Low-cost short-circuit protection circuit and method for distribution automation terminal

Abstract

The invention discloses a low-cost short-circuit protection circuit and method for a power distribution automation terminal. The short-circuit protection circuit comprises a power supply switch circuit, a short-circuit detection circuit, a circulation control circuit and a turn-off control circuit. The power supply switch circuit is used for controlling on-off of a power supply loop; the short-circuit detection circuit is used for detecting whether the load is short-circuited and sending a short-circuit signal to the circulation control circuit during short-circuit; the circulation control circuit controls the power supply switch circuit to disconnect the power supply loop through the turn-off control circuit after receiving the short circuit signal, and controls the power supply switch circuit to re-connect the power supply loop through the turn-off control circuit after a certain time interval after disconnection. The device has the advantages of being small in size and low in production cost, automatic cut-off and timing recovery can be achieved in time, special personnel maintenance is not needed, the maintenance cost is reduced, and the stability and reliability of the system are improved.

Description

Technical Field

[0001] The invention belongs to the field of power distribution, and in particular relates to a short-circuit protection circuit of a power distribution automation terminal, and also relates to a short-circuit protection method. Background Art

[0002] During the switch energy storage, opening and closing process and debugging of the distribution automation terminal, if a short circuit occurs, it will cause excessive current, thereby damaging the load or distribution terminal and causing economic losses. In order to improve the reliability of the distribution terminal, a short-circuit protection circuit needs to be added to the distribution automation terminal.

[0003] Most existing protection schemes use fuses as a protective measure. Although fuses are easy to use, they are large in size and inconvenient to replace. In particular, after the fuse is blown, special maintenance is required, which significantly increases the cost. Secondly, some systems lack protective measures. The large current generated during a short circuit will directly damage the load or other components, and the safe and stable operation of the system cannot be ensured. Summary of the invention

[0004] The present invention proposes a low-cost short-circuit protection circuit and method for distribution automation terminals, the purpose of which is to solve the problems of existing solutions such as large volume, inconvenient replacement, and inability to prevent short-circuit current from damaging equipment.

[0005] The technical solution of the present invention is as follows: A low-cost short-circuit protection circuit for a distribution automation terminal, the distribution automation terminal comprising a main power supply positive connection terminal V+, a main power supply negative connection terminal V-, an output positive connection terminal Vout and an output negative connection terminal GND, a load is connected between the output positive connection terminal Vout and the output negative connection terminal GND, the main power supply negative connection terminal V- is grounded, and the short-circuit protection circuit comprises a power supply switch circuit, a short-circuit detection circuit, a circulation control circuit and a shutdown control circuit; The output positive connection terminal Vout is connected to the output negative connection terminal GND through a short-circuit detection circuit, a main power supply positive connection terminal V+, a main power supply negative connection terminal V- and a power supply switch circuit to form a power supply circuit; The power supply switch circuit is used to control the on and off of the power supply circuit; The short-circuit signal transmitting end of the short-circuit detection circuit is connected to the signal input end of the circulation control circuit, and is used to detect whether the load is short-circuited and send a short-circuit signal to the circulation control circuit when a short-circuit occurs; The circulation control circuit is connected to the power supply switch circuit through the shutdown control circuit, and is used to control the power supply switch circuit to disconnect the power supply circuit through the shutdown control circuit after receiving a short-circuit signal, and to control the power supply switch circuit to reconnect the power supply circuit after a certain time interval after the disconnection.

[0006] As a further improvement of the low-cost short-circuit protection circuit of the distribution automation terminal: the short-circuit detection circuit includes a resistor R1, a resistor R2, a resistor R3, a capacitor C1 and a PNP transistor V1; One end of the resistor R2 is connected to the output positive connection terminal Vout, and the other end is connected to the main power supply positive connection terminal V+, one end of the resistor R1 is connected to one end of the resistor R2, and the other end is connected to one end of the resistor R3, the other end of the resistor R3 is connected to the other end of the resistor R2, and the capacitor C1 is connected in parallel with the resistor R3; one end of the resistor R3 is also connected to the base of the PNP transistor V1, and the other end is also connected to the emitter of the PNP transistor V1, and the collector of the PNP transistor V1 is used to be connected to the short-circuit signal transmitting end of the short-circuit detection circuit.

