Over-temperature protection circuit applied to pure hardware circuit

Abstract

The utility model provides a kind of over-temperature protection circuit applied to pure hardware circuit, cooperate power supply circuit, power supply circuit is connected with safety switch.The over-temperature protection circuit includes safety switch control circuit, first and second temperature detection circuit, shutdown latch circuit and disablement circuit.The first temperature detection circuit includes NTC thermistor NTC1 and ground resistance, NTC1 is connected with power supply, and it is connected with ground resistance after series connection and ground.The second temperature detection circuit includes pull-up resistance and NTC thermistor NTC2, pull-up resistance is connected with power supply, and it is connected with NTC2 after series connection and ground.Shutdown latch circuit is used to when the common junction voltage of NTC1 and ground resistance is greater than first voltage threshold, safety switch is locked in shutdown state by safety switch control circuit;Disablement circuit is used to when the common junction voltage of pull-up resistance and NTC2 is greater than second voltage threshold, disablement shutdown latch circuit.The utility model implementation cost is low, and reliable over-temperature protection can be realized.

Description

Technical Field

[0001] This utility model relates to an over-temperature protection circuit. Background Technology

[0002] Common controllers, control modules, and power modules are all designed with over-temperature protection. Figure 1 This diagram illustrates a common over-temperature protection circuit integrated into a control module. It includes a resistor divider (consisting of an NTC thermistor NTC3 and resistor R41), an RC filter, and an MCU. The resistor divider is connected to power supply VDD1, which also powers the MCU and is typically generated by an SBC (System Base Chip) or LDO (Low Dropout Linear Regulator). The SBC contains an LDO, a switching voltage regulator, and a high-side switch, all equipped with physical layer transceivers (CAN, LIN, PSI5). The SBC is controlled by the MCU via an SPI interface. It also features various power-saving modes such as standby, sleep, and stop, as well as wake-up and watchdog timer functions.

[0003] The MCU's AD port acquires temperature information by sampling the output voltage of a resistor divider. When the control module operates continuously under high-temperature, heavy-load conditions, the temperature of the power devices will continue to rise. Generally, an over-temperature protection point is set to protect the power devices. When the MCU detects that the temperature has reached the over-temperature protection point, it will pull down the enable pin of the DC / DC converter, stopping the DC / DC converter from operating. The enable pin will only be released when the temperature of the control module drops to the over-temperature recovery point, allowing the DC / DC converter to resume operation.

[0004] There is usually a hysteresis between the over-temperature protection point and the over-temperature recovery point. For example, the protection point is 130℃, and the recovery point is 110℃, with a 20℃ hysteresis in between to prevent damage from frequent switching of the controller. To achieve this hysteresis, a comparator is generally required. The comparator needs a power supply and may also require an additional LDO or SBC.

[0005] Pure hardware circuits (such as pure hardware controllers, pure hardware power supplies, or pure hardware control modules) do not have SBC / LDOs or MCUs, requiring no software engineer involvement in development, resulting in lower R&D and component costs. However, because pure hardware circuits lack an MCU, over-temperature protection functions cannot be implemented using over-temperature protection circuits with the aforementioned circuit structures. If a resistor divider composed of the NTC thermistor NTC3 and resistor R41 is directly applied to the enable pin of the DC / DC converter, the over-temperature protection point and the over-temperature recovery point will be very close, with no hysteresis, inevitably causing frequent on / off switching of the control module and damaging it. Summary of the Invention

[0006] The technical problem to be solved by this utility model is to provide an over-temperature protection circuit that can be applied to pure hardware circuits, has low implementation cost, and has sufficient hysteresis between the over-temperature protection point and the over-temperature recovery point.

