CN111555626B - Control method and system of active clamp flyback converter - Google Patents

Abstract

The invention discloses a control method of an active clamp flyback converter and a system thereof. A working mode combining non-complementary energy storage and complementary energy discharge is adopted. In the non-complementary energy storage working mode, the energy of leakage inductance It is stored in the clamping capacitor. After each cycle, the voltage across the clamping capacitor rises. When the set threshold voltage is reached, the converter changes from the non-complementary energy storage mode to the complementary energy discharge mode. After working in the working mode for one cycle, jump to the non-complementary energy storage mode again, which can realize the ZVS of the main switch tube and the clamp switch tube without losing the duty cycle, and reduce the energy consumption in each cycle. Primary current rms value I _rms .

Description

A control method and system for an active clamp flyback converter

technical field

The invention relates to a switching power supply, in particular to a control method and a system of an active clamp flyback converter.

Background technique

In the application of low-power converters, the flyback converter is one of the commonly adopted topologies. In the actual working process, due to the existence of leakage inductance, the flyback converter often needs a clamping circuit. In recent years, the active-clamp flyback converter can achieve leakage inductance energy recovery and soft switching, which greatly improves the operating frequency and efficiency, and has gradually become a low-power converter to improve power density, switching frequency and efficiency. solution.

Generally speaking, designers usually design the active-clamp flyback converter as a continuous operation mode and use a complementary control strategy under the condition of low input voltage. The circuit in this working state can realize ZVS (zero voltage) of all switches. switch). And because it is a complementary drive, the clamp switch tube will always be in a conducting state during the operation of the clamp circuit, and the body diode will not have a reverse recovery problem. In addition, due to the long conduction time of the clamp switch, the current change slope in the circuit is small, and the EMI performance is better. As the input voltage increases, or the output power decreases, the circuit will enter a discontinuous mode of operation. If the complementary control strategy is still used in the discontinuous operation mode, although ZVS of all switches can be achieved, the excitation current and leakage inductance current on the primary side of the transformer will surge in the reverse direction after losing the output clamp on the secondary side.

In view of the above situation, the non-complementary control strategy is gradually developed. The literature "A Novel Noncomplementary Active Clamp Flyback Control Technique" proposes a new non-complementary control strategy for the active clamp flyback converter. As shown in Figure 1, its topology is the same as the traditional synchronous rectification active-clamp flyback converter, but it has some innovations in the control strategy. The traditional non-complementary control strategy is shown in Figure 2, where I _s is the current on the secondary side, I _p represents the current flowing through the transformer, and the dotted line represents the magnetizing current, V _ds is the main voltage across the switch tube, and V _gsw is the main The drive waveform of the switch tube, V _gsa is the drive waveform of the clamp switch tube, and V _gsr is the drive waveform of the synchronous rectifier switch tube.

As shown in Figure 2: at time t ₀ , the main switch tube is disconnected, the clamp switch tube and the synchronous rectifier switch tube have not been turned on, at this time the leakage inductance and excitation inductance charge the output capacitor of the main switch tube, and the clamp switch tube When the voltage across the main switch tube rises to the point where the body diode of the clamp switch tube is turned on, that is, at time _t1 , the synchronous rectifier switch tube is turned on. During the time period from _t1 to _t2 , the leakage At the same time, the excitation inductance is clamped by the secondary side, which couples the energy to the secondary side, and at t ₂ , all the leakage inductance energy is transferred. From t ₂ to t ₃ , only the synchronous rectifier switch is turned on. , at this time, the excitation inductance continuously transmits energy to the secondary side. At the time of _t3 , all the energy of the excitation inductance is transmitted. At this moment, the clamp switch is turned on, and the clamp capacitor and the transformer form a loop, coupling part of the energy on the clamp capacitor to the The secondary side resonates with the leakage inductance at the same time. _At time t4, the clamp switch and the synchronous rectifier switch are turned off. At this time, the leakage inductance discharges the output capacitor of the main switch and charges the output capacitor of the clamp switch until t At time ₅ , the output capacitor of the main switch tube is completely discharged to realize the ZVS of the main switch tube. At this moment, the main switch tube is turned on, and the power supply excites the excitation inductor to form a complete cycle.

In this mode, the ZVS of the main switch tube can be well realized, but at the same time there are some disadvantages: the clamp switch tube is disconnected in the time period of t ₁ ~ t ₂ , and the clamp capacitor is charged through the body diode, resulting in diode conduction. Loss, usually the body diode reverse recovery characteristics are very poor, fast current change rate will cause the body diode reverse recovery current of the clamping switch to increase, and the body diode reverse recovery will also affect the service life of the device. During the time period from t ₃ to t ₄ , the circulating energy on the primary side loop is too large, resulting in a higher I _rms (root mean square value of the primary side current), resulting in a greater conduction loss.

