High-reliability multi-stage overheating protection circuit applied to airborne product

Abstract

The invention belongs to the technical field of aviation electrics, and particularly relates to a high-reliability multi-stage overheating protection circuit applied to airborne products. Comprising three sensor temperature acquisition circuits, three high-low overheat hysteresis comparator circuits, three high-low temperature overheat judgment circuits, an overheat logic judgment circuit, a time delay circuit, a software redundancy control circuit, a reset protection circuit, a hardware rapid short circuit protection circuit and an overheat relay cut-off circuit. By collecting three temperature sensors, executing a first-stage software overheating protection logic, executing a hardware overheating logic protection circuit logic by a second-stage overheating protection, and executing a reset protection overheating logic by a third-stage overheating protection, an overheating relay is quickly and directly cut off; and the execution logic of the fourth-stage hardware rapid short-circuit protection circuit does not need the participation of the temperature values of the previous three-stage sensors, and microsecond-stage rapid overheating protection can be directly realized. The safety and reliability of the system are improved, and the safety of pilots is ensured.

Description

Technical Field

[0001] The invention belongs to the field of aviation electrical technology, and in particular relates to a high-reliability multi-stage overheat protection circuit applied to airborne products. Background Art

[0002] With the development trend of large aircraft and more electric aircraft, there are more and more electric heating control systems on aircraft. The importance and reliability requirements of electric heating control systems on aircraft are getting higher and higher. When the aircraft heating system is overheated, the temperature exceeds the limit temperature value. When the aircraft is in a high-altitude environment, there is a risk of rupture and fire of the onboard products, which affects flight safety and poses a huge hazard. Therefore, the overheat protection function of the aircraft electric heating system is one of the necessary functions of airborne products. The overheat protection of traditional aircraft electric heating is mainly based on the product software control logic. The overheat protection method of traditional aircraft electric heating is single, the redundancy design is not comprehensive, the protection time is long, the protection parameters are not convenient to set, and the reliability is low. When the product software fails, the overheat protection function of the aircraft electric heating is lost, which reduces the reliability of the product and affects flight safety. Summary of the invention

[0003] Purpose of the invention: To provide a high-reliability multi-stage overheat protection circuit for airborne products.

[0004] Technical solution:

[0005] A high-reliability multi-stage overheat protection circuit for airborne products comprises: a three-way sensor temperature acquisition circuit, a three-way high and low overheat hysteresis comparator circuit, a three-way high and low temperature overheat judgment circuit, an overheat logic judgment circuit, a delay circuit, a software redundancy control circuit, a reset protection circuit, a hardware fast short circuit protection circuit, and an overheat relay cut-off circuit, wherein the output ends of the three-way sensor temperature acquisition circuit are respectively connected to the inverting input ends of the corresponding high and low overheat hysteresis comparator circuits, the same-direction input end of the high overheat hysteresis comparator in the high and low overheat hysteresis comparator circuit is connected to the high overheat threshold reference voltage, and the same-direction input end of the low overheat hysteresis comparator in the high and low overheat hysteresis comparator circuit is connected to the low overheat threshold reference voltage; the two input ends of the high and low temperature overheat judgment circuit are respectively connected to the corresponding low overheat hysteresis comparator circuits. The output end of the overheating logic judgment circuit is connected to the output end of the high overheating hysteresis comparator; the output ends of the three-way high and low temperature overheating judgment circuits and the BIT online injection command are respectively connected to the four input ends of the overheating logic judgment circuit; the output end of the overheating logic judgment circuit is connected to the input end of the delay circuit, the output end of the delay circuit and the relay cut-off control signal command are respectively connected to the two input ends of the software redundancy control circuit, the output end of the software redundancy control circuit and the reset RESET are respectively connected to the two input ends of the reset protection circuit; the output end of the reset protection circuit and the short-circuit protection command are respectively connected to the two input ends of the hardware fast short-circuit protection circuit; the output end of the hardware fast short-circuit protection circuit is connected to the input end of the overheating relay cut-off circuit; the output end of the overheating relay cut-off circuit is used to output the overheating relay shutdown command.

[0006] Furthermore, the temperature acquisition circuits of the three sensors are the same and all of them are temperature sensors.

