Flyback power supply output short circuit protection circuit

Abstract

The utility model provides a flyback power supply output short-circuit protection circuit. The protection circuit comprises a flyback power supply input circuit, a flyback power supply output circuit, a control chip output circuit, a control chip, a comparison circuit, a short-circuit protection control circuit and a control chip power supply circuit, the control chip power supply circuit is connected between the flyback power supply input circuit and the comparison circuit; the control chip comprises a first output end, a second output end, a third output end, a fourth output end and a fifth output end, the control chip output circuit is connected between the first output end and the flyback power supply input circuit, and the second output end is connected with the control chip power supply circuit and the first end of the short-circuit protection control circuit. According to the embodiment of the invention, when the flyback circuit output circuit is short-circuited, wave sealing processing can be carried out in time, the wave sealing time length can be controlled, and the time length from wave sealing to next wave sending can be controlled, so that the temperature rise of a device can be controlled, the thermal failure of the device can be avoided, and the safety of the protection circuit is improved.

Description

Technical Field

[0001] The present application relates to the technical field of flyback power supplies, and in particular to a flyback power supply output short-circuit protection circuit. Background Art

[0002] In recent years, in the application of power electronics technology, flyback switching power supply is the power supply method used by most control circuits, and its working stability and reliability are becoming increasingly important.

[0003] The traditional technology is that when a short circuit occurs in the output of the flyback power supply, its control chip will detect the short-circuit current of the power winding. When the short-circuit current of the power winding increases to the chip threshold, the chip will reduce the duty cycle and reduce the short-circuit current of the power winding to a safe threshold. The chip then starts to treat it as a normal operating condition and increases the duty cycle. When the control chip detects the short-circuit current of the power winding again, it performs a cycle process. This method does not perform wave sealing processing, which will cause the junction temperature of the power device to continue to rise. When the temperature is greater than the maximum allowable temperature, it will cause the devices in the circuit to fail. Utility Model Content

[0004] The present application provides a flyback power supply output short-circuit protection circuit to solve the problems mentioned in the above background technology.

[0005] The present application provides a flyback power supply output short-circuit protection circuit, comprising: a flyback power supply input circuit, a flyback power supply output circuit, a control chip output circuit, a control chip, a comparison circuit, a short-circuit protection control circuit and a control chip power supply circuit;

[0006] The control chip power supply circuit is connected between the flyback power supply input circuit and the comparison circuit;

[0007] The control chip comprises: a first output terminal, a second output terminal, a third output terminal, a fourth output terminal and a fifth output terminal, the control chip output circuit is connected between the first output terminal and the flyback power supply input circuit, the second output terminal is respectively connected to the control chip power supply circuit and the first terminal of the short-circuit protection control circuit, the third output terminal is connected to the positive input terminal of the comparison circuit, the fourth output terminal is connected to the negative input terminal of the comparison circuit, and the fifth output terminal is grounded;

[0008] The output end of the comparison circuit is connected to the second end of the short-circuit protection control circuit, and the third end of the short-circuit protection control circuit is grounded.

[0009] Optionally, the comparison circuit includes: a comparator, a first voltage divider circuit and a second voltage divider circuit, the first voltage divider circuit is connected between the third output terminal and the positive input terminal of the comparator, and the first voltage divider circuit is also connected to the control chip power supply circuit;

[0010] The second voltage divider circuit is connected between the fourth output terminal and the negative input terminal of the comparator;

[0011] The output end of the comparator is connected to the second end of the short-circuit protection control circuit.

[0012] Optionally, the short-circuit protection control circuit includes: a transistor, a B pole of the transistor is connected to the output end of the comparator, a C pole of the transistor is connected to the second output end, and an E pole of the transistor is grounded.

[0013] Optionally, the control chip power supply circuit includes a first resistor, a second resistor, a third resistor and a first capacitor, the first resistor, the second resistor and the third resistor are connected in series between the flyback power supply input circuit and the comparison circuit, the second output end is connected between the second resistor and the third resistor, and the third resistor is connected in parallel with the first capacitor and to the ground.

[0014] Optionally, the control chip output circuit includes: a MOS tube switch, the S pole of the MOS tube switch is connected to the flyback power supply input circuit, the G pole of the MOS tube switch is connected to the first output end, and the G pole of the MOS tube switch is grounded.