[0007] This utility model embodiment provides an over-temperature protection circuit for a purely hardware circuit, used in conjunction with a power supply circuit. The output terminal of the power supply circuit is connected to the first terminal of a safety switch, and the second terminal of the safety switch is used to connect to a subsequent circuit. The over-temperature protection circuit includes a safety switch control circuit, a first temperature detection circuit, a second temperature detection circuit, a shutdown latch circuit, and a disable circuit. The output terminal of the safety switch control circuit is connected to the controlled terminal of the safety switch. The first temperature detection circuit includes a power supply VDD, an NTC thermistor NTC1, and a grounding resistor R21. One end of the NTC thermistor NTC1 is connected to the power supply VDD, and the other end of the NTC thermistor NTC1 is connected to ground in series with the grounding resistor R21. The second temperature detection circuit includes a power supply VDD, a pull-up resistor R22, and an NTC thermistor NTC2. One end of the pull-up resistor R22 is connected to the power supply VDD. The other end of the pull-up resistor R22 is connected in series with the NTC thermistor NTC2 and then grounded. The first input terminal of the shutdown latch circuit is connected to the common junction of the NTC thermistor NTC1 and the grounding resistor R21. The output terminal of the shutdown latch circuit is connected to the input terminal of the safety switch control circuit. The shutdown latch circuit is used to latch the safety switch in the off state through the safety switch control circuit when the voltage at the common junction of the NTC thermistor NTC1 and the grounding resistor R21 is greater than a preset first voltage threshold. The input terminal of the disable circuit is connected to the common junction of the pull-up resistor R22 and the NTC thermistor NTC2. The output terminal of the disable circuit disables the second input terminal of the shutdown latch circuit. The disable circuit is used to disable the shutdown latch circuit when the voltage at the common junction of the pull-up resistor R22 and the NTC thermistor NTC2 is greater than a preset second voltage threshold, so that the safety switch control circuit controls the safety switch to turn on.

[0008] This utility model has at least the following technical effects:

[0009] 1. This utility model embodiment can be applied to pure hardware circuits without MCU or LDO / SBC, and can realize reliable over-temperature protection for pure hardware circuits;

[0010] 2. The over-temperature protection circuit of this utility model embodiment is composed of discrete components, eliminating the need for comparators and LDOs, thus reducing costs.

[0011] 3. This utility model embodiment can have an over-temperature protection point and an over-temperature recovery point, just like a traditional over-temperature protection circuit, and ensures sufficient hysteresis to avoid frequent system start-up and shutdown. Attached Figure Description

[0012] Figure 1 The circuit diagram of a common over-temperature protection circuit is shown.

[0013] Figure 2 A circuit diagram of an over-temperature protection circuit applied to a purely hardware circuit according to an embodiment of the present invention is shown. Detailed Implementation

[0014] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0015] Figure 2 A circuit diagram of an over-temperature protection circuit applied to a purely hardware circuit according to an embodiment of the present invention is shown below. Please refer to [link / reference]. Figure 2 This over-temperature protection circuit works in conjunction with power supply circuit 1. The output terminal of power supply circuit 1 is connected to the first terminal of safety switch 2, and the second terminal of safety switch 2 is used to connect to the subsequent circuit so that the output voltage Vo_DCDC of power supply circuit 1 is output to the subsequent circuit.

[0016] In this embodiment, power supply circuit 1 and Figure 1 The existing power supply circuits shown have basically the same structure, including a DC / DC converter 11, switching transistors Q13 and Q14, an inductor L11, and a capacitor C11. The safety switch 2 uses an NMOS transistor Q11, and the gate, drain, and source of the NMOS transistor Q11 constitute the controlled terminal, the first terminal, and the second terminal of the safety switch 2, respectively. The DC / DC converter has a built-in LDO, which will only work after being enabled.

[0017] An over-temperature protection circuit for a purely hardware circuit according to an embodiment of the present invention includes a safety switch control circuit 30, a first temperature detection circuit 31, a second temperature detection circuit 32, a shutdown latch circuit 33, and a disable circuit 34.

[0018] The output terminal of the safety switch control circuit 30 is connected to the controlled terminal of the safety switch 2.

[0019] The first temperature detection circuit 31 includes an NTC thermistor NTC1 and a grounding resistor R21. One end of the NTC thermistor NTC1 is connected to the power supply VDD, and the other end of the NTC thermistor NTC1 is connected in series with the grounding resistor R21 and then grounded.

[0020] The second temperature detection circuit 32 includes a pull-up resistor R22 and an NTC thermistor NTC2. One end of the pull-up resistor R22 is connected to the power supply VDD, and the other end of the pull-up resistor R22 is connected in series with the NTC thermistor NTC2 and then grounded.

[0021] The first input terminal of the shutdown latch circuit 33 is connected to the common junction of the NTC thermistor NTC1 and the grounding resistor R21. The output terminal of the shutdown latch circuit 33 is connected to the input terminal of the safety switch control circuit 30. The shutdown latch circuit 33 is used to latch the safety switch 2 into the off state through the safety switch control circuit 30 when the voltage at the common junction of the NTC thermistor NTC1 and the grounding resistor R21 is greater than a preset first voltage threshold.