[0007] Furthermore, the three high and low overheat hysteresis comparator circuits are the same. The first high and low overheat hysteresis comparator circuit includes: resistor R4, resistor R5, resistor R6, resistor R7, resistor R8, resistor R9, capacitor C2, diode D1, diode D2, comparator IC1A, and comparator IC1B, wherein the same-direction input terminal of comparator IC1A is connected to the voltage divider of the low overheat bridge circuit and one end of resistor R4; the other end of resistor R4 is connected to the output terminal of comparator IC1A as the output of the low overheat hysteresis comparator; the reverse input terminal of comparator IC1A is connected to diode D1. The anode, cathode of diode D2, one end of resistor R5 and one end of capacitor C2 are connected; the cathode of diode D1 is connected to the power supply; the other end of resistor R5 is connected to the output end of the sensor temperature acquisition circuit; the other end of diode D2 and capacitor C2 are grounded; the same-direction input end of comparator IC1B is connected to the high superheat bridge circuit voltage divider and one end of resistor R9; the other end of resistor R9 is connected to the output end of comparator IC1B as the output of the high superheat hysteresis comparator; the reverse input end of comparator IC1B is connected to the anode of diode D1, the cathode of diode D2, one end of resistor R5 and one end of capacitor C2.

[0008] Furthermore, the low overheat bridge voltage divider circuit includes: a resistor R1, a resistor R2, and a resistor R3, wherein one end of the resistor R1 is connected to one end of the resistor R2 and one end of the resistor R3; the other end of the resistor R1 is connected to a power supply; the other end of the resistor R2 and the other end of the resistor R3 are grounded.

[0009] Furthermore, the high overheat bridge circuit includes: resistor R6, resistor R7, and resistor R8, wherein one end of resistor R6 is connected to one end of resistor R7 and one end of resistor R8; the other end of resistor R6 is connected to a power supply; the other end of resistor R7 and the other end of resistor R8 are grounded.

[0010] Furthermore, the three high and low temperature overheat judgment circuits have the same structure. The first high and low temperature overheat judgment circuit includes an XOR gate IC2 and a capacitor C1, wherein the two input ends of the XOR gate IC2 are respectively connected to the output end of the corresponding high overheat hysteresis comparator and the output end of the low overheat hysteresis comparator; one end of the capacitor C1 is connected to the power supply of the XOR gate IC2, and the other end of the capacitor C1 is connected to the ground of the XOR gate IC2.

[0011] Furthermore, the overheating logic judgment circuit includes: a NOR gate IC4A and a NOR gate IC4B, wherein the four input ends of the NOR gate IC4A are respectively connected to the output ends of the three high and low temperature overheating judgment circuits and the BIT online injection command; the output end of the NOR gate IC4A and the input end of the NOR gate IC4B, and the output end of the NOR gate IC4B serve as the output of the overheating logic judgment circuit.

[0012] Furthermore, the delay circuit includes a resistor R14, a resistor R17, a diode D5 and a capacitor C5, wherein one end of the resistor R14 is connected to the cathode of the diode D5 as an input end of the delay circuit; the other end of the resistor R14 is connected to one end of the resistor R17 and one end of the capacitor C5 as an output end of the delay circuit; the other end of the resistor R17 is connected to the anode of the diode D5; and the other end of the capacitor C5 is grounded.

[0013] Furthermore, the software redundancy control circuit is a NOR gate IC5, the reset protection circuit is an AND gate UA2, and the hardware fast short-circuit protection circuit is an AND gate UA3.

[0014] Furthermore, the overheating relay cut-off circuit includes: a diode D3, a resistor R16, a capacitor C4, and a MOS tube Q1, wherein the anode of the diode D3 serves as the input end of the diode D3, and the cathode of the diode D3 is connected to one end of the resistor R16, one end of the capacitor C4, and the gate of the MOS tube Q1; the drain of the MOS tube Q1 serves as the output end of the overheating relay cut-off circuit, and the other end of the resistor R16, the other end of the capacitor C4, and the source of the MOS tube Q1 are grounded.

[0015] Beneficial effects:

[0016] In view of the shortcomings of traditional overheat protection technology, such as low reliability, single protection mode, and long protection time, the high-reliability multi-level overheat protection method of the present invention has rich overheat protection margin and high reliability level, which greatly improves the reliability of the product. The rich and perfect control logic method of the present invention effectively ensures that when the airborne product is overheated, the product has no power output, which improves the stability and safety of the electric heating system. The reliability of the aircraft electric heating system is greatly improved to ensure flight safety. The entire circuit design, calculation process, and control logic method of the present invention meet the forward design requirements of aviation airborne products. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the principle block diagram of a high reliability multi-stage overheat protection circuit.

