CN211653052U

CN211653052U - Clamp switch tube abnormity detection circuit and switch circuit

Info

Publication number: CN211653052U
Application number: CN201921975705.XU
Authority: CN
Inventors: 黄必亮; 蒋香华; 周逊伟
Original assignee: Joulwatt Technology Hangzhou Co Ltd
Current assignee: Joulwatt Technology Co Ltd
Priority date: 2019-11-15
Filing date: 2019-11-15
Publication date: 2020-10-09
Anticipated expiration: 2029-11-15

Abstract

The utility model discloses a clamp switch tube abnormity detection circuit and a switch circuit, wherein an active clamp flyback circuit comprises a clamp switch tube, a main switch tube and a transformer; when a control signal of the clamping switch tube is effective, detecting the voltage on a switch node or an auxiliary winding or the excitation inductive current, and when the voltage on the switch node or the auxiliary winding or the excitation inductive current oscillates or the voltage on the switch node is smaller than a first voltage threshold or the voltage on the auxiliary winding is smaller than a second voltage threshold, judging that the clamping switch tube is abnormal or a driving circuit of the clamping switch tube is abnormal; the switch node is a common node of the transformer and the main switch tube; the transformer comprises a primary winding, a secondary winding and an auxiliary winding. The utility model discloses can accurately detect out and damage when clamp switch tube or clamp switch tube drive circuit, improve system reliability.

Description

Clamp switch tube abnormity detection circuit and switch circuit

Technical Field

The utility model relates to a power electronic technology field, concretely relates to clamp switch tube anomaly detection circuit and switching circuit.

Background

Fig. 1 is a circuit diagram of an active clamp flyback circuit. The active clamping flyback circuit comprises a clamping circuit 100, wherein the clamping circuit 100 comprises a clamping switching tube MSA and a clamping capacitor CSA; the clamp switching tube driving circuit 400 receives a clamp switching tube control signal HI and controls the on and off of a clamp switching tube, when the clamp switching tube or the clamp switching tube driving circuit 400 is damaged, the active clamp flyback circuit still can work in a plurality of switching cycles, but the voltage VC on a clamp capacitor CSA can rise, and when the voltage VC on the clamp capacitor CSA rises to be larger than the highest withstand voltage of the clamp capacitor CSA, the clamp capacitor can be damaged, so that the whole flyback circuit is damaged; in the prior art, a clamping diode is connected in parallel with a clamping capacitor CSA, so that when the voltage VC on the clamping capacitor CSA is clamped below the highest withstand voltage of the clamping diode CSA, the entire flyback circuit cannot be damaged. However, when the clamp switch or the clamp switch driver circuit 400 is damaged, the clamp diode has a large power consumption, which results in a decrease in system efficiency.

Therefore, how to detect whether the clamp switching tube and the driving circuit thereof are normal is an important problem in the active clamp flyback circuit.

SUMMERY OF THE UTILITY MODEL

In view of this, the present invention provides a clamp switch tube abnormality detection circuit and a switch circuit, so as to solve the problem that when a clamp switch tube or a clamp switch tube driving circuit is damaged in the prior art, a clamp diode has a large power consumption, resulting in a reduction in system efficiency.

The utility model provides a clamp switch tube abnormity detection method.A passive clamp flyback circuit comprises a clamp switch tube, a main switch tube and a transformer; when a control signal of the clamping switch tube is effective, detecting the voltage on a switch node or an auxiliary winding or the excitation inductive current, and when the voltage on the switch node or the auxiliary winding or the excitation inductive current oscillates or the voltage on the switch node is smaller than a first voltage threshold or the voltage on the auxiliary winding is smaller than a second voltage threshold, judging that the clamping switch tube is abnormal or a driving circuit of the clamping switch tube is abnormal; the switch node is a common node of the transformer and the main switch tube; the transformer comprises a primary winding, a secondary winding and an auxiliary winding;

voltage on the auxiliary winding is divided to obtain feedback voltage, and the voltage on the auxiliary winding is represented; or the feedback current is obtained by connecting the first resistor to the auxiliary winding to represent the voltage on the auxiliary winding.

Optionally, the active clamp flyback circuit works in an intermittent conduction mode, and the clamp switching tube is respectively conducted before and after the main switching tube is conducted; and detecting the voltage on the auxiliary winding or the switch node voltage when the control signal of the clamping switch tube is effective before the main switch tube is conducted, wherein when the switch node voltage in Q continuous switching periods is less than a first voltage threshold value or the voltage on the auxiliary winding is less than a second voltage threshold value, the driving circuit of the clamping switch tube or the clamping switch tube is abnormal, wherein Q is a natural number which is more than or equal to 1.

Optionally, the active clamp flyback circuit works in a critical conduction mode or an intermittent conduction mode, and the control signal of the clamp switching tube is changed from invalid to valid after the main switching tube is turned off; in every M switching cycles, one switching cycle is that when the exciting inductance current is zero, timing is started, when the first time is reached, the control signal of the clamping switching tube is changed from effective to ineffective, and the timing is ended;

in the timing process, detecting the voltage on the auxiliary winding or the voltage of a switching node, if the voltage on the auxiliary winding or the voltage of the switching node or the excitation inductive current is detected to oscillate, judging that the clamping switching tube is abnormal or a driving circuit of the clamping switching tube is abnormal, otherwise, judging that the driving circuit of the clamping switching tube and the driving circuit of the clamping switching tube are normal;

or in the timing, detecting the voltage on the auxiliary winding or the voltage of the switching node, if detecting that the voltage on the auxiliary winding or the voltage of the switching node or the exciting inductive current oscillates, continuing for P switching periods later, and changing the control signal of the clamping switching tube from invalid to valid after the main switching tube is switched off; when the exciting inductance current is zero, timing is started, when the first time is reached, the control signal of the clamping switch tube is changed from effective to ineffective, and the timing is ended; continuously performing P +1 switching cycles, detecting the voltage on the auxiliary winding or the voltage of a switching node in the timing, and if the voltage on the auxiliary winding or the voltage of the switching node or the excitation inductive current is detected to oscillate, judging that the clamping switching tube is abnormal or a driving circuit of the clamping switching tube is abnormal;

wherein M and P are both natural numbers of 1 or more.

Optionally, the active clamp flyback converter operates in a critical conduction mode, and the control signal of the clamp switching tube is changed from invalid to valid after the main switching tube is turned off; adjusting the time when the control signal of the clamping switch tube is changed from effective to ineffective to enable the main switch tube to realize zero voltage conduction, detecting the voltage on an auxiliary winding or the voltage of a switch node or the exciting inductive current when the control signal of the clamping switch tube is effective, and when the voltage on the auxiliary winding does not oscillate or the voltage of the switch node does not oscillate or the exciting inductive current does not oscillate, the driving circuit of the clamping switch tube and the clamping switch tube is normal, otherwise, the driving circuit of the clamping switch tube or the clamping switch tube is abnormal.