[0022] The input terminal of the disable circuit 34 is connected to the common junction of the pull-up resistor R22 and the NTC thermistor NTC2, and the output terminal of the disable circuit 34 is connected to the second input terminal of the turn-off latch circuit 33. The disable circuit 34 is used to disable the turn-off latch circuit 31 when the voltage at the common junction of the pull-up resistor R22 and the NTC thermistor NTC2 is greater than a preset second voltage threshold, so that the safety switch control circuit 30 controls the safety switch 2 to be turned on.

[0023] In this embodiment, the shutdown latch circuit 33 includes a first voltage divider circuit, switching transistors Q1, Q2, and Q3. The input terminal of the first voltage divider circuit is connected to the common junction of the NTC thermistor NTC1 and the grounding resistor R21. The output terminal of the first voltage divider circuit is connected to the controlled terminal of switching transistor Q2. The first terminal of switching transistor Q2 is connected to the controlled terminal of switching transistor Q1, and the second terminal of switching transistor Q2 is grounded. The first terminal of switching transistor Q1 is connected to the controlled terminal of switching transistor Q3, and the second terminal of switching transistor Q1 is connected to the power supply of the shutdown latch circuit. The first terminal of switching transistor Q3 serves as the output terminal of the shutdown latch circuit 33, and the second terminal of switching transistor Q3 is grounded.

[0024] Specifically, the first voltage divider circuit includes resistors R2 and R4. The first terminal of resistor R2 forms the input terminal of the first voltage divider circuit, and the common connection point of the second terminal of resistor R2 and the first terminal of resistor R4 forms the output terminal of the first voltage divider circuit. The second terminal of resistor R4 is grounded. Switch Q1 is a PNP transistor, and the base, collector, and emitter of the PNP transistor form the controlled terminal, the first terminal, and the second terminal of switch Q1, respectively. Switch Q2 is an NPN transistor, and the base, collector, and emitter of the NPN transistor form the controlled terminal, the first terminal, and the second terminal of switch Q2, respectively. Switch Q3 is an NMOS transistor, and the gate, drain, and source of the NMOS transistor form the controlled terminal, the first terminal, and the second terminal of switch Q3, respectively.

[0025] Furthermore, the shutdown latch circuit 33 also includes a first RC filter circuit. The input terminal of the first RC filter circuit constitutes the first input terminal of the shutdown latch circuit 33, and the output terminal of the first RC filter circuit is connected to the input terminal of the first voltage divider circuit. The first RC filter circuit includes a resistor R1 and a capacitor C1. The first end of the resistor R1 constitutes the input terminal of the first RC filter circuit, the common junction of the resistor R1 and the capacitor C1 constitutes the output terminal of the first RC filter circuit, and the second end of the capacitor C1 is grounded.

[0026] In this embodiment, the shutdown latch circuit 33 includes resistors R3, R5, R6, R7, and R8. One end of resistor R3 is connected to the controlled terminal of switch Q2 and the output terminal of the first voltage divider circuit, respectively, and the other end of resistor R3 is connected to the first terminal of switch Q1. One end of resistor R5 is connected to the power supply of the shutdown latch circuit and the second terminal of switch Q1, respectively, and the common junction of the other end of resistor R5 and one end of resistor R6 is connected to the controlled terminal of switch Q1. The other end of resistor R6 is connected to the first terminal of switch Q2. One end of resistor R7 is connected to the common junction of the other end of resistor R3 and the first terminal of switch Q1, and the common junction of the other end of resistor R7 and one end of resistor R8 is connected to the controlled terminal of switch Q3. The other end of resistor R8 is grounded.

[0027] In this embodiment, the power supply VDD is provided by the LDO integrated into the DC / DC converter 11, and the power supply for the shutdown latch circuit is the output voltage Vo_DCDC of the power supply circuit 1. Since the temperature detection circuit consumes very little current, less than 5mA, the LDO integrated into the DC / DC converter can be used, eliminating the need for an additional LDO. In other embodiments, the power supply VDD is used as the power supply for the shutdown latch circuit.

[0028] In this embodiment, the disable circuit 34 includes a second voltage divider circuit and a switch Q4. The input terminal of the second voltage divider circuit is connected to the common junction of the pull-up resistor R22 and the NTC thermistor NTC2. The output terminal of the second voltage divider circuit is connected to the controlled terminal of the switch Q4. The first terminal of the switch Q4 is connected to the controlled terminal of the switch Q2, and the second terminal of the switch Q4 is grounded.