[0018] Figure 2 This is a high reliability multi-stage overheat protection circuit diagram. DETAILED DESCRIPTION

[0019] like Figure 1 A high reliability multi-stage overheat protection circuit for airborne products, including: a three-way sensor temperature acquisition circuit, a three-way high and low overheat hysteresis comparator circuit, a three-way high and low temperature overheat judgment circuit, an overheat logic judgment circuit, a delay circuit, a software redundancy control circuit, a reset protection circuit, a hardware fast short circuit protection circuit, and an overheat relay cut-off circuit.

[0020] Among them, three completely identical temperature acquisition circuits, high and low overheat hysteresis comparator circuits, high and low temperature overheat judgment circuits and overheat logic judgment circuits ensure that when any sensor is overheated or fails, the redundancy design can reliably and effectively cut off the overheat relay. The BIT online injection command CPU_BIT can perform online self-test and periodic self-test on the circuit to monitor the circuit status and improve product reliability. The relay cut-off control signal command is a high-priority protection design. When the normal software overheat protection logic works, the relay cut-off control signal command (software control) first participates in the control. When the relay cut-off control signal command (software control) fails, the hardware overheat protection participates in the control. The priority of the relay cut-off control signal command (software control) is higher than that of the hardware protection. At the same time, when the software fails, the hardware overheat protection can effectively cut off the overheat relay. The combination of software and hardware redundancy protection can reliably ensure that the product has no three-phase 115V AC PHA, 115V AC PHB, 115VAC PHC AC power output, ensuring the safety of the aircraft electric heating system.

[0021] First-level software overheat protection logic: The collected temperature sensor values ​​are processed by the CPU processor, and the software overheat protection logic is executed. When it is judged to be overheated, the overheat relay shutdown command is output. The entire software overheat protection time cycle is about 2S. After 2S, if any software determines that the overheating exceeds 60℃, the software overheat protection is executed, the overheat relay shutdown command is output, and the overheat relay is cut off. The software overheat protection logic has a higher priority than the hardware protection logic.

[0022] The second-level hardware overheat protection logic is as follows: when any of the three sensors is overheated, the overheat protection logic can be executed through the high-reliability multi-stage overheat protection circuit to directly cut off the overheat relay. The hardware overheat protection time is about 5S. When the high-reliability multi-stage overheat protection circuit recognizes that any sensor is overheated for 5S, the overheat relay is cut off. The above-mentioned hardware overheat protection logic does not need to pass through the CPU processor, and does not need to execute the software overheat protection logic to directly turn off the overheat relay. When the CPU processor fails or the software crashes, the hardware overheat protection logic can also complete the overheat relay shutdown to ensure that the product has no power output.

[0023] The third-level fault reset protection logic (RESET): When the product fault is reset, the safety margin capability of the first two levels of overheat protection is improved, which increases the reliability of the product. At the same time, the solution has a BIT online detection function to detect in real time whether the overheat protection function of the product is operating normally.

[0024] The fourth level hardware short-circuit protection logic (short-circuit protection), when the product identifies a short circuit, the hardware short-circuit protection logic quickly cuts off the overheating relay in microseconds, effectively ensuring the safety of the system.

[0025] In order to make the purpose, content, and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 The principle block diagram of the high reliability multi-stage overheat protection circuit and the control logic method are as follows:

[0027] ①The first-level software overheat protection logic is as follows: The software overheat protection logic collects the temperature sensor value and processes it through the CPU processor. By executing the software overheat protection logic, it is determined that the overheating is executed, and the software overheat protection is executed, and the overheat relay shutdown command is output. The entire software overheat protection time cycle is about 2S. After 2S, any software determines that the overheating is over 60℃, that is, the software overheat protection is executed, the overheat relay shutdown command is output, and the overheat relay is cut off.

[0028] ②The second-level hardware overheat protection logic is as follows: The three input sensor voltage values are collected and compared with the high and low overheat hysteresis comparators. When the input sensor temperature exceeds the threshold reference temperature of the hysteresis comparator, the hysteresis comparator outputs a low level. When the input sensor temperature is lower than the threshold reference temperature of the hysteresis comparator, the hysteresis comparator outputs a high level. The output results of the two comparators corresponding to 55°C and 100°C are fed into an exclusive-OR gate to perform high and low overheat logic judgment to determine whether it is low overheat or high overheat.