The new non-complementary control strategy proposed in the article "A Novel Noncomplementary Active Clamp Flyback Control Technique" is shown in Figure 3. The meanings of all variables in Figure 3 are not different from those shown in Figure 2. The difference is t ₁ ~ t ₂ During the time period, the clamp switch is turned on, which reduces the conduction loss of the body diode in the clamp switch _. During the time period of _t3 to t4, the synchronous rectifier switch is turned off, the clamp switch is turned on, and the main switch is turned on. The tube is disconnected, and the excitation inductance and the leakage inductance are discharged at the same time through the clamping tube, so that the falling rate of I _p is reduced, so as to achieve the effect of reducing I _rms . However, the drawbacks it brings are also obvious. The energy transferred to the secondary side in each cycle is reduced, and due to the reduced rate of I _p decline, it takes more time to reset the clamping capacitor, which leads to The duty cycle of its main switch tube decreases within one cycle, and the loss of the duty cycle will lead to a decrease in the load capacity of the entire system.

To sum up the above, although the non-complementary control strategy solves the problem of reverse surge in the traditional complementary active clamp flyback circuit when the high input voltage enters the discontinuous operation mode, the excitation current and leakage inductance current of the primary side of the transformer loses the secondary side output clamp. , the non-complementary control strategy also has some problems, that is, the energy transmitted from the primary side to the secondary side decreases, and there is a duty cycle loss, which leads to a decrease in its load capacity.

SUMMARY OF THE INVENTION

Based on the problems existing in the prior art, the present invention proposes a control method and system for an active clamp flyback converter, specifically a control method and system combining non-complementary and complementary synchronous rectification , can realize the ZVS of the main switch tube and the clamp switch tube without losing the duty cycle, while reducing the primary current rms value I _rms in each cycle, thereby improving the overall converter work efficiency.

In order to achieve the above purpose of the invention, the technical solution adopted in the present invention is as follows: a control method of an active clamp flyback converter, based on the circuit topology of the active clamp flyback converter, including an input voltage source Vin, a main switch tube Sw, the clamping switch Sa, the clamping capacitor Cclamp, the synchronous rectification switch Sr, the leakage inductance Lr of the transformer on the primary side, the excitation inductance Lm of the transformer, the output filter capacitor Co, the load R and the output voltage Vo, among which the clamping capacitor Cclamp It is connected in series with the clamping switch tube Sa to form a clamping circuit;

It is characterized in that: a working mode combining non-complementary energy storage and complementary energy discharge is adopted. In the non-complementary energy storage working mode, the energy of the leakage inductance Lr is stored in the clamping capacitor Cclamp, and a non-complementary energy storage working mode is completed. After the cycle, the voltage across the clamping capacitor Cclamp rises, and when the voltage at the drain terminal of the main switch Sw reaches the set threshold voltage Vth, the converter changes from the non-complementary energy storage mode to the complementary energy discharge mode. After working in the working mode for one cycle, it will jump to the non-complementary energy storage mode again;

The non-complementary energy storage working mode includes the following steps:

S1, first, the main switch Sw is turned on, the clamp switch Sa and the synchronous rectifier switch Sr are turned off, and the voltage source Vin stores energy to the excitation inductor Lm;

S2, after the conduction time of the main switch Sw, the main switch Sw is turned off, and the excitation inductance Lm and the leakage inductance Lr charge the junction capacitance of the main switch Sw during the dead time, and the clamping switch Sa and the synchronization The junction capacitance of the rectifier switch Sr is discharged, and the drain voltage of the main switch Sw rises;

S3, after the dead time, the clamp switch Sa and the synchronous rectifier switch Sr are turned on, the remaining leakage inductance Lr energy is stored in the clamp capacitor Cclamp, and at the same time, the energy of the primary excitation inductance Lm is transmitted to On the secondary side, at this time, by detecting the drain voltage Vds of the main switch Sw and comparing it with the set threshold voltage Vth, if Vds>=Vth, it will jump to the complementary discharge mode after this work cycle is completed, otherwise, The next working cycle is still the non-complementary energy storage working mode;

S4, the leakage inductance current is close to 0, the clamping switch Sa is turned off to prevent the current reverse of the clamping capacitor Cclamp, the excitation inductance Lm continues to transmit energy to the secondary side, and at the same time, the secondary side current is detected, and when the secondary side excitation current exceeds At zero time, the synchronous rectifier switch Sr is triggered to turn off;

S5, in the dead time period after the synchronous rectification switch Sr is turned off and before the main switch Sw is turned on, the clamp switch Sa is turned on, and the excitation inductance Lm and the leakage inductance Lr are reversely excited, so that the main switch Sw achieves zero Prepare the voltage switch ZVS;

S6 , the clamping switch Sa is turned off after the on-time of the clamping switch Sa; then the main switch Sw is turned on to realize ZVS; a working cycle of the non-complementary energy storage working mode is completed.