[0015] Optionally, the flyback power input circuit comprises: a power input terminal, a first primary winding and a second primary winding of a flyback transformer;

[0016] The flyback power supply output circuit comprises: a secondary winding of a flyback transformer and a power supply output terminal;

[0017] The power input end is connected to the control chip power supply circuit and the first primary winding, the first primary winding is connected to the control chip output circuit, one end of the second primary winding is connected to the second output end, and the other end is grounded;

[0018] The secondary winding has mutual inductance with the first primary winding and the second primary winding, and the secondary winding is connected to the power output end.

[0019] Optionally, the first voltage divider circuit includes: a fourth resistor, a fifth resistor and a second capacitor, the fourth resistor and the fifth resistor are connected in series between the third output terminal and ground, the fifth resistor and the second capacitor are connected in parallel, and the positive input terminal of the comparator is connected between the fourth resistor and the fifth resistor.

[0020] Optionally, the second voltage divider circuit includes: a sixth resistor, a seventh resistor and a third capacitor, the sixth resistor and the seventh resistor are connected in series between the fourth output terminal and ground, the seventh resistor and the third capacitor are connected in parallel, and the negative input terminal of the comparator is connected between the sixth resistor and the seventh resistor.

[0021] Optionally, a fourth capacitor is connected between the second output terminal and the fifth output terminal.

[0022] In this embodiment, the flyback power supply output short-circuit protection circuit includes: a first output terminal, a second output terminal, a third output terminal, a fourth output terminal and a fifth output terminal, the control chip output circuit is connected between the first output terminal and the flyback power supply input circuit, the second output terminal is respectively connected to the control chip power supply circuit and the first terminal of the short-circuit protection control circuit, the third output terminal is connected to the positive input terminal of the comparison circuit, the fourth output terminal is connected to the negative input terminal of the comparison circuit, and the fifth output terminal is grounded; the output terminal of the comparison circuit is connected to the second terminal of the short-circuit protection control circuit, and the third terminal of the short-circuit protection control circuit is grounded. Compared with the prior art, the present application connects the second output terminal to the short-circuit protection control circuit. When the flyback power supply output circuit is short-circuited, the second output terminal is grounded through the short-circuit protection control circuit, so that the control chip stops working, the wave sealing time can be controlled in time, and the duty cycle can be reduced to reduce the short-circuit current, thereby avoiding overheating of the device, causing failure of the device in the circuit, and improving the safety of the protection circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 A logic diagram of a flyback power supply output short-circuit protection circuit provided in an embodiment of the present application;

[0025] Figure 2 A logic schematic diagram of a flyback power supply output short-circuit protection circuit provided by another embodiment of the present application;

[0026] Figure 3 A circuit connection diagram of a flyback power supply output short-circuit protection circuit provided in one embodiment of the present application.

[0027] In the figure: 1-flyback power supply input circuit; 2-control chip output circuit; 3-control chip; 4-comparison circuit; 5-short circuit protection control circuit; 6-control chip power supply circuit; 7-comparator; 8-first voltage divider circuit; 9-second voltage divider circuit; 10-flyback power supply output circuit. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application is clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work also fall within the scope of protection of the present application.

[0029] Figure 1 A flyback power supply output short-circuit protection circuit is shown according to an embodiment of the present application. Figure 1 As shown, combined with Figure 2 and Figure 3 , the protection circuit includes: a flyback power supply input circuit 1, a flyback power supply output circuit 10, a control chip output circuit 2, a control chip 3, a comparison circuit 4, a short circuit protection control circuit 5 and a control chip power supply circuit 6;

[0030] The control chip power supply circuit 6 is connected between the flyback power supply input circuit 1 and the comparison circuit 4;

[0031] The control chip 3 includes: a first output terminal OUT, a second output terminal Vdd, a third output terminal Comp, a fourth output terminal REF and a fifth output terminal AGND, the control chip output circuit 2 is connected between the first output terminal OUT and the flyback power supply input circuit 1, the second output terminal Vdd is respectively connected to the control chip power supply circuit 6 and the first end of the short-circuit protection control circuit 5, the third output terminal Comp is connected to the positive input terminal of the comparison circuit 4, the fourth output terminal REF is connected to the negative input terminal of the comparison circuit 4, and the fifth output terminal AGND is grounded;

[0032] The output terminal of the comparison circuit 4 is connected to the second terminal of the short-circuit protection control circuit 5 , and the third terminal of the short-circuit protection control circuit 5 is grounded.

