A switching power supply protection control circuit and method

Abstract

The present invention provides a switching power supply protection control circuit and method. In the switching power supply protection, when a fault occurs, the fault signal triggers the protection device after a certain time delay, and controls the power unit to be turned off; after a certain time delay, the power unit is released, and the fault state is detected again. The circuit structure is simplified, and the protection trigger time and the locking time after protection can be effectively and accurately controlled, thereby improving the control protection of the switching power supply. The protection control circuit has a simple structure and is easy to operate. It can realize the output short circuit protection and output overvoltage protection functions of the switching power supply, and has the characteristics of simple circuit structure, low cost and multi-function.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a switching power supply protection control circuit and method. Background Art

[0002] The switching power supply utilizes the characteristics of inductor and capacitor energy storage, combined with the pulse width modulation method, to achieve high-efficiency power conversion. The power module based on this technology has the characteristics of high efficiency, high density and high reliability, and the products are widely used in the field of electronics. As the core unit of power supply and distribution of electronic systems, the power module directly affects the reliability of electronic systems. With the development of integrated circuit technology, multi-functional and precise control has become possible. Various protection functions such as output short circuit protection, output overvoltage protection, over-temperature protection, etc. are integrated inside the power module. The reliability of the power module is also constantly improving, becoming an indispensable key component in the electronic system. However, the implementation of various protection functions is inseparable from the precise, complex and expensive control chip, making it difficult to balance the high reliability and low cost of the power module.

[0003] The basic principle of switching power supply protection (output short circuit protection, output overvoltage protection) is: when a fault (short circuit, overvoltage) occurs, the fault signal triggers the protection device after a certain time delay, and controls the shutdown of the power unit; after another certain time delay, the power unit is released and the fault state is detected again. If the fault still exists, the above process is repeated. Based on this, many control methods have emerged for the protection control of switching power supplies, and these methods have various problems in application.

[0004] Patent No.: CN101699686A discloses a protection device for a switching power supply, which is composed of a triode, a voltage regulator, a diode, a resistor, and a capacitor. The specific implementation circuit is as follows: Figure 1 As shown. Transistors Q1 and Q2 form a self-locking circuit. Vcc comes from the auxiliary winding of the transformer. The output control signal controls the VCOMP terminal of the control unit of the switching power supply through diode D2. When the power supply output is short-circuited (overloaded), the Vcc voltage is greater than the breakdown voltage of the voltage regulator D1, and the voltage regulator reversely breaks down. At this time, the base voltage of Q2 increases, Q2 is saturated and turned on, and the base of Q1 is pulled down, so that Q1 is saturated and turned on, further raising the base voltage of Q2, and finally making the self-locking circuit composed of (Q1, Q2) enter deep saturation, while pulling down the VCOMP terminal, turning off the output pulse width drive signal, and realizing short-circuit protection. When the short-circuit fault is removed, the Vcc voltage drops, the voltage regulator D1 cannot be broken down, and the capacitors C1 and C2 discharge through the resistors R2 and R3. When Q2 exits saturation and enters the cut-off state due to the drop in base voltage, the collector voltage of Q2 rises, and Q1 also exits saturation and enters the cut-off state synchronously. At this time, the self-locking circuit outputs a high level, and VCOMP increases through diode D2, and then the switching power supply resumes normal operation.

[0005] This method uses the auxiliary winding of the transformer to detect the fault state of the main output. Due to the influence of the coupling degree of the two windings of the transformer and the load adjustment degree, there is a large signal acquisition error. At the same time, the protection triggering process requires the fault signal Vcc to break through the voltage regulator D1, and the voltage regulator D1 adopts an ordinary reverse pn structure, and its voltage regulation accuracy and temperature coefficient are poor, making it difficult to accurately control the protection triggering time and the locking time after protection, which greatly affects the protection effect.