[0029] Specifically, the second voltage divider circuit includes resistors R10 and R11. The first terminal of resistor R10 forms the input terminal of the second voltage divider circuit, and the common connection point of the second terminal of resistor R10 and the first terminal of resistor R11 forms the output terminal of the second voltage divider circuit. The second terminal of resistor R11 is grounded. The switching transistor Q4 is an NPN transistor. The base, collector, and emitter of the NPN transistor form the controlled terminal, the first terminal, and the second terminal of the switching transistor Q4, respectively.

[0030] Furthermore, the disable circuit 34 includes a second RC filter circuit. The input terminal of the second RC filter circuit constitutes the input terminal of the disable circuit 34, and the output terminal of the second RC filter circuit is connected to the input terminal of the second voltage divider circuit. The second RC filter circuit includes a resistor R9 and a capacitor C2. The first end of the resistor R9 constitutes the input terminal of the second RC filter circuit, the common junction of the resistor R9 and the capacitor C2 constitutes the output terminal of the second RC filter circuit, and the second end of the capacitor C2 is grounded.

[0031] In this embodiment, the safety switch control circuit 30 includes resistors R31 and R32, Zener diode ZD1, switching transistor Q22, and a third voltage divider circuit.

[0032] The first terminal of resistor R31, the first terminal of switching transistor Q22, the first terminal of the third voltage divider circuit, and the first terminal of safety switch 2 are all connected to the output terminal of power supply circuit 1. The common junction of the second terminal of resistor R31 and the first terminal of resistor R32 is connected to the controlled terminal of switching transistor Q22. The common junction of the second terminal of resistor R32 and the cathode of Zener diode ZD1 is connected to the output terminal of turn-off latch circuit 33. The anode of Zener diode ZD1 is grounded. The second terminal of switching transistor Q22 and the output terminal of the third voltage divider circuit are both connected to the controlled terminal of safety switch 2. The second terminal of the third voltage divider circuit is grounded.

[0033] Specifically, the third voltage divider circuit includes resistors R33 and R34. The first terminal of resistor R33 forms the first terminal of the third voltage divider circuit, the common junction of the second terminal of resistor R33 and the first terminal of resistor R34 forms the output terminal of the third voltage divider circuit, and the second terminal of resistor R34 forms the second terminal of the third voltage divider circuit. The switching transistor Q22 is a PNP transistor, and its base, emitter, and collector form the controlled terminal, the first terminal, and the second terminal of switching transistor Q22, respectively.

[0034] Furthermore, the safety switch control circuit 30 includes an acceleration capacitor C1, which is connected in parallel with a resistor R34.

[0035] The following combination Figure 2 The working process of the over-temperature protection circuit of this utility model embodiment will be further explained.

[0036] Operating Condition 1: From normal operation to triggering over-temperature protection:

[0037] The resistance values ​​of NTC thermistors NTC1 and NTC2 decrease as the temperature increases. At the same time, the voltage across the grounding resistor R21 increases, while the voltage across the NTC thermistor NTC2 decreases.

[0038] The voltage across the grounding resistor R21 gradually increases. When it reaches the set over-temperature protection point, the voltage across R21 will turn on switch Q2. After switch Q2 turns on, switch Q1 also turns on, interlocking with switch Q2 to form a latch state. After switch Q1 turns on, switch Q3 turns on, which in turn turns on switch Q22. After switch Q22 turns on, NMOS transistor Q11 turns off. After NMOS transistor Q11 turns off, the voltage output terminal Vo connected to the second terminal of the safety switch no longer outputs voltage, which is equivalent to removing the load. The entire module is in an unloaded operating state, greatly reducing power consumption, and the temperature of the PCB circuit board and the power devices on it will decrease accordingly.

[0039] Since the enable pin of the DC / DC converter chip is not pulled out, the LDO built into the DC / DC converter chip is still in operation. VDD still provides a stable power supply to the first temperature detection circuit 31 and the second temperature detection circuit. When the DC / DC converter 11 is in an unloaded state, the power supply circuit 1 still has a stable output voltage Vo_DCDC, which provides power to the shutdown latch circuit 33.

[0040] Operating Condition 2: Recovery from over-temperature protection state to normal operating state:

[0041] After the over-temperature protection is activated, the temperature of the control module decreases. As the temperature drops to the temperature recovery point, the voltage across the grounding resistor R21 decreases, which is insufficient to maintain the switching transistor Q2. The switching transistor Q2 is then maintained by the voltage provided by the switching transistor Q1.

[0042] The resistance values ​​of NTC thermistors NTC1 and NTC2 increase as the temperature decreases, the voltage across the grounding resistor R21 decreases, and the voltage across the NTC thermistor NTC2 increases.

