A kind of control method of auxiliary switching tube of active clamp flyback converter
The present invention relates to the controlling party converters owned by France of auxiliary switching tube of active clamp flyback converter.
The traditional control method that flyback converter leakage inductance reclaims has three kinds below:
1:RCD clamp circuit
RCD clamp circuit structure is the simplest, and cost is minimum, be easy to realize, but the energy in leakage inductance all consumes in buffer resistance, has reduced the efficiency of converter, and it is applicable to and the cost strict occasion controlled less demanding to efficiency.
2:LCD clamp circuit
LCD clamp circuit can be realized the leakage inductance energy feedback of passive and nondestructive, but need outer coilloading, parameter tuning is more difficult, but larger LC resonance current has increased the conduction loss of power switch during high frequency, is generally applicable to the occasion of switching frequency not too high (as tens kHz)
3: active clamp circuit
Active clamp circuit has increased an electric capacity and auxiliary switch, and traditional active clamp control method, in one-period, main switch and and the complementary conducting of auxiliary switch, can realize leakage inductance energy feedback, realize the soft switch of main switch and auxiliary switch, can realize high frequency conversion.Although at full load, traditional active clamp flyback control circuit efficiency is very high, when underloading, efficiency is still not high.
Summary of the invention
The object of the invention is to the defect existing for above-mentioned prior art, develop and a kind ofly can overcome now defectively, efficiency is not high, inverse-excitation type direct current-stream power supply change-over device that particularly light-load efficiency is not high.
Inverse-excitation type direct current-stream power supply change-over device of realizing above-mentioned purpose is comprised of inverse-excitation type main circuit and active clamp circuit.Circuit of reversed excitation comprises an input port, one or more transformers, and former limit switching tube, secondary rectifier diode, filter capacitor and an output port form.When switching tube conducting, rectifier diode cut-off, the energy of power supply input is stored in transformer with the form of magnetic energy, and when switching tube ends, the Energy Transfer storing in transformer is to load.Active clamp circuit comprises an auxiliary switch, a parasitic diode and an Absorption Capacitance.Wherein parasitic diode is the inverse parallel body diode of auxiliary switch parasitism.Auxiliary switch and the Absorption Capacitance composition auxiliary circuit that is in series.Auxiliary branch is connected in parallel on transformer primary side winding two ends or the switching tube two ends, former limit in parallel of circuit of reversed excitation.Each cycle of former limit switching tube is open-minded, and auxiliary switch is just open-minded every several cycles.
In control circuit, the production method of the control signal of auxiliary switch S2 is for (take voltage threshold circuit 2 as example, as Fig. 2): when the voltage in clamp capacitor Cr runs up to a certain value, the voltage Vr obtaining by divider resistance R1 and R2 also can rise to a certain value, this value is by the reference voltage V ref comparison with artificial setting, when voltage Vr is less than reference voltage V ref, low level of comparator output is to reset terminal R, now Q ' keeps low level always, auxiliary switch S2 in off state, clamp capacitor Cr is in charged state, charging can continue one-period or several cycle.When clamp capacitor Cr is charged to a certain degree, voltage Vr can be greater than reference voltage V ref, a high level of now comparator output is to reset terminal R, now drive signal Vpulse in low level state, Q ' can export a high level, thereby can make auxiliary switch S2 open-minded, property list by SR latch can be found out, as long as set end S is low level state, Q ' can export a high level always, makes auxiliary switch S2 always open-minded.Because the clamp capacitor Cr velocity of discharge is very fast, comparator can be exported a low level very soon, so the service time of auxiliary switch S2 can be by driving signal Vpulse to set.After clamp capacitor Cr has discharged, can set and drive signal Vpulse high level, auxiliary switch S2 turn-offs immediately.Note, open-minded in the time of for fear of S1 and S2 two pipe, drive signal Vpulse high level just to arrange before arriving at the signal of opening of former limit switching tube S1.