[0033] Specifically, the flyback power input circuit 1 is used to provide power to the flyback power output circuit 10. When the flyback power input circuit 1 and the flyback power output circuit 10 work normally, the control chip output circuit 2 needs to be intermittently turned on. Since the control chip output circuit 2 is connected to the first output terminal OUT of the control chip 3, its conduction is controlled by the voltage outputted by the first output terminal OUT of the control chip 3.

[0034] Among them, the second output terminal Vdd of the control chip 3 is connected to the control chip power supply circuit 6, which is used to make the voltage of the second output terminal Vdd greater than the minimum operating voltage of the control chip 3 after voltage division and current limiting by the control chip power supply circuit 6, so that the control chip 3 can work normally, so that the control chip 3 controls the first output terminal OUT to alternately output high and low levels, thereby controlling the flyback power supply input circuit 1 and the flyback power supply output circuit 10 to be turned on and off at intervals.

[0035] Among them, the third output terminal Comp of the control chip 3 is connected to the positive input terminal of the comparison circuit 4, and the fourth output terminal REF of the control chip 3 is connected to the negative input terminal of the comparison circuit 4, which is used to control the voltage of the third output terminal Comp input to the comparison circuit 4 and the voltage of the fourth output terminal REF input to the comparison circuit 4, thereby controlling the output value of the comparison circuit 4.

[0036] The fifth output terminal AGND of the control chip 3 is grounded.

[0037] Among them, the short-circuit protection control circuit 5 is connected to the comparison circuit 4 and the second output terminal Vdd, and is used for when the flyback power supply output circuit 10 is working normally, the comparison circuit 4 outputs a low level, and the short-circuit protection control circuit 5 is not turned on, so that the control chip 3 works normally; when the flyback power supply output circuit 10 is short-circuited, the comparison circuit 4 outputs a high level, and the short-circuit protection control circuit 5 is turned on, so that the second output terminal Vdd is grounded, and when the voltage of the second output terminal Vdd is less than the minimum operating voltage of the control chip 3, the control chip 3 stops working.

[0038] The working process of the above-mentioned flyback power supply output short-circuit protection circuit is as follows:

[0039] In normal operation, after the flyback power supply input is powered, the control chip power supply circuit 6 divides the input voltage of the flyback power supply input circuit 1, so that the voltage of the second output terminal Vdd is greater than the minimum operating voltage of the control chip 3, so that the control chip 3 operates normally. The output terminal OUT of the control chip 3 outputs a duty cycle to control the on and off of the control chip output circuit 2. The voltage output by the third output terminal Comp is less than the voltage of the fourth output terminal REF, so that the comparison circuit 4 outputs a low level, and the short-circuit protection control circuit 5 is not turned on;

[0040] When a short circuit occurs in the flyback power supply output circuit 10, the voltage of the third output terminal Comp increases rapidly, so that the voltage of the positive input terminal of the comparison circuit 4 is greater than the voltage of the reverse input terminal of the comparison circuit 4, and the comparison circuit 4 outputs a high level, controlling the short circuit protection control circuit 5 to be turned on, so that the second output terminal Vdd is grounded and eventually decreases to 0. In practice, the voltage of the second output terminal Vdd gradually decreases until the voltage of the second output terminal Vdd is less than the minimum operating voltage of the control chip 3. After the undervoltage protection of the control chip 3 is triggered, the control chip 3 stops working, performs wave sealing processing, and the entire flyback power supply circuit stops working;

[0041] After the control chip 3 is sealed, the voltage of the second output terminal Vdd is the voltage across the control chip power supply circuit 6. The control chip power supply circuit 6 gradually increases the voltage of the second output terminal Vdd. When the voltage of the second output terminal Vdd reaches the minimum operating voltage of the control chip 3, the control chip 3 restarts, and the first output terminal OUT of the control chip 3 alternately outputs the duty cycle to control the on and off of the control chip output circuit 2, so that the flyback power supply input circuit 1 and the flyback power supply output circuit 10 work normally. When a short circuit is detected again, the sealing process starts again, and the process is cyclical;

