corresponding winding of the second transformer, and the different name terminal and the ground terminal of the corresponding winding of the second transformer are connected to the ground terminal. an intermediate node between the first bipolar transistor and the second bipolar transistor.

9 . The constant current control circuit according to claim 8 , wherein the driving module is connected to the control terminals of the first transistor and the second transistor to provide a switch control signal. 10 .

10 . The constant current control circuit according to claim 1 , wherein the first transformer comprises a primary winding and a secondary winding, the primary winding is a part of a resonant circuit, and the secondary winding is the same as the primary winding. 11 . side windings are coupled to provide a resonant output voltage,

Wherein, the output current calculation module obtains the compensation signal according to the current sampling signal of the resonance current and the voltage feedback signal of the resonance output voltage.

11. The constant current control circuit according to claim 10, wherein the output current calculation module comprises:

The third operational amplifier and the third transistor connected to the output terminal are used to generate the first current;

the fourth operational amplifier and the fourth transistor connected to the output terminal are used for generating the second current;

a plurality of current mirrors for subtracting the first current and the second current to generate an equivalent charging current; and

a capacitor for integrating the equivalent charging current to generate the compensation signal,

Wherein, the non-inverting input terminals of the third operational amplifier and the fourth operational amplifier respectively receive the first reference voltage and the second reference voltage, and the inverting input of one of the third operational amplifier and the fourth operational amplifier One terminal receives the current sampling signal, and the other inverting input terminal is grounded.

12. The constant current control circuit according to claim 11, wherein the output current calculation module further comprises:

a first switch, used for selectively grounding the inverting input terminal of the third operational amplifier or receiving the current sampling signal;

a second switch, used for selectively grounding the inverting input terminal of the fourth operational amplifier or receiving the current sampling signal;

a comparator that compares the voltage feedback signal with a third reference voltage to generate control signals for the first switch and the second switch.

13. The constant current control circuit of claim 11, wherein the second reference voltage is greater than the first reference voltage.

14. The constant current control circuit according to claim 1, wherein the driving module further comprises:

an oscillator that generates a clock signal based on the ramp signal and the compensation signal; and

The logic module generates a turn-on signal or a switch control signal according to the clock signal.

15. A constant current control method for an LLC resonant converter comprising a first transformer, a first bipolar transistor and a second bipolar transistor, the first bipolar transistor and The second bipolar transistor works in a self-excited oscillation mode, so that the resonant current and the excitation current flow through the primary winding of the first transformer, and the constant current control method includes:

calculating the average value of the absolute value of the difference between the resonance current signal and the first transformer excitation current signal to obtain a compensation signal;

Control the conduction state of the switching element according to the compensation signal so as to realize the control of the resonant frequency, so as to realize the constant current control,

Wherein, the driving current of at least one of the first bipolar transistor and the second bipolar transistor is short-circuited when the switching element is turned on.

16. The constant current control method according to claim 15, wherein the step of obtaining the compensation signal comprises:

comparing the current sampling signal of the resonant current signal with a first reference voltage to generate a first current;

using a second reference voltage to generate a second current;

subtracting the first current and the second current to generate an equivalent charging current; and

integrating the equivalent charging current to generate the compensation signal,

Wherein, the second reference voltage is greater than the first reference voltage.

17. The constant current control method according to claim 16, further comprising: switching the path of the current sampling signal according to the resonant output voltage signal to obtain the difference between the resonant current signal and the first transformer excitation current signal. The average of the absolute values of the differences.

18. The constant current control method of claim 17, wherein the resonant output voltage signal is compared with a third reference voltage to obtain a path switching signal of the circuit sampling signal.

19. The constant current control method according to claim 15, further comprising performing negative voltage clamping on the control terminals of the first bipolar transistor and the second bipolar transistor.