[0007] As a further improvement of the low-cost short-circuit protection circuit of the distribution automation terminal: the short-circuit detection circuit also includes a diode V3, the collector of the PNP transistor V1 is connected to the positive electrode of the diode V3, and the negative electrode of the diode V3 is the short-circuit signal transmitting end.

[0008] As a further improvement of the low-cost short-circuit protection circuit of the distribution automation terminal: the power supply switch circuit includes an N-channel enhancement type MOSFET tube V11, a resistor R11, a resistor R4, a resistor R13 and a diode V2; The source of the N-channel enhancement type MOSFET tube V11 is connected to the negative electrode connection terminal V- of the main power supply, the drain is connected to the negative output connection terminal GND, and the resistor R11 is connected between the negative electrode connection terminal V- of the main power supply and the gate of the N-channel enhancement type MOSFET tube V11; The positive connection terminal V+ of the main power supply is connected to the positive electrode of the diode V2, the negative electrode of the diode V2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the resistor R13, the other end of the resistor R13 is grounded, and the other end of the resistor R4 is also connected to the gate of the N-channel enhancement MOSFET tube V11; The gate of the N-channel enhancement type MOSFET tube V11 is the control input terminal of the power supply switch circuit.

[0009] As a further improvement of the low-cost short-circuit protection circuit of the distribution automation terminal: the shutdown control circuit includes a resistor R5, a resistor R16 and an NPN transistor V7; One end of the resistor R5 is connected to the control input end of the shutdown control circuit, and the other end is connected to one end of the resistor R16, and the other end of the resistor R16 is grounded; The other end of the resistor R5 is also connected to the base of the NPN transistor V7. The collector of the NPN transistor V7 is the control output end of the shutdown control circuit and is connected to the control input end of the power supply switch circuit. The emitter of the NPN transistor V7 is grounded.

[0010] As a further improvement of the low-cost short-circuit protection circuit of the distribution automation terminal: the circulation control circuit includes a PNP transistor V5, an NPN transistor V10, an NPN transistor V8, a capacitor C5, a resistor R7, a resistor R8, a resistor R9, a resistor R10, a resistor R12, a resistor R14, a resistor R15 and a diode V6; The collector of the PNP transistor V5 is both a signal input terminal of the circulation control circuit and a control output terminal of the circulation control circuit connected to the control input terminal of the shutdown control circuit; The anode of the diode V6 is connected to the output anode connection terminal Vout, and the cathode is connected to the emitter of the PNP transistor V5. The resistor R9 is connected between the base and the emitter of the PNP transistor V5. The base of the PNP transistor V5 is also connected to the collector of the NPN transistor V10 through the resistor R10. The emitter of the NPN transistor V10 is grounded. The collector of the PNP transistor V5 is also connected to one end of the resistor R7, the other end of the resistor R7 is connected to one end of the resistor R14 and the base of the NPN transistor V10, and the other end of the resistor R14 is grounded; The collector of the PNP transistor V5 is also connected to one end of the resistor R8, the other end of the resistor R8 is grounded through the capacitor C5 and is also connected to one end of the resistor R12, the other end of the resistor R12 is connected to one end of the resistor R15, and the other end of the resistor R15 is grounded; the other end of the resistor R12 is also connected to the base of the NPN transistor V8; the collector of the NPN transistor V8 is connected to one end of the resistor R14, and the emitter is grounded.

[0011] As a further improvement of the low-cost short-circuit protection circuit of the distribution automation terminal: the circulation control circuit further includes a capacitor C4, one end of which is connected to the positive electrode of the diode V6, and the other end is grounded.

[0012] As a further improvement of the low-cost short-circuit protection circuit of the distribution automation terminal: the circulation control circuit also includes a diode V4, the positive electrode of the diode V4 is connected to the other end of the resistor R8, and the negative electrode is connected to one end of the resistor R8.