[0042] In this embodiment, the flyback power supply output short-circuit protection circuit includes: a first output terminal OUT, a second output terminal Vdd, a third output terminal Comp, a fourth output terminal REF and a fifth output terminal AGND, the control chip output circuit 2 is connected between the first output terminal OUT and the flyback power supply input circuit 1, the second output terminal Vdd is respectively connected to the control chip power supply circuit 6 and the first terminal of the short-circuit protection control circuit 5, the third output terminal Comp is connected to the positive input terminal of the comparison circuit 4, the fourth output terminal REF is connected to the negative input terminal of the comparison circuit 4, and the fifth output terminal AGND is grounded; the output terminal of the comparison circuit 4 is connected to the second terminal of the short-circuit protection control circuit 5, and the third terminal of the short-circuit protection control circuit 5 is grounded. Compared with the prior art, the present application connects the second output terminal Vdd to the short-circuit protection control circuit 5. When the flyback power supply output circuit 10 is short-circuited, the second output terminal Vdd is controlled to be grounded by the short-circuit protection control circuit 5, so that the control chip 3 stops working, the wave sealing time can be controlled in time, and the duty cycle is reduced to reduce the short-circuit current, thereby avoiding overheating of the device, causing the device in the circuit to fail, and improving the safety of the protection circuit.

[0043] Alternatively, see Figure 2 and Figure 3 The comparison circuit 4 includes: a comparator 7, a first voltage divider circuit 8 and a second voltage divider circuit 9, the first voltage divider circuit 8 is connected between the third output terminal Comp and the positive input terminal of the comparator 7, and the first voltage divider circuit 8 is also connected to the control chip power supply circuit 6;

[0044] The second voltage divider circuit 9 is connected between the fourth output terminal REF and the negative input terminal of the comparator 7;

[0045] The output terminal of the comparator 7 is connected to the second terminal of the short-circuit protection control circuit 5 .

[0046] The comparator 7 includes an output terminal, a positive input terminal and a negative input terminal. The output terminal of the comparator 7 is connected to the short-circuit protection control circuit 5 for comparing the voltages of the positive input terminal and the negative input terminal, thereby controlling the on and off of the short-circuit protection control circuit 5.

[0047] Among them, the first voltage divider circuit 8 is used to control the voltage input to the positive input terminal of the comparator 7, and the second voltage divider circuit 9 is used to control the voltage input to the negative input terminal of the comparator 7. When the flyback power supply output circuit 10 is working normally, the first voltage divider circuit 8 and the second voltage divider circuit 9 make the voltage input to the positive input terminal of the comparator 7 less than the voltage input to the negative input terminal of the comparator 7, so that the output terminal of the comparator 7 outputs a low level. In the low level state, the short-circuit protection control circuit 5 is not turned on, so that the second output terminal Vdd connected to the short-circuit protection control circuit 5 is a high level, and the control chip 3 works normally.

[0048] When a short circuit occurs in the flyback power supply output circuit 10, the voltage input to the positive input terminal of the comparator 7 is made greater than the voltage input to the negative input terminal of the comparator 7 through the first voltage divider circuit 8 and the second voltage divider circuit 9, so that the output terminal of the comparator 7 outputs a high level. In the high level state, the short-circuit protection control circuit 5 is turned on, so that the second output terminal Vdd connected to the short-circuit protection control circuit 5 is grounded, and the voltage of the second output terminal Vdd gradually decreases until it is less than the minimum operating voltage of the control chip 3, and the control chip 3 stops working.

[0049] Furthermore, the voltage magnitudes of the positive input terminal and the negative input terminal of the input comparator 7 are ensured by the first voltage divider circuit 8 and the second voltage divider circuit 9 .

[0050] Alternatively, see Figure 3 The short circuit protection control circuit 5 includes: a transistor S1, a B pole of the transistor S1 is connected to the output end of the comparator 7, a C pole of the transistor S1 is connected to the second output end Vdd, and an E pole of the transistor S1 is grounded.

[0051] Among them, the transistor S1 is an NPN transistor S1.

[0052] Among them, when the flyback power supply output circuit 10 is in normal operation, the voltage of the third output terminal Comp is less than the voltage of the fourth output terminal REF, and the voltage of the positive input terminal of the comparator 7 is less than the voltage of the negative input terminal of the comparator 7, so that the output terminal of the comparator 7 outputs a low level, and the B pole of the transistor S1 connected to the output terminal of the comparator 7 receives a low level, so that the transistor S1 is not turned on, and the C pole of the transistor S1 is connected to the second output terminal Vdd, so that the voltage of the second output terminal Vdd is the circuit at both ends of the control chip power supply circuit 6.