In the non-complementary energy storage working mode, the switching waveforms of the main switch Sw and the clamping switch Sa are not complementary waveforms; in the complementary energy releasing working mode, the switching waveforms of the main switch Sw and the clamping switch Sa are: Complementary waveform.

The control system for realizing the control method of the active clamp flyback converter is characterized in that: the setting includes a peak current sampling circuit, a drain-source voltage sampling circuit, an output current detection circuit, an output voltage isolation sampling circuit, a control logic circuit and a gate The control system composed of the drive circuit forms a closed loop with the active clamp flyback converter topology; the peak current sampling circuit samples the peak current Ics when the main switch Sw is turned on through the sampling resistor Rcs, and the drain-source voltage sampling circuit samples the main switch Sw. The drain voltage is proportionally reduced to a size Vds that can be recognized by the control logic circuit, and the output current detection circuit obtains the output current Io by detecting the voltage at both ends of the synchronous rectification switch Sr during the conduction period of the synchronous rectification switch Sr. The above The peak current Ics, the proportionally reduced drain voltage Vds, the output current Io, and the output voltage Vo obtained by the output voltage isolation sampling circuit are all connected to the control logic circuit, and the output of the control logic circuit is connected to the gate drive circuit. The circuit outputs three control signals Vgsa, Vgsw and Vgsr which are respectively connected to the gates of the main switch Sw, the clamp switch Sa and the synchronous rectifier switch Sr.

The control logic circuit includes a comparator A, a non-complementary energy storage controller, a complementary energy discharge controller and a PWM gate signal generation module. The positive input terminal of the comparator A is connected to the drain terminal voltage Vds output by the drain-source voltage sampling circuit, The negative input terminal of the comparator A is connected to the set threshold voltage Vth, and the output of the comparator A is connected to the input terminals of the non-complementary energy storage controller and the complementary energy discharge controller respectively. The non-complementary energy storage controller also has a peak current Ics , output current Io and output voltage Vo three input terminals, the output of the non-complementary energy storage controller and the output of the complementary energy amplifying controller are connected to the PWM gate signal generation module, and the three gates output by the PWM gate signal generation module The logic signals generate corresponding three control signals Vgsa, Vgsw and Vgsr through the gate driving circuit.

触发器A的置位端

连接或门的输出端，触发器A的输出端Q输出栅极逻辑信号Vgsw；栅极逻辑信号Vgsr和Vgsa分别连接或门的两个输入端；触发器A的输出端

连接触发器B的置位端

触发器B的复位端

连接比较器C的输出端，比较器C的正输入端连接输出电流Io，比较器C的负输入端接地，触发器B的输出端Q输出栅极逻辑信号Vgsr并连接定时器A的输入端，定时器A输出栅极逻辑信号Vgsa。The non-complementary energy storage controller includes a compensation network, a comparator B, a comparator C, a flip-flop A, a flip-flop B, a timer A and an OR gate, and two input ends of the compensation network are respectively connected to the reference voltage Vref and the output voltage Vo, the compensation network output reference current Iref is connected to the positive input of comparator B, the peak current Ics is connected to the negative input of comparator B, and the output of comparator B is connected to the reset terminal of flip-flop A

The set terminal of flip-flop A

The output terminal of the OR gate is connected, the output terminal Q of the flip-flop A outputs the gate logic signal Vgsw; the gate logic signals Vgsr and Vgsa are respectively connected to the two input terminals of the OR gate; the output terminal of the flip-flop A

Connect the set terminal of flip-flop B

Reset terminal of flip-flop B

Connect the output terminal of the comparator C, the positive input terminal of the comparator C is connected to the output current Io, the negative input terminal of the comparator C is grounded, the output terminal Q of the flip-flop B outputs the gate logic signal Vgsr and is connected to the input terminal of the timer A , the timer A outputs the gate logic signal Vgsa.

The complementary energy amplifying controller includes a timer B, an inverter A and an inverter B. The input of the timer B is connected to the output of the comparator A, and the timer B outputs the gate logic signal Vgsw and outputs it through the inverter A. The gate logic signal Vgsa passes through the inverter B and outputs the gate logic signal Vgsr.

Advantages and significant effects of the present invention: The control method and system for combining non-complementary energy storage and complementary energy discharge proposed by the present invention can realize the main switch tube and the clamp switch without losing the duty cycle. While reducing the ZVS of the tube, the primary current root mean square value I _rms in each cycle is reduced, thereby improving the working efficiency of the entire converter.