[0029] ③The truth table of the exclusive-OR gate is that the output is low level 0 when the inputs are the same, and the output is high level 1 when the inputs are different. The logic of the three-way exclusive-OR gate is the same. Taking the first-way high and low overheat logic analysis as an example, when the input sensor temperature T° ≤ 55°C, the output of the exclusive-OR gate is low level 0, and the product considers the sensor normal. When the input sensor temperature 60°C < T° ≤ 100°C, the output of the exclusive-OR gate is high level 1, and the product considers the sensor to be in low overheat. When the input sensor temperature 100°C < T°, the output of the exclusive-OR gate is low level 0, and the product considers the sensor to be open-circuited, and the high and low overheat logic is high overheat. Among them, the number 1 represents high level, and the number 0 represents low level.

[0030] ④Then, the outputs of the three exclusive-OR gates and the BIT online injection command output by the product CPU form a 4-input 1-output OR gate logic. When one of the four inputs is high level, the output is all high 1. The output result of the OR gate passes through an RC delay circuit. When the output result of the 4-input 1-output OR gate is high 1, an overheat delay of 5S is executed, and after 5S, a high level is output. When the output result of the OR gate is low 0, a non-overheat delay of 0.2S is executed, and after 0.2S, a low level is output.

[0031] ⑤The output of the RC delay circuit and the relay cut-off control signal command (software control) output by the CPU perform a NOR gate logic. When both inputs of the NOR gate are low, the output is high level 1, and the rest of the outputs are all low level 0.

[0032] ⑥The output of the NOR gate is fed to the gate control terminal of the NMOS. The drain output of the NMOS is the overheat relay turn-off command and also the coil control terminal of the overheat relay. When the output of the NOR gate is high level 1, the product overheat logic considers non-overheat, and the drain output of the NMOS is low level 0. The relay coil circuit is turned on, the AC relay contact is closed, the overheat relay is not turned off, and the three-phase 115V AC power is normally output, and the product power output function is normal. When the output of the NOR gate is low level 0, the product overheat logic considers overheat, and the drain output of the NMOS is high level 1. The relay coil circuit is not turned on, the AC relay contact is opened, the overheat relay is turned off, the three-phase 115V AC power is not output, the product power has no output, and heating is no longer protected to ensure the flight safety of the pilot.

[0033] ⑦ The reset protection logic is that when the product fault is reset, the RESET signal is pulled low, and the execution of the AND gate logic can effectively cut off the overheating relay.

[0034] ⑧The hardware fast short-circuit protection logic is that when a product short circuit is detected, the HW_SC signal is directly pulled low. After executing the AND gate logic, the subsequent stage directly and quickly cuts off the overheating relay to effectively ensure system safety.

[0035] As shown in the overheat protection logic control table in Table 1, the specific execution logic mainly includes the 9 working conditions in Table 1. The electric heating overheating logic protection method has a high reliability multi-level protection design, rich logic, comprehensive control methods, and a high system safety level.

[0036] The complete control logic implemented by the present invention is shown in Table 1

[0037] Table 1 Overheat protection logic control table

[0038]

[0039] The product working status mainly includes the above 9 working conditions. The electric heating overheating logic protection method has a high reliability and redundancy design, rich logic and comprehensive control method.