[0013] As a further improvement of the low-cost short-circuit protection circuit of the distribution automation terminal: it also includes a short-circuit indication circuit; The short circuit indication circuit includes a resistor R6 and a light emitting diode V9. One end of the resistor R6 is connected to the control output end of the circulation control circuit, and the other end is connected to the positive electrode of the light emitting diode V9. The negative electrode of the light emitting diode V9 is grounded.

[0014] The present invention also provides a low-cost short-circuit protection method for a distribution automation terminal, which is based on the above-mentioned low-cost short-circuit protection circuit for the distribution automation terminal; Short circuit protection methods include: Step 1, when the short-circuit detection circuit detects an overcurrent, a high-level pulse signal as a short-circuit signal will be sent through the short-circuit signal transmitting end; after the signal input end of the cyclic control circuit receives the high-level pulse signal, the voltage across the resistor R14 will turn on the NPN transistor V10, at this time, the output positive connection end Vout is connected to the ground end through the diode V6, the resistor R9, the resistor R10 and the NPN transistor V10, the voltage across the resistor R9 turns on the PNP transistor V5, after the PNP transistor V5 is turned on, the NPN transistor V10 is kept in the on state through the resistor R7 and the resistor R14, and then the PNP transistor V5 is continuously turned on, and the control output end of the cyclic control circuit continuously sends a high-level shutdown control signal; Step 2: After receiving a continuous high-level shutdown control signal, the control input end of the shutdown control circuit disconnects the power supply circuit through the power supply switch circuit and stops supplying power to the load; In the process that the control output end of the circulation control circuit continuously sends out the high-level shutdown control signal, the capacitor C5 is charged first. When the voltage across the capacitor C5 reaches a certain value, the NPN transistor V8 is turned on through the resistors R12 and R18, and then the two ends of the resistor R14 are short-circuited, so that the NPN transistor V10 is turned off, and then the PNP transistor V5 is turned off; at this time, the capacitor C5 starts to discharge, and when it is discharged to the point that the control output end of the circulation control circuit cannot maintain an effective high-level shutdown control signal, the power supply switch circuit will resume the connected state, so that the main power supply can supply power to the load again; Step 3: After the load is powered on again, if the short-circuit fault still exists, the short-circuit detection circuit will detect overcurrent again and jump to step 1; if the short-circuit fault has been eliminated, the load will operate normally until the short-circuit fault occurs again and automatically jump to step 1.

[0015] Compared with the prior art, the present invention has the following positive effects: 1. The circuit of the present invention is composed of components such as resistors, diodes, and triodes, has a simple design, few components, is integrated on the circuit board of the device without occupying other space, and has the advantage of low cost.

[0016] 2. The present invention can automatically cut off the power supply when the current is too large, and automatically restore the power supply after a preset time. If the short circuit fault has not disappeared, it can still be automatically cut off. No special maintenance by personnel is required, the maintenance cost is low, and the reliability is good.

[0017] 3. The present invention can cut off the power output in time when the load is short-circuited, effectively preventing the circuit from being overloaded, thereby protecting the circuit and equipment and ensuring the safe and stable operation and work of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the short-circuit protection circuit of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is described in detail below with reference to the accompanying drawings: like Figure 1 The distribution automation terminal includes a main power supply positive connection terminal V+, a main power supply negative connection terminal V-, an output positive connection terminal Vout and an output negative connection terminal GND. The load is connected between the output positive connection terminal Vout and the output negative connection terminal GND, and the main power supply negative connection terminal V- is grounded. The positive electrode Vbat of the backup power supply is connected to the main power supply positive connection terminal V+ through a diode V0, and the negative electrode is connected to the main power supply negative connection terminal V-. A capacitor C2 is connected between the output positive connection terminal Vout and the output negative connection terminal GND, and a capacitor C3 is connected between the main power supply positive connection terminal V+ and the main power supply negative connection terminal V-.

[0020] Equipped with a backup power supply, it can automatically and seamlessly switch into operation when the main power supply is insufficient or disappears. When the main power supply is restored, the terminal automatically switches back to the main power supply.