Description of drawings

Fig. 1 is a circuit schematic diagram of a typical active clamp synchronous rectification flyback converter in the prior art;

FIG. 2 is a key signal waveform diagram of a typical non-complementary mode active-clamp synchronous rectification flyback converter in the prior art;

Figure 3 is the key signal waveform diagram of the non-complementary control strategy proposed in "A Novel Noncomplementary Active Clamp Flyback ControlTechnique";

Fig. 4 is the control system principle diagram of the present invention;

Fig. 5 is the key signal waveform diagram of the control method of the present invention;

Fig. 6 is the circuit structure of the control system of the present invention;

Fig. 7 is the structure of the non-complementary energy storage controller in the control system of the present invention;

FIG. 8 is the structure of the complementary energy releasing controller in the control system of the present invention.

Detailed ways

The present invention adopts the working mode of the combination of non-complementary energy storage and complementary energy discharge. In the non-complementary energy storage working mode, the energy of the leakage inductance Lr is stored in the clamping capacitor Cclamp, and after one cycle of the non-complementary energy storage working mode is completed , the voltage across the clamp capacitor Cclamp rises. When the voltage at the drain terminal of the main switch Sw reaches the set threshold voltage Vth, the converter changes from the non-complementary energy storage mode to the complementary energy discharge mode. In the complementary energy discharge mode Re-jump to non-complementary energy storage mode after working for one cycle;

The non-complementary energy storage working mode includes the following steps:

S1, first, the main switch Sw is turned on, the clamp switch Sa and the synchronous rectifier switch Sr are turned off, and the voltage source Vin stores energy to the excitation inductor Lm;

S2, after the conduction time of the main switch Sw, the main switch Sw is turned off, and the excitation inductance Lm and the leakage inductance Lr charge the junction capacitance of the main switch Sw during the dead time, and the clamping switch Sa and the synchronization The junction capacitance of the rectifier switch Sr is discharged, and the drain voltage of the main switch Sw rises;

S3, after the dead time, the clamp switch Sa and the synchronous rectifier switch Sr are turned on, the remaining leakage inductance Lr energy is stored in the clamp capacitor Cclamp, and at the same time, the energy of the primary excitation inductance Lm is transmitted to On the secondary side, at this time, by detecting the drain voltage Vds of the main switch Sw and comparing it with the set threshold voltage Vth, if Vds>=Vth, it will jump to the complementary discharge mode after this work cycle is completed, otherwise, The next working cycle is still the non-complementary energy storage working mode;

S4, the leakage inductance current is close to 0, the clamping switch Sa is turned off to prevent the current reverse of the clamping capacitor Cclamp, the excitation inductance Lm continues to transmit energy to the secondary side, and at the same time, the secondary side current is detected, and when the secondary side excitation current exceeds At zero time, the synchronous rectifier switch Sr is triggered to turn off;

S5, in the dead time period after the synchronous rectification switch Sr is turned off and before the main switch Sw is turned on, the clamp switch Sa is turned on, and the excitation inductance Lm and the leakage inductance Lr are reversely excited, so that the main switch Sw achieves zero Prepare the voltage switch ZVS;

S6 , the clamping switch Sa is turned off after the on-time of the clamping switch Sa; then the main switch Sw is turned on to realize ZVS; a working cycle of the non-complementary energy storage working mode is completed.

Non-complementary working energy storage mode: the switching waveforms of the main switch Sw and the clamping switch Sa are not complementary waveforms, and each cycle charges the clamping capacitor Cclamp, so that the voltage across the clamping capacitor Cclamp rises, and at the same time the main switch Sw is The drain voltage rises. Specific steps are as follows:

(1) The main switch Sw is turned on, the clamping switch Sa and the synchronous rectification switch Sr are turned off, the voltage source Vin stores energy to the excitation inductance Lm, the main switch Sw is turned off, and the excitation inductance Lm and the leakage inductance Lr are supplied to the main switch The junction capacitance of the tube Sw is charged, and the junction capacitance of the clamp switch Sa and the synchronous rectifier switch Sr is discharged, the drain voltage of Sw rises, and the clamp switch Sa is turned on to store the remaining leakage inductance energy through the clamp capacitor Cclamp. , at the same time turn on the synchronous rectification switch tube Sr to transmit the energy of the primary side excitation inductance to the secondary side, and turn off the clamp switch tube Sa when the leakage inductance energy transmission is completed.

(2) During the off period of the main switch Sw, the current of the secondary side is detected by the secondary side current detection circuit, and the zero-crossing moment of the secondary side current is detected. At this time, the synchronous rectification switch Sr is turned off, the clamp switch Sa is turned on, and the clamp The bit capacitor Cclamp resonates with the excitation inductance Lm and the leakage inductance Lr to form a negative current that can realize ZVS (zero voltage switching) of the main switch tube Sw.

(3) After a period of dead time, the main switch Sw realizes ZVS, the main switch Sw is turned on, and the non-complementary energy storage mode completes one cycle.

