Relay overload protection circuit

Abstract

The utility model provides a relay overload protection circuit. The relay overload protection circuit comprises a relay; the relay control circuit is connected with a control winding of the relay, and the relay control circuit is used for controlling whether the second power supply supplies power to the control winding or not; the overload detection circuit is connected between the switch unit of the relay and the load and is used for detecting whether the load is overloaded or short-circuited and outputting a detection signal for detecting whether the load is overloaded or short-circuited through an overload output end of the overload detection circuit; the input end of the overload protection circuit is connected with the overload output end, the output end of the overload protection circuit is connected with the relay control circuit, and when overload or short circuit of the load is detected, the overload protection circuit drives the relay control circuit, so that the second power supply does not supply power to the control winding. Compared with the prior art, the load condition of the power loop of the relay is detected through a simple hardware circuit, and if the load is overloaded or short-circuited, the relay can be turned off in time, so that the relay is protected from being damaged.

Description

TECHNICAL FIELD

[0001] The utility model relates to circuit design technical field, especially relates to a relay overload protection circuit. BACKGROUND

[0002] Relay is a kind of electronic controller, is often used in control system and passive control system, and the realization principle of relay is mainly through small current or small voltage signal control large current and high voltage system. Relay is all through the control winding control power loop output, and the control end cannot know the load condition of power loop end, if power loop appears overload or short circuit condition, it is easy to cause relay damage, causes the entire system to work abnormally.

[0003] Therefore, it is necessary to provide a new technical scheme to solve the above problems. UTILITY MODEL CONTENTS

[0004] One of the purposes of the utility model is to provide a kind of relay overload protection circuit, it detects the load condition of relay power loop by simple hardware circuit, if load appears overload or short circuit condition, can promptly shut down relay, to protect relay from being damaged.

[0005] According to one aspect of the utility model, the utility model provides a kind of relay overload protection circuit, it includes: relay, including control winding and switch unit, the control winding is used to control the switch unit and turns on or shuts down, first power supply Vdd is powered to load by the switch unit, second power supply VCC is powered to the control winding;Relay control circuit is connected with the control winding, and the relay control circuit is used to control whether the second power supply VCC is powered to the control winding, when the second power supply VCC is powered to the control winding, the switch unit is turned on;When the second power supply VCC is not powered to the control winding, the switch unit is disconnected;Overload detection circuit is connected between the switch unit and load, and the overload detection circuit includes overload output end A, and the overload detection circuit is used to detect whether overload or short circuit exists in the load, and whether overload or short circuit detection signal is output through the overload output end A;Overload protection circuit, input end is connected with the overload output end A, and its output end B is connected with the relay control circuit, when the overload detection circuit detects that overload or short circuit exists in the load, the overload protection circuit drives the relay control circuit through its output end B, so that the second power supply VCC is not powered to the control winding.

[0006] Further, the relay control circuit comprises a switching device Q1, a resistor R7 and a resistor R8, a first connection end of the switching device Q1 is connected with one end of the control winding, the other end of the control winding is connected with the second power supply VCC, a second connection end of the switching device Q1 is grounded, a control end of the switching device Q1 is connected with the output end B of the overload protection circuit; one end of the resistor R7 is connected with the control end of the switching device Q1, and the other end thereof is connected with the control signal input end C; one end of the resistor R8 is connected with the control end of the switching device Q1, and the other end thereof is grounded; whether the switching device Q1 is turned on or not is controlled according to the control signal received by the control signal input end C, when the switching device Q1 is turned on, the second power supply VCC supplies power to the control winding; when the switching device Q1 is turned off, the second power supply VCC does not supply power to the control winding.

[0007] Further, the overload detection circuit comprises a resistor R1 and a switching device Q2, the resistor R1 is connected in series between the switching unit and the load, a first connection end of the switching device Q2 is connected with one end of the resistor R1, a second connection end thereof is connected with the overload output end A of the overload detection circuit, and a control end thereof is connected with the other end of the resistor R1, one end of the resistor R1 is connected with the switching unit k1, and the other end of the resistor R1 is connected with the load, when the switching device Q2 is turned on, it indicates that the load exists overload or short circuit; when the switching device Q2 is turned off, it indicates that the load does not exist overload or short circuit.

