A short circuit protection circuit

Abstract

The utility model belongs to circuit technical field discloses a short circuit protection circuit, including the timing end Voff of internal oscillator, the one end of resistance R10 is connected to the timing end Voff of internal oscillator, the other end of resistance R10 is connected to the positive end of photoelectric coupler OT2, the negative end of photoelectric coupler OT2 is connected to port DGND, the one end of resistance R11 is connected to the collector of photoelectric coupler OT2, the other end of resistance R11 is connected to the one end of resistance R12, the one end of resistance R13 and the one end of capacitor C5, the other end of R12 is connected to reference port VREF, the other end of R13 is connected to the one end of R14 and the pin 1 of switch tube Q2, the one end of R15 is connected to the pin 2 of Q2, the other end of R15 is connected to the timing end Voff of internal oscillator, the other end of C5, the other end of R14, the pin 3 of Q2 and port GND are connected to the emitter of OT2. The utility model has the advantages of: when output short circuit, power enters the state of belching, avoids the situation that power has short circuit current for a long time.

Description

Technical Field

[0001] This utility model relates to the field of circuit technology, and in particular to a short-circuit protection circuit. Background Technology

[0002] Flyback switching power supplies are widely used in consumer electronics, such as charging station power supplies, LED power supplies, and mobile phone chargers. Flyback circuits have a simple topology, require fewer components, and can achieve multiple outputs. They are commonly used to power control circuits, protection circuits, communication circuits, and switching transistor drive circuits in power supplies. This type of flyback circuit is generally referred to as the auxiliary power supply circuit of a switching power supply.

[0003] The operation of a flyback power supply affects the reliability of the entire switching power supply; therefore, short-circuit protection is one of the most important functions of a flyback power supply. Traditional flyback power supplies achieve short-circuit protection using the chip's internal overcurrent protection function. When the power supply output circuit is open, the chip's protection activates, stopping PWM waveform generation. This function detects the peak current of the primary winding to achieve short-circuit protection. However, when the input voltage range of the flyback power supply is wide, it is difficult to set the primary protection current threshold. If the primary protection current threshold is set too high, the short-circuit current in the output circuit will not reach the protection current threshold, and the chip's internal overcurrent protection function will not activate. If the primary protection current is set too low, the overcurrent protection will be triggered before full load is reached when the input voltage is low, resulting in the inability to output at full load.

[0004] Therefore, it is necessary to provide a short-circuit protection circuit that enables wide input voltage and allows the flyback power supply to achieve output short-circuit protection. Utility Model Content

[0005] This utility model discloses a short-circuit protection circuit, belonging to the field of power electronics, specifically relating to a flyback power supply output short-circuit protection circuit, which can effectively solve the technical problems involved in the background art.

[0006] To achieve the above objectives, the technical solution of this utility model is as follows:

[0007] A short-circuit protection circuit includes a timing terminal Voff of an internal oscillator. The timing terminal Voff of the internal oscillator is connected to one end of a resistor R10. The other end of the resistor R10 is connected to the positive terminal of an optocoupler OT2. The negative terminal of the optocoupler OT2 is connected to port DGND. The collector of the optocoupler OT2 is connected to one end of a resistor R11. The other end of the resistor R11 is connected to one end of a resistor R12, one end of a resistor R13, and one end of a capacitor C5. The other end of the resistor R12 is connected to a reference port VREF. The other end of the resistor R13 is connected to one end of a resistor R14 and pin 1 of a switching transistor Q2. Pin 2 of the switching transistor Q2 is connected to one end of a resistor R15. The other end of the resistor R15 is connected to the timing terminal Voff of the internal oscillator. The emitter of the optocoupler OT2 is connected to the other end of the capacitor C5, the other end of the resistor R14, pin 3 of the switching transistor Q2, and port GND.

[0008] As a preferred improvement of this utility model: the switching transistor Q2 is a triode, wherein pin 1 is the base, pin 2 is the collector, and pin 3 is the emitter.

[0009] As a preferred improvement of this utility model, the port GND and the port DGND are respectively connected to different grounding terminals.