Complementary work amplifying working mode: the switching waveforms of the main switch Sw and the clamping switch Sa are complementary waveforms, and the duty cycle of the main switch Sw is smaller than that of the non-complementary work amplifying mode, and in this working mode, in In one cycle, the clamping capacitor Cclamp is discharged and coupled to the secondary side, so that the voltage at both ends of the clamping capacitor Cclamp drops, and at the same time, the voltage at the drain terminal of the main switch tube Sw is lowered. Specific steps are as follows:

(1) The main switch Sw is turned on, the clamping switch Sa and the synchronous rectification switch Sr are turned off, the voltage source Vin stores energy to the excitation inductance Lm, the main switch Sw is turned off, and the excitation inductance Lm and the leakage inductance Lr are supplied to the main switch The junction capacitance of the tube Sw is charged, and the junction capacitance of the clamp switch Sa and the synchronous rectifier switch Sr is discharged, the drain voltage of the main switch Sw rises, and the clamp switch Sa is turned on to transfer the remaining leakage inductance energy to the clamp capacitor Cclamp The energy is stored, and the clamping switch Sa is turned on to transfer the energy of the primary side excitation inductance to the secondary side.

(2) Turn off the clamp switch Sa and the synchronous rectifier switch Sr, stop the discharge of the clamp capacitor Cclamp, and at the same time, the negative current formed by the leakage inductance and the excitation inductance enables the ZVS of the main switch Sw to be realized. Then the main switch is turned on. The switch tube Sw is switched from the complementary energy discharge working mode to the non-complementary energy storage working mode.

The converter charges the clamping capacitor in multiple cycles of non-complementary energy storage working mode, so that the energy stored in the clamping capacitor increases in each cycle. By detecting that the main switch Sw is turned off in the non-complementary working mode, the clamping switch When the transistor Sa is turned on, the drain voltage of the main switch Sw is compared with the set threshold voltage Vth. If the drain voltage of the main switch Sw is greater than the set threshold voltage Vth, after this non-complementary energy storage working cycle , switch to the complementary working energy discharging mode, and switch to the non-complementary energy storage working mode here after the complementary energy discharging working mode is completed.

It is converted from the non-complementary energy storage mode to the complementary energy discharge mode, and then the complementary energy discharge mode works for one cycle and then changes to the non-complementary energy storage mode. The conversion stage is shown in Figure 5.

The non-complementary energy storage working mode states are as follows:

所以磁化电感以及漏感电流线性增大。0～t ₀ : The main switch Sw is turned on, the clamp switch Sa and the synchronous rectifier switch Sr are disconnected, and the power supply excites the magnetizing inductance and leakage inductance, there are

Therefore, the magnetizing inductance and the leakage inductance current increase linearly.

t ₀ ~ t ₁ : It is shown by magnification in Figure 5 that the dead time is actually very small. At this moment, the main switch Sw is turned off, and the leakage inductance and magnetizing inductance charge the output capacitor of the main switch Sw, and the clamp switch The output capacitor of Sa is discharged, and at this stage, the voltage V _ds across the main switch Sw increases approximately linearly. When it rises to about V _in +V _c , the body diode of the clamp switch Sa is turned on.

线性下降。t ₁ ～ t ₂ : Turn on the clamping switch Sa and the synchronous rectification switch Sr, at this stage V _ds is clamped by the secondary side, the magnetizing inductance transfers energy to the secondary side through the magnetic core, and the leakage inductance passes through the clamping switch Sa to the secondary side. The clamping capacitor Cclamp is charged, and the leakage inductance current decreases approximately linearly at this stage, and the magnetizing inductance is

Linear decline.

t ₂ ～ t ₃ : At the moment of t ₂ , the leakage inductance current is close to 0, and the clamping switch Sa is turned off. At this stage, only the magnetizing inductance transfers energy to the secondary side.

其中Im_为为了实现主开关管Sw零电压开关所需要的负电流，Csw为等效结电容，Vds为主开关管Sw两端电压，Lm为励磁电感的感值。t ₃ ~ t ₄ : At time t ₃ , the magnetizing inductance energy is fully coupled to the secondary side, the synchronous rectifier switch Sr is turned off, the clamping switch Sa is turned on, and the magnetizing inductance and leakage inductance are reversely charged through the clamping capacitor Cclamp, which is The main switch tube Sw is ready to realize ZVS. At this stage, the clamp capacitor Cclamp is not completely reset, but only releases part of the energy to realize the ZVS of the main switch Sw, which should meet the

Among them, Im_ is the negative current required to realize the zero-voltage switching of the main switch tube Sw, Csw is the equivalent junction capacitance, Vds is the voltage across the main switch tube Sw, and Lm is the inductance value of the excitation inductance.

t ₄ to t ₅ : at time t ₄ , the clamping switch Sa is turned off during the time period of t ₄ to t ₅ . Since the leakage inductance and the current in the magnetizing inductance cannot change abruptly, they resonate with the capacitance of the main switch Sw and the clamp switch Sa. During this process, after the output capacitance of the main switch Sw drops to 0, the leakage is realized through the body diode. Inductance and freewheeling of the magnetizing inductance realize the ZVS of the main switch Sw.