[0008] Further, the overload protection circuit comprises a diode D1, a diode D2, a resistor R5, a resistor R6 and a switching device Q4, one end of the resistor R6 is connected with the overload output end A of the overload detection circuit, and the other end thereof is grounded; the positive electrode of the diode D2 is connected with the overload output end A of the overload detection circuit, and the negative electrode thereof is connected with the control end of the switching device Q4 through the resistor R5; the positive electrode of the diode D1 is connected with the control end of the switching device Q1 as the output end B of the overload protection circuit, and the negative electrode thereof is connected with the first connection end of the switching device Q4; the second connection end of the switching device Q4 is grounded; when the overload detection circuit detects that the load Load exists overload or short circuit, the switching device Q2 is turned on, thereby causing the switching device Q4 to be turned on, and further causing the switching device Q1 to be turned off.

[0009] Further, the overload protection circuit further comprises a positive feedback loop, the positive feedback loop comprising a resistor R2, a resistor R3, a resistor R4 and a switching device Q3, one end of the resistor R2 being connected with the second power supply VCC, the other end of the resistor R2 being connected with a node D; one end of the resistor R3 being connected with the node D, the other end of the resistor R3 being connected with a first connection end of the switching device Q4; a first connection end of the switching device Q3 being connected with the second power supply VCC, a control end of the switching device Q3 being connected with the node D, a second connection end of the switching device Q3 being connected with a control end of the switching device Q4 through the resistor R4, when the overload detection circuit detects that the load exists overload or short circuit, the switching device Q4 is turned on, so that the switching device Q3 is turned on, and then the switching device Q4 is kept in the conduction state.

[0010] Further, the switching device Q1 is an NPN type triode, the first connection end, the second connection end and the control end of the switching device Q1 are the collector, the emitter and the base of the NPN type triode respectively; the switching device Q2 is a PNP type triode, the first connection end, the second connection end and the control end of the switching device Q2 are the emitter, the collector and the base of the PNP type triode respectively; the switching device Q3 is a PNP type triode, the first connection end, the second connection end and the control end of the switching device Q3 are the emitter, the collector and the base of the PNP type triode respectively; the switching device Q4 is an NPN type triode, the first connection end, the second connection end and the control end of the switching device Q4 are the collector, the emitter and the base of the NPN type triode respectively.

[0011] Further, the resistance value of the resistor R1 is selected to satisfy: when the load is in the normal working condition, the voltage difference between the two ends of the resistor R1 is less than the conduction voltage threshold of the switching device Q2, so that the switching device Q2 is in the off state; when the load appears short circuit or overload, the voltage difference between the two ends of the resistor R1 is greater than the conduction voltage threshold of the switching device Q2, so that the switching device Q2 is in the conduction state; the resistance values of the resistor R2 and the resistor R3 are selected to satisfy: when the switching device Q4 is turned on, the voltage value of the voltage division on the resistor R2 is greater than the conduction voltage threshold of the switching device Q3, so that the switching device Q3 is in the conduction state; the resistance values of the resistor R7 and the resistor R8 are selected to satisfy: when the load is in the normal working condition, the control signal input end C of the relay control circuit is high level, the voltage value of the voltage division on the resistor R8 is greater than the conduction voltage threshold of the switching device Q1, so that the switching device Q1 is in the conduction state.

[0012] Compared with the prior art, the utility model discloses a simple hardware circuit to detect the load condition of the relay power loop, if the load appears overload or short circuit, can turn off the relay in time, thereby protecting the relay from being damaged. [Attached Image Description]

[0013] To more clearly illustrate the technical solutions of 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. Among them:

[0014] Figure 1 This is a circuit diagram of a relay overload protection circuit in one embodiment of the present invention.

Detailed Implementation Methods

[0015] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. Unless otherwise specified, the terms coupling, connection, linking, and interconnection used herein to indicate electrical connection mean direct or indirect connection. For example, A being connected to B includes both a direct electrical connection between A and B and a connection between A and B via electrical components or circuits.

[0017] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "back", "positive", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0018] Please refer to Figure 1 As shown, it is a circuit diagram of a relay overload protection circuit in one embodiment of the present invention. Figure 1 The relay overload protection circuit shown includes a relay 110, a relay control circuit 120, an overload detection circuit 130, and an overload protection circuit 140.