Optionally, the active clamp flyback circuit works in a critical conduction mode or an intermittent conduction mode, and the control signal of the clamp switching tube is changed from invalid to valid after the main switching tube is turned off; in M-1 periods in every M switching periods, when the exciting inductance current is near zero, the control signal of the clamping switching tube is changed from effective to ineffective; delaying the moment when a control signal of a clamping switch tube is changed from effective to ineffective for a third time in one switch period of every M switch periods, and when the control signal of the clamping switch tube is effective, if the voltage on an auxiliary winding or the voltage of a switch node or the excitation inductive current is detected to oscillate, judging that the clamping switch tube is abnormal or a driving circuit of the clamping switch tube is abnormal, otherwise, judging that the driving circuits of the clamping switch tube and the clamping switch tube are normal;

or when the clamp switch tube control signal is effective, if the voltage on the auxiliary winding or the switch node voltage or the excitation inductive current is detected to oscillate, delaying the moment of changing the clamp switch tube control signal from effective to ineffective for a third time for P +1 switching cycles continuously in the next P switching cycles, and when the clamp switch tube control signal is effective, if the voltage on the auxiliary winding or the switch node voltage or the excitation inductive current is detected to oscillate, the clamp switch tube is abnormal or the clamp switch tube driving circuit is abnormal;

wherein M and P are natural numbers of 1 or more.

Optionally, when the duty ratio of the main switching tube is greater than a first threshold, the clamp switching tube abnormality detection is started.

Optionally, the active clamp flyback circuit includes a clamp capacitor, where a voltage on the clamp capacitor is a clamp voltage, and when the clamp voltage or the output voltage is greater than a fifth voltage threshold, the clamp switching tube abnormality detection is started.

Optionally, when the clamp switch tube or the clamp switch tube driving circuit is abnormal, both the main switch tube and the clamp switch tube are turned off, and when the turn-off time of both the main switch tube and the clamp switch tube reaches the fourth time, the main switch tube and the clamp switch tube are controlled to be turned on and off again; or when the clamping switch tube or the clamping switch tube driving circuit is abnormal, the main switch tube and the clamping switch tube are switched off, and when power is supplied again, the main switch tube and the clamping switch tube are controlled to be switched on and off.

The utility model also provides a clamp switch tube abnormity detection circuit, the active clamp flyback circuit comprises a clamp switch tube, a main switch tube and a transformer; when a control signal of the clamping switch tube is effective, the clamping switch tube abnormity detection circuit detects the voltage on a switch node or an auxiliary winding or the excitation inductive current, and when the voltage on the switch node or the auxiliary winding or the excitation inductive current oscillates or the voltage on the switch node is smaller than a first voltage threshold or the voltage on the auxiliary winding is smaller than a second voltage threshold, the clamping switch tube abnormity detection circuit judges that the clamping switch tube is abnormal or a driving circuit of the clamping switch tube is abnormal; the switch node is a common node of the transformer and the main switch tube; the transformer comprises a primary winding, a secondary winding and an auxiliary winding;

voltage on the auxiliary winding is divided to obtain feedback voltage, and the voltage on the auxiliary winding is represented; or the clamp switch tube abnormity detection circuit is connected to the auxiliary winding through the first resistor to obtain feedback current and represent voltage on the auxiliary winding.

Optionally, the clamp switching tube abnormality detection circuit includes a comparison circuit and a clamp switching tube abnormality judgment circuit, the output voltage of the clamp switching tube abnormality judgment circuit is a clamp switching tube abnormality signal, the comparison circuit receives the voltage on the auxiliary winding or the switch node voltage, the clamp switching tube abnormality judgment circuit receives the output voltage of the comparison circuit and judges whether the clamp switching tube and the clamp switching tube driving circuit are abnormal, when the clamp switching tube or the clamp switching tube driving circuit is abnormal, the clamp switching tube abnormality signal is valid, otherwise, the clamp switching tube abnormality signal is invalid; and the clamp switch tube and the main switch tube control circuit receive the abnormal signal of the clamp switch tube and control the on and off of the main switch tube and the clamp switch tube.

Optionally, the active clamp flyback circuit works in an intermittent conduction mode, and the clamp switching tube is respectively conducted before and after the main switching tube is conducted; when the control signal of the clamping switch tube is effective before the main switch tube is conducted, the comparison circuit compares the voltage on the auxiliary winding with a first voltage threshold value or the voltage of a switch node with a second voltage threshold value, when the voltage of the switch node in Q continuous switching periods is smaller than the first voltage threshold value or the voltage on the auxiliary winding is smaller than the second voltage threshold value, the output voltage of the clamping switch tube abnormity judgment circuit is effective, and the clamping switch tube or the clamping switch tube driving circuit is judged to be abnormal, wherein Q is a natural number which is larger than or equal to 1.

Optionally, the clamp switching tube abnormality detection circuit includes an inductive current detection circuit, and the inductive current detection circuit receives the voltage of the auxiliary winding and determines whether the inductive current is zero or not according to the voltage on the auxiliary winding; the clamp switching tube abnormity judging circuit outputs a clamp switching tube prolonged conduction signal, and the clamp switching tube and the main switching tube control circuit receive the clamp switching tube prolonged conduction signal; when the clamp switch tube prolongs the conduction signal to be effective, the clamp switch tube and the main switch tube control circuit delay the time from the effective state to the ineffective state of the clamp switch tube control signal;

the active clamp flyback circuit works in a critical conduction mode or an intermittent conduction mode, and a control signal of the clamp switch tube is changed from invalid to valid after the main switch tube is turned off; in every M switching cycles, one switching cycle is that when the inductive current detection circuit detects that the exciting inductive current is zero, the clamp switch tube and the main switch tube control circuit receive a clamp switch tube extended conduction signal output by the clamp switch tube abnormity judgment circuit, the clamp switch tube abnormity judgment circuit starts timing, when the timing reaches the first time, the clamp switch tube and the main switch tube control circuit control the clamp switch tube control signal to be changed from effective to invalid, and the timing is ended;

in the timing process, the comparison circuit detects the voltage on the auxiliary winding or the voltage of a switch node, if the voltage on the auxiliary winding or the voltage of the switch node is detected to oscillate, or the inductive current detection circuit detects the excitation inductive current to oscillate, an abnormal signal of the clamping switch tube is effective, the clamping switch tube is judged to be abnormal or the driving circuit of the clamping switch tube is judged to be abnormal, otherwise, the abnormal signal of the clamping switch tube is ineffective, and the clamping switch tube and the driving circuit of the clamping switch tube are judged to be normal;