_At time t5, the main switch is turned on to complete a cycle.

In the above operating modes, the clamping capacitor Cclamp is charged every cycle.

Complementary discharge mode states are as follows:

t ₅ to t ₆ : During this time period, the main switch Sw is turned on, the clamp switch Sa and the synchronous rectifier switch Sr are turned off, the power supply excites the leakage inductance and the magnetizing inductance, and the current increases linearly. Compared with the first working state, this time period is smaller, and at the same time, the ZVS of the clamping switch tube Sa can be realized.

t ₆ to t ₇ : During this time period, the main switch Sw is turned off, the leakage inductance and the magnetizing inductance charge the output capacitance of the main switch Sw, discharge the output capacitance of the clamp switch Sa, and the two ends of the main switch Sw The voltage rises to about V _in +V _c , realizing the ZVS of the clamp switch Sa, and can.

t ₇ ~ t ₈ : During this time period, the main switch Sw is turned off, the clamp switch Sa and the synchronous rectifier switch Sr are turned on, at this moment the magnetizing inductance couples and transmits energy to the secondary side, and the leakage inductance resonates with the clamp inductance, During this time, the leakage inductance resonates with the clamping capacitor to reset the energy stored in the capacitor during the previous cycles.

t ₈ to t ₉ : During this time period, the clamp switch Sa and the synchronous rectifier switch Sr are turned off, and the leakage inductance resonates with the output capacitance of the main switch Sw at this moment, the absolute value of the leakage inductance current decreases, and the main switch The voltage at both ends of Sw drops to realize the ZVS of the main switch Sw.

t ₉ to t ₁₀ : At time t ₉ , the energy of the leakage inductance and the magnetizing inductance returns to the power supply, and at time t ₁₀ , the next control state is started.

所以磁化电感以及漏感电流线性增大。重复进入非互补导通储能模式。t ₁₀ ~ t ₁₁ : the main switch Sw is turned on, the clamp switch Sa and the synchronous rectifier switch Sr are disconnected, and the power supply excites the magnetizing inductance and the leakage inductance, there are

Therefore, the magnetizing inductance and the leakage inductance current increase linearly. Repeatedly enter the non-complementary conduction energy storage mode.

As shown in Figure 4, the control system for realizing the control method of the active clamp flyback converter includes a peak current sampling circuit, a drain-source voltage sampling circuit, an output current detection circuit, an output voltage isolation sampling circuit, a control logic circuit and a gate drive The control system formed by the circuit forms a closed loop with the active clamp flyback converter topology. Among them, the peak current sampling circuit, the drain-source voltage sampling circuit, the output current detection circuit, the output voltage isolation sampling circuit and the gate driving circuit are all well-known circuits.

As shown in Figure 6, the control logic circuit includes two different controllers as well as a comparator A and a PWM signal generation module. The output terminal of the comparator A is connected to the enabling terminal of the non-complementary energy storage controller and the complementary energy discharge controller. The non-complementary energy storage controller is active at a high level and controls the converter to work in the non-complementary energy storage working mode; the complementary energy discharge The controller is active low and controls the converter to work in the complementary amplifying mode. At the end of each duty cycle, the comparator A compares the signal Vds sampled by the drain-source voltage sampling circuit with the set threshold voltage Vth to determine whether the system is switched from the non-complementary energy storage mode to the complementary energy discharge mode.

As shown in FIG. 7 , the non-complementary energy storage controller includes a compensation network, a comparator B, a comparator C, a flip-flop A, a flip-flop B, an OR gate, and a timer A. Among them, the compensation network is to realize the closed-loop stability and dynamic response speed required for the realization of the switching power supply. Usually, the two-type compensation network and the third-type compensation network are used, which are already mature technologies and will not be repeated here. Among them, the falling edge of timer A is triggered to generate a constant pulse width signal.

The non-complementary energy storage controller outputs the voltage signal Vo and the peak current signal Ics, and adjusts the duty cycle of the gate signal of the main switch tube through the peak current closed-loop feedback, thereby stably controlling the output voltage of the converter. The ratio of the collected voltage output signal Vo and the set reference voltage Vref is passed through the compensation network to generate a peak current reference signal, and the current signal Ics sampled by the peak current sampling circuit is compared with the signal Iref in the comparator B to generate Control the gate signal Vgsw logic signal of the main switch Sw, when Ics<=Iref, the main switch Sw maintains the original state, when Ics>Iref, the main switch Sw is disconnected through the trigger, so when the load or input When the voltage changes, the on-time of the main switch Sw can be controlled by the peak current feedback, thereby achieving a stable voltage output.

