A control circuit for active clamp converter

Abstract

The present invention discloses a control circuit of an active clamp converter, including an active clamp tube control circuit, which generates an on-enable signal by detecting the voltage across the drain and source of the active clamp tube to determine whether the zero voltage on condition is met, and generates an off-enable signal according to whether the power transformer, i.e., the magnetizing inductor, is completely magnetically reset, thereby realizing accurate control of the active clamp tube; a main switch tube on-enable circuit generates an on-enable signal of the main switch tube according to the source-to-ground voltage of the active clamp tube. The present invention does not require a secondary-side synchronous rectification control circuit or an isolation transformer, and the circuit is simple to implement, which is beneficial to improving the power density of the converter; and does not require generating an active clamp tube control signal based on the secondary-side synchronous rectification control circuit, and does not have the problem of premature shutdown caused by the package parasitic inductance; at the same time, the magnetizing inductor can be magnetically reset cycle by cycle, and the magnetizing inductor current can be reset to zero cycle by cycle, thereby ensuring soft switching and improving converter efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic conversion, in particular to a control circuit of an active clamping converter. Background Art

[0002] Compared with passive clamping technology (such as Zener diode clamping, RCD clamping, etc.), active clamping technology can recover the leakage inductance energy of the transformer, effectively suppress voltage spike problems, and reduce the voltage stress of the device. At the same time, the switch tube can realize soft switching to reduce switching losses. Therefore, it is widely used in power conversion occasions requiring high efficiency, high switching frequency, and high power density.

[0003] Figure 1 (a) shows a typical active clamp converter circuit topology - active clamp flyback converter, which is mainly composed of the primary side main switch tube S P , Active clamp tube S C , power transformer T1 (including magnetizing inductor L m And the primary side equivalent leakage inductance L r ), clamping capacitor C L , secondary rectifier diode D1 and output filter capacitor C o The typical working waveform of the converter is as follows: Figure 1 As shown in (b), the converter has two main working stages in one switching cycle, including the input energy storage stage (t0~t1) and the power transmission stage (t1~t2). In the input energy storage stage (t0~t1), the primary main switch tube S P On, input voltage V in Applied to the primary side of the power transformer T1, due to the leakage inductance L r Small magnetizing inductance L m , magnetizing inductor current i Lm Linear rise, slope is V in / L m . At time t1, S P The input energy storage phase ends, and then the active clamp tube S C The secondary rectifier diode D1 is turned on, and the converter enters the power transmission stage (t1~t2). The magnetizing inductor L m Transfer energy to the load, exciting the inductor current i Lm Linear decrease, slope is -V C / L m , where V C is the clamping capacitor C L The voltage across the terminals is due to L r Much smaller than L m , then V C / n=V o, where n is the ratio of the primary turns to the secondary turns of the power transformer T1. Lm After reaching zero, the secondary rectifier diode D1 realizes zero current shutdown and no reverse recovery problem, and then the active clamping tube S C The power transmission phase ends, and then the primary main switch tube S P The converter enters the next switching cycle.

[0004] From the above analysis, we can see that the active clamp tube S C The breaking moment of the active clamping diode S is consistent with the breaking moment of the secondary rectifier diode D1. Therefore, the active clamping transistor S can be accurately controlled according to the breaking state of the secondary rectifier diode D1. C , the magnetizing inductor is completely reset cycle by cycle, and the magnetizing inductor current is reset to zero cycle by cycle, thereby ensuring the soft switching of the switch tube and reducing the converter loss. However, this solution requires the secondary side of the converter to adopt synchronous rectification control, and then transmit the driving control signal of the synchronous rectifier tube to the primary side through isolation transformers, which will significantly increase the size of the converter and reduce the power density. Once the secondary side synchronous rectification control causes premature shutdown due to packaging parasitic inductance, it will also cause the active clamp tube S C Early shutdown. Summary of the invention

[0005] The object of the present invention is to provide a control circuit for an active clamp converter in view of the problems existing in the prior art.