[0010] As a preferred improvement of this utility model: the port VREF is connected to one end of the resistor R4, the other end of the resistor R4 is connected to pin 1 of the chip U1 and the collector of the optocoupler OT1, pin 3 of the chip U1 is connected to the port CS, pin 4 of the chip U1 is connected to the port Voff, one end of the resistor R5 and one end of the capacitor C2, the other end of the resistor R5 is connected to the port VREF, and the other end of the capacitor C2 is connected to the emitter of the optocoupler OT1 and the port GND;

[0011] Pin 5 of chip U1 is connected to port VREF. Pin 6 of chip U1 is connected to port VCC and one end of resistor R2. The other end of resistor R2 is connected to port Vin, one end of capacitor C1, one end of resistor R1, and pin 1 of transformer T1. The other end of capacitor C1 is connected to the other end of resistor R1 and the negative terminal of diode D1. The positive terminal of diode D1 is connected to pin 2 of transformer T1 and pin 2 of switching transistor Q1. Pin 7 of chip U1 is connected to one end of resistor R3. The other end of resistor R3 is connected to pin 1 of switching transistor Q1. Pin 3 of switching transistor Q1 is connected to port CS and one end of resistor R6. The other end of resistor R6 is connected to port GND. Pin 8 of chip U1 is connected to port GND.

[0012] Pin 3 of transformer T1 is connected to the positive terminal of diode D2. The negative terminal of diode D2 is connected to one end of capacitor C3, one end of resistor R7, one end of resistor R8, and the timing terminal Voff of the internal oscillator. Pin 4 of transformer T1 is connected to the other end of capacitor C3 and port DGND. The other end of resistor R7 is connected to the positive terminal of optocoupler OT1. The negative terminal of optocoupler OT1 is connected to pin 3 of controllable precision voltage regulator Z1. The other end of resistor R8 is connected to pin 1 of controllable precision voltage regulator Z1 and one end of resistor R9. The other end of resistor R9 is connected to pin 2 of controllable precision voltage regulator Z1 and port DGND.

[0013] Pin 5 of the transformer T1 is connected to the positive terminal of diode D3, the negative terminal of diode D3 is connected to one end of capacitor C4 and port VCC, and pin 6 of the transformer T1 is connected to the other end of capacitor C4 and port GND.

[0014] As a preferred improvement of this utility model: the switching transistor Q1 is a MOS transistor, wherein pin 1 is the gate, pin 2 is the drain, and pin 3 is the source.

[0015] As a preferred improvement of this utility model, the chip U1 is model number UC2843BD1R2G.

[0016] As a preferred improvement of this utility model: the controllable precision voltage regulator Z1 is an AZ431, wherein pin 1 is the reference terminal, pin 2 is the anode, and pin 3 is the cathode.

[0017] As a preferred improvement of this utility model: pin 1 and pin 2 of the transformer T1 share a common coil, pin 3 and pin 4 of the transformer T1 share a common coil, and pin 5 and pin 6 of the transformer T1 share a common coil, wherein pin 2, pin 3 and pin 5 are terminals with the same name.

[0018] The beneficial effects of this utility model are as follows:

[0019] By adding a flyback power supply output short-circuit protection circuit, the power supply enters a hiccup state when the output is short-circuited, avoiding the situation where the power supply has short-circuit current for a long time. When the short-circuit fault is eliminated, the power supply can return to normal working state, thus realizing the short-circuit protection function of the auxiliary power supply output circuit. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0021] Figure 1 This is a schematic diagram of the flyback power supply section;

[0022] Figure 2 A schematic diagram of the protected section;

[0023] Figure 3 for Figure 1 Enlarged illustration Figure 1 ;

[0024] Figure 4 for Figure 1 Enlarged illustration Figure 2 . Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0027] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0028] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0030] A flyback power supply output short-circuit protection circuit is disclosed, including a flyback power supply circuit and a flyback power supply output short-circuit protection circuit. The output short-circuit protection circuit consists of 6 resistors, 1 optocoupler, 1 capacitor and 1 transistor. Figure 1 It is a flyback power supply circuit. Figure 2 This is a short-circuit protection circuit for the flyback power supply output.

