A high-reliability multi-stage overheat protection circuit applied to airborne products

Abstract

The present invention belongs to the field of aviation electrical technology, and particularly relates to a highly reliable multi-stage overheat protection circuit applied to airborne products. It includes: 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, and overheat relay cut-off circuit. By collecting three temperature sensors, the first-level software overheat protection logic is executed, the second-level overheat protection executes the logic of the hardware overheat logic protection circuit, the third-level executes the reset protection overheat logic to quickly and directly cut off the overheat relay, and the fourth-level hardware fast short-circuit protection circuit executes the logic without the participation of the temperature values of the first three-level sensors, and can directly achieve microsecond-level fast overheat protection. It improves the safety and reliability of the system and ensures the safety of pilots.

Description

Technical Field

[0001] The present invention belongs to the technical field of aviation electrics, and particularly 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 aircraft electric heating control systems. The importance and reliability requirements of the electric heating control systems on the aircraft are getting higher and higher. When the aircraft heating system overheats and the temperature exceeds the defined temperature value, there is a risk of rupture and fire of airborne products in the high-altitude environment of the aircraft, which affects flight safety and is extremely harmful. Therefore, the overheat protection function of the aircraft electric heating system is one of the essential functions of airborne products. The traditional overheat protection of aircraft electric heating mainly relies on the product software control logic. The traditional overheat protection method of 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, reducing the product reliability and affecting flight safety. Summary of the Invention

[0003] Object of the Invention: To provide a high-reliability multi-stage overheat protection circuit applied to airborne products.

[0004] Technical Solution:

[0005] A high-reliability multi-stage overheat protection circuit for airborne products, comprising: three-way sensor temperature acquisition circuits, three-way high-low overheat hysteresis comparator circuits, three-way high-low temperature overheat judgment circuits, 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. Among them, the output terminals of the three-way sensor temperature acquisition circuits are respectively connected to the inverting input terminals of the corresponding high-low overheat hysteresis comparator circuits. The non-inverting input terminal of the high overheat hysteresis comparator in the high-low overheat hysteresis comparator circuit is connected to the high overheat threshold reference voltage, and the non-inverting input terminal of the low overheat hysteresis comparator in the high-low overheat hysteresis comparator circuit is connected to the low overheat threshold reference voltage. The two input terminals of the high-low temperature overheat judgment circuit are respectively connected to the output terminals of the corresponding low overheat hysteresis comparator and the output terminal of the high overheat hysteresis comparator. The output terminals of the three-way high-low temperature overheat judgment circuits and the BIT online injection command are respectively connected to the four input terminals of the overheat logic judgment circuit. The output terminal of the overheat logic judgment circuit is connected to the input terminal of the delay circuit. The output terminal of