[0006] The technical solution to achieve the purpose of the present invention is: a control circuit of an active clamp converter, including an active clamp tube control circuit and a main switch tube opening enable circuit, wherein the active clamp tube control circuit generates an opening enable signal by detecting the voltage across the drain and source of the active clamp tube to determine whether the zero voltage opening condition is met, and generates an opening enable signal according to the power transformer T1, that is, the excitation inductance L m Whether the magnetic reset is complete to generate a shutdown enable signal to realize the active clamping tube S C Accurate control of the main switch tube; the main switch tube is turned on to enable the circuit according to the active clamp tube S C The source-to-ground voltage v S That is, the main switch tube S P The drain voltage to ground generates the main switch tube S P The enable signal v GSP_on .

[0007] Furthermore, the active clamping tube control circuit includes a zero voltage turn-on detection circuit, a volt-second balance control circuit, an RS trigger RS1 and a driver B1; wherein the zero voltage turn-on detection circuit is used to detect the active clamping tube S C The drain voltage v D and source voltage v S, to determine whether the zero voltage turn-on condition is met to generate the active clamp tube S C The enable signal v on The volt-second balance control circuit is used to detect the voltage across the primary side of the power transformer T1, that is, V in -v S , determine the magnetizing inductance L m Is the magnetic reset complete to generate the active clamp tube S C The shutdown enable signal v off ; The RS trigger RS1 is based on the signal v on and v off The output control signal is amplified by the driver B1 and then output to the active clamping tube S C The driving control signal v GSC ; where V in is the input voltage.

[0008] Furthermore, the zero voltage switch-on detection circuit includes a comparator CP1 and a single pulse trigger circuit 1. The comparator CP1 determines whether the active clamping tube S C The voltage difference between the drain and source (v D -v S ) and the first threshold voltage V th1 The output signal is triggered by a single pulse circuit 1 to generate an active clamp tube S C The enable signal v on ;

[0009] In the input energy storage stage, the main switch tube S P Conducting, active clamp tube S C The voltage difference between the drain and source is v D -v S =V in +V C , greater than the first threshold voltage V th1 , comparator CP1 outputs low level, single pulse trigger circuit 1 outputs low level, where V C is the clamping capacitor C L Voltage across both ends; main switch tube S P After shutdown, the magnetizing inductor current has an effect on the active clamp transistor S C The junction capacitance is discharged until the active clamp transistor S C The voltage difference between the drain and source is v D -v S decreases to zero, which is less than the first threshold voltage V th1 , comparator CP1 outputs a high level, the rising edge of comparator CP1 output changes from low to high triggers the single pulse trigger circuit 1 to output a high level pulse, RS trigger RS1 outputs a high level, and after the driver B1 amplifies the current capability, the drive control signal v GSCOutput high level, turn on active clamp tube S C ; where V th1 >0.

[0010] Furthermore, the volt-second balance control circuit includes a voltage-controlled current source VCCS, a capacitor C1, a switch tube Q1, a comparator CP2, a comparator CP3, an RS trigger RS2 and a single pulse trigger circuit 2; the input voltage of the voltage-controlled current source VCCS is V in -v S The output end is connected in parallel with capacitor C1 and switch tube Q1, and is connected to the negative input end of comparator CP3. The positive input end of comparator CP3 inputs the third threshold voltage V th3 The output of comparator CP3 outputs active clamp transistor S C The shutdown enable signal v off , and connected to the input end of the single pulse trigger circuit 2 at the same time. The positive input end and negative input end of the comparator CP2 are the input voltage V in and the second threshold voltage V th2 The output of comparator CP2 and the output of single pulse trigger circuit 2 are connected to the R and S terminals of RS trigger RS2 respectively. The Q terminal of RS trigger RS2 acts on switch tube Q1. V th2 >0,V th3 >0.