[0019] The relay 110 includes a control winding Relay and a switching unit k1, the control winding Relay is used to control the switching unit k1 to be turned on or turned off, a first power supply Vdd supplies power to a load Load through the switching unit k1 (or a first power supply terminal Vdd is connected with the load Load through the switching unit k1), and a second power supply VCC supplies power to the control winding Relay. The relay control circuit 120 is connected with the control winding Relay, and the relay control circuit 120 is used to control whether the second power supply VCC supplies power to the control winding Relay. When the second power supply VCC supplies power to the control winding Relay, the switching unit k1 is turned on (i.e. the relay 110 is closed), so as to drive the load Load to work. When the second power supply VCC does not supply power to the control winding Relay, the switching unit k1 is turned off (i.e. the relay 110 is turned off), so as to make the load Load stop working. The overload detection circuit 130 is connected between the switching unit k1 and the load Load, and the overload detection circuit 130 includes an overload output terminal A. The overload detection circuit 130 is used to detect whether the load Load has overload or short circuit, and outputs a detection signal of whether overload or short circuit through the overload output terminal A. The input terminal of the overload protection circuit 140 is connected with the overload output terminal A of the overload detection circuit 130, and the output terminal B of the overload protection circuit 140 is connected with the relay control circuit 120. When the overload detection circuit 130 detects that the load Load has overload or short circuit, the overload protection circuit 140 drives the relay control circuit 120 through the output terminal B, so as to make the second power supply VCC not supply power to the control winding Relay.

[0020] The relay control circuit 120 includes a switching device Q1, a resistor R7 and a resistor R8. The first connection terminal of the switching device Q1 is connected with one end of the control winding Relay of the relay 110, the other end of the control winding Relay is connected with the second power supply VCC, the second connection terminal of the switching device Q1 is grounded, and the control terminal of the switching device Q1 is connected with the output terminal B of the overload protection circuit 140. One end of the resistor R7 is connected with the control terminal of the switching device Q1 (or the output terminal B of the overload protection circuit 140), and the other end of the resistor R7 is connected with a control signal input terminal C (or a relay control IO terminal). One end of the resistor R8 is connected with the control terminal of the switching device Q1 (or the output terminal B of the overload protection circuit 140), and the other end of the resistor R8 is grounded.

[0021] The switching device Q1 is controlled to be turned on or turned off according to the control signal received by the control signal input terminal C. When the switching device Q1 is turned on, the second power supply VCC supplies power to the control winding Relay, so as to make the switching unit k1 be turned on. When the switching device Q1 is turned off, the second power supply VCC does not supply power to the control winding Relay, so as to make the switching unit k1 be turned off.

[0022] The overload detection circuit 130 comprises a resistor R1 and a switching device Q2. The resistor R1 is connected in series between the switching unit k1 of the relay 110 and the load Load. The first connection end of the switching device Q2 is connected to one end of the resistor R1. The second connection end of the switching device Q2 is connected to the overload output end A of the overload detection circuit 130. The control end of the switching device Q2 is connected to the other end of the resistor R1. The one end of the resistor R1 is connected to the switching unit k1. The other end of the resistor R1 is connected to the load Load. When the switching device Q2 is turned on, it indicates that the load Load has overload or short circuit. When the switching device Q2 is turned off, it indicates that the load Load has no overload or short circuit.

[0023] The overload protection circuit 140 comprises a diode D1, a diode D2, a resistor R5, a resistor R6 and a switching device Q4. One end of the resistor R6 is connected to the overload output end A of the overload detection circuit 130. The other end of the resistor R6 is connected to the ground. The positive electrode of the diode D2 is connected to the overload output end A of the overload detection circuit 130. The negative electrode of the diode D2 is connected to the control end of the switching device Q4 through the resistor R5. The positive electrode of the diode D1 is connected to the control end of the switching device Q1 as the output end B of the overload protection circuit 140. The negative electrode of the diode D1 is connected to the first connection end of the switching device Q4. The second connection end of the switching device Q4 is connected to the ground. When the overload detection circuit 130 detects that the load Load has overload or short circuit, the switching device Q2 is turned on, thereby causing the switching device Q4 to be turned on, and further causing the switching device Q1 to be turned off.