[0053] Among them, when the flyback power supply output circuit 10 is short-circuited, when the voltage of the third output terminal Comp is greater than the voltage of the fourth output terminal REF, the voltage of the positive input terminal of the comparator 7 is greater than the voltage of the negative input terminal of the comparator 7, and the output terminal of the comparator 7 outputs a high level. The B pole of the transistor S1 connected to the output terminal of the comparator 7 receives the high level, and the transistor S1 is turned on. Since the C pole of the transistor S1 is connected to the second output terminal Vdd and the E pole of the transistor S1 is grounded, the second output terminal Vdd is grounded, and the voltage of the second output terminal Vdd gradually decreases until it is less than the minimum operating voltage of the control chip 3, so that the control chip 3 stops working and performs wave sealing processing, and the first output terminal OUT continues to output a low level.

[0054] Among them, an eighth resistor R8 is arranged between the output end of the comparator 7 and the E pole of the transistor S1, which is used to limit the current or voltage output by the comparator 7 to the B pole of the transistor S1 through the eighth resistor R8 when the comparator 7 outputs a high level, so as to prevent the comparator 7 from outputting excessive voltage or current and causing damage to the transistor S1.

[0055] Furthermore, by providing the transistor S1 , the voltage of the second output terminal Vdd is controlled according to the on / off state of the transistor S1 , thereby controlling the working state of the control chip 3 .

[0056] Optionally, the control chip power supply circuit 6 includes a first resistor R1, a second resistor R2, a third resistor R3 and a first capacitor C1, the first resistor R1, the second resistor R2 and the third resistor R3 are connected in series between the flyback power supply input circuit 1 and the comparison circuit 4, the second output terminal Vdd is connected between the second resistor R2 and the third resistor R3, and the third resistor R3 is connected in parallel with the first capacitor C1 and the ground terminal.

[0057] Among them, the first resistor R1, the second resistor R2 and the third resistor R3 are connected in series between the flyback power supply input circuit 1 and the comparison circuit 4, the second output terminal Vdd is connected between the second resistor R2 and the third resistor R3, and the third resistor R3 is grounded, so that the voltage of the second output terminal Vdd is the voltage across the third resistor R3, so that the first resistor R1, the second resistor R2 and the third resistor R3 are voltage-divided, and the first resistor R1 and the second resistor R2 are connected in series to shunt the input current of the flyback power supply input circuit 1.

[0058] Furthermore, the second output terminal Vdd is connected between the second resistor R2 and the third resistor R3. When the control chip 3 works normally, the voltage of the second output terminal Vdd is the voltage across the third resistor R3. The first capacitor C1 is connected in parallel with the third resistor R3. The voltage of the second output terminal Vdd is actually the voltage across the first capacitor C1.

[0059] Among them, the first capacitor C1 is connected in parallel with the third resistor R3, and is used to control the time between the control chip 3 sealing the wave and the next wave. When the capacity of the first capacitor C1 is larger, the time for the first capacitor C1 to be fully charged is longer. After the sealing process, the voltage of the second output terminal Vdd rises more slowly, and the time from the control chip 3 to the next wave is longer. The smaller the capacity of the first capacitor C1, the shorter the time for the first capacitor C1 to be fully charged. After the sealing process, the voltage of the second output terminal Vdd rises faster, and the time from the first output terminal OUT of the control chip 3 to the next high-level and low-level alternating output is shorter, that is, the time from the next wave is shorter.

[0060] Furthermore, the control chip power supply circuit 6 divides the input voltage of the flyback power supply input circuit 1 through the first resistor R1 , the second resistor R2 and the third resistor R3 , and provides a voltage to maintain the normal operation of the control chip 3 .

[0061] Optionally, the control chip output circuit 2 includes: a MOS switch S2, an S pole of the MOS switch S2 is connected to the flyback power input circuit 1, a G pole of the MOS switch S2 is connected to the first output terminal OUT, and a D pole of the MOS switch S2 is grounded.

[0062] Among them, when the flyback power supply output circuit 10 works normally, the first output terminal OUT continuously outputs high level and low level alternately. When the first output terminal OUT outputs high level, the G pole of the MOS tube switch S2 receives high level, the D pole of the MOS tube switch S2 is grounded, and the S pole of the MOS tube switch S2 outputs current. At this time, the MOS tube switch S2 is in the on state. When the first output terminal OUT outputs low level, the G pole of the MOS tube switch S2 receives low level, the D pole of the MOS tube switch S2 is grounded, and the S pole of the MOS tube switch S2 stops current. At this time, the MOS tube switch S2 is in the cut-off state.