[0011] Furthermore, the main switch tube enabling circuit includes a capacitor C2, a resistor R1, a comparator CP4 and a single pulse trigger circuit 3, and the positive input terminal of the comparator CP4 is connected to the active clamp tube S through the capacitor C2. C The source voltage v S , and connect the bias voltage V through resistor R1 bias , the negative input terminal of the comparator CP4 inputs the fourth threshold voltage V th4 The output of comparator CP4 passes through single pulse trigger circuit 3 and then outputs the main switch tube S P The enable signal v GSP_on ; where V bias >V th4 >0.

[0012] Compared with the prior art, the present invention has the following significant advantages: (1) no secondary-side synchronous rectification control circuit or isolation transformer is required, the circuit is simple to implement, and is conducive to improving the power density of the converter; (2) no active clamping tube control signal is required to be generated based on the secondary-side synchronous rectification control circuit, and there is no problem of premature shutdown caused by package parasitic inductance; (3) the magnetizing inductor can be magnetically reset cycle by cycle, and the magnetizing inductor current can be reset to zero cycle by cycle, ensuring soft switching and improving converter efficiency.

[0013] The present invention is further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Figure 2 is the circuit topology diagram and typical operating waveform of the active clamp flyback converter, where Figure (a) is the circuit topology diagram and Figure (b) is the typical operating waveform diagram.

[0015] Figure 2 It is a schematic diagram of the control circuit structure of the active clamp converter of the present invention.

[0016] Figure 3 The zero voltage turn-on detection circuit of the present invention and its key point working waveform diagram, wherein Figure (a) is the zero voltage turn-on detection circuit diagram, and Figure (b) is the key point working waveform diagram.

[0017] Figure 4 The volt-second balance control circuit of the present invention and its key point working waveform diagram, wherein Figure (a) is the volt-second balance control circuit diagram, and Figure (b) is the key point working waveform diagram.

[0018] Figure 5 The main switch tube enabling circuit of the present invention and its key point working waveform diagram, wherein Figure (a) is the main switch tube enabling circuit diagram, and Figure (b) is the key point working waveform diagram.

[0019] Figure 6 , Figure 7 They are respectively the simulation waveform and the experimental result schematic diagram of the active clamp converter control circuit of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0021] The present invention takes an active clamped flyback converter as an embodiment. It should be noted that the scheme of the present invention can also be used in circuit topologies such as an active clamped forward converter and a double clamped zero voltage converter.

[0022] According to the working principle analysis of the active clamp flyback converter, the active clamp tube S C In the main switch tube S P It is turned on after being turned off, that is, it is turned on when the magnetizing inductor current is at its peak value. This is also the moment when the magnetizing inductor current begins to reset, and the active clamp tube S C The turn-off moment of the active clamp tube S corresponds to the moment when the magnetizing inductor current is reset to zero. C Accurate control can be achieved by balancing the power transformer T1 cycle by cycle on a volt-second basis and resetting the magnetizing inductor current to zero cycle by cycle.

[0023] Figure 2 The structure diagram of the active clamp converter control circuit of the present invention is given, which includes an active clamp tube control circuit and a main switch tube opening enable circuit, wherein the active clamp tube control circuit generates its opening enable signal by detecting the voltage across the drain and source of the active clamp tube to determine whether the zero voltage opening condition is met, and generates the opening enable signal according to the power transformer T1 (i.e., the magnetizing inductance L m ) Whether the magnetic reset is complete to generate a shutdown enable signal to realize the active clamping tube S C Accurate control of the main switch tube; the main switch tube is turned on to enable the circuit according to the active clamp tube S C The source-to-ground voltage v S (i.e. the main switch tube S P The drain voltage to ground) generates the main switch tube S P The enable signal v GSP_on .