or in the timing, the comparison circuit detects the voltage on the auxiliary winding or the voltage of the switching node, if the voltage on the auxiliary winding or the voltage of the switching node is detected to oscillate, or the inductive current detection circuit detects the excitation inductive current to oscillate, the next P switching periods are continued, and the control signal of the clamping switching tube is changed from invalid to valid after the main switching tube is switched off; when the inductive current detection circuit detects that the exciting inductive current is zero, the clamp switching tube abnormity judgment circuit starts timing, when the first time is reached, the clamp switching tube and the main switching tube control circuit control and control the clamp switching tube control signal to be changed from effective to ineffective, and the timing is finished; continuously carrying out P +1 switching cycles, detecting the voltage on the auxiliary winding or the voltage of a switching node in the timing, and if the voltage on the auxiliary winding or the voltage of the switching node is detected to oscillate or an inductive current detection circuit detects that the exciting inductive current oscillates, judging whether the clamping switching tube is abnormal or a driving circuit of the clamping switching tube is abnormal if an abnormal signal of the clamping switching tube is valid;

wherein M and P are both natural numbers of 1 or more.

Optionally, the active clamp flyback converter operates in a critical conduction mode, and the control signal of the clamp switching tube is changed from invalid to valid after the main switching tube is turned off; the clamp switch tube control circuit adjusts the time when the clamp switch tube control signal changes from active to inactive, so that the main switch tube realizes zero voltage conduction, when the clamp switch tube control signal is active, the comparison circuit detects the voltage on the auxiliary winding or the switch node voltage, or the inductive current detection circuit detects the exciting inductive current, when the voltage on the auxiliary winding does not oscillate or the switch node voltage does not oscillate or the exciting inductive current does not oscillate, the clamp switch tube abnormal signal is invalid, the clamp switch tube and the clamp switch tube driving circuit are judged to be normal, otherwise, the clamp switch tube abnormal signal is active, and the clamp switch tube or the clamp switch tube driving circuit is judged to be abnormal.

Optionally, the clamp switching tube abnormality judgment circuit outputs a clamp switching tube extended conduction signal, and the clamp switching tube and the main switching tube control circuit receive the clamp switching tube extended conduction signal; when the clamp switch tube prolongs the conduction signal to be effective, the clamp switch tube and the main switch tube control circuit delay the time from the effective state to the ineffective state of the clamp switch tube control signal;

the active clamp flyback circuit works in a critical conduction mode or an intermittent conduction mode, and a control signal of the clamp switch tube is changed from invalid to valid after the main switch tube is turned off; in M-1 periods in every M switching periods, when the exciting inductance current is near zero, the control signal of the clamping switching tube is changed from effective to ineffective; in one switching period of every M switching periods, prolonging the conduction signal of the clamping switching tube to be effective, delaying the moment when the control signal of the clamping switching tube is changed from effective to ineffective for a third time, and when the control signal of the clamping switching tube is effective, if a comparison circuit detects that the voltage on an auxiliary winding or the voltage of a switching node oscillates or an inductive current detection circuit detects that the exciting inductive current oscillates, judging that the abnormal signal of the clamping switching tube is effective, judging that the clamping switching tube is abnormal or a driving circuit of the clamping switching tube is abnormal, otherwise, judging that the abnormal signal of the clamping switching tube is ineffective, and judging that the driving circuits of the clamping switching tube and the clamping switching tube are normal;

or, when the clamp switch tube control signal is valid, if the comparison circuit detects that the voltage on the auxiliary winding or the voltage at the switch node oscillates, or the inductive current detection circuit detects that the excitation inductive current oscillates, then the next P consecutive switch cycles delay the moment when the clamp switch tube control signal changes from valid to invalid for a third time, and continue for P +1 switch cycles, and when the clamp switch tube control signal is valid, if the voltage on the auxiliary winding or the voltage at the switch node oscillates, or the inductive current detection circuit detects that the excitation inductive current oscillates, then the clamp switch tube abnormal signal is valid, and the clamp switch tube abnormality or the clamp switch tube driving circuit abnormality is determined;

wherein M and P are both natural numbers of 1 or more.

Optionally, when the duty ratio of the main switching tube is greater than the first threshold, the clamp switching tube abnormality detection circuit is started.

Optionally, when the clamp switch tube or the clamp switch tube driving circuit is abnormal, the clamp switch tube and the main switch tube control circuit turns off both the main switch tube and the clamp switch tube, and when the turn-off time of both the main switch tube and the clamp switch tube reaches a fourth time, the clamp switch tube and the main switch tube control circuit controls the main switch tube and the clamp switch tube to be switched on and off again; or when the clamping switch tube or the clamping switch tube driving circuit is abnormal, the clamping switch tube and the main switch tube control circuit turn off the main switch tube and the clamping switch tube, and when power is electrified again, the clamping switch tube and the main switch tube control circuit control the main switch tube and the clamping switch tube to be switched on and off.

The utility model also provides a switch circuit.

Adopt the utility model discloses a circuit structure and method, compared with the prior art, have following advantage: the damage of the clamping switch tube or the clamping switch tube driving circuit can be accurately detected, and the system reliability is improved.

Drawings

Fig. 1 is a circuit schematic diagram of an active clamp flyback circuit;

fig. 2 is a schematic diagram of an active clamp flyback circuit with a clamp switching tube abnormality detection circuit 200 and a clamp switching tube and main switching tube control circuit 300;

FIG. 3 is an embodiment of detecting auxiliary winding voltage in one embodiment;

FIG. 4 is a block diagram of clamp switch tube anomaly detection circuitry 200 in one embodiment;

FIG. 5 shows a control signal LI of the main switch tube, a control signal HI of the clamp switch tube, and an exciting inductor current i when the active clamp flyback circuit is in an intermittent conduction mode and the clamp switch tube is conducted twice in one switching period and the clamp switch tube is normal_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

FIG. 6 shows the main switch tube control signal LI, clamp switch tube control signal HI, and exciting inductor current i when the active clamp flyback circuit is in the discontinuous conduction mode and the clamp switch tube is conducted twice in one switching period and the clamp switch tube is abnormal_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