[0043] When the temperature drops to the over-temperature recovery point, the voltage across the NTC thermistor NTC2 will turn on switch Q4, thereby pulling switch Q2 off. After switch Q2 is pulled off, switch Q1 will turn off. After switch Q1 turns off, switch Q3 will also turn off, causing switch Q22 to turn off. After switch Q22 turns off, NMOS transistor Q11 will turn on, and the output voltage Vo connected to the second terminal of the safety switch will recover, restoring the entire control module to its load-bearing operating state.

[0044] This invention can have over-temperature protection points and over-temperature recovery points like traditional over-temperature protection circuits, and ensures sufficient hysteresis to avoid frequent system start-up and shutdown.

[0045] Obviously, those skilled in the art can make various modifications and variations to this utility model without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this utility model and their equivalents, this utility model also intends to include these modifications and variations.

Claims

1. An over-temperature protection circuit applied to a purely hardware circuit, used in conjunction with a power supply circuit, wherein the output terminal of the power supply circuit is connected to a first terminal of a safety switch, and the second terminal of the safety switch is used to connect to a subsequent circuit; characterized in that, The over-temperature protection circuit applied to a purely hardware circuit includes a safety switch control circuit, a first temperature detection circuit, a second temperature detection circuit, a shutdown latch circuit, and a power-disable circuit. The output terminal of the safety switch control circuit is connected to the controlled terminal of the safety switch; The first temperature detection circuit includes an NTC thermistor NTC1 and a grounding resistor R21. One end of the NTC thermistor NTC1 is connected to the power supply VDD, and the other end of the NTC thermistor NTC1 is connected to the grounding resistor R21 in series and then grounded. The second temperature detection circuit includes a pull-up resistor R22 and an NTC thermistor NTC2. One end of the pull-up resistor R22 is connected to the power supply VDD, and the other end of the pull-up resistor R22 is connected in series with the NTC thermistor NTC2 and then grounded. The first input terminal of the shutdown latch circuit is connected to the common junction of the NTC thermistor NTC1 and the grounding resistor R21, and the output terminal of the shutdown latch circuit is connected to the input terminal of the safety switch control circuit. The shutdown latch circuit is used to latch the safety switch in the off state through the safety switch control circuit when the voltage at the common junction of the NTC thermistor NTC1 and the grounding resistor R21 is greater than a preset first voltage threshold. The input terminal of the disable circuit is connected to the common junction of the pull-up resistor R22 and the NTC thermistor NTC2, and the output terminal of the disable circuit is connected to the second input terminal of the shutdown latch circuit. The disable circuit is used to disable the shutdown latch circuit when the voltage at the common junction of the pull-up resistor R22 and the NTC thermistor NTC2 is greater than a preset second voltage threshold, so that the safety switch control circuit controls the safety switch to be turned on.

2. The over-temperature protection circuit applied to a purely hardware circuit according to claim 1, characterized in that, The shutdown latch circuit includes a first voltage divider circuit, a switching transistor Q1, a switching transistor Q2, and a switching transistor Q3; The input terminal of the first voltage divider circuit is connected to the common junction of the NTC thermistor NTC1 and the grounding resistor R21. The output terminal of the first voltage divider circuit is connected to the controlled terminal of the switching transistor Q2. The first terminal of the switching transistor Q2 is connected to the controlled terminal of the switching transistor Q1, and the second terminal of the switching transistor Q2 is grounded. The first terminal of the switching transistor Q1 is connected to the controlled terminal of the switching transistor Q3, and the second terminal of the switching transistor Q1 is connected to the power supply of the shutdown latch circuit. The first terminal of the switching transistor Q3 serves as the output terminal of the shutdown latch circuit, and the second terminal of the switching transistor Q3 is grounded.

3. The over-temperature protection circuit applied to a purely hardware circuit according to claim 2, characterized in that, The shutdown latch circuit includes a first RC filter circuit, the input terminal of the first RC filter circuit constitutes the first input terminal of the shutdown latch circuit, and the output terminal of the first RC filter circuit is connected to the input terminal of the first voltage divider circuit. The first voltage divider circuit includes resistors R2 and R4. The first end of resistor R2 forms the input terminal of the first voltage divider circuit, and the common connection point of the second end of resistor R2 and the first end of resistor R4 forms the output terminal of the first voltage divider circuit. The second end of resistor R4 is grounded.