[0024] Furthermore, the active clamping tube control circuit includes a zero voltage turn-on detection circuit, a volt-second balance control circuit, an RS trigger RS1 and a driver B1, wherein the zero voltage turn-on detection circuit detects the active clamping tube S C The drain voltage v D and source voltage v S , to determine whether the zero voltage turn-on condition is met to generate the active clamp tube S C The enable signal v on The volt-second balance control circuit detects the voltage across the primary side of the power transformer T1 (i.e. V in -v S ), determine the magnetizing inductance L m Is the magnetic reset complete to generate the active clamp tube S C The shutdown enable signal v off ; RS flip-flop RS1 according to the signal v on and v off The output control signal is amplified by the driver B1 and then output to the active clamping tube S C The driving control signal v GSC .

[0025] Figure 3 The specific implementation of the zero voltage turn-on detection circuit in the control circuit and its key working waveforms are given. Figure 3 As shown in (a), the zero voltage turn-on detection circuit is composed of a comparator CP1 and a single pulse trigger circuit 1. th1 is the first threshold voltage, and V th1 >0. Combining the working principle of active clamp flyback converter and Figure 3(b) shows the key working waveforms, and the principle of the zero voltage turn-on detection circuit is described as follows: In the input energy storage stage, the main switch S P Conducting, active clamp tube S C The voltage difference between the drain and source is v D -v S =V in +V C , greater than the first threshold voltage V th1 , comparator CP1 outputs low level, single pulse trigger circuit 1 outputs low level; main switch S P After shutdown, the magnetizing inductor current has an effect on the active clamp transistor S C The junction capacitance is discharged until the active clamp transistor S C The voltage difference between the drain and source is v D -v S decreases to zero, which is less than the threshold voltage V th1 , comparator CP1 output (v o_CP1 ) high level, the rising edge of the comparator CP1 output changes from low to high, triggering the single pulse trigger circuit 1 to output a high level pulse, and the RS trigger RS1 outputs a high level, and after the driver B1 amplifies the current capability, the drive control signal v GSC Output high level, turn on active clamp tube S C .

[0026] Figure 4 The specific implementation of the volt-second balance control circuit in the control circuit and its key working waveforms are given. Figure 4 As shown in (a), the volt-second balance control circuit is composed of a voltage-controlled current source VCCS, a capacitor C1, a switch tube Q1, a comparator CP2, a comparator CP3, an RS trigger RS2 and a single pulse trigger circuit 2. th2 and V th3 are the second and third threshold voltages respectively, and V th2 >0, V th3 >0,v C1 is the voltage across capacitor C1, i C1 is the output current of the voltage controlled current source VCCS, and

[0027] i C1 =k c ·(V in -v S ) (1)

[0028] where k c is the conversion coefficient of the voltage controlled current source VCCS, and k c >0,V in -v Sis the voltage difference at the input of the voltage-controlled current source VCCS. Figure 4 (b) shows the key working waveform, and the principle of the volt-second balance control circuit is described as follows:

[0029] In the power transmission stage, the active clamp tube S C The secondary rectifier diode D1 is in the on state. At this time, the voltage across the primary side of the power transformer T1, i.e., the magnetizing inductance L m The voltage difference between the two ends is V in -v S =-V C , is less than the second threshold voltage V th2 , comparator CP2 output (v o_CP2 ) low level, RS trigger RS2 will not reset; active clamp tube S C The secondary rectifier diode D1 is turned off, and the power transmission phase ends. Then the main switch tube S P Turn on, the converter enters the input energy storage stage, the magnetizing inductor L m The voltage difference between the two ends is V in -v S =V in , greater than the second threshold voltage V th2 , comparator CP2 outputs high level, RS trigger RS2 is reset and outputs low level, switch tube Q1 is turned off, and the voltage at the input terminal of voltage controlled current source VCCS is V in -v S =V in , its output current i C1 =k c ·V in >0, the capacitor C1 will be charged, and the voltage across the capacitor C1 will rise linearly, with a rate of change of:

[0030]

[0031] In the input energy storage stage, the magnetizing inductor current i Lm Linear increase, the rate of change is