FIG. 7 shows control signals LI of the main switch tube and the clamp switch tube when the clamp switch tube is normal in the discontinuous conduction mode of the active clamp flyback circuitControl signal HI, excitation inductance current i_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

fig. 8(a) shows, in an embodiment, when the clamp switching tube is abnormal in the discontinuous conduction mode of the active clamp flyback circuit, the main switching tube control signal LI, the clamp switching tube control signal HI, and the exciting inductor current i_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

fig. 8(b) shows, in another embodiment, when the clamp switching tube is abnormal in the discontinuous conduction mode of the active clamp flyback circuit, the main switching tube control signal LI, the clamp switching tube control signal HI, and the exciting inductor current i_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

fig. 9 shows a main switching tube control signal LI, a clamping switching tube control signal HI, and an excitation inductor current i when the clamping switching tube is normal in the critical conduction mode of the active clamping flyback circuit_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

fig. 10 shows a main switching tube control signal LI, a clamping switching tube control signal HI, and an excitation inductor current i when a clamping switching tube is abnormal in a critical conduction mode of the active clamping flyback circuit_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

fig. 11 is a block diagram of a clamp switching tube anomaly detection circuit 200 in another embodiment;

fig. 12 is a diagram illustrating a main switch control signal LI, a clamp switch control signal HI, and an exciting inductor current i when the clamp switch is normal in the critical conduction mode of the active clamp flyback circuit in another embodiment_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

fig. 13 shows another embodiment of the active clamp flyback circuit in the critical conduction mode, where the clamp switching transistor is abnormal, and the main switching transistor control signal LI, the clamp switching transistor control signal HI, and the excitation inductor current i_LMSwitch, and electronic device using the sameNode voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a);

fig. 14 illustrates an embodiment of the inductor current detection circuit 230.

Detailed Description

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to only these embodiments. The present invention covers any alternatives, modifications, equivalents, and alternatives falling within the spirit and scope of the present invention.

In the following description of the preferred embodiments of the present invention, specific details are set forth in order to provide a thorough understanding of the present invention, and it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

The invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the drawings are simplified and in non-precise proportion, and are only used for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

The utility model provides a clamp switch tube abnormity detection circuit, please refer to fig. 2, the active clamp flyback circuit includes clamp switch tube MSA, main switch tube M1 and transformer T1; when the clamp switch tube control signal HI is valid, the clamp switch tube abnormality detection circuit 200 detects the switch node voltage V_SWOr the voltage V on the auxiliary winding_AUXOr exciting inductor current i_LMWhen the switch node voltage V_SWOr the voltage V on the auxiliary winding_AUXOr exciting inductor current i_LMOscillating, or switching, node voltage V_SWLess than a first voltage threshold or a voltage V across the auxiliary winding_AUXWhen the voltage is smaller than the second voltage threshold, the clamp switching tube abnormality detection circuit 200 judges that the clamp switching tube is abnormal or the clamp switching tube driving circuit is abnormal; the switch node V_SWIs the common node of the transformer T1 and the main switching tube M1; the transformer T1 comprises a primary winding Np, a secondary winding Ns and an auxiliary winding Naux, and the voltage V on the auxiliary winding_AUXObtaining feedback voltage after voltage divisionV_FB. Due to the voltage V on the auxiliary winding_AUXThe voltage sampling of the clamp switching tube abnormality detection circuit is generally low voltage, for example, lower than 5V, so that a voltage division mode is generally adopted, and a feedback voltage V is adopted_FBTo characterize the voltage V across the auxiliary winding_AUX。

FIG. 3 is a schematic diagram of another method for detecting the voltage of the auxiliary winding; due to the feedback voltage V_FBA negative voltage is reached and it is more convenient for the clamp switch tube abnormality detection circuit 200 to detect a positive voltage than a negative voltage. Therefore, another way to detect the voltage on the auxiliary winding is to connect the auxiliary winding to the clamp switch tube abnormality detection circuit 200 through the resistor RFB3, connect the resistor RFB3 to one end of the clamp switch tube abnormality detection circuit 200 for clamping, generally to a positive voltage, by detecting the current I on the resistor RFB3_FBThe voltage on the auxiliary winding can be detected. Therefore, in the latter embodiment, V is used at the input of the clamp switching tube abnormality detection circuit 200_FB/I_FBIndicating that V can be detected by means of resistance voltage division_FBOr current sensing means I_FBTo obtain the voltage on the auxiliary winding.

Referring to fig. 4, the clamp switching tube abnormality detection circuit includes a comparison circuit 210 and a clamp switching tube abnormality judgment circuit 220, an output voltage of the clamp switching tube abnormality judgment circuit 220 is a clamp switching tube abnormality signal, and the comparison circuit 210 receives a voltage on an auxiliary winding or a switching node voltage V_SWThe clamp switching tube abnormality judgment circuit 220 receives the output voltage of the comparison circuit 210, and judges whether the clamp switching tube and the clamp switching tube driving circuit are abnormal, when the clamp switching tube or the clamp switching tube driving circuit is abnormal, the clamp switching tube abnormality signal is valid, otherwise, the clamp switching tube abnormality signal is invalid; and the clamp switch tube and the main switch tube control circuit receive the abnormal signal of the clamp switch tube and control the on and off of the main switch tube and the clamp switch tube. In FIG. 4, comparison circuit 210 receives V_FB/I_FBThereby obtaining the voltage on the auxiliary winding.

In one embodiment, please refer to fig. 5, which illustrates that when the active clamp flyback circuit is in the discontinuous conduction mode and the clamp switch is turned on twice in one switching period, and the clamp switch is normal, the main switch control signal LI, the clamp switch control signal HI, and the exciting inductor current i_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a); referring to fig. 6, when the active clamp flyback circuit is in the discontinuous conduction mode and the clamp switch is turned on twice in one switching period and the clamp switch is abnormal, the main switch control signal LI, the clamp switch control signal HI, and the exciting inductor current i are set to be equal to each other_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a). In FIGS. 5 and 6, the feedback voltage V is used_FBTo characterize the auxiliary winding voltage, the feedback current may also be used to characterize the auxiliary winding voltage or to detect the switch node voltage. The active clamping flyback circuit works in an intermittent conduction mode, and the clamping switch tube is respectively conducted before and after the main switch tube is conducted; when the control signal of the clamping switch tube is effective before the main switch tube is conducted, the comparison circuit compares the voltage on the auxiliary winding with a first voltage threshold value or the voltage of a switch node with a second voltage threshold value, when the voltage of the switch node in Q continuous switching periods is smaller than the first voltage threshold value or the voltage on the auxiliary winding is smaller than the second voltage threshold value, the output voltage of the clamping switch tube abnormity judgment circuit is effective, and the clamping switch tube or the clamping switch tube driving circuit is judged to be abnormal, wherein Q is a natural number which is larger than or equal to 1. Referring to fig. 5, when the clamp switching tube and the clamp switching tube driving circuit are both normal, and before the main switching tube is turned on, the clamp switching tube is turned on when the control signal of the clamp switching tube is valid, the switching node voltage stops oscillating and rises to Vin + N Vo, where N is the turn ratio of the primary side and the secondary side in the flyback circuit. Due to the voltage V on the auxiliary winding_AUX＝(V_SWVin) ((Np/Naux), so the determination can also be made by detecting the feedback voltage or current to derive the voltage on the auxiliary winding. Referring to FIG. 6, when the clamp switch or the clamp switch driving circuit is usedWhen the circuit is abnormal, when the control signal of the clamping switch tube is effective before the main switch tube is conducted, the clamping switch tube is conducted, the voltage of the switch node can continue to oscillate, and the feedback voltage also continues to oscillate.