[0031] Figure 1 The diagram illustrates the flyback power supply circuit. The U1 chip is an ON Semiconductor UC2843BD1R2G. T1-A is the primary winding of the flyback transformer T1. The opposite-named terminal of T1-A is connected to the positive input Vin, and the same-named terminal is connected to the drain of the switching MOSFET Q1. The source of Q1 is connected to ground GND via the current sampling resistor R6. The anode of D1 is connected to the drain of Q1, and the cathode of D1 is connected to Vin via parallel resistors R1 and C1. R1, C1, and D1 form an RCD snubber circuit. CS is connected to pin 3 of U1. R2 is a high-voltage start-up resistor, with one end connected to Vin and the other end connected to pin 6 of U1 and VCC. The drive output OUTPUT of U1 is connected to the gate of Q1 via pin 7 through the current-limiting resistor R3. The reference voltage VREF of U1 is connected to Voff of U1 and pin 4 via R5. Pin 4 is connected to ground GND via C2. R5 and C2 form an oscillation circuit. The reference voltage VREF is connected to pin 3 of optocoupler OT1_B via resistor R4. Pin 4 of OT1_B is grounded to GND, and pin 8 of U1 is connected to GND. The same-name terminal of the flyback transformer secondary winding T1_B is connected to the anode of D2, and the cathode of D2 is connected to the output Vout. C3 is a filter capacitor, and the opposite-name terminal of T1_B is connected to DGND. Vout is connected to pin 1 of optocoupler OT1_A via resistor R7, and pin 2 of OT1_A is connected to pin 3 of Z1. Vout is connected to pin 1 of Z1 via resistor R8, and pin 1 of Z1 is connected to pin 2 of Z1 via resistor R9, and then both are connected to DGND. The same-name terminal of the flyback transformer secondary winding T1_C is connected to the anode of D3, and the cathode of D3 is connected to the output VCC. C4 is a filter capacitor, and the opposite-name terminal of T1_C is connected to GND.

[0032] Figure 2This diagram illustrates a flyback power supply output short-circuit protection circuit. Vout is connected to pin 1 of OT2_A via R10, and pin 2 of OT2_A is connected to DGND. Pin 3 of OT2_B is connected to C5 via R11, and the other end of C5 is connected to pin 4 of OT2_B, which is then connected to GND. VREF is connected to R13 via R12, and the other end of R13 is connected to the base of Q2. One end of R14 is connected to the base of Q2, and the other end is connected to GND. Voff is connected to pin 4 of U1, and Voff is connected to the drain of Q2 via R15. The collector of Q2 is connected to GND. It should be further noted that any other components used to achieve the above effects should fall within the inventive concept of this utility model and should be protected within the scope of this utility model.

[0033] Working principle:

[0034] When the switch is turned on normally, the Vout voltage has not yet been established, the optocoupler OT2 is not working, and OT2_B is in a high impedance state. Due to the current limiting of R12 and the relatively large capacitance value of C5, the voltage of C5 is approximately 0V when the switch is turned on. At this time, Q2 is in the cutoff state, and the voltage of Voff is determined by VREF.

[0035] When the VCC voltage reaches the turn-on voltage of U1, VREF rises to 5V, the oscillation circuit composed of R5 and C2 works, U1 generates waves normally, the Vout voltage rises to the rated voltage, OT2 is in the conducting state, and the voltage of C5 is still 0V.

[0036] When a short circuit fault occurs at the output of the switching power supply, the output voltage Vout drops, the optocoupler current of OT2_A decreases, and OT2_B exhibits a high impedance state. At this time, C5 is charged by the VREF voltage, the base voltage of Q2 rises, the base current increases, the transistor saturates and conducts, the Voff voltage is pulled low, the oscillation circuit does not work, and chip U1 stops working. After the chip stops working, the VREF voltage decreases, capacitor C5 discharges, the base voltage of Q2 drops, the base current decreases, the transistor gradually enters the cutoff region, and the Voff voltage is not pulled low. At this time, the chip resumes its working state. The flyback auxiliary power supply then enters a power-on-power-off-power-hiccup state. The frequency of the hiccups depends on the capacitance of C5 and the resistance values ​​of R11 and R12.

[0037] When the output short circuit fault is cleared, the voltage of C5 is consumed by R13 and R14 to a low level, Q2 enters the cutoff state, and pin 4 of U1 normally generates an oscillation signal from VREF, and U1 resumes normal operation.