[0021] The low-cost short-circuit protection circuit of the distribution automation terminal includes a power supply switch circuit, a short-circuit detection circuit, a circulation control circuit and a shutdown control circuit.

[0022] The output positive connection terminal Vout is connected to the output negative connection terminal GND through the short-circuit detection circuit, the main power supply positive connection terminal V+, the main power supply negative connection terminal V- and the power supply switch circuit to form a power supply circuit. The power supply switch circuit is used to control the on and off of the power supply circuit. When it is connected, it supplies power to the load. When it is disconnected, the main power supply cannot supply power to the load.

[0023] Specifically, the power supply switch circuit includes an N-channel enhancement type MOSFET tube V11, a resistor R11, a resistor R4, a resistor R13 and a diode V2.

[0024] The source of the N-channel enhancement type MOSFET tube V11 is connected to the negative electrode connection terminal V- of the main power supply, the drain is connected to the negative output connection terminal GND, and the resistor R11 is connected between the negative electrode connection terminal V- of the main power supply and the gate of the N-channel enhancement type MOSFET tube V11.

[0025] The positive connection terminal V+ of the main power supply is connected to the positive electrode of the diode V2, the negative electrode of the diode V2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the resistor R13, the other end of the resistor R13 is grounded, and the other end of the resistor R4 is also connected to the gate of the N-channel enhancement MOSFET tube V11.

[0026] The gate of the N-channel enhancement type MOSFET tube V11 is the control input terminal of the power supply switch circuit. When the input is high level, the N-channel enhancement type MOSFET tube V11 is turned on, otherwise it is turned off.

[0027] The short-circuit signal transmitting end of the short-circuit detection circuit is connected to the signal input end of the circulation control circuit, and is used to detect whether the load is short-circuited and send a short-circuit signal to the circulation control circuit when a short-circuit occurs.

[0028] Specifically, the short circuit detection circuit includes a resistor R1, a resistor R2, a resistor R3, a capacitor C1 and a PNP transistor V1.

[0029] One end of the resistor R2 is connected to the output positive connection terminal Vout, and the other end is connected to the main power supply positive connection terminal V+, one end of the resistor R1 is connected to one end of the resistor R2, and the other end is connected to one end of the resistor R3, the other end of the resistor R3 is connected to the other end of the resistor R2, and the capacitor C1 is connected in parallel with the resistor R3; one end of the resistor R3 is also connected to the base of the PNP transistor V1, and the other end is also connected to the emitter of the PNP transistor V1, and the collector of the PNP transistor V1 is used to be connected to the short-circuit signal transmitting end of the short-circuit detection circuit.

[0030] The overcurrent sampling resistor generally uses a chip alloy sampling resistor, which has the advantages of high precision, small temperature coefficient, good stability, light weight, and convenient welding. The overcurrent sampling resistor should take a smaller resistance value. If the tube voltage drop between the emitter and base voltage of the PNP transistor V1 is 0.6V, the load capacity of the distribution terminal is required to be not less than 16A, and the overcurrent current threshold can be set to 30A, then the resistor R3 can be set to 0Ω, and the capacitor C1 and the resistor R1 form a smaller delay time for anti-shake processing, and the overcurrent sampling resistor resistance can be taken as 0.6V divided by 30A equal to 20 milliohms. Of course, the resistor R3 and the resistor R1 can also take different resistance values ​​for voltage division, so as to achieve different combinations to achieve the purpose of adjusting the threshold, and at the same time, when the PNP transistor V1 is cut off, the capacitor C1 can be quickly discharged. On the other hand, at this time, the drain and source continuous current of the N-channel enhancement MOSFET tube V11 needs to be greater than 30A, and the selection of the N-channel enhancement MOSFET tube should consider the on-resistance.

[0031] Furthermore, the short-circuit detection circuit also includes a diode V3, the collector of the PNP transistor V1 is connected to the anode of the diode V3, and the cathode of the diode V3 is the short-circuit signal transmitting end.