When Q is 1, namely the voltage of a switching node in one switching period is only required to be smaller than a first voltage threshold, or the voltage on the auxiliary winding is smaller than a second voltage threshold, the output voltage of the clamping switching tube abnormity judgment circuit is effective, and the clamping switching tube or the clamping switching tube driving circuit is judged to be abnormal; otherwise, the output voltage of the clamp switch tube abnormity judging circuit is invalid, and the clamp switch tube driving circuit are judged to be normal. When Q is greater than or equal to 2, in order to prevent misjudgment, it is necessary to detect that the voltage at the switching node is smaller than the first voltage threshold value or the voltage on the auxiliary winding is smaller than the second voltage threshold value in consecutive Q switching cycles, and the output voltage of the clamp switching tube abnormality judgment circuit is valid, and the clamp switching tube or the clamp switching tube driving circuit is judged to be abnormal.

In an embodiment, referring to fig. 7, fig. 8(a) and fig. 8(b), fig. 7 shows that when the clamp switch is normal in the discontinuous conduction mode of the active clamp flyback circuit, the main switch control signal LI, the clamp switch control signal HI, and the exciting inductor current i are set as the main switch control signal LI, the clamp switch control signal HI, and the exciting inductor current i_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a); fig. 8(a) and 8(b) show the main switch tube control signal LI, the clamp switch tube control signal HI, and the exciting inductor current i when the clamp switch tube is abnormal in the discontinuous conduction mode of the active clamp flyback circuit in two different embodiments_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a); the active clamp flyback circuit works in an intermittent conduction mode or a critical conduction mode, and a control signal of the clamp switch tube is changed from invalid to valid after the main switch tube is turned off; in each M switching periods, M-1 switching periods are that a clamping switching tube control signal is changed from effective to ineffective when the exciting inductance current is near zero, in one switching period in each M switching periods, a clamping switching tube prolonging conduction signal output by the clamping switching tube abnormity judging circuit is effective, and the clamping switching tube prolonging conduction signal is output by the clamping switching tube abnormity judging circuit and is used for judging whether the clamping switching tube prolonging conduction signal is effective or notThe clamp switch tube and main switch tube control circuit receives the clamp switch tube prolonged conduction signal, and delays the moment when the clamp switch tube is changed from effective to ineffective for a third time, when the clamp switch tube control signal is effective, if a comparison circuit detects that the voltage on an auxiliary winding or the voltage of a switch node oscillates or an inductive current detection circuit detects that the exciting inductive current oscillates, the clamp switch tube abnormal signal is effective, the clamp switch tube is judged to be abnormal or a clamp switch tube driving circuit is judged to be abnormal, otherwise, the clamp switch tube abnormal signal is ineffective, and the clamp switch tube and clamp switch tube driving circuit is judged to be normal; or, when the clamp switch tube control signal is valid, if the comparison circuit detects that the voltage on the auxiliary winding or the voltage at the switch node oscillates, or the inductive current detection circuit detects that the excitation inductive current oscillates, then the next P consecutive switch cycles delay the moment when the clamp switch tube control signal changes from valid to invalid for a third time, and continue for P +1 switch cycles, and when the clamp switch tube control signal is valid, if the voltage on the auxiliary winding or the voltage at the switch node oscillates, or the inductive current detection circuit detects that the excitation inductive current oscillates, then the clamp switch tube abnormal signal is valid, and the clamp switch tube abnormality or the clamp switch tube driving circuit abnormality is determined; wherein M and P are both natural numbers greater than or equal to 1, and the third time is related to the resonance period. The clamp switching tube abnormity judging circuit outputs a clamp switching tube prolonged conduction signal, and the clamp switching tube and the main switching tube control circuit receive the clamp switching tube prolonged conduction signal; when the clamp switch tube prolongs the conduction signal to be effective, the clamp switch tube and the main switch tube control circuit delay the time from the effective state to the ineffective state of the clamp switch tube control signal; in fig. 7, the active time of the clamp switch transistor control signal of the third switching cycle is extended by a third time, the start of the extension of the clamp switch transistor control signal HI being indicated by a dashed line; referring to fig. 7, when the clamp switching transistor and the clamp switching transistor driving circuit are both normal, and the clamp switching transistor control signal HI is valid, the switching node voltage does not oscillate and is Vin + N × Vo; please refer to the drawings8(a), when the switch node voltage in one switching period oscillates when the clamp switch tube control signal is effective, the clamp switch tube or the clamp switch tube driving circuit is judged to be abnormal. In order to prevent misjudgment, if the switching node voltage oscillates when the clamping switching tube control signal of one switching period is effective, the moment when the clamping switching tube control signal changes from effective to ineffective needs to be delayed for a third time for the next P switching periods, and in the next P switching periods, the switching node voltage oscillates when the clamping switching tube control signal is effective, and the clamping switching tube or the clamping switching tube driving circuit is judged to be abnormal. Referring to fig. 8(b), when P is equal to 1, in the third switching period, the switching node voltage oscillates already when the clamp switching transistor control signal of one switching period is active, in the fourth switching period, the time when the clamp switching transistor control signal is continuously changed from active to inactive is delayed by the third time, and the switching node voltage oscillates when the clamp switching transistor control signal is active, so that it is determined that the clamp switching transistor or the clamp switching transistor driving circuit is abnormal. It should be noted that this circuit and method are also applicable to the critical conduction mode, and fig. 7, 8(a) and 8(b) only illustrate the case of the discontinuous conduction mode. And when the duty ratio of the main switching tube is larger than a first threshold value, starting abnormal detection of the clamping switching tube.