[0032]

[0033] Main power tube S P The shutdown and input energy storage phase ends, after which the active clamp tube S C It is turned on under the action of zero voltage turn-on detection and other circuits. At the same time, the secondary rectifier diode D1 is turned on, and the converter enters the power transmission stage. The magnetizing inductor L m The voltage difference between the two ends is V in -v S =-V C , is less than the threshold voltage Vth2 , comparator CP2 outputs low level, RS trigger RS2 will not reset, at this time the voltage controlled current source VCCS input voltage is V in -v S =-V C , its output current i C1 =-k c ·V C <0, the capacitor C1 will be discharged, and the voltage across the capacitor C1 will decrease linearly, and the rate of change is:

[0034]

[0035] In the power transmission stage, the magnetizing inductor current i Lm Linear decrease, the rate of change is:

[0036]

[0037] From equations (2) to (5), we can see that the voltage across capacitor C1 is C1 The rate of change of the magnetizing inductor current i Lm The conversion rate is proportional to the voltage v across the capacitor C1. C1 Get the magnetizing inductance L m The magnetizing information, and the magnetizing inductance L m The moment when the magnetic reset is complete coincides with the moment when the voltage across capacitor C1 returns to its initial value.

[0038] During the power transmission phase, the voltage controlled current source VCCS outputs a current i C1 =-k c ·V C <0, discharge the capacitor C1, and the voltage across the capacitor C1 decreases linearly. When it is discharged to v C1 is less than the third threshold voltage V th3 When the comparator CP3 outputs a high level, the RS trigger RS1 in the active clamp control circuit is reset and outputs a low level. After the driver B1 amplifies the current capability, the drive control signal v GSC Output low level, turn off the active clamp tube S C The third threshold voltage V th3 >0, used to realize active clamping tube S C Shut down a certain time in advance to improve system stability.

[0039] At the same time, the rising edge of the comparator CP3 output changes from low to high, triggering the single pulse trigger circuit 2 to output a high level pulse (v S_RS2), the RS trigger RS2 is set and outputs a high level, the switch tube Q1 is turned on, and the voltage across the capacitor C1 remains zero. After the converter enters the input energy storage stage of the next switching cycle, the comparator CP2 outputs a high level, the RS trigger RS2 is reset and outputs a low level, the switch tube Q1 is turned off, and the voltage-controlled current source VCCS outputs current to charge and discharge the capacitor C1 again.

[0040] Figure 5 The specific implementation method of the main switch tube enabling circuit and its key working waveforms are given. Figure 5 As shown in (a), the main switch tube enabling circuit is composed of a capacitor C2, a resistor R1, a comparator CP4 and a single pulse trigger circuit 3. bias is the bias voltage, V th4 is the fourth threshold voltage, and V bias >V th4 >0. When designing, ensure that the capacitance of capacitor C2 is much smaller than that of the main switch tube S P The junction capacitance C between the drain and source oss_P , according to Kirchhoff's voltage law,

[0041] v S =v C2 +v R1 +V bias (6)

[0042] Where v C2 and v R1 are the voltages across capacitor C2 and resistor R1 respectively. Taking the derivative of both sides of equation (6), we can get

[0043]

[0044] Ignoring the quadratic differential term, we can get

[0045]

[0046] Furthermore, we can get the positive input voltage v of comparator CP4 CP4+ for

[0047]

[0048] Next, combining the converter working principle and Figure 5 (b) shows the key working waveforms, and the principle of the main switch tube enabling circuit is described as follows: When the converter is in the input energy storage stage, the main switch tube S P is turned on, its drain voltage to ground is v S =0, and dv s / dt=0, at this time, the voltage v CP4+ =V bias, higher than the fourth threshold voltage V th4 , comparator CP4 outputs a high level. When the converter enters the power transmission stage from the input energy storage stage, the main switch tube S P Drain to ground voltage v S From zero to V in +V C , that is, dv s / dt>0, then