[0063] When the flyback power supply output circuit 10 is short-circuited, the first output terminal OUT outputs a low level, the G pole of the MOS tube switch S2 receives the low level, the D pole of the MOS tube switch S2 is grounded, and the S pole of the MOS tube switch S2 stops the current. At this time, the MOS tube switch S2 is in a cut-off state.

[0064] Furthermore, the control chip 3 controls the on-off of the MOS switch S2 by controlling the level of the output of the first output terminal OUT.

[0065] By setting the MOS switch S2, when the first output terminal OUT outputs high and low levels alternately, the switch state is quickly switched to reduce the energy loss in the switching transition process and improve the stability.

[0066] Optionally, the flyback power input circuit 1 comprises: a power input terminal Vin, a first primary winding A1 and a second primary winding A2 of a flyback transformer;

[0067] The flyback power supply output circuit 10 comprises: a secondary winding B of a flyback transformer and a power supply output terminal;

[0068] The power input terminal Vin is connected to the control chip power supply circuit 6 and the first primary winding A1, the first primary winding A1 is connected to the control chip output circuit 2, one end of the second primary winding A2 is connected to the second output terminal Vdd, and the other end is grounded;

[0069] The secondary winding B is mutually inductive with the first primary winding A1 and the second primary winding A2, and the secondary winding B is connected to the output end of the power supply.

[0070] The power input terminal Vin is used to provide voltage to the first primary winding A1 , the second primary winding A2 and the control chip 3 of the flyback transformer.

[0071] Among them, when the control chip 3 outputs a high level, the MOS tube switch S2 is turned on, and the inductive current of the first primary winding A1 and the second primary winding A2 begins to rise. At this time, the flyback transformer stores energy, and the flyback transformer supplies the stored energy to the secondary winding B. When the control chip 3 outputs a low level, the MOS tube switch S2 is not turned on, and the inductive induced voltage of the first primary winding A1 and the second primary winding A2 is reversed. At this time, the energy stored in the flyback transformer supplies power to the secondary winding B.

[0072] The flyback power supply output circuit 10 further includes a fifth capacitor C5, a first diode D1 and a power load RL. The fifth capacitor C5 is connected in parallel with the power load RL and connected to the power output end, and is connected in series with the first diode D1 and the secondary winding B.

[0073] Furthermore, when the inductive current of the first primary winding A1 and the second primary winding A2 begins to rise, the first diode D1 stops conducting, so that the flyback transformer stores electrical energy, and the fifth capacitor C5 provides electrical energy to the electrical load RL. When the inductive induced voltage of the first primary winding A1 and the second primary winding A2 is reversed, the electrical energy stored in the flyback transformer provides electrical energy to the electrical load RL and charges the fifth capacitor C5.

[0074] The flyback power input circuit 1 further includes: a second diode D2 and a third diode D3, the second diode D2 is connected to the MOS switch S2 and the first primary winding A1, and the third diode D3 is connected between the third output terminal Comp and the second primary winding A2.

[0075] The flyback power supply input circuit 1 and the flyback power supply output circuit 10 are used to precisely adjust the output voltage, thereby improving the voltage stability.

[0076] Alternatively, see Figure 2 and Figure 3 The first voltage divider circuit 8 includes: a fourth resistor R4, a fifth resistor R5 and a second capacitor C2. The fourth resistor R4 and the fifth resistor R5 are connected in series between the third output terminal Comp and the ground. The fifth resistor R5 is connected in parallel with the second capacitor C2. The positive input terminal of the comparator 7 is connected between the fourth resistor R4 and the fifth resistor R5.

[0077] Among them, the fourth resistor R4 and the fifth resistor R5 are connected in series between the third output terminal Comp and the ground, and the positive input terminal of the comparator 7 is connected between the fourth resistor R4 and the fifth resistor R5, so that the voltage input to the positive input terminal of the comparator 7 is the voltage of the fifth resistor R5, thereby dividing the voltage of the third output terminal Comp to prevent the voltage input to the positive input terminal of the comparator 7 from being too large, thereby causing damage to the comparator 7.