[0032] The circulation control circuit is connected to the power supply switch circuit through the shutdown control circuit, and is used to control the power supply switch circuit to disconnect the power supply circuit through the shutdown control circuit after receiving a short-circuit signal, and to control the power supply switch circuit to reconnect the power supply circuit after a certain time interval after the disconnection.

[0033] Wherein, the shutdown control circuit includes a resistor R5, a resistor R16 and an NPN transistor V7. One end of the resistor R5 is connected to the control input end of the shutdown control circuit, and the other end is connected to one end of the resistor R16, and the other end of the resistor R16 is grounded. The other end of the resistor R5 is also connected to the base of the NPN transistor V7, the collector of the NPN transistor V7 is the control output end of the shutdown control circuit and is connected to the control input end of the power supply switch circuit, and the emitter of the NPN transistor V7 is grounded. When the control input end of the shutdown control circuit is at a high level, the NPN transistor V7 is turned on, which will make the control input end of the power supply switch circuit become a low level.

[0034] The circulation control circuit includes a PNP transistor V5, an NPN transistor V10, an NPN transistor V8, a capacitor C5, a resistor R7, a resistor R8, a resistor R9, a resistor R10, a resistor R12, a resistor R14, a resistor R15 and a diode V6.

[0035] The collector of the PNP transistor V5 is both a signal input terminal of the circulation control circuit and a control output terminal of the circulation control circuit for connecting to a control input terminal of the shutdown control circuit.

[0036] The anode of the diode V6 is connected to the output anode connection terminal Vout, and the cathode is connected to the emitter of the PNP transistor V5. The resistor R9 is connected between the base and the emitter of the PNP transistor V5. The base of the PNP transistor V5 is also connected to the collector of the NPN transistor V10 through the resistor R10. The emitter of the NPN transistor V10 is grounded.

[0037] The collector of the PNP transistor V5 is also connected to one end of the resistor R7, the other end of the resistor R7 is connected to one end of the resistor R14 and the base of the NPN transistor V10, and the other end of the resistor R14 is grounded.

[0038] The collector of the PNP transistor V5 is also connected to one end of the resistor R8, the other end of the resistor R8 is grounded through the capacitor C5 and is also connected to one end of the resistor R12, the other end of the resistor R12 is connected to one end of the resistor R15, and the other end of the resistor R15 is grounded; the other end of the resistor R12 is also connected to the base of the NPN transistor V8; the collector of the NPN transistor V8 is connected to one end of the resistor R14, and the emitter is grounded.

[0039] Furthermore, the circulation control circuit also includes a capacitor C4 and a diode V4. One end of the capacitor C4 is connected to the positive electrode of the diode V6, and the other end is grounded. The circulation control circuit also includes a diode V4, the positive electrode of the diode V4 is connected to the other end of the resistor R8, and the negative electrode is connected to one end of the resistor R8, to help the capacitor C5 to discharge quickly.

[0040] The low-cost short-circuit protection circuit of the distribution automation terminal also includes a short-circuit indication circuit composed of a resistor R6 and a light-emitting diode V9. One end of the resistor R6 is connected to the control output end of the circulation control circuit, and the other end is connected to the positive electrode of the light-emitting diode V9, and the negative electrode of the light-emitting diode V9 is grounded. When the control output end of the circulation control circuit sends a high-level signal, the light-emitting diode V9 lights up to prompt the user that a short-circuit fault has occurred.

[0041] When there is no short circuit, the voltage between network V+ and network V- is normal. If it is FTU, the voltage rating is 24V, and if it is DTU, the voltage rating is 48V. At this time, the gate and source voltage difference of the N-channel enhancement MOSFET tube V11 is high level, the drain and the source are turned on, so that the network V- and the network GND are short-circuited, realizing power supply for external loads.

[0042] If a short circuit occurs, the circuit automatically completes the following steps to implement the protection function: Step 1. When a short circuit occurs, a large current will flow through the resistor R2 of the short circuit detection circuit, and a certain voltage difference will be formed across the resistor R2. When the current reaches a certain value, current will flow between the emitter and the base of the PNP transistor V1, thereby conducting the emitter and the collector of the PNP transistor V1, and then generating a high-level pulse signal on the diode V3 as a short circuit signal.