[0024] The overload protection circuit 140 further comprises a positive feedback loop 142. The positive feedback loop 142 comprises a resistor R2, a resistor R3, a resistor R4 and a switching device Q3. One end of the resistor R2 is connected to the second power supply VCC. The other end of the resistor R2 is connected to a node D. One end of the resistor R3 is connected to the node D. The other end of the resistor R3 is connected to the first connection end of the switching device Q4. The first connection end of the switching device Q3 is connected to the second power supply VCC. The control end of the switching device Q3 is connected to the node D. The second connection end of the switching device Q3 is connected to the control end of the switching device Q4 through the resistor R4. When the overload detection circuit 130 detects that the load Load has overload or short circuit, the switching device Q4 is turned on, thereby causing the switching device Q3 to be turned on, and further causing the switching device Q4 to be kept in the turned-on state.

[0025] In Figure 1In the specific embodiment shown, the switching device Q1 is an NPN triode, the first connection end, the second connection end and the control end of the switching device Q1 are the collector, the emitter and the base of the NPN triode respectively; the switching device Q2 is a PNP triode, the first connection end, the second connection end and the control end of the switching device Q2 are the emitter, the collector and the base of the PNP triode respectively; the switching device Q3 is a PNP triode, the first connection end, the second connection end and the control end of the switching device Q3 are the emitter, the collector and the base of the PNP triode respectively; the switching device Q4 is an NPN triode, the first connection end, the second connection end and the control end of the switching device Q4 are the collector, the emitter and the base of the NPN triode respectively.

[0026] The resistance values of the resistors R7 and R8 are selected to satisfy: when the load Load is in a normal working condition, the control signal input end C (or the relay control IO end) of the relay control circuit 120 is at a high level, and the voltage value of the voltage division on the resistor R8 is greater than the turn-on voltage threshold of the switching device Q1, so that the switching device Q1 is in a turn-on state.

[0027] The resistance value of the resistor R1 is selected to satisfy: when the load Load is in a normal working condition, the voltage difference across the resistor R1 is less than the turn-on voltage threshold of the switching device Q2, so that the switching device Q2 is in an off state; when the load Load is in a short circuit or transient overload condition, the voltage difference across the resistor R1 is greater than the turn-on voltage threshold of the switching device Q2, so that the switching device Q2 is in a turn-on state.

[0028] The resistance values of the resistors R2 and R3 are selected to satisfy: when the switching device Q4 is turned on, the voltage value of the voltage division on the resistor R2 is greater than the turn-on voltage threshold of the switching device Q3, so that the switching device Q3 is in a turn-on state.

[0029] The working principle of the relay overload protection circuit shown will be specifically introduced below. Figure 1 The working principle of the relay overload protection circuit shown will be specifically introduced below.

[0030] 1. When the system is working normally (i.e. the load Load is in normal working condition), the control signal input end C of the relay control circuit 120 (or the relay control IO end) is high, and after being divided by the resistors R7 and R8, the voltage value of the voltage division on the resistor R8 is greater than the turn-on voltage threshold of the switching device Q1. Since the switching device Q1 is an NPN transistor, the voltage value of the voltage division on the resistor R8 (which is equal to the voltage between the base and the emitter of the NPN transistor Q1) is greater than the turn-on voltage threshold of the NPN transistor Q1 (or the PN junction voltage of the NPN transistor Q1), which meets the turn-on condition of the NPN transistor Q1, so that the NPN transistor Q1 is turned on, and the collector of the NPN transistor Q1 is pulled down to 0V. The second power supply VCC is sequentially conducted to the ground through the control winding Relay of the relay 110 and the NPN transistor Q1 (i.e. the second power supply VCC supplies power to the control winding Relay), and the switching unit k1 is turned on (i.e. the relay 110 is closed or attracted), so that the first power supply Vdd can drive the load Load to work through the resistor R1.