[0038] Although the embodiments of this utility model have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for this utility model. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, this utility model is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A short-circuit protection circuit, characterized in that: The device includes a timing terminal Voff of an internal oscillator. Voff is connected to one end of resistor R10. The other end of resistor R10 is connected to the positive terminal of optocoupler OT2. The negative terminal of optocoupler OT2 is connected to port DGND. The collector of optocoupler OT2 is connected to one end of resistor R11. The other end of resistor R11 is connected to one end of resistor R12, one end of resistor R13, and one end of capacitor C5. The other end of resistor R12 is connected to the reference port VREF. The other end of resistor R13 is connected to one end of resistor R14 and pin 1 of switching transistor Q2. Pin 2 of switching transistor Q2 is connected to one end of resistor R15. The other end of resistor R15 is connected to the timing terminal Voff of the internal oscillator. The emitter of optocoupler OT2 is connected to the other end of capacitor C5, the other end of resistor R14, pin 3 of switching transistor Q2, and port GND.

2. The short-circuit protection circuit according to claim 1, characterized in that: The switching transistor Q2 is a triode, with pin 1 being the base, pin 2 being the collector, and pin 3 being the emitter.

3. A short-circuit protection circuit according to claim 1, characterized in that: The port GND and the port DGND are connected to different grounding terminals.

4. A short-circuit protection circuit according to claim 1, characterized in that: The port VREF is connected to one end of resistor R4, and the other end of resistor R4 is connected to pin 1 of chip U1 and the collector of optocoupler OT1. Pin 3 of chip U1 is connected to port CS. Pin 4 of chip U1 is connected to port Voff, one end of resistor R5 and one end of capacitor C2. The other end of resistor R5 is connected to port VREF, and the other end of capacitor C2 is connected to the emitter of optocoupler OT1 and port GND. Pin 5 of chip U1 is connected to port VREF. Pin 6 of chip U1 is connected to port VCC and one end of resistor R2. The other end of resistor R2 is connected to port Vin, one end of capacitor C1, one end of resistor R1, and pin 1 of transformer T1. The other end of capacitor C1 is connected to the other end of resistor R1 and the negative terminal of diode D1. The positive terminal of diode D1 is connected to pin 2 of transformer T1 and pin 2 of switching transistor Q1. Pin 7 of chip U1 is connected to one end of resistor R3. The other end of resistor R3 is connected to pin 1 of switching transistor Q1. Pin 3 of switching transistor Q1 is connected to port CS and one end of resistor R6. The other end of resistor R6 is connected to port GND. Pin 8 of chip U1 is connected to port GND. Pin 3 of transformer T1 is connected to the positive terminal of diode D2. The negative terminal of diode D2 is connected to one end of capacitor C3, one end of resistor R7, one end of resistor R8, and the timing terminal Voff of the internal oscillator. Pin 4 of transformer T1 is connected to the other end of capacitor C3 and port DGND. The other end of resistor R7 is connected to the positive terminal of optocoupler OT1. The negative terminal of optocoupler OT1 is connected to pin 3 of controllable precision voltage regulator Z1. The other end of resistor R8 is connected to pin 1 of controllable precision voltage regulator Z1 and one end of resistor R9. The other end of resistor R9 is connected to pin 2 of controllable precision voltage regulator Z1 and port DGND. Pin 5 of the transformer T1 is connected to the positive terminal of diode D3, the negative terminal of diode D3 is connected to one end of capacitor C4 and port VCC, and pin 6 of the transformer T1 is connected to the other end of capacitor C4 and port GND.

5. A short-circuit protection circuit according to claim 4, characterized in that: The switching transistor Q1 is a MOSFET, with pin 1 being the gate, pin 2 being the drain, and pin 3 being the source.

6. A short-circuit protection circuit according to claim 4, characterized in that: The chip U1 is model number UC2843BD1R2G.

7. A short-circuit protection circuit according to claim 4, characterized in that: The controllable precision voltage regulator Z1 is an AZ431, where pin 1 is the reference terminal, pin 2 is the anode, and pin 3 is the cathode.

8. A short-circuit protection circuit according to claim 4, characterized in that: The transformer T1 has a common coil for pins 1 and 2, a common coil for pins 3 and 4, and a common coil for pins 5 and 6, wherein pins 2, 3, and 5 are terminals with the same name.

Images