[0043] After the signal input end of the cyclic control circuit receives a high-level pulse signal, the voltage across the resistor R14 causes a current to flow between the base and emitter of the NPN transistor V10, which turns on the NPN transistor V10. At this time, the output positive connection end Vout is connected to the ground end through the diode V6, the resistor R9, the resistor R10 and the NPN transistor V10, and the voltage across the resistor R9 turns on the PNP transistor V5. After the PNP transistor V5 is turned on, the NPN transistor V10 is kept turned on through the resistor R7 and the resistor R14, and then the PNP transistor V5 is continuously turned on, and the control output end of the cyclic control circuit continuously sends a high-level shutdown control signal.

[0044] Step 2: After the control input end of the shutdown control circuit receives a continuous high-level shutdown control signal, current flows between the base and emitter of the NPN transistor V7, thereby turning on the NPN transistor V7, and then making the gate and source voltage difference of the N-channel enhancement MOSFET tube V11 low, the drain and the source are cut off, and the load stops being supplied with power.

[0045] In the process of the control output end of the cycle control circuit continuously sending a high-level shutdown control signal, the capacitor C5 is first charged through the resistor R8. After a period of charging delay, the voltage across the capacitor C5 reaches a certain value, and the NPN transistor V8 is turned on through the resistor R12 and the resistor R18, and then the two ends of the resistor R14 are short-circuited, so that the NPN transistor V10 is turned off, and then the PNP transistor V5 is turned off. At this time, the capacitor C5 is no longer charged and begins to discharge through the diode V4: part of the current flows through the resistor R6 and the light-emitting diode V9, another part of the current flows through the resistor R5 and the resistor R16 and between the base and emitter of the NPN transistor V7, and another part of the current flows through the resistor R7 and between the collector and emitter of the NPN transistor V8, and the last part of the current flows through the resistor R12 and the resistor R15 and between the base and emitter of the NPN transistor V8. When the discharge cycle control circuit fails to maintain a valid high-level shutdown control signal at its control output, the NPN transistor V7 returns to the cut-off state, and the power switch circuit returns to the connected state, allowing the main power supply to supply power to the load again.

[0046] When the control output terminal of the cycle control circuit outputs a high level, the light-emitting diode V9 is in a light-on state, reminding the user that a short-circuit fault occurs in the load at this time and the load should be disconnected in time.

[0047] Step 3: After the load is powered on again, if the short-circuit fault still exists, the short-circuit detection circuit will detect overcurrent again and jump to step 1. The load will cycle power off and power on again, and V9 will flash continuously. If the short-circuit fault has been eliminated, the load will operate normally until the short-circuit fault occurs again and automatically jump to step 1.

[0048] During design, the cycle time can be roughly controlled by selecting different resistors R8, R12, R15, and C5. For example, if the voltage difference between the network V+ and the network V- is 24V, the resistance of the resistor R8 is 100KΩ, the resistor R12 is 630KΩ, the resistor R15 is 10KΩ, and the capacitor C5 is 10uF. At the same time, the voltage drop of the diode V6 is 0.7V, and the voltage drop between the base and emitter of the NPN transistor V8 is 0.6V. Then the voltage of the capacitor C5 will stop charging after it is charged to (24V-0.7V)*(630K+10K) / (100K+630K+10K)=20.15V. When the RC delay time is t=2R*C, the charging voltage is about 0.865*(24V-0.7V)=20.15V, and the charging time is 2*100K*10uF=2S. The capacitor discharge time is much shorter than the charging time and can be ignored.