触发器B的复位端

接比较器C的输出信号。输出电流检测电路通过采样获得的输出电流Io与零比较，当输出电流Io下降至零是输出低电平，下降沿触发触发器B，从而控制Vgsr逻辑信号由高电平转为低电平。Vgsr逻辑信号接入定时器A，下降沿触发定时器，输出一个恒定脉宽的Vgsa逻辑信号，在该时间内，钳位开关管导通，通过钳位电容与励磁电感谐振，从而获得实现主开关管Sw的ZVS。The Vgsr logic signal and the Vgsa logic signal are connected to the OR gate. If and only when the Vgsr logic signal and the Vgsa logic signal are both low level, trigger the main switch Sw to output a high level signal through the trigger A, and control the main switch Sw to conduct Pass. The Q terminal of the flip-flop B outputs the Vgsw logic signal, and the output terminal of the other terminal outputs the synchronous rectification switch, which is connected to the set terminal of the flip-flop B.

Reset terminal of flip-flop B

Connect to the output signal of comparator C. The output current detection circuit compares the output current Io obtained by sampling with zero. When the output current Io drops to zero, it outputs a low level, and the falling edge triggers the flip-flop B, thereby controlling the Vgsr logic signal to change from a high level to a low level. The Vgsr logic signal is connected to the timer A, the falling edge triggers the timer, and outputs a Vgsa logic signal with a constant pulse width. During this time, the clamp switch is turned on, and the clamp capacitor resonates with the excitation inductance, so as to achieve the main ZVS of switch Sw.

As shown in Figure 8, the complementary amplifying energy controller includes timer B and two inverters, in which the rising edge of timer B is triggered and outputs a constant pulse width signal. The input terminal of timer B is connected to the output terminal of comparator A, the output terminal of timer B is Vgsw logic signal, the output terminal of timer B is also connected to inverter A and inverter B respectively, and inverter A outputs Vgsa Logic signal, inverter B outputs the Vgsr logic signal.

When the complementary energy discharge controller starts to work, the main switch Sw for a fixed time is turned on to excite the excitation inductance in a positive direction, then the main switch Sw is turned off, and the clamp switch Sa and the synchronous rectifier switch are turned on for a constant time. The tube Sr releases the energy stored in the clamping inductor. The complementary energy discharge controller is turned off, and the non-complementary energy storage controller is turned on, and the cycle is repeated.

Claims (7)

1. A control method of an active clamp flyback converter is based on a circuit topology of the active clamp flyback converter and comprises an input voltage source Vin, a main switching tube Sw, a clamp switching tube Sa, a clamp capacitor Cclamp, a synchronous rectification switching tube Sr, a leakage inductance Lr of a transformer on the primary side, an excitation inductance Lm of the transformer, an output filter capacitor Co, a load R and an output voltage Vo, wherein the clamp capacitor Cclamp and the clamp switching tube Sa are connected in series to form a clamp circuit;

the method is characterized in that: the energy storage and complementary energy release combined working mode is adopted, the energy of the leakage inductance Lr is stored to a clamping capacitor Cclamp in the non-complementary energy storage working mode, after the non-complementary energy storage working mode finishes one period, the voltage at two ends of the clamping capacitor Cclamp rises, when the voltage sampling value of the drain end of a main switching tube Sw reaches a set threshold voltage Vth, a converter is converted into a complementary energy release working mode from the non-complementary energy storage working mode, and the converter jumps to the non-complementary energy storage mode again after the complementary energy release working mode works for one period;

the non-complementary energy storage operating mode comprises the following steps:

s1, firstly, the main switch tube Sw is switched on, the clamping switch tube Sa and the synchronous rectification switch tube Sr are switched off, and the voltage source Vin stores energy to the excitation inductor Lm;

s2, after the conduction time of the main switching tube Sw, the main switching tube Sw is turned off, the excitation inductor Lm and the leakage inductor Lr charge the junction capacitor of the main switching tube Sw in the dead time, the junction capacitor of the clamping switching tube Sa and the synchronous rectification switching tube Sr is discharged, and the voltage of the leakage end of the main switching tube Sw rises;

s3, after dead time, the clamp switch tube Sa and the synchronous rectification switch tube Sr are conducted, the rest energy of the leakage inductance Lr is stored in the clamp capacitor Ccclamp, meanwhile, the energy of the primary side excitation inductance Lm is transmitted to the secondary side, at the moment, the voltage of the leakage end of the main switch tube Sw is detected to obtain a sampling value Vds of the voltage of the leakage end, the sampling value Vds is compared with the set threshold voltage Vth, if Vds > is Vth, the complementary energy releasing working mode is jumped to after the working period is finished, otherwise, the non-complementary energy storing working mode is still set in the next working period;

s4, when the leakage inductance current is close to 0, the clamping switch tube Sa is turned off to prevent the current of the clamping capacitor Ccclamp from reversing, the excitation inductor Lm continues to transmit energy to the secondary side, and meanwhile, the secondary side current is detected, and when the excitation current of the secondary side passes through zero, the synchronous rectification switch tube Sr is triggered to be turned off;

s5, in the dead time after the synchronous rectification switch tube Sr is turned off and before the main switch tube Sw is turned on, the clamping switch tube Sa is turned on, and reverse excitation is carried out on the excitation inductor Lm and the leakage inductor Lr to prepare for the main switch tube Sw to realize a zero-voltage switch ZVS;

s6, turning off the clamp switching tube Sa after the on time of the clamp switching tube Sa; then the main switching tube Sw is switched on to realize ZVS; completing one working cycle of the non-complementary energy storage working mode.