Referring to fig. 9 and 10, fig. 9 shows a main switch tube control signal LI, a clamp switch tube control signal HI, and an exciting inductor current i when the clamp switch tube is normal in the critical conduction mode of the active clamp flyback circuit_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a); fig. 10 shows a main switching tube control signal LI, a clamping switching tube control signal HI, and an excitation inductor current i when a clamping switching tube is abnormal in a critical conduction mode of the active clamping flyback circuit_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a); the active clamping flyback circuit works in a critical conduction mode, and the control signal of the clamping switch tube is changed from invalid to valid after the main switch tube is switched off; the clamping switch tube control circuit adjusts the clamping switch tube controlWhen the control signal is changed from effective to ineffective, the main switching tube is enabled to realize zero voltage conduction, when the clamping switching tube control signal is effective, the comparison circuit detects the voltage on the auxiliary winding or the voltage of a switching node or the inductive current detection circuit detects the exciting inductive current, when the voltage on the auxiliary winding does not oscillate or the voltage of the switching node does not oscillate or the exciting inductive current does not oscillate, the abnormal signal of the clamping switching tube is invalid, the driving circuit of the clamping switching tube and the clamping switching tube is judged to be normal, otherwise, the abnormal signal of the clamping switching tube is effective, and the abnormal signal of the clamping switching tube or the driving circuit of the clamping switching tube is judged to be abnormal. In a critical conduction mode, when the clamp switch tube and the clamp switch tube driving circuit are normal, the main switch tube can be controlled to realize zero voltage conduction by controlling the turn-off time of the clamp switch tube. The specific method for controlling zero voltage conduction is that a clamp switch tube control signal is preset as effective time, and the effective time is generally shorter than the conduction time of a clamp switch tube under the condition that a main switch tube realizes zero voltage conduction; and detecting whether the main switching tube is conducted by zero voltage or not, if not, delaying the moment from effective to ineffective of the clamping switching tube in the next switching period until the main switching tube is conducted by zero voltage, and not delaying the time from effective to ineffective of the clamping switching tube. If the clamp switch tube or the clamp switch tube driving circuit is abnormal, the clamp switch tube of the next switching period is delayed from effective to ineffective, the zero voltage conduction of the main switch tube can not be realized always, and when the excitation inductive current is delayed to be less than zero, the auxiliary winding can generate oscillation when the conduction control signal of the clamp switch tube is effective.

In one embodiment, referring to fig. 11, the clamp switching tube abnormality detection circuit includes an inductor current detection circuit 230, which receives the voltage of the auxiliary winding and determines whether the inductor current is zero according to the voltage on the auxiliary winding; the clamp switching tube abnormity judging circuit outputs a clamp switching tube prolonged conduction signal, and the clamp switching tube and the main switching tube control circuit receive the clamp switching tube prolonged conduction signal; when the clamp switch tube prolongs the conduction signal to be effective, the clamp switch tube and the main switch tube control circuit delay the time from the effective state to the ineffective state of the clamp switch tube control signal;

the active clamp flyback circuit works in a critical conduction mode or an intermittent conduction mode, and the clamp switch tube control signal HI is changed from invalid to valid after the main switch tube is turned off; in every M switching cycles, one switching cycle is that when the inductive current detection circuit detects that the exciting inductive current is zero, the clamp switch tube and main switch tube control circuit receives a clamp switch tube extension conduction signal output by the clamp switch tube abnormality judgment circuit, the clamp switch tube abnormality judgment circuit starts timing, when the timing reaches the first time, the clamp switch tube and main switch tube control circuit 300 controls a clamp switch tube control signal HI to be changed from effective to ineffective, and the timing is ended; in the timing process, the comparison circuit detects the voltage on the auxiliary winding or the voltage of a switch node, if the voltage on the auxiliary winding or the voltage of the switch node is detected to oscillate, or the inductive current detection circuit detects the excitation inductive current to oscillate, an abnormal signal of the clamping switch tube is effective, the clamping switch tube is judged to be abnormal or the driving circuit of the clamping switch tube is judged to be abnormal, otherwise, the abnormal signal of the clamping switch tube is ineffective, and the clamping switch tube and the driving circuit of the clamping switch tube are judged to be normal; or in the timing, the comparison circuit detects the voltage on the auxiliary winding or the voltage of the switching node, if the voltage on the auxiliary winding or the voltage of the switching node is detected to oscillate, or the inductive current detection circuit detects the excitation inductive current to oscillate, the next P switching periods are continued, and the control signal of the clamping switching tube is changed from invalid to valid after the main switching tube is switched off; when the inductive current detection circuit detects that the exciting inductive current is zero, the clamp switching tube abnormity judgment circuit starts timing, when the first time is reached, the clamp switching tube and the main switching tube control circuit control and control the clamp switching tube control signal to be changed from effective to ineffective, and the timing is finished; continuously carrying out P +1 switching cycles, detecting the voltage on the auxiliary winding or the voltage of a switching node in the timing, and if the voltage on the auxiliary winding or the voltage of the switching node is detected to oscillate or an inductive current detection circuit detects that the exciting inductive current oscillates, judging whether the clamping switching tube is abnormal or a driving circuit of the clamping switching tube is abnormal if an abnormal signal of the clamping switching tube is valid; wherein M and P are both natural numbers of 1 or more.

Referring to fig. 12 and 13, when the clamp switch tube is normal and abnormal in the critical conduction mode of the active clamp flyback circuit, respectively, the main switch tube control signal LI, the clamp switch tube control signal HI, and the exciting inductor current i are respectively_LMSwitch node voltage V_SWAnd a feedback voltage V_FBA waveform diagram of (a); in M periods, the control signals of the clamping switch tube in M-1 switching periods can be changed from effective to ineffective when the exciting inductive current is larger than zero, and can be changed from effective to ineffective when the exciting inductive current is smaller than zero in one switching period, so that whether the clamping switch tube and the clamping switch tube driving circuit are normal or not is judged.

In order to prevent misjudgment, if the switch node voltage oscillates in the extended conduction period of one switching period, the time when the clamp switch tube control signal changes from active to inactive needs to be extended for the following P switching periods until the exciting inductance current is negative, and in the following P switching periods, the switch node voltage also oscillates in the extended conduction period, so that the clamp switch tube or the clamp switch tube driving circuit is judged to be abnormal.