The control method of active clamp anti exciting converter of the present invention, has following advantages, and leakage inductance energy has obtained recovery, and the Energy Transfer of leakage inductance, to output, is realized in the cycle of opening at auxiliary switch simultaneously, the soft switch of former limit switch; By controlling opening and turn-offing of auxiliary switch, can reduce the on-off times of auxiliary switch, reduced the switching loss of auxiliary switch, can greatly improve the efficiency of circuit under underloading, reduce no-load loss.
Accompanying drawing explanation
The anti exciting converter schematic diagram of the control method of the active clamp auxiliary switch that the first that Fig. 1 this patent proposes is new.In figure shown in dotted line frame is voltage threshold control circuit 1.
The anti exciting converter schematic diagram of the control method of the active clamp auxiliary switch that the second that Fig. 2 this patent proposes is new.In figure shown in dotted line frame is voltage threshold control circuit 2.
The active clamp auxiliary switch control method of Fig. 3 based on voltage threshold control circuit 2, the gate pulse of anti exciting converter main switch and auxiliary switch and work wave.
The anti exciting converter work schematic diagram of the new control method of the active clamp auxiliary switch based on voltage threshold control circuit 2 that Fig. 4 this patent proposes.Work schematic diagram when figure (a) opens for main switch S1; Figure (b) is that main open pipe S1 closes the schematic diagram of having no progeny to parasitic capacitance C1 charging; Figure (c) is that leakage inductance energy is to the schematic diagram of clamp capacitor Cr charging; When the voltage that figure (d) is got by resistance for clamp capacitor Cr reaches fiducial value, auxiliary switch S2 is open-minded, the schematic diagram of clamp capacitor Cr electric discharge
(1) in conjunction with Fig. 3, constantly, auxiliary switch S2 is turned off t0, and former limit switching tube S1 and auxiliary switch S2 are simultaneously in off state.T
1former limit switching tube S1 conducting constantly, primary current rises, transformer storage power, auxiliary switch S2 and output rectifier diode D cut-off.Magnetizing inductance Lm and leakage inductance Lr linear-charging.Clamp capacitor Cr constant in energy, both end voltage also remains unchanged.
2constantly, the switching tube S1 conducting of former limit is turned off, and resonant inductance electric current is with resonance manner to parasitic capacitance C1 charging, and due to magnetizing inductance, Lm is larger, and former limit switching tube S1 drain-source both end voltage Vds approximately linear rises.
3constantly, Vds rises to Vi+Vc, and now the energy in leakage inductance Lr stores in clamp capacitor Cr by the body diode of auxiliary switch S2.The voltage linear at clamp capacitor Cr two ends rises.
4constantly, the energy in leakage inductance Lr is all absorbed by clamp capacitor Cr, and the voltage at Cr two ends rises to a stable value, is less than the voltage threshold of setting, remains unchanged.Primary current Ip drops to zero.The energy of magnetizing inductance Lm storage is released to outlet side, and Ilm is linear to decline, output rectifier diode D conducting.
5constantly, if the energy that clamp capacitor Cr absorbs has reached threshold value, directly enter t
6constantly.If no, circuit repeats the action in last cycle.The leakage inductance energy being stored in clamp capacitor Cr due to upper one-period does not discharge, so clamp capacitor Cr energy again increases on the basis of upper one-period, the voltage at clamp capacitor Cr two ends also rises to a stationary value again.Through the time in several cycles, the voltage at clamp capacitor Cr two ends can present a stair-stepping growth.
6constantly, the voltage at clamp capacitor Cr two ends has reached threshold voltage, and by divider resistance, by voltage Vr and Vref comparison, auxiliary switch S2 is opened, clamp capacitor Cr and leakage inductance Lr resonance, and clamp capacitor Cr discharges immediately.An energy part in Cr is discharged into output by transformer, and a part stores in leakage inductance.T
7primary current Ip discharges into maximum, oppositely increases subsequently.
8constantly, auxiliary switch S2 is turned off, leakage inductance Lr and parasitic capacitance C1 resonance.Parasitic capacitance C1 electric discharge, Vds declines.
9constantly, former limit switching tube S1 drain-source both end voltage Vds drops to zero.In order to prevent the common of S1 and S2, now S1 is still in off state.Until next cycle while arriving is open-minded by former limit switching tube S1, now to have realized no-voltage open-minded for S1.