Claims

1. A low-cost short-circuit protection circuit for a distribution automation terminal, the distribution automation terminal comprising a main power supply positive connection terminal V+, a main power supply negative connection terminal V-, an output positive connection terminal Vout and an output negative connection terminal GND, a load is connected between the output positive connection terminal Vout and the output negative connection terminal GND, and the main power supply negative connection terminal V- is grounded, characterized in that: The short circuit protection circuit includes a power supply switch circuit, a short circuit detection circuit, a circulation control circuit and a shutdown control circuit; The output positive connection terminal Vout is connected to the output negative connection terminal GND through a short-circuit detection circuit, a main power supply positive connection terminal V+, a main power supply negative connection terminal V- and a power supply switch circuit to form a power supply circuit; The power supply switch circuit is used to control the on and off of the power supply circuit; The short-circuit signal transmitting end of the short-circuit detection circuit is connected to the signal input end of the circulation control circuit, and is used to detect whether the load is short-circuited and send a short-circuit signal to the circulation control circuit when a short-circuit occurs; The circulation control circuit is connected to the power supply switch circuit through the shutdown control circuit, and is used to control the power supply switch circuit to disconnect the power supply circuit through the shutdown control circuit after receiving a short-circuit signal, and to control the power supply switch circuit to reconnect the power supply circuit after a certain time interval after the disconnection.

2. The low-cost short-circuit protection circuit for distribution automation terminals as claimed in claim 1, characterized in that: The short circuit detection circuit includes a resistor R1, a resistor R2, a resistor R3, a capacitor C1 and a PNP transistor V1; One end of the resistor R2 is connected to the output positive connection terminal Vout, and the other end is connected to the main power supply positive connection terminal V+, one end of the resistor R1 is connected to one end of the resistor R2, and the other end is connected to one end of the resistor R3, the other end of the resistor R3 is connected to the other end of the resistor R2, and the capacitor C1 is connected in parallel with the resistor R3; one end of the resistor R3 is also connected to the base of the PNP transistor V1, and the other end is also connected to the emitter of the PNP transistor V1, and the collector of the PNP transistor V1 is used to be connected to the short-circuit signal transmitting end of the short-circuit detection circuit.

3. The low-cost short-circuit protection circuit for distribution automation terminals as claimed in claim 2, characterized in that: The short-circuit detection circuit further includes a diode V3. The collector of the PNP transistor V1 is connected to the anode of the diode V3. The cathode of the diode V3 is the short-circuit signal transmitting end.

4. The low-cost short-circuit protection circuit for distribution automation terminals as claimed in claim 1, characterized in that: The power supply switch circuit includes an N-channel enhancement type MOSFET tube V11, a resistor R11, a resistor R4, a resistor R13 and a diode V2; The source of the N-channel enhancement type MOSFET tube V11 is connected to the negative electrode connection terminal V- of the main power supply, the drain is connected to the negative output connection terminal GND, and the resistor R11 is connected between the negative electrode connection terminal V- of the main power supply and the gate of the N-channel enhancement type MOSFET tube V11; The positive connection terminal V+ of the main power supply is connected to the positive electrode of the diode V2, the negative electrode of the diode V2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the resistor R13, the other end of the resistor R13 is grounded, and the other end of the resistor R4 is also connected to the gate of the N-channel enhancement MOSFET tube V11; The gate of the N-channel enhancement type MOSFET tube V11 is the control input terminal of the power supply switch circuit.

5. The low-cost short-circuit protection circuit for distribution automation terminals as claimed in claim 1, characterized in that: The shutdown control circuit includes a resistor R5, a resistor R16 and an NPN transistor V7; One end of the resistor R5 is connected to the control input end of the shutdown control circuit, and the other end is connected to one end of the resistor R16, and the other end of the resistor R16 is grounded; The other end of the resistor R5 is also connected to the base of the NPN transistor V7. The collector of the NPN transistor V7 is the control output end of the shutdown control circuit and is connected to the control input end of the power supply switch circuit. The emitter of the NPN transistor V7 is grounded.

6. The low-cost short-circuit protection circuit for distribution automation terminals as claimed in claim 1, characterized in that: The cycle control circuit includes a PNP transistor V5, an NPN transistor V10, an NPN transistor V8, a capacitor C5, a resistor R7, a resistor R8, a resistor R9, a resistor R10, a resistor R12, a resistor R14, a resistor R15 and a diode V6; The collector of the PNP transistor V5 is both a signal input terminal of the circulation control circuit and a control output terminal of the circulation control circuit connected to the control input terminal of the shutdown control circuit; The anode of the diode V6 is connected to the output anode connection terminal Vout, and the cathode is connected to the emitter of the PNP transistor V5. The resistor R9 is connected between the base and the emitter of the PNP transistor V5. The base of the PNP transistor V5 is also connected to the collector of the NPN transistor V10 through the resistor R10. The emitter of the NPN transistor V10 is grounded. The collector of the PNP transistor V5 is also connected to one end of the resistor R7, the other end of the resistor R7 is connected to one end of the resistor R14 and the base of the NPN transistor V10, and the other end of the resistor R14 is grounded; The collector of the PNP transistor V5 is also connected to one end of the resistor R8, the other end of the resistor R8 is grounded through the capacitor C5 and is also connected to one end of the resistor R12, the other end of the resistor R12 is connected to one end of the resistor R15, and the other end of the resistor R15 is grounded; the other end of the resistor R12 is also connected to the base of the NPN transistor V8; the collector of the NPN transistor V8 is connected to one end of the resistor R14, and the emitter is grounded.

7. The low-cost short-circuit protection circuit for distribution automation terminals as claimed in claim 6, characterized in that: The circulation control circuit further includes a capacitor C4, one end of which is connected to the anode of the diode V6, and the other end of which is grounded.

8. The low-cost short-circuit protection circuit for distribution automation terminals as claimed in claim 6, characterized in that: The circulation control circuit further includes a diode V4, wherein the anode of the diode V4 is connected to the other end of the resistor R8, and the cathode of the diode V4 is connected to one end of the resistor R8.

9. The low-cost short-circuit protection circuit for distribution automation terminals as claimed in claim 1, characterized in that: Also included is a short circuit indication circuit; The short circuit indication circuit includes a resistor R6 and a light emitting diode V9. One end of the resistor R6 is connected to the control output end of the circulation control circuit, and the other end is connected to the positive electrode of the light emitting diode V9. The negative electrode of the light emitting diode V9 is grounded.

10. A low-cost short-circuit protection method for distribution automation terminals, characterized in that: Based on the low-cost short-circuit protection circuit for distribution automation terminals as described in any one of claims 6 to 9; Short circuit protection methods include: Step 1, when the short-circuit detection circuit detects an overcurrent, a high-level pulse signal as a short-circuit signal will be sent through the short-circuit signal transmitting end; after the signal input end of the cyclic control circuit receives the high-level pulse signal, the voltage across the resistor R14 will turn on the NPN transistor V10, at this time, the output positive connection end Vout is connected to the ground end through the diode V6, the resistor R9, the resistor R10 and the NPN transistor V10, the voltage across the resistor R9 turns on the PNP transistor V5, after the PNP transistor V5 is turned on, the NPN transistor V10 is kept in the on state through the resistor R7 and the resistor R14, and then the PNP transistor V5 is continuously turned on, and the control output end of the cyclic control circuit continuously sends a high-level shutdown control signal; Step 2: After receiving a continuous high-level shutdown control signal, the control input end of the shutdown control circuit disconnects the power supply circuit through the power supply switch circuit and stops supplying power to the load; In the process that the control output end of the circulation control circuit continuously sends out the high-level shutdown control signal, the capacitor C5 is charged first. When the voltage across the capacitor C5 reaches a certain value, the NPN transistor V8 is turned on through the resistors R12 and R18, and then the two ends of the resistor R14 are short-circuited, so that the NPN transistor V10 is turned off, and then the PNP transistor V5 is turned off; at this time, the capacitor C5 starts to discharge, and when it is discharged to the point that the control output end of the circulation control circuit cannot maintain an effective high-level shutdown control signal, the power supply switch circuit will resume the connected state, so that the main power supply can supply power to the load again; Step 3: After the load is powered on again, if the short-circuit fault still exists, the short-circuit detection circuit will detect overcurrent again and jump to step 1; if the short-circuit fault has been eliminated, the load will operate normally until the short-circuit fault occurs again and automatically jump to step 1.

Images