Fig. 14 shows an embodiment of an inductor current detection circuit. Information on the magnetizing inductor current can be obtained by detecting the voltage on the auxiliary winding. In the above embodiment, information of the zero crossing of the exciting inductor current is required. When the main switching tube is switched on, the exciting inductive current rises and the volt-second integral rises, when the main switching tube is switched off, the exciting inductive current falls and the volt-second integral falls, and when the exciting inductive current falls to zero, the volt-second integral also becomes zero. Therefore, the point at which the magnetizing inductor current is zero can be determined by means of a volt-second integral. Due to voltage on the auxiliary winding and excitation inductanceThe ratio of the voltages on the auxiliary winding is equal to the turn ratio thereof, and therefore, the voltage-second integration can be performed by detecting the voltage on the auxiliary winding. The current source i231 is a voltage-controlled current source whose current magnitude is determined by the voltage V on the auxiliary winding_AUXThe control is typically a fixed proportion of the voltage on the auxiliary winding. The controlled current source i231 charges and discharges the capacitor C231, and in one embodiment, when the main switching tube is turned on and the exciting inductor current rises, the controlled current source i231 charges the capacitor C231 and the voltage on the capacitor C231 rises from Vref; when the main switch tube is turned off, when the exciting inductance current drops, the controlled current source i231 discharges the capacitor C231, the voltage on the capacitor C231 drops, the comparator 232 compares the voltage VC231 on the capacitor C231 with the reference voltage Vref, and when VC231 drops to the reference voltage Vref, the comparator overturns to represent the zero crossing of the exciting inductance current. In another embodiment, when the main switch tube is turned on, the controlled current source i231 discharges the capacitor C231 when the exciting inductor current rises; when the main switch tube is turned off, the controlled current source i231 charges the capacitor C231 when the exciting inductor current drops.

Referring to fig. 2, the active clamp flyback circuit includes a clamp capacitor CSA, where a voltage of the clamp capacitor is a clamp voltage VC, and when the clamp voltage VC or the output voltage Vo is greater than a fifth voltage threshold, the clamp switching device is started to detect an abnormality.

When the clamp switch tube or the clamp switch tube driving circuit is abnormal, the clamp switch tube and main switch tube control circuit 300 turns off the main switch tube M1 and the clamp switch tube MSA, and when the turn-off time of the main switch tube M1 and the clamp switch tube MSA reaches the fourth time, the clamp switch tube and main switch tube control circuit 300 controls the main switch tube M1 and the clamp switch tube MSA to be switched again; or when the clamp switch tube or the clamp switch tube driving circuit is abnormal, the clamp switch tube and main switch tube control circuit 300 turns off the main switch tube M1 and the clamp switch tube MSA, and when power is to be re-electrified, the clamp switch tube and main switch tube control circuit 300 controls the main switch tube M1 and the clamp switch tube MSA to be switched on and off.

It should be noted that, in one embodiment, the high level may be valid, and the low level may be invalid; in another embodiment, the active may correspond to a low level and the inactive corresponds to a high level.

In one embodiment, the clamp switching tube abnormality detection circuit comprises a comparison circuit and a clamp switching tube abnormality judgment circuit, wherein the output voltage of the clamp switching tube abnormality judgment circuit is a clamp switching tube abnormality signal, the comparison circuit receives the voltage on the auxiliary winding or the switch node voltage, the clamp switching tube abnormality judgment circuit receives the output voltage of the comparison circuit and judges whether a clamp switching tube and a clamp switching tube driving circuit are abnormal, when the clamp switching tube or the clamp switching tube driving circuit is abnormal, the clamp switching tube abnormality signal is valid, otherwise, the clamp switching tube abnormality signal is invalid; and the clamp switch tube and the main switch tube control circuit receive the abnormal signal of the clamp switch tube and control the on and off of the main switch tube and the clamp switch tube.

In one embodiment, the active clamping flyback circuit works in an intermittent conduction mode, and the clamping switching tubes are respectively conducted before and after the main switching tube is conducted; when the control signal of the clamping switch tube is effective before the main switch tube is conducted, the comparison circuit compares the voltage on the auxiliary winding with a first voltage threshold value or the voltage of a switch node with a second voltage threshold value, when the voltage of the switch node in Q continuous switching periods is smaller than the first voltage threshold value or the voltage on the auxiliary winding is smaller than the second voltage threshold value, the output voltage of the clamping switch tube abnormity judgment circuit is effective, and the clamping switch tube or the clamping switch tube driving circuit is judged to be abnormal, wherein Q is a natural number which is larger than or equal to 1.

In one embodiment, the clamp switching tube abnormality detection circuit comprises an inductive current detection circuit, wherein the inductive current detection circuit receives the voltage of the auxiliary winding and judges whether the inductive current is zero or not according to the voltage on the auxiliary winding; the clamp switching tube abnormity judging circuit outputs a clamp switching tube prolonged conduction signal, and the clamp switching tube and the main switching tube control circuit receive the clamp switching tube prolonged conduction signal; when the clamp switch tube prolongs the conduction signal to be effective, the clamp switch tube and the main switch tube control circuit delay the time from the effective state to the ineffective state of the clamp switch tube control signal;

wherein M and P are both natural numbers of 1 or more.

In one embodiment, the active clamp flyback circuit operates in a critical conduction mode, and the control signal of the clamp switching tube is changed from invalid to valid after the main switching tube is turned off; the clamp switch tube control circuit adjusts the time when the clamp switch tube control signal changes from active to inactive, so that the main switch tube realizes zero voltage conduction, when the clamp switch tube control signal is active, the comparison circuit detects the voltage on the auxiliary winding or the switch node voltage, or the inductive current detection circuit detects the exciting inductive current, when the voltage on the auxiliary winding does not oscillate or the switch node voltage does not oscillate or the exciting inductive current does not oscillate, the clamp switch tube abnormal signal is invalid, the clamp switch tube and the clamp switch tube driving circuit are judged to be normal, otherwise, the clamp switch tube abnormal signal is active, and the clamp switch tube or the clamp switch tube driving circuit is judged to be abnormal.

In one embodiment, the clamp switching tube abnormality judgment circuit outputs a clamp switching tube extended conduction signal, and the clamp switching tube and main switching tube control circuit receives the clamp switching tube extended conduction signal; when the clamp switch tube prolongs the conduction signal to be effective, the clamp switch tube and the main switch tube control circuit delay the time from the effective state to the ineffective state of the clamp switch tube control signal;

wherein M and P are both natural numbers of 1 or more.

In one embodiment, when the duty ratio of the main switching tube is larger than a first threshold value, the clamping switching tube abnormity detection circuit is started.

In one embodiment, the active clamp flyback circuit comprises a clamp capacitor, the voltage on the clamp capacitor is a clamp voltage, and the clamp switching tube abnormality detection is started after the clamp voltage or the output voltage is greater than a fifth voltage threshold.

In one embodiment, when the clamp switch tube or the clamp switch tube driving circuit is abnormal, the clamp switch tube and the main switch tube control circuit turns off both the main switch tube and the clamp switch tube, and when the turn-off time of both the main switch tube and the clamp switch tube reaches a fourth time, the clamp switch tube and the main switch tube control circuit controls the main switch tube and the clamp switch tube to be switched again; or when the clamping switch tube or the clamping switch tube driving circuit is abnormal, the clamping switch tube and the main switch tube control circuit turn off the main switch tube and the clamping switch tube, and when power is electrified again, the clamping switch tube and the main switch tube control circuit control the main switch tube and the clamping switch tube to be switched on and off.