[0078] Among them, the fifth resistor R5 and the second capacitor C2 are connected in parallel, and are used to control the delay time of the transistor S1 of the control chip 3 after the control chip 3 stops working and performs wave sealing. When the voltage of the third output terminal Comp is greater than the voltage of the fourth output terminal REF, the larger the capacity of the second capacitor C2, the less likely it is for the second capacitor C2 to be fully charged, and the slower the voltage from the third output terminal Comp to the positive input terminal of the comparator 7 rises, so that the voltage input from the third output terminal Comp to the positive input terminal of the comparator 7 is greater than the voltage input from the fourth output terminal REF to the negative input terminal of the comparator 7, and the longer the time required for the voltage input from the third output terminal Comp to the positive input terminal of the comparator 7 to be less than the voltage input from the fourth output terminal REF to the negative input terminal of the comparator 7.

[0079] When the voltage of the third output terminal Comp is less than the voltage of the fourth output terminal REF, the smaller the capacity of the second capacitor C2 is, the easier it is for the second capacitor C2 to be fully charged, and the faster the voltage from the third output terminal Comp to the positive input terminal of the comparator 7 rises, so that the time required for the voltage from the third output terminal Comp input to the positive input terminal of the comparator 7 to be less than the voltage from the fourth output terminal REF input to the negative input terminal of the comparator 7 to be greater than the voltage from the fourth output terminal REF input to the negative input terminal of the comparator 7 is shorter.

[0080] The voltage at the positive input terminal of the input comparator 7 is ensured by the first voltage divider circuit 8 .

[0081] Alternatively, see Figure 2 and Figure 3 The second voltage divider circuit 9 includes: a sixth resistor R6, a seventh resistor R7 and a third capacitor C3, the sixth resistor R6 and the seventh resistor R7 are connected in series between the fourth output terminal REF and the ground, the seventh resistor R7 and the third capacitor C3 are connected in parallel, and the negative input terminal of the comparator 7 is connected between the sixth resistor R6 and the seventh resistor R7.

[0082] Among them, the sixth resistor R6 and the seventh resistor R7 are connected in series between the fourth output terminal REF and the ground, and the negative input terminal of the comparator 7 is connected between the sixth resistor R6 and the seventh resistor R7, which is used to divide the voltage of the fourth output terminal REF to prevent the comparator 7 from being damaged due to excessive voltage.

[0083] Among them, the seventh resistor R7 and the third capacitor C3 are connected in parallel, and are used to control the delay time of the transistor S1 of the control chip 3 after the control chip 3 is blocked. When the voltage of the third output terminal Comp is less than the voltage of the fourth output terminal REF, the larger the capacity of the third capacitor C3, the less likely it is that the third capacitor C3 will be fully charged, and the slower the voltage from the fourth output terminal REF to the negative input terminal of the comparator 7 rises, so that the voltage input from the third output terminal Comp to the positive input terminal of the comparator 7 is greater than the voltage input from the fourth output terminal REF to the negative input terminal of the comparator 7, and the longer the time required for the voltage from the third output terminal Comp to the positive input terminal of the comparator 7 to be less than the voltage from the fourth output terminal REF to the negative input terminal of the comparator 7.

[0084] When the voltage of the third output terminal Comp is less than the voltage of the fourth output terminal REF, the smaller the capacity of the third capacitor C3 is, the easier it is to fully charge the third capacitor C3, and the faster the voltage from the third output terminal Comp to the negative input terminal of the comparator 7 rises, so that the time required for the voltage from the third output terminal Comp input to the positive input terminal of the comparator 7 to be less than the voltage from the fourth output terminal REF input to the negative input terminal of the comparator 7 to be greater than the voltage from the fourth output terminal REF input to the negative input terminal of the comparator 7 is shorter.

[0085] The second voltage divider circuit 9 ensures the magnitude of the voltage at the negative input terminal of the input comparator 7 .

[0086] Optionally, a fourth capacitor C4 is connected between the second output terminal Vdd and the fifth output terminal AGND.

[0087] Among them, the fourth capacitor C4 is used to control the length of time from the control chip 3 closing the wave to the next wave transmission. When the control chip 3 closes the wave, the voltage of the third output terminal Comp is greater than the voltage of the fourth output terminal REF, and the transistor S1 is disconnected, so that the voltage of the second output terminal Vdd is the voltage across the third resistor R3. The larger the capacity of the fourth capacitor C4, the longer it takes to be fully charged. Therefore, the slower the voltage of the second output terminal Vdd rises, and the longer the time to the next wave transmission.