[0031] 2. When the load Load is short-circuited or instantaneously overloaded, the current through the resistor R1 is very large, and the switching device Q2 is a PNP transistor. When the voltage value on the resistor R1 is greater than the PN junction voltage of the PNP transistor Q2, the PNP transistor Q2 is saturated and turned on. At this time, the collector voltage and the emitter voltage of the PNP transistor Q2 are equal to the voltage of the first power supply Vdd. Since the resistor R6 is connected to the collector of the PNP transistor Q2, the voltage on the resistor R6 is also equal to the voltage of the first power supply Vdd. The first power supply Vdd is conducted to the control end of the switching device Q4 through the diode D2 and the resistor R5. The switching device Q4 is an NPN transistor, which is saturated and turned on at this time. The collector voltage of the NPN transistor Q4 is pulled down to 0V. Since the negative electrode of the diode D1 is also connected to the collector of the NPN transistor Q4, the base voltage of the NPN transistor Q1 is instantaneously pulled down to about 0.3V due to the clamping effect of the diode. The NPN transistor Q1 changes from the on state to the off state, and the switching unit k1 is turned on (i.e. the relay 110 is turned off), thereby protecting the relay 110 from being damaged by the large current.

[0032] 3. Since the collector voltage of the NPN transistor Q4 is pulled down to 0V, the base voltage of the PNP transistor Q3 is the voltage divided by the resistor R2 and the resistor R3 to the second power supply VCC, and the Q3 is a PNP transistor, at this time, the voltage divided by the resistor R2 (which is equal to the voltage between the base and the emitter of the PNP transistor Q3) is greater than the turn-on voltage threshold of the PNP transistor Q3 (or the PN junction voltage of the PNP transistor Q3), which satisfies the saturation turn-on condition of the PNP transistor Q3, and the PNP transistor Q3 is saturated and turned on, and the collector voltage of the PNP transistor Q3 is also equal to the voltage of the second power supply VCC, and the second power supply VCC passes through the resistor R4 to the base of the NPN transistor Q4, which also satisfies the turn-on condition of the NPN transistor Q4. Such a positive feedback working principle makes the load Load appear a short circuit and an overload condition, that is, the relay 110 can be continuously turned off, and the relay 110 will not be damaged due to the intermittent short circuit or the oscillation overload protection of the relay 110 caused by the intermittent short circuit or the oscillation overload of the load Load.

[0033] In summary, the relay overload protection circuit has the following beneficial effects:

[0034] 1. The circuit is simple and reliable, and is a pure hardware scheme. The overload detection circuit 130 detects the current condition of the load Load. If the current on the load Load is too large, the overload protection circuit 140 will be triggered, and then the relay 110 is turned off, so that the relay 110 works below the normal current value, and the cost is relatively low.

[0035] 2. The positive feedback loop 142 can ensure that the load Load appears an overload or a short circuit condition, and the relay 110 can be continuously turned off, so that the relay 110 will not be damaged due to the oscillation protection.

[0036] It should be pointed out that any modification made by the skilled in the art to the specific embodiments of the utility model does not deviate from the scope of the claims of the utility model. Correspondingly, the scope of the claims of the utility model is not limited to the foregoing specific embodiments.

Claims

1. A relay overload protection circuit, characterized by comprising: It includes: A relay including a control winding and a switching unit, the control winding being used to control the switching unit to be on or off, a first power supply Vdd supplying power to a load through the switching unit, and a second power supply VCC supplying power to the control winding; A relay control circuit connected to the control winding, the relay control circuit being used to control whether the second power supply VCC supplies power to the control winding, the switching unit being on when the second power supply VCC supplies power to the control winding, and the switching unit being off when the second power supply VCC does not supply power to the control winding; An overload detection circuit connected between the switching unit and the load, the overload detection circuit including an overload output terminal A, the overload detection circuit being used to detect whether the load has an overload or a short circuit, and output a detection signal of whether there is an overload or a short circuit through the overload output terminal A; An overload protection circuit having an input terminal connected to the overload output terminal A and an output terminal B connected to the relay control circuit, the overload protection circuit driving the relay control circuit through the output terminal B when the overload detection circuit detects that the load has an overload or a short circuit, so that the second power supply VCC does not supply power to the control winding.

2. The relay overload protection circuit according to claim 1, wherein The relay control circuit includes a switching device Q1, a resistor R7 and a resistor R8, A first connection terminal of the switching device Q1 is connected to one end of the control winding, the other end of the control winding is connected to the second power supply VCC, a second connection terminal of the switching device Q1 is grounded, and a control terminal of the switching device Q1 is connected to the output terminal B of the overload protection circuit; one end of the resistor R7 is connected to the control terminal of the switching device Q1, and the other end of the resistor R7 is connected to a control signal input terminal C; one end of the resistor R8 is connected to the control terminal of the switching device Q1, and the other end of the resistor R8 is grounded; The switching device Q1 is controlled by the control signal received by the control signal input terminal C to be on or off, the second power supply VCC supplies power to the control winding when the switching device Q1 is on, and the second power supply VCC does not supply power to the control winding when the switching device Q1 is off.