4. The over-temperature protection circuit applied to a purely hardware circuit according to claim 2, characterized in that, Switch Q1 is a PNP transistor, with its base, collector, and emitter forming the controlled terminal, first terminal, and second terminal, respectively. Switch Q2 is an NPN transistor, with its base, collector, and emitter forming the controlled terminal, first terminal, and second terminal, respectively. Switch Q3 is an NMOS transistor, with its gate, drain, and source forming the controlled terminal, first terminal, and second terminal, respectively. The shutdown latch circuit includes resistors R3, R5, R6, R7, and R8. One end of resistor R3 is connected to the controlled terminal of switch Q2 and the output terminal of the first voltage divider circuit, and the other end of resistor R3 is connected to the first terminal of switch Q1. One end of resistor R5 is connected to the power supply of the shutdown latch circuit and the second terminal of switch Q1, and the common connection point of the other end of resistor R5 and one end of resistor R6 is connected to the controlled terminal of switch Q1. The other end of resistor R6 is connected to the first terminal of switch Q2. One end of resistor R7 is connected to the common connection point of the other end of resistor R3 and the first terminal of switch Q1. The common connection point of the other end of resistor R7 and one end of resistor R8 is connected to the controlled terminal of switch Q3. The other end of resistor R8 is grounded. The power supply for the shutdown latch circuit is the output voltage of the power supply circuit or the power supply VDD.

5. The over-temperature protection circuit applied to a purely hardware circuit according to claim 1, characterized in that, The power-disabled circuit includes a second voltage divider circuit and a switching transistor Q4; The input terminal of the second voltage divider circuit is connected to the common junction of the pull-up resistor R22 and the NTC thermistor NTC2. The output terminal of the second voltage divider circuit is connected to the controlled terminal of the switching transistor Q4. The first terminal of the switching transistor Q4 is connected to the controlled terminal of the switching transistor Q2, and the second terminal of the switching transistor Q4 is grounded. The switching transistor Q4 is an NPN transistor. The base, collector, and emitter of the NPN transistor constitute the controlled terminal, the first terminal, and the second terminal of the switching transistor Q4, respectively.

6. The over-temperature protection circuit applied to a purely hardware circuit according to claim 5, characterized in that, The power-disabled circuit includes a second RC filter circuit, the input terminal of which constitutes the input terminal of the power-disabled circuit, and the output terminal of which is connected to the input terminal of the second voltage divider circuit. The second voltage divider circuit includes resistors R10 and R11. The first end of resistor R10 forms the input terminal of the second voltage divider circuit, and the common connection point of the second end of resistor R10 and the first end of resistor R11 forms the output terminal of the second voltage divider circuit. The second end of resistor R11 is grounded.

7. The over-temperature protection circuit applied to a purely hardware circuit according to claim 1, characterized in that, The safety switch control circuit includes resistor R31, resistor R32, Zener diode ZD1, switching transistor Q22, and a third voltage divider circuit; The first terminal of resistor R31, the first terminal of switching transistor Q22, the first terminal of the third voltage divider circuit, and the first terminal of the safety switch are all connected to the output terminal of the power supply circuit. The common connection point of the second terminal of resistor R31 and the first terminal of resistor R32 is connected to the controlled terminal of switching transistor Q22. The common connection point of the second terminal of resistor R32 and the cathode of Zener diode ZD1 is connected to the output terminal of the turn-off latch circuit. The anode of Zener diode ZD1 is grounded. The second terminal of the switching transistor Q22 and the output terminal of the third voltage divider circuit are respectively connected to the controlled terminal of the safety switch, and the second terminal of the third voltage divider circuit is grounded; the switching transistor Q22 is a PNP transistor, and the base, emitter and collector of the PNP transistor constitute the controlled terminal, the first terminal and the second terminal of the switching transistor Q22, respectively.

8. The over-temperature protection circuit applied to a purely hardware circuit according to claim 7, characterized in that, The third voltage divider circuit includes resistors R33 and R34; the first end of resistor R33 forms the first end of the third voltage divider circuit, the common connection point of the second end of resistor R33 and the first end of resistor R34 forms the output end of the third voltage divider circuit, and the second end of resistor R34 forms the second end of the third voltage divider circuit. The safety switch control circuit includes an acceleration capacitor C1, which is connected in parallel with a resistor R34.

9. The over-temperature protection circuit applied to a purely hardware circuit according to any one of claims 1 to 8, characterized in that, The safety switch is an NMOS transistor Q11. The gate, drain, and source of the NMOS transistor Q11 constitute the controlled terminal, the first terminal, and the second terminal of the safety switch, respectively.

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