The utility model also provides an active clamp flyback circuit, including above-mentioned clamp switch tube anomaly detection method or detection circuitry.

Although the embodiments have been described and illustrated separately, it will be apparent to those skilled in the art that some common techniques may be substituted and integrated between the embodiments, and reference may be made to one of the embodiments not explicitly described, or to another embodiment described.

The above-described embodiments do not limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the above-described embodiments should be included in the protection scope of the technical solution.

Claims

1. The clamp switch tube abnormity detection circuit is characterized in that: the active clamping flyback circuit comprises a clamping switch tube, a main switch tube and a transformer; when a control signal of the clamping switch tube is effective, the clamping switch tube abnormity detection circuit detects the voltage on a switch node or an auxiliary winding or the excitation inductive current, and when the voltage on the switch node or the auxiliary winding or the excitation inductive current oscillates or the voltage on the switch node is smaller than a first voltage threshold or the voltage on the auxiliary winding is smaller than a second voltage threshold, the clamping switch tube abnormity detection circuit judges that the clamping switch tube is abnormal or a driving circuit of the clamping switch tube is abnormal; the switch node is a common node of the transformer and the main switch tube; the transformer comprises a primary winding, a secondary winding and an auxiliary winding;

2. The clamp switching tube abnormality detection circuit of claim 1, characterized in that: the clamp switching tube abnormity detection circuit comprises a comparison circuit and a clamp switching tube abnormity judgment circuit, wherein the output voltage of the clamp switching tube abnormity judgment circuit is a clamp switching tube abnormity signal, the comparison circuit receives the voltage on the auxiliary winding or the switch node voltage, the clamp switching tube abnormity judgment circuit receives the output voltage of the comparison circuit and judges whether the clamp switching tube and a clamp switching tube driving circuit are abnormal or not, when the clamp switching tube or the clamp switching tube driving circuit is abnormal, the clamp switching tube abnormity signal is valid, otherwise, the clamp switching tube abnormity signal is invalid; and the clamp switch tube and the main switch tube control circuit receive the abnormal signal of the clamp switch tube and control the on and off of the main switch tube and the clamp switch tube.

3. The clamp switching tube abnormality detection circuit of claim 2, characterized in that: the active clamping flyback circuit works in an intermittent conduction mode, and the clamping switch tube is respectively conducted before and after the main switch tube is conducted; when the control signal of the clamping switch tube is effective before the main switch tube is conducted, the comparison circuit compares the voltage on the auxiliary winding with a first voltage threshold value or the voltage of a switch node with a second voltage threshold value, when the voltage of the switch node in Q continuous switching periods is smaller than the first voltage threshold value or the voltage on the auxiliary winding is smaller than the second voltage threshold value, the output voltage of the clamping switch tube abnormity judgment circuit is effective, and the clamping switch tube or the clamping switch tube driving circuit is judged to be abnormal, wherein Q is a natural number which is larger than or equal to 1.

4. The clamp switching tube abnormality detection circuit of claim 2, characterized in that: the clamp switching tube abnormity detection circuit comprises an inductive current detection circuit, wherein the inductive current detection circuit receives the voltage of the auxiliary winding and judges whether the inductive current is zero or not according to the voltage on the auxiliary winding; the clamp switching tube abnormity judging circuit outputs a clamp switching tube prolonged conduction signal, and the clamp switching tube and the main switching tube control circuit receive the clamp switching tube prolonged conduction signal; when the clamp switch tube prolongs the conduction signal to be effective, the clamp switch tube and the main switch tube control circuit delay the time from the effective state to the ineffective state of the clamp switch tube control signal;

wherein M and P are both natural numbers of 1 or more.

5. The clamp switching tube abnormality detection circuit of claim 2, characterized in that: the active clamping flyback circuit works in a critical conduction mode, and the control signal of the clamping switch tube is changed from invalid to valid after the main switch tube is switched off; the clamp switch tube control circuit adjusts the time when the clamp switch tube control signal changes from active to inactive, so that the main switch tube realizes zero voltage conduction, when the clamp switch tube control signal is active, the comparison circuit detects the voltage on the auxiliary winding or the switch node voltage, or the inductive current detection circuit detects the exciting inductive current, when the voltage on the auxiliary winding does not oscillate or the switch node voltage does not oscillate or the exciting inductive current does not oscillate, the clamp switch tube abnormal signal is invalid, the clamp switch tube and the clamp switch tube driving circuit are judged to be normal, otherwise, the clamp switch tube abnormal signal is active, and the clamp switch tube or the clamp switch tube driving circuit is judged to be abnormal.

6. The clamp switching tube abnormality detection circuit of claim 2, characterized in that: the clamp switching tube abnormity judging circuit outputs a clamp switching tube prolonged conduction signal, and the clamp switching tube and the main switching tube control circuit receive the clamp switching tube prolonged conduction signal; when the clamp switch tube prolongs the conduction signal to be effective, the clamp switch tube and the main switch tube control circuit delay the time from the effective state to the ineffective state of the clamp switch tube control signal;

wherein M and P are both natural numbers of 1 or more.

7. The clamp switching tube abnormality detection circuit of claim 6, characterized in that: and when the duty ratio of the main switching tube is larger than a first threshold value, starting the clamp switching tube abnormity detection circuit.

8. The clamp switching tube abnormality detection circuit according to any one of claims 1 to 7, characterized in that: the active clamping flyback circuit comprises a clamping capacitor, the voltage on the clamping capacitor is clamping voltage, and when the clamping voltage or the output voltage is larger than a fifth voltage threshold value, abnormal detection of a clamping switch tube is started.

9. The clamp switching tube abnormality detection circuit according to any one of claims 1 to 7, characterized in that: when the clamp switch tube or the clamp switch tube driving circuit is abnormal, the clamp switch tube and the main switch tube control circuit turn off the main switch tube and the clamp switch tube, and when the turn-off time of the main switch tube and the clamp switch tube reaches the fourth time, the clamp switch tube and the main switch tube control circuit control the main switch tube and the clamp switch tube to be switched again; or when the clamping switch tube or the clamping switch tube driving circuit is abnormal, the clamping switch tube and the main switch tube control circuit turn off the main switch tube and the clamping switch tube, and when power is electrified again, the clamping switch tube and the main switch tube control circuit control the main switch tube and the clamping switch tube to be switched on and off.

10. A switching circuit, characterized by: the clamp switch tube abnormity detection circuit comprises the clamp switch tube abnormity detection circuit as claimed in any one of claims 1-9.