[0049]

[0050] The output of comparator CP4 remains high. After that, the converter works stably in the input energy storage stage. At this time, the main switch tube S P Drain to ground voltage v S =V in +V C , and dv s / dt=0, the voltage at the positive input terminal of comparator CP4 is v CP4+ =V bias , higher than the threshold voltage V th4 , the comparator CP4 output continues to maintain a high level; when the converter enters the next switching cycle input energy storage stage from the power transmission stage, the main switch tube S P Drain voltage v S From V in +V C Start to decline, i.e. dv s / dt<0, when the descending slope is faster

[0051]

[0052] Comparator CP4 outputs a low level; when the main switch tube S P Drain voltage v S When the falling slope slows down, that is, the voltage v S When the comparator CP4 positive input voltage v CP4+ >V th4 , output high level, comparator CP4 outputs rising edge from low to high, triggering single pulse trigger circuit 3 to output high level pulse v GSP_on , this signal is used to enable the main switch tube S P The main switch tube enabling circuit can ensure that the magnetizing inductor current is reset to zero at the end of the switching cycle, thereby ensuring the soft switching of the switch tube. For example, when a disturbance occurs in the system and causes the active clamp tube S C When the device is turned off prematurely, the magnetizing inductor current i Lm If the current is still greater than zero, the secondary rectifier diode D1 continues to be turned on, and the main switch tube S P Drain to ground voltage v SRemain unchanged, still V in +V C , then the main switch tube S P There will be no loss of soft switching due to premature activation.

[0053] It should be noted that the main switch tube S P The shutdown moment depends on the load power and is implemented by the output voltage closed-loop control of the converter. This part is similar to the output voltage closed-loop control implementation of a conventional converter and will not be repeated in this application.

[0054] To further verify the effectiveness of the control circuit of the present invention, Figure 6 and Figure 7 The simulation and experimental results of a specific embodiment are given. It can be seen from the figure that the control circuit is used in the active clamping tube S C The voltage difference between the drain and source is v D -v S After it drops to zero (or the main switch tube S P Drain to ground voltage v S Rising to V in +V C ), whose driving control signal v GSC Then set it high to achieve zero voltage turn-on; the voltage across capacitor C1 achieves the magnetizing inductor current i Lm Accurate tracking detection, and based on the volt-second balance control circuit, the active clamping tube S is turned off when the excitation inductance is completely magnetically reset. C At the same time, the magnetizing inductor current is reset to zero cycle by cycle, which can ensure the soft switching of the switch tube and reduce losses.