[0040] right Figure 2The electric heating overheat protection method is developed. The input sensor temperature acquisition circuit acquires signals to participate in the software and hardware overheat protection logic. The first-level software overheat protection logic is mainly processed by the CPU. The second-level hardware overheat protection logic is executed as follows: The acquisition result is filtered by the first order and protected by the diode to the reverse input of the hysteresis comparator. The middle part of the circuit is composed of R5, C2, D1, D2, R15, C6, R26, C8, D7, and D8. The reference level of the positive input of the sensor 1 low overheat hysteresis comparator is composed of the bridge voltage divider composed of R1, R2, and R3. The comparator IC1A and R4 are hysteresis comparators. The hysteresis interval is calculated to be 55℃≤T≤60℃. The reference level of the positive input terminal of the high overheat hysteresis comparator of sensor 1 is composed of resistors R6, R7, and R8 to form a bridge voltage divider. The comparator chip is IC1, and R9 is the feedback resistor of the hysteresis comparator. The hysteresis interval is calculated to be 95℃≤T≤100℃. Similarly, the principle of the hysteresis comparator corresponding to sensor 2 and sensor 3 is consistent with that of sensor 1, and is composed of R10-R13, R18-R21, R22-R25, R27-R30, IC3, and IC7. The high and low temperature overheat judgment circuit is composed of logic chip XOR gate IC2, IC6 and IC8, the two input pins of the XOR gate are connected to the output of the hysteresis comparator respectively, the XOR gate truth table of the logic chip is that the output is low level (0) when the input is the same, and the output is high level (1) when the input is different, C1-C3 are the decoupling capacitors of the chip, the overheating logic judgment circuit is composed of the logic chip 4 input 1 output NOR gate, IC4 chip, the output pin of the 3-way XOR gate chip is connected to the three input pins of the chip IC4A, and the other input pin of the chip IC4A is connected to the online self-test injection test command output by the CPU processor for online, periodic BIT self-test, the output of IC4A The pin is connected to the input of IC4B, and the output pin of IC4B is connected to the delay circuit. The logic of the 4-input 1-output NOR gate is that if any input is 1, the output is 0. The output is 1 only when all 4 inputs are 0. When the output pin of IC4B outputs a high level, the circuit is considered to be in an overheated state. The RC overheat delay circuit consists of R14 and C5. The full charge delay is calculated to be about 5S. When the output pin of IC4B outputs a low level, the circuit is considered to be in a non-overheated state. The RC non-overheat delay circuit consists of D5, R17, and C5. The D5 diode is used to prevent reverse in the non-overheated state. The discharge delay is calculated to be 0.2S or so, the software redundancy control circuit is a logic chip or gate IC5, one input of which is connected to the relay cut-off control signal command (software control) RELAY_OPEN_CMD output by the CPU processor, and the other input is connected to the delay circuit output. The 2-input 1-output or gate logic is that any input is 1 and the output is 0, and the output is 1 only when both inputs are 0. When the software output control command is low level (0), the output pin state of the or gate is only related to the input state of its other input pin. This working condition is the second-level overheat protection working condition of the product. The result of the entire hardware overheat protection is related to the result of the RC delay circuit. The output of the software redundancy control circuit IC5 is connected to the D3 anti-reverse diode and R16, C4 to Q1 NMOS gate control end, when the output of IC5 outputs high level, Q1 conducts, Q1 drain output is low level, overheat relay shutdown circuit RELAY_CTL signal is low level, MOS tube Q1 drain output is connected to overheat shutdown relay coil, when MOS tube Q1 drain is low level, coil conducts, relay contacts are energized, three-phase 115V AC power is output normally, on the contrary, when the circuit is considered to be in overheat state, or the output of the non-gate IC5 output is low, MOS tube Q1 drain output is high level, relay coil is not conducted, overheat relay contacts are disconnected, three-phase 115V AC power output is disconnected, effectively ensuring that the product power is not output when the product is in overheat state, and the product overheat protection function is effective. Two AND gates UA2 and UA3 participate in the third-level reset protection logic and hardware fast protection logic of the product. .

[0041] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several changes and modifications can be made without departing from the technical principles of the present invention. These changes and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high reliability multi-stage overheat protection circuit for airborne products, characterized in that: include: Three-way sensor temperature acquisition circuit, three-way high and low overheat hysteresis comparator circuit, three-way high and low temperature overheat judgment circuit, overheat logic judgment circuit, delay circuit, software redundancy control circuit, reset protection circuit, hardware fast short circuit protection circuit, overheat relay cut-off circuit, wherein the output ends of the three-way sensor temperature acquisition circuit are respectively connected to the reverse input ends of the corresponding high and low overheat hysteresis comparator circuits, the same-direction input end of the high overheat hysteresis comparator in the high and low overheat hysteresis comparator circuit is connected to the high overheat threshold reference voltage, and the same-direction input end of the low overheat hysteresis comparator in the high and low overheat hysteresis comparator circuit is connected to the low overheat threshold reference voltage; the two input ends of the high and low temperature overheat judgment circuit are respectively connected to the output end of the corresponding low overheat hysteresis comparator and the high overheat hysteresis comparator. The output end of the overheating logic judgment circuit is connected; the output ends of the three-way high and low temperature overheating judgment circuit and the BIT online injection command are respectively connected to the four input ends of the overheating logic judgment circuit; the output end of the overheating logic judgment circuit is connected to the input end of the delay circuit, the output end of the delay circuit and the relay cut-off control signal command are respectively connected to the two input ends of the software redundancy control circuit, the output end of the software redundancy control circuit and the reset RESET are respectively connected to the two input ends of the reset protection circuit; the output end of the reset protection circuit and the short-circuit protection command are respectively connected to the two input ends of the hardware fast short-circuit protection circuit; the output end of the hardware fast short-circuit protection circuit is connected to the input end of the overheating relay cut-off circuit; the output end of the overheating relay cut-off circuit is used to output the overheating relay shutdown command.

2. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The temperature acquisition circuits of the three sensors are the same and they are all temperature sensors.

3. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The three high and low overheat hysteresis comparator circuits are the same. The first high and low overheat hysteresis comparator circuit includes: resistor R4, resistor R5, resistor R6, resistor R7, resistor R8, resistor R9, capacitor C2, diode D1, diode D2, comparator IC1A, comparator IC1B, wherein, The same-direction input terminal of the comparator IC1A is connected to the voltage divider of the low overheat bridge circuit and one end of the resistor R4; the other end of the resistor R4 is connected to the output terminal of the comparator IC1A as the output of the low overheat hysteresis comparator; the reverse input terminal of the comparator IC1A is connected to the anode of the diode D1, the cathode of the diode D2, one end of the resistor R5, and one end of the capacitor C2; the cathode of the diode D1 is connected to the power supply; the other end of the resistor R5 is connected to the output terminal of the sensor temperature acquisition circuit; the other ends of the diode D2 and the capacitor C2 are grounded; The same-direction input terminal of the comparator IC1B is connected to the high superheat bridge circuit voltage divider and one end of the resistor R9; the other end of the resistor R9 is connected to the output terminal of the comparator IC1B as the output of the high superheat hysteresis comparator; the reverse input terminal of the comparator IC1B is connected to the anode of the diode D1, the cathode of the diode D2, one end of the resistor R5, and one end of the capacitor C2.

4. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The low overheat bridge voltage divider circuit includes: a resistor R1, a resistor R2, and a resistor R3, wherein one end of the resistor R1 is connected to one end of the resistor R2 and one end of the resistor R3; the other end of the resistor R1 is connected to a power supply; the other end of the resistor R2 and the other end of the resistor R3 are grounded.

5. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The high overheat bridge circuit includes: resistor R6, resistor R7, and resistor R8, wherein one end of resistor R6 is connected to one end of resistor R7 and one end of resistor R8; the other end of resistor R6 is connected to a power supply; the other end of resistor R7 and the other end of resistor R8 are grounded.

6. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The three high and low temperature overheat judgment circuits have the same structure. The first high and low temperature overheat judgment circuit includes an XOR gate IC2 and a capacitor C1, wherein the two input ends of the XOR gate IC2 are respectively connected to the output end of the corresponding high overheat hysteresis comparator and the output end of the low overheat hysteresis comparator; one end of the capacitor C1 is connected to the power supply of the XOR gate IC2, and the other end of the capacitor C1 is connected to the ground of the XOR gate IC2.

7. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The overheat logic judgment circuit includes: a NOR gate IC4A and a NOR gate IC4B, wherein the four input ends of the NOR gate IC4A are respectively connected to the output ends of the three high and low temperature overheat judgment circuits and the BIT online injection command; the output end of the NOR gate IC4A and the input end of the NOR gate IC4B, and the output end of the NOR gate IC4B serve as the output of the overheat logic judgment circuit.

8. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The delay circuit includes a resistor R14, a resistor R17, a diode D5 and a capacitor C5, wherein one end of the resistor R14 is connected to the cathode of the diode D5 as the input end of the delay circuit; the other end of the resistor R14 is connected to one end of the resistor R17 and one end of the capacitor C5 as the output end of the delay circuit; the other end of the resistor R17 is connected to the anode of the diode D5; and the other end of the capacitor C5 is grounded.

9. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The software redundancy control circuit is the NOR gate IC5, the reset protection circuit is the AND gate UA2, and the hardware fast short-circuit protection circuit is the AND gate UA3.

10. The high-reliability multi-stage overheat protection circuit for airborne products according to claim 1, characterized in that: The overheating relay cut-off circuit includes: a diode D3, a resistor R16, a capacitor C4, and a MOS tube Q1, wherein the anode of the diode D3 serves as the input end of the diode D3, and the cathode of the diode D3 is connected to one end of the resistor R16, one end of the capacitor C4, and the gate of the MOS tube Q1; the drain of the MOS tube Q1 serves as the output end of the overheating relay cut-off circuit, and the other end of the resistor R16, the other end of the capacitor C4, and the source of the MOS tube Q1 are grounded.

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