2. The method of controlling an active-clamp flyback converter according to claim 1, wherein: in the non-complementary energy storage working mode, the switching waveforms of the main switching tube Sw and the clamping switching tube Sa are not complementary waveforms.

3. The method of controlling an active-clamp flyback converter according to claim 1, wherein: in the complementary discharging working mode, the switching waveforms of the main switching tube Sw and the clamping switching tube Sa are complementary waveforms.

4. A control system for implementing the control method of the active-clamp flyback converter of claim 1, characterized in that: the method comprises the steps that a control system consisting of a peak current sampling circuit, a drain-source voltage sampling circuit, an output current detection circuit, an output voltage isolation sampling circuit, a control logic circuit and a grid electrode driving circuit is arranged to form a closed loop with an active clamping flyback converter topology; the peak current sampling circuit samples a peak current Ics when the main switching tube Sw is switched on through a sampling resistor Rcs, the drain-source voltage sampling circuit samples the drain end voltage of the main switching tube Sw and reduces the drain end voltage in an equal proportion to a magnitude Vds which can be identified by the control logic circuit, the output current detection circuit obtains an output current Io by detecting the voltage at two ends of the synchronous rectification switching tube Sr in the conduction time period of the synchronous rectification switching tube Sr, the peak current Ics, the drain end voltage Vds after the equal proportion reduction, the output current Io and the output voltage Vo obtained by the output voltage isolation sampling circuit are all connected to the control logic circuit, the output of the control logic circuit is connected with a grid driving circuit, and the grid driving circuit outputs three control signals Vgsw, Vgsa and Vgsr which are respectively correspondingly connected with the grids of the main switching tube Sw, the clamping switching tube Sa and the synchronous rectification switching tube Sr.

5. The control system for realizing the control method of the active-clamp flyback converter according to claim 4, wherein: the control logic circuit comprises a comparator A, a non-complementary energy storage controller, a complementary energy release controller and a PWM grid signal generation module, wherein the positive input end of the comparator A is connected with a drain end voltage Vds output by a drain-source voltage sampling circuit, the negative input end of the comparator A is connected with a set threshold voltage Vth, the output of the comparator A is respectively connected with the input ends of the non-complementary energy storage controller and the complementary energy release controller, the non-complementary energy storage controller is further provided with three input ends of peak current Ics, output current Io and output voltage Vo, the output of the non-complementary energy storage controller and the output of the complementary energy release controller are respectively connected with the PWM grid signal generation module, and three grid logic signals output by the PWM grid signal generation module generate corresponding three control signals Vgsa, Vgsw and Vgsr through a grid driving circuit.

6. The control system for implementing the control method of the active-clamp flyback converter according to claim 5, wherein: the non-complementary energy storage controller comprises a compensation network, a comparator B, a comparator C, a trigger A, a trigger B, a timer A and an OR gate, wherein two input ends of the compensation network are respectively connected with a reference voltage Vref and an output voltage Vo, the compensation network outputs a reference current Iref to be connected with a positive input end of the comparator B, a peak current Ics to be connected with a negative input end of the comparator B, and the output of the comparator B is connected with a reset end of the trigger A

Set terminal of trigger A

The output end of the OR gate is connected, and the output end Q of the trigger A outputs a gate logic signal Vgsw; the grid logic signals Vgsr and Vgsa are respectively connected with two input ends of the OR gate; output terminal of flip-flop A

Set terminal connected with trigger B

Reset terminal of trigger B

The output end of the comparator C is connected, the positive input end of the comparator C is connected with the output current Io, the negative input end of the comparator C is grounded, the output end Q of the trigger B outputs a grid logic signal Vgsr and is connected with the input end of the timer A, and the timer A outputs a grid logic signal Vgsa.

7. The control system for implementing the control method of the active-clamp flyback converter according to claim 5, wherein: the complementary discharging controller comprises a timer B, an inverter A and an inverter B, wherein the input of the timer B is connected with the output of the comparator A, the timer B outputs a grid logic signal Vgsw and outputs a grid logic signal Vgsa through the inverter A, and the grid logic signal Vgsw outputs a grid logic signal Vgsr through the inverter B.

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