[0006] Patent No.: CN202172253U protects a peak current detection protection circuit, which includes a current detection conversion circuit, a limiting filter circuit, a high-speed comparison circuit, and a protection delay circuit. The specific circuits are as follows Figure 2 As shown. The specific working principle is that after the fault signal is collected by the current transformer, it is full-wave rectified by diodes (D1, D2, D5, D6), and the rectified signal is converted into a voltage signal by resistor R1; the signal is output to the high-speed comparison circuit after passing through the limiter circuit composed of diodes (D3, D4). The high-speed comparison circuit determines whether the fault occurs, and then controls the protection delay circuit to shut down the PWM control loop, thereby realizing short-circuit protection. The 555 timer is used in this scheme to form a high-speed comparison circuit and a delay circuit, which is the key to implementing protection. The high-speed comparison circuit is implemented by a 555 timer, which is equivalent to completing the role of a comparator; the delay circuit is composed of a 555 timer, which is equivalent to completing the role of a monostable circuit. The 555 timer contains two comparators and an RS trigger, which has signal comparison and logic operation capabilities, can independently complete the functions of high-speed comparison and delay, and has the problem of complex circuits. Summary of the invention

[0007] In view of the problems of poor protection accuracy, complex circuits and single functions in the prior art, the present invention provides a switching power supply protection control circuit and method. The protection control circuit has a simple structure and is easy to operate. It can realize the output short-circuit protection and output overvoltage protection functions of the switching power supply and has the characteristics of simple circuit structure, low cost and multi-function.

[0008] The present invention is achieved through the following technical solutions:

[0009] A switching power supply protection control circuit comprises a fault signal judgment, a monostable trigger circuit, an output overvoltage signal acquisition conversion circuit and an output short-circuit signal acquisition conversion circuit; the fault signal judgment and monostable trigger circuit comprises a 555 timer U1; the 555 timer U1 comprises a Vcc terminal, a Reset terminal, a Threshold terminal, a Trig terminal and an OUT terminal, wherein the Vcc terminal and the Reset terminal are connected to a reference output voltage Vref terminal of a switching power supply pulse width controller; the OUT terminal is connected to a COMP terminal of the switching power supply pulse width controller; the Threshold terminal and the Trig terminal are connected to the output overvoltage signal acquisition conversion circuit and the output short-circuit signal acquisition conversion circuit respectively after being connected.

[0010] Preferably, the output overvoltage signal acquisition and conversion circuit includes a voltage reference TLV431, a transistor Q2, a resistor 1, a resistor 2, a resistor 3 and a resistor 4; the voltage reference TLV431 is provided with a K terminal, an R terminal and an A terminal; one end of the resistor 1, the resistor 3 and the resistor 4 are all connected to the output voltage Vo of the switching power supply; the other end of the resistor 1 and one end of the resistor 2 are both connected to the R terminal of the voltage reference TLV431; the other end of the resistor 3 is connected to the K terminal of the voltage reference TLV431 and then to the base of the transistor Q2; the other end of the resistor 2 is connected to the A terminal of the voltage reference TLV431 and then to ground, and the other end of the resistor 4 is connected to the emitter of the transistor Q2; the collector of the transistor Q2 is connected to the Thres terminal and the Trig terminal of the 555 timer U1.

[0011] Furthermore, the transistor Q2 is a P-type transistor.

[0012] Furthermore, the output short-circuit signal acquisition and conversion circuit includes a current transformer T1, a switching diode D1, a resistor R5, a resistor R6 and a capacitor C1; the primary winding Np of the current transformer T1 is connected in series with the primary winding of the switching power supply transformer; one end of the transformer secondary winding Ns is connected to the anode of the diode D1; the other end of Ns is grounded, the cathode of the diode D1 is connected to the resistor R5 and the resistor R6 respectively, one end of the capacitor C1 is connected to the resistor R6 and then connected to the Thres end and Trig end of the 555 timer U1, and the other end of the capacitor C1 is connected to the other end of the resistor R5 and then grounded.

[0013] Preferably, a capacitor C2 is connected between the Vcc terminal and the Reset terminal after they are combined and the reference output voltage Vref terminal of the switching power supply pulse width controller, wherein the other end of the capacitor C2 is grounded.

[0014] Preferably, the 555 timer U1 is further provided with a Disch terminal, and the Disch terminal is connected to the connection point of the Thres terminal and the Trig terminal through a resistor R7.

[0015] Preferably, a diode D1 is provided between the OUT terminal and the COMP terminal of the switching power supply pulse width controller, wherein the OUT terminal is connected to the cathode of the diode D1, and the anode of the diode D1 is connected to the COMP terminal of the switching power supply pulse width controller.

[0016] A control method for a switching power supply protection control circuit, based on the above-mentioned switching power supply protection control circuit, comprises the following steps:

[0017] When the power output Vo is short-circuited, the output current increases rapidly, which is reflected in the rapid increase in the proportion of the primary current Ip of the power transformer. At the same time, a pulse voltage Vs that increases cycle by cycle is obtained through the current transformer T1, the rectifier diode D1, and the resistor R5. The pulse voltage Vs forms a gradually rising signal voltage Vc after passing through the integration circuit R6 and C1; when the Vc voltage rises to more than 2 / 3Vcc, the OUT end of the 555 timer U1 outputs a low level and the Disch end is pulled low; at this time, the OUT end signal quickly pulls down the COMP end of the PWM controller through the diode D2, turns off the drive signal of the power MOS tube Q3, and then turns off the power output, the Ip current drops rapidly, and the Vs voltage stops rising; at the same time, the Disch end pulls one end of the resistor R7 to the ground potential, C1 slowly discharges through R5, R6 and R7, and the Vc voltage slowly drops;

[0018] When the Vc voltage drops below 2 / 3Vcc, the OUT terminal and Disch of U1 remain at a low level;

[0019] When the Vc voltage continues to drop below 1 / 3 Vcc, the OUT and Disch terminals of U1 flip to high level; the COMP terminal signal is released, PWM resumes working, and the switching power supply resumes working; if Vo1 is still in a short-circuit state at this time, the Ip current will increase rapidly, and then repeat the above protection action;

[0020] After the output is short-circuited, the short-circuit protection is triggered after a delay of t1-t0. After the protection, the COMP terminal is released after a delay of t2-t1, and the output fault status is detected again;

[0021] When the output voltage Vo of the output overvoltage signal acquisition conversion circuit rises, the sampling voltage VR rises synchronously. When the VR voltage reaches the 1.2V reference voltage, the output K terminal of the voltage reference TLV431 flips to a low level. At this time, Q2 is turned on, and the Vo voltage charges the capacitor C1 through the resistor R4. The Vc voltage rises rapidly. When the Vc voltage rises to more than 2 / 3Vcc, the output OUT terminal of U1 is pulled low, and then the COMP terminal of the PWM controller is pulled low through the diode D2, turning off the drive of the power MOS tube Q3, turning off the power circuit, and Vo and VR drop rapidly to zero.

[0022] When Vo drops to zero, capacitor C1 discharges slowly and Vc voltage drops slowly. When Vc voltage is less than 1 / 3Vcc, U1 output OUT turns to high level. At this time, PWM controller COMP terminal is released and Vo voltage starts to rise again. When Vo voltage continues to rise again and VR voltage is greater than 1.2V reference, protection is triggered after the above cycle.

[0023] The time period t2-t0 is the output Vo overvoltage delay time, and the time period t3-t2 is the delay time after the protection is triggered.

[0024] Preferably, the signal voltages at the Trig and Thres terminals in the 555 timer U1 start to rise from 0. When the signal voltage is less than 1 / 3Vcc, the Disch terminal is high impedance and the OUT terminal is high level. When the signal voltage is greater than 1 / 3Vcc and less than 2 / 3Vcc, the Disch terminal maintains high impedance and the OUT terminal maintains high level. When the signal voltage continues to rise and is greater than 2 / 3Vcc, the Disch terminal is low impedance and the OUT terminal flips to a low level.

[0025] Preferably, when the output of the switching power supply is short-circuited, the output current increases, and at the same time, the peak current Ip of the primary winding of the transformer also increases rapidly; after the current Ip is sampled by the primary winding Np of the current transformer T1, it is converted into a sampling current Is by the secondary winding Ns of the transformer and output through the diode D1. The sampling current Is is converted into a sampling voltage Vs through the resistor R5, and Vs is integrated by R6 and C1 to form a short-circuit control signal Vc.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects:

[0027] The present invention provides a switching power supply protection control circuit. In the switching power supply protection, when a fault occurs, the fault signal triggers the protection device after a certain time delay, and controls the power unit to be turned off; after another certain time delay, the power unit is released, and the fault state is detected again. The circuit is simplified while the circuit structure is simplified, and the protection trigger time and the locking time after the protection can be effectively and accurately controlled, thereby improving the control protection of the switching power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the structure of a short-circuit protection circuit based on a triode in the prior art;

[0029] Figure 2 It is a schematic diagram of the structure of a peak current detection protection circuit in the prior art;

[0030] Figure 3It is a schematic diagram of the structure of the switch power supply protection control circuit in the present invention;

[0031] Figure 4 It is a schematic diagram of the structure of the fault signal judgment and monostable trigger circuit in the present invention;

[0032] Figure 5 A schematic diagram of waveforms of key nodes in the fault signal judgment and monostable trigger circuit of the present invention;

[0033] Figure 6 A schematic diagram of waveforms of key nodes in the output overvoltage signal acquisition and conversion circuit of the present invention;

[0034] Figure 7 A schematic diagram of waveforms of key nodes in the output short-circuit signal acquisition and conversion circuit of the present invention;

[0035] Figure 8 A schematic diagram of a protection control circuit in an embodiment of the present invention applied to a single-ended flyback switching power supply;

[0036] Fig. 9 A schematic diagram of waveforms of key nodes of short-circuit protection in an embodiment of the present invention;

[0037] Fig.10 It is the waveform of the key node of output undervoltage protection in the embodiment of the present invention.

[0038] In the figure: 1-fault signal judgment, monostable trigger circuit; 2-output overvoltage signal acquisition and conversion circuit; 3-output short-circuit signal acquisition and conversion circuit. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0040] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0041] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0042] The present invention provides a switching power supply protection control circuit and method. The protection control circuit has a simple structure and is easy to operate. It can realize the switching power supply output short circuit protection and output overvoltage protection functions, and has the characteristics of simple circuit structure, low cost and multi-function.

[0043] Specifically, according to Figure 3 As shown, the switch power supply protection control circuit includes a fault signal judgment, monostable trigger circuit 1, an output overvoltage signal acquisition conversion circuit 2 and an output short circuit signal acquisition conversion circuit 3; the fault signal judgment, monostable trigger circuit 1 includes a 555 timer U1. Figure 4 As shown, the 555 timer U1 includes a Vcc terminal, a Reset terminal, a Thres terminal, a Trig terminal and an OUT terminal, wherein the Vcc terminal and the Reset terminal are connected to the reference output voltage Vref terminal of the switching power supply pulse width controller; the OUT terminal is connected to the COMP terminal of the switching power supply pulse width controller; the Thres terminal and the Trig terminal are connected to the output overvoltage signal acquisition conversion circuit 2 and the output short circuit signal acquisition conversion circuit 3 after being connected. Among them, the capacitor C2 is connected between the Vcc terminal and the Reset terminal after being combined and the reference output voltage Vref terminal of the switching power supply pulse width controller, wherein the other end of the capacitor C2 is grounded. The 555 timer U1 is also provided with a Disch terminal, and the Disch terminal is connected to the connection between the Thres terminal and the Trig terminal through a resistor R7. A diode D1 is provided between the OUT terminal and the COMP terminal of the switching power supply pulse width controller, wherein the OUT terminal is connected to the cathode of the diode D1, and the anode of the diode D1 is connected to the COMP terminal of the switching power supply pulse width controller.

[0044] Specifically, the logic relationship of the 555 timer U1 is shown in Table 1, where the 1 / 3Vcc and 2 / 3Vcc thresholds are obtained by dividing the Vcc voltage by three resistors inside the 555 timer. The working waveform of this unit circuit is as follows: Figure 5 As shown, the signal voltage at the Trig and Thres terminals starts to rise from 0. When the signal voltage is less than 1 / 3Vcc, the Disch terminal is high impedance and the OUT terminal is high level. When the signal voltage is greater than 1 / 3Vcc and less than 2 / 3Vcc, the Disch terminal maintains high impedance and the OUT terminal maintains high level. When the signal voltage continues to rise and is greater than 2 / 3Vcc, the Disch terminal becomes low impedance and the OUT terminal flips to a low level.

[0045] Trig Thres Reset Disch Out X X 0 Low resistance 0 <1 / 3Vcc <2 / 3Vcc 1 High resistance 1 >1 / 3Vcc <2 / 3Vcc 1 Keep Keep >1 / 3Vcc >2 / 3Vcc 1 Low resistance 0

[0046] Table 1 555 timer internal logic relationship

[0047] Specifically, the output overvoltage signal acquisition and conversion circuit 2 includes a voltage reference TLV431, a transistor Q2, a resistor 1, a resistor 2, a resistor 3 and a resistor 4; the voltage reference TLV431 is provided with a K terminal, an R terminal and an A terminal; one end of each of the resistors 1, 3 and 4 is connected to the output voltage Vo of the switching power supply; the other end of the resistor 1 and one end of the resistor 2 are both connected to the R terminal of the voltage reference TLV431; the other end of the resistor 3 is connected to the K terminal of the voltage reference TLV431 and then to the base of the transistor Q2; the other end of the resistor 2 is connected to the A terminal of the voltage reference TLV431 and then to ground, and the other end of the resistor 4 is connected to the emitter of the transistor Q2; the collector of the transistor Q2 is connected to the Thres terminal and the Trig terminal of the 555 timer U1, wherein the transistor Q2 is a P-type transistor.

[0048] The specific working process is as follows: when the Vo voltage increases, after being sampled by resistors R1 and R2, it exceeds the internal reference voltage (1.2V) of the voltage reference TLV431, and the K-pole level of TLV431 is pulled down, causing Q2 to saturate and conduct, and further the collector level of Q2 is pulled up through resistor R4. The specific working waveform is as follows Figure 6 shown.

[0049] Specifically, the output short-circuit signal acquisition and conversion circuit 3 includes a current transformer T1, a switching diode D1, a resistor R5, a resistor R6 and a capacitor C1; the primary winding Np of the current transformer T1 is connected in series with the primary winding of the switching power supply transformer; one end of the transformer secondary winding Ns is connected to the anode of the diode D1; the other end of Ns is grounded, the cathode of the diode D1 is connected to the resistor R5 and the resistor R6 respectively, one end of the capacitor C1 is connected to the resistor R6 and then connected to the Thres end and Trig end of the 555 timer U1, and the other end of the capacitor C1 is connected to the other end of the resistor R5 and then grounded.

[0050] The specific working process is as follows: when the output of the switching power supply is short-circuited, the output current increases, and at the same time, the peak current Ip of the primary winding of the transformer also increases rapidly; after the current Ip is sampled by the primary winding Np of the current transformer T1, it is converted into a sampling current Is by the secondary winding Ns of the transformer and output through the diode D1. The sampling current Is is converted into a sampling voltage Vs through the resistor R5, and Vs is integrated by R6 and C1 to form a short-circuit control signal Vc. As the primary peak current Ip increases, the integrated voltage Vc also gradually increases with time accumulation. Figure 7 The waveforms of the key nodes of the unit circuit 3 are shown, where Ts is the switching period of the switching power supply, Iav is the rated load current of the switching power supply, Is is the sampling current of the current transformer Ns, Is = Ip / n (n = Ns / Np).

[0051] Example

[0052] The proposed protection control circuit is explained by taking the single-ended flyback switching power supply as an example, but it is not limited to the single-ended flyback power supply and can also be applied to other power topologies such as single-ended forward, push-pull, half-bridge, full-bridge, etc. Figure 8 shown.

[0053] This embodiment provides a control method for a switching power supply protection control circuit, based on the above-mentioned switching power supply protection control circuit, characterized in that it includes the following steps:

[0054] (1) Working principle of short circuit protection

[0055] Key node waveforms are as follows Fig. 9 As shown, when the output voltage Vo1 is short-circuited, the output current increases rapidly, which is reflected in the proportional rapid increase of the primary current Ip of the power transformer. At the same time, the pulse voltage Vs (the pulse period is the switching frequency of the switching power supply) that increases period by period is obtained through the current transformer T1, the rectifier diode D1, and the resistor R5; the pulse voltage Vs forms a gradually rising signal voltage Vc after passing through the integration circuit R6 and C1; when the Vc voltage rises more than 2 / 3Vcc, the OUT end of U1 outputs a low level and the Disch end is pulled low. At this time, the OUT end signal quickly pulls down the COMP end of the PWM controller through the diode D2, turns off the drive signal of the power MOS tube Q3, and then turns off the power output, the Ip current drops rapidly, and the Vs voltage stops rising. At the same time, the Disch end pulls one end of the resistor R7 to the ground potential, C1 slowly discharges through R5, R6 and R7, and the Vc voltage slowly drops.

[0056] When the Vc voltage drops below 2 / 3Vcc, the OUT terminal of U1, Disch, remains at a low level.

[0057] When the Vc voltage continues to drop below 1 / 3 Vcc, the OUT and Disch terminals of U1 flip to high level. The COMP terminal signal is released, PWM resumes working, and the switching power supply resumes working. If Vo1 is still in a short-circuit state at this time, the Ip current will increase rapidly, and then repeat the above protection action.

[0058] After the output is short-circuited, the short-circuit protection is triggered by a delay of t1-t0. After the protection, the COMP terminal is released after a delay of t2-t1, and the output fault status is detected again.

[0059] (2) Output overvoltage protection working principle

[0060] Key node waveforms are as follows Fig.10 As shown, when the output voltage Vo rises, the sampling voltage VR rises synchronously. When the VR voltage reaches the reference voltage of 1.2V, the output K terminal of TLV431 flips to a low level. At this time, Q2 is turned on, and the Vo voltage charges the capacitor C1 through the resistor R4. The Vc voltage rises rapidly. When the Vc voltage rises to more than 2 / 3Vcc, the output OUT terminal of U1 is pulled low, and then the COMP terminal of the PWM controller is pulled low through the diode D2, turning off the drive of the power MOS tube Q3, turning off the power circuit, and Vo drops rapidly to zero at VR.

[0061] When Vo drops to zero, capacitor C1 discharges slowly and Vc voltage drops slowly. When Vc voltage is less than 1 / 3Vcc, U1 output OUT terminal flips to high level. At this time, PWM controller COMP terminal is released and Vo voltage starts to rise again. When Vo voltage continues to rise again and makes VR voltage greater than 1.2V reference, the protection is triggered after the above cycle.

[0062] The time period t2-t0 is the output Vo overvoltage delay time, and the time period t3-t2 is the delay time after the protection is triggered.

[0063] In summary, the present invention provides a switching power supply protection control circuit and method. In the switching power supply protection, when a fault occurs, the fault signal triggers the protection device after a certain time delay, and controls the shutdown of the power unit; after another certain time delay, the power unit is released, and the fault state is detected again. It is composed of a fault signal judgment, a monostable trigger circuit, an output overvoltage signal acquisition and conversion circuit, and an output short-circuit signal acquisition and conversion circuit. While simplifying the circuit structure, it can effectively and accurately control the protection trigger time and the locking time after the protection, thereby improving the control protection of the switching power supply.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A switching power supply protection control circuit, It is characterized in that It comprises a fault signal judgment and monostable trigger circuit (1), an output overvoltage signal acquisition and conversion circuit (2) and an output short-circuit signal acquisition and conversion circuit (3); the fault signal judgment and monostable trigger circuit (1) comprises a 555 timer U1; the 555 timer U1 comprises a Vcc terminal, a Reset terminal, a Threshold terminal, a Trig terminal and an OUT terminal, wherein the Vcc terminal and the Reset terminal are connected to a reference output voltage Vref terminal of a switching power supply pulse width controller; the OUT terminal is connected to a COMP terminal of the switching power supply pulse width controller; the Threshold terminal and the Trig terminal are connected to the output overvoltage signal acquisition and conversion circuit (2) and the output short-circuit signal acquisition and conversion circuit (3) respectively after being connected; The output overvoltage signal acquisition and conversion circuit (2) comprises a voltage reference TLV431, a transistor Q2, a resistor 1, a resistor 2, a resistor 3 and a resistor 4; the voltage reference TLV431 is provided with a K terminal, an R terminal and an A terminal; one end of each of the resistors 1, 3 and 4 is connected to the output voltage Vo of the switching power supply; the other end of the resistor 1 and one end of the resistor 2 are connected to the R terminal of the voltage reference TLV431; the other end of the resistor 3 is connected to the K terminal of the voltage reference TLV431 and then to the base of the transistor Q2; the other end of the resistor 2 is connected to the A terminal of the voltage reference TLV431 and then to ground, and the other end of the resistor 4 is connected to the emitter of the transistor Q2; the collector of the transistor Q2 is connected to the Thres terminal and the Trig terminal of the 555 timer U1; The output short-circuit signal acquisition and conversion circuit (3) comprises a current transformer T1, a switching diode D1, a resistor R5, a resistor R6 and a capacitor C1; the primary winding Np of the current transformer T1 is connected in series with the primary winding of the switching power supply transformer; one end of the transformer secondary winding Ns is connected to the anode of the diode D1; the other end of Ns is grounded, the cathode of the diode D1 is connected to the resistor R5 and the resistor R6 respectively, one end of the capacitor C1 is connected to the resistor R6 and then connected to the Thres terminal and Trig terminal of the 555 timer U1, and the other end of the capacitor C1 is connected to the other end of the resistor R5 and then grounded.

2. A switching power supply protection control circuit according to claim 1, It is characterized in that The transistor Q2 is a P-type transistor.

3. A switching power supply protection control circuit according to claim 1, It is characterized in that A capacitor C2 is connected between the Vcc terminal and the Reset terminal after being combined and the reference output voltage Vref terminal of the switching power supply pulse width controller, wherein the other end of the capacitor C2 is grounded.

4. A switching power supply protection control circuit according to claim 1, It is characterized in that The 555 timer U1 is further provided with a Disch terminal, and the Disch terminal is connected to the connection point between the Thres terminal and the Trig terminal through a resistor R7.

5. A switching power supply protection control circuit according to claim 1, It is characterized in that A diode D1 is provided between the OUT terminal and the COMP terminal of the switching power supply pulse width controller, wherein the OUT terminal is connected to the cathode of the diode D1, and the anode of the diode D1 is connected to the COMP terminal of the switching power supply pulse width controller.

6. A control method for a switching power supply protection control circuit, based on the switching power supply protection control circuit according to any one of claims 1 to 5, It is characterized in that The steps include: When the power output Vo is short-circuited, the output current increases rapidly, which is reflected in the rapid increase in the proportion of the primary current Ip of the power transformer. At the same time, a pulse voltage Vs that increases cycle by cycle is obtained through the current transformer T1, the rectifier diode D1, and the resistor R5. The pulse voltage Vs forms a gradually rising signal voltage Vc after passing through the integration circuit R6 and C1; when the Vc voltage rises to more than 2 / 3Vcc, the OUT end of the 555 timer U1 outputs a low level and the Disch end is pulled low; at this time, the OUT end signal quickly pulls down the COMP end of the PWM controller through the diode D2, turns off the drive signal of the power MOS tube Q3, and then turns off the power output, the Ip current drops rapidly, and the Vs voltage stops rising; at the same time, the Disch end pulls one end of the resistor R7 to the ground potential, C1 slowly discharges through R5, R6 and R7, and the Vc voltage slowly drops; When the Vc voltage drops below 2 / 3Vcc, the OUT terminal and Disch of U1 remain at a low level; When the Vc voltage continues to drop below 1 / 3 Vcc, the OUT and Disch terminals of U1 flip to high level; the COMP terminal signal is released, PWM resumes working, and the switching power supply resumes working; if Vo1 is still in a short-circuit state at this time, the Ip current will increase rapidly, and then repeat the above protection action; After the output is short-circuited, the short-circuit protection is triggered after a delay of t1-t0. After the protection, the COMP terminal is released after a delay of t2-t1, and the output fault status is detected again; When the output voltage Vo of the output overvoltage signal acquisition conversion circuit (2) rises, the sampling voltage VR rises synchronously. When the VR voltage reaches the 1.2V reference voltage, the output K terminal of the voltage reference TLV431 flips to a low level. At this time, Q2 is turned on, and the Vo voltage charges the capacitor C1 through the resistor R4. The Vc voltage rises rapidly. When the Vc voltage rises to more than 2 / 3Vcc, the output OUT terminal of U1 is pulled down, and then the COMP terminal of the PWM controller is pulled down through the diode D2, turning off the drive of the power MOS tube Q3, turning off the power circuit, and Vo and VR drop rapidly to zero. When Vo drops to zero, capacitor C1 discharges slowly and Vc voltage drops slowly. When Vc voltage is less than 1 / 3Vcc, U1 output OUT turns to high level. At this time, PWM controller COMP terminal is released and Vo voltage starts to rise again. When Vo voltage continues to rise again and VR voltage is greater than 1.2V reference, protection is triggered after the above cycle. The time period t2-t0 is the output Vo overvoltage delay time, and the time period t3-t2 is the delay time after the protection is triggered.

7. A control method for a switching power supply protection control circuit according to claim 6, It is characterized in that The signal voltages at the Trig and Thres terminals in the 555 timer U1 start to rise from 0. When the signal voltage is less than 1 / 3Vcc, the Disch terminal is high impedance and the OUT terminal is high level. When the signal voltage is greater than 1 / 3Vcc and less than 2 / 3Vcc, the Disch terminal maintains high impedance and the OUT terminal maintains high level. When the signal voltage continues to rise and is greater than 2 / 3Vcc, the Disch terminal is low impedance and the OUT terminal flips to a low level.

8. A control method for a switching power supply protection control circuit according to claim 6, It is characterized in that When the output of the switching power supply is short-circuited, the output current increases, and at the same time, the peak current Ip of the primary winding of the transformer also increases rapidly; after the current Ip is sampled by the primary winding Np of the current transformer T1, it is converted into a sampling current Is by the secondary winding Ns of the transformer and output through the diode D1. The sampling current Is is converted into a sampling voltage Vs through the resistor R5, and Vs is integrated by R6 and C1 to form a short-circuit control signal Vc.

Images