[0055] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A control circuit for an active clamp converter, characterized in that: The active clamping tube control circuit includes an active clamping tube control circuit and a main switch tube opening enabling circuit. The active clamping tube control circuit generates an opening enabling signal by detecting the voltage across the drain and source of the active clamping tube to determine whether the zero voltage opening condition is met, and generates an opening enabling signal according to the power transformer T1, that is, the magnetizing inductance L m Whether the magnetic reset is complete to generate a shutdown enable signal to realize the active clamping tube S C Accurate control of the main switch tube; the main switch tube is turned on to enable the circuit according to the active clamp tube S C The source-to-ground voltage v S That is, the main switch tube S P The drain voltage to ground generates the main switch tube S P The enable signal v GSP_on ; The active clamp control circuit includes a zero voltage turn-on detection circuit, a volt-second balance control circuit, an RS trigger RS1 and a driver B1; wherein the zero voltage turn-on detection circuit is used to detect the active clamp S C The drain voltage v D and source voltage v S , to determine whether the zero voltage turn-on condition is met to generate the active clamp tube S C The enable signal v on The volt-second balance control circuit is used to detect the voltage across the primary side of the power transformer T1, that is, V in -v S , determine the magnetizing inductance L m Is the magnetic reset complete to generate the active clamp tube S C The shutdown enable signal v off ; The RS trigger RS1 is based on the signal v on and v off The output control signal is amplified by the driver B1 and then output to the active clamping tube S C The driving control signal v GSC ; where V in is the input voltage; The zero voltage switch-on detection circuit comprises a comparator CP1 and a single pulse trigger circuit 1. The comparator CP1 determines whether the active clamping tube S C The voltage difference between the drain and source is v D -v S With the first threshold voltage V th1 The output signal is triggered by a single pulse circuit 1 to generate an active clamp tube S C The enable signal v on ; In the input energy storage stage, the main switch tube S P Conducting, active clamp tube S C The voltage difference between the drain and source is v D -v S =V in +V C , greater than the first threshold voltage V th1 , comparator CP1 outputs low level, single pulse trigger circuit 1 outputs low level, where V C is the clamping capacitor C L Voltage across both ends; main switch tube S P After shutdown, the magnetizing inductor current has an effect on the active clamp transistor S C The junction capacitance is discharged until the active clamp transistor S C The voltage difference between the drain and source is v D -v S decreases to zero, which is less than the first threshold voltage V th1 , comparator CP1 outputs a high level, the rising edge of comparator CP1 output changes from low to high triggers the single pulse trigger circuit 1 to output a high level pulse, RS trigger RS1 outputs a high level, and after the driver B1 amplifies the current capability, the drive control signal v GSC Output high level, turn on active clamp tube S C ; where V th1 >0; The volt-second balance control circuit comprises a voltage-controlled current source VCCS, a capacitor C1, a switch tube Q1, a comparator CP2, a comparator CP3, an RS trigger RS2 and a single pulse trigger circuit 2; the input voltage of the voltage-controlled current source VCCS is V in -v S The output end is connected in parallel with capacitor C1 and switch tube Q1, and is connected to the negative input end of comparator CP3. The positive input end of comparator CP3 inputs the third threshold voltage V th3 The output of comparator CP3 outputs active clamp transistor S C The shutdown enable signal v off , and connected to the input end of the single pulse trigger circuit 2 at the same time. The positive input end and negative input end of the comparator CP2 are the input voltage V in and the second threshold voltage V th2 The output of comparator CP2 and the output of single pulse trigger circuit 2 are connected to the R and S terminals of RS trigger RS2 respectively. The Q terminal of RS trigger RS2 acts on switch tube Q1. V th2 >0,V th3 >0, the third threshold voltage is used to realize the active clamping tube S C Shut down a certain time in advance.

2. The control circuit of the active clamp converter according to claim 1, characterized in that: The output current i of the voltage controlled current source VCCS is C1 for: i C1 =k c ·(V in -v S ) In the formula, k c is the conversion coefficient of the voltage controlled current source VCCS, and k c >0.

3. The control circuit of the active clamp converter according to claim 1, characterized in that: The main switch tube enabling circuit includes a capacitor C2, a resistor R1, a comparator CP4 and a single pulse trigger circuit 3. The positive input terminal of the comparator CP4 is connected to the active clamp tube S through the capacitor C2. C The source voltage v S , and connect the bias voltage V through resistor R1 bias , the negative input terminal of the comparator CP4 inputs the fourth threshold voltage V th4 The output of comparator CP4 passes through single pulse trigger circuit 3 and then outputs the main switch tube S P The enable signal v GSP_on ; where V bias >V th4 >0.

4. The control circuit of the active clamp converter according to claim 3, characterized in that: The capacitance of the capacitor C2 is much smaller than that of the main switch S P The junction capacitance C between the drain and source oss_P .

5. The control circuit of the active clamp converter according to claim 4, characterized in that: According to Kirchhoff's voltage law, v S =v C2 +v R1 +V bias In the formula, v C2 and v R1 To differentiate the voltages across capacitor C2 and resistor R1, we can get Ignoring the quadratic differential term, we can get Furthermore, we can get the positive input voltage v of comparator CP4 CP4+ for:

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