[0088] When the control chip 3 is closed, the voltage of the third output terminal Comp is greater than the voltage of the fourth output terminal REF, and the transistor S1 is disconnected. At this time, the voltage of the second output terminal Vdd is the voltage across the third resistor R3, and the voltage is provided by the power input terminal Vin. The smaller the capacity of the fourth capacitor C4, the shorter the time required for full charge. Therefore, the voltage of the second output terminal Vdd rises faster, and the time to the next wave is shorter.

[0089] Finally, it should be noted that all contents not described in the technical solution of this application can be implemented using existing technologies. In addition, the above embodiments are only used to illustrate the technical solution of this application, rather than to limit it; although the application is described in detail with reference to the above embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the above embodiments, or replace some or all of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A flyback power supply output short-circuit protection circuit, characterized in that: include: A flyback power supply input circuit, a flyback power supply output circuit, a control chip output circuit, a control chip, a comparison circuit, a short-circuit protection control circuit and a control chip power supply circuit; The control chip power supply circuit is connected between the flyback power supply input circuit and the comparison circuit; The control chip comprises: a first output terminal, a second output terminal, a third output terminal, a fourth output terminal and a fifth output terminal, the control chip output circuit is connected between the first output terminal and the flyback power supply input circuit, the second output terminal is respectively connected to the control chip power supply circuit and the first terminal of the short-circuit protection control circuit, the third output terminal is connected to the positive input terminal of the comparison circuit, the fourth output terminal is connected to the negative input terminal of the comparison circuit, and the fifth output terminal is grounded; The output end of the comparison circuit is connected to the second end of the short-circuit protection control circuit, and the third end of the short-circuit protection control circuit is grounded; The comparison circuit comprises: a comparator, a first voltage divider circuit and a second voltage divider circuit, wherein the first voltage divider circuit is connected between the third output terminal and the positive input terminal of the comparator, and the first voltage divider circuit is also connected to the control chip power supply circuit; The second voltage divider circuit is connected between the fourth output terminal and the negative input terminal of the comparator; The output end of the comparator is connected to the second end of the short-circuit protection control circuit; The short-circuit protection control circuit comprises: a transistor, wherein the B pole of the transistor is connected to the output end of the comparator, the C pole of the transistor is connected to the second output end, and the E pole of the transistor is grounded; Wherein, the transistor is an NPN transistor.

2. The flyback power supply output short-circuit protection circuit according to claim 1, characterized in that: The control chip power supply circuit includes a first resistor, a second resistor, a third resistor and a first capacitor, the first resistor, the second resistor and the third resistor are connected in series between the flyback power supply input circuit and the comparison circuit, the second output end is connected between the second resistor and the third resistor, and the third resistor is connected in parallel with the first capacitor and the ground end.

3. The flyback power supply output short-circuit protection circuit according to claim 1, characterized in that: The control chip output circuit includes: a MOS tube switch, the S pole of the MOS tube switch is connected to the flyback power supply input circuit, the G pole of the MOS tube switch is connected to the first output end, and the G pole of the MOS tube switch is grounded.

4. The flyback power supply output short-circuit protection circuit according to claim 1, characterized in that: The flyback power supply input circuit comprises: a power supply input terminal, a first primary winding and a second primary winding of a flyback transformer; The flyback power supply output circuit comprises: a secondary winding of a flyback transformer and a power supply output terminal; The power input end is connected to the control chip power supply circuit and the first primary winding, the first primary winding is connected to the control chip output circuit, one end of the second primary winding is connected to the second output end, and the other end is grounded; The secondary winding has mutual inductance with the first primary winding and the second primary winding, and the secondary winding is connected to the power output end.

5. The flyback power supply output short-circuit protection circuit according to claim 1, characterized in that: The first voltage divider circuit includes: a fourth resistor, a fifth resistor and a second capacitor, the fourth resistor and the fifth resistor are connected in series between the third output terminal and the ground, the fifth resistor and the second capacitor are connected in parallel, and the positive input terminal of the comparator is connected between the fourth resistor and the fifth resistor.

6. The flyback power supply output short-circuit protection circuit according to claim 1, characterized in that: The second voltage divider circuit includes: a sixth resistor, a seventh resistor and a third capacitor, the sixth resistor and the seventh resistor are connected in series between the fourth output terminal and the ground, the seventh resistor and the third capacitor are connected in parallel, and the negative input terminal of the comparator is connected between the sixth resistor and the seventh resistor.

7. The flyback power supply output short-circuit protection circuit according to any one of claims 1 to 6, characterized in that: A fourth capacitor is connected between the second output terminal and the fifth output terminal.

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