3. The relay overload protection circuit according to claim 2, wherein The overload detection circuit includes a resistor R1 and a switching device Q2, the resistor R1 is connected in series between the switching unit and the load, a first connection terminal of the switching device Q2 is connected to one end of the resistor R1, a second connection terminal of the switching device Q2 is connected to the overload output terminal A of the overload detection circuit, and a control terminal of the switching device Q2 is connected to the other end of the resistor R1, One end of the resistor R1 is connected to the switching unit k1, and the other end of the resistor R1 is connected to the load, The switching device Q2 is on when the load has an overload or a short circuit, and the switching device Q2 is off when the load does not have an overload or a short circuit.

4. The relay overload protection circuit according to claim 3, wherein The overload protection circuit comprises a diode D1, a diode D2, a resistor R5, a resistor R6 and a switching device Q4, one end of the resistor R6 is connected with an overload output end A of the overload detection circuit, and the other end is grounded; the positive electrode of the diode D2 is connected with the overload output end A of the overload detection circuit, and the negative electrode is connected with the control end of the switching device Q4 through the resistor R5; the positive electrode of the diode D1 is connected with the control end of the switching device Q1 as an output end B of the overload protection circuit, and the negative electrode is connected with the first connection end of the switching device Q4; the second connection end of the switching device Q4 is grounded; When the overload detection circuit detects that the load Load exists overload or short circuit, the switching device Q2 is turned on, so as to cause the switching device Q4 to be turned on, and further cause the switching device Q1 to be turned off.

5. The relay overload protection circuit of claim 4, wherein, The overload protection circuit further comprises a positive feedback loop, The positive feedback loop comprises a resistor R2, a resistor R3, a resistor R4 and a switching device Q3, one end of the resistor R2 is connected with the second power supply VCC, and the other end is connected with a node D; one end of the resistor R3 is connected with the node D, and the other end is connected with the first connection end of the switching device Q4; the first connection end of the switching device Q3 is connected with the second power supply VCC, the control end is connected with the node D, and the second connection end is connected with the control end of the switching device Q4 through the resistor R4, When the overload detection circuit detects that the load exists overload or short circuit, the switching device Q4 is turned on, so as to cause the switching device Q3 to be turned on, and further cause the switching device Q4 to remain in the on state.

6. The relay overload protection circuit according to claim 5, wherein The switching device Q1 is an NPN type triode, and the first connection end, the second connection end and the control end of the switching device Q1 are the collector, the emitter and the base of the NPN type triode respectively; The switching device Q2 is a PNP type triode, and the first connection end, the second connection end and the control end of the switching device Q2 are the emitter, the collector and the base of the PNP type triode respectively; The switching device Q3 is a PNP type triode, and the first connection end, the second connection end and the control end of the switching device Q3 are the emitter, the collector and the base of the PNP type triode respectively; The switching device Q4 is an NPN type triode, and the first connection end, the second connection end and the control end of the switching device Q4 are the collector, the emitter and the base of the NPN type triode respectively.

7. The relay overload protection circuit according to claim 6, wherein The resistance value of the resistor R1 is selected to meet: when the load is in normal working condition, the voltage difference between the two ends of the resistor R1 is less than the turn-on voltage threshold of the switching device Q2, so that the switching device Q2 is in the off state; when the load appears short circuit or overload, the voltage difference between the two ends of the resistor R1 is greater than the turn-on voltage threshold of the switching device Q2, so that the switching device Q2 is in the on state. The resistance values of the resistors R2 and R3 are selected to satisfy: when the switching device Q4 is turned on, the voltage value of the voltage division on the resistor R2 is greater than the turn-on voltage threshold of the switching device Q3, so that the switching device Q3 is in the turn-on state; The resistance values of the resistors R7 and R8 are selected to satisfy: when the load is in the normal working condition, the control signal input end C of the relay control circuit is at high level, the voltage value of the voltage division on the resistor R8 is greater than the turn-on voltage threshold of the switching device Q1, so that the switching device Q1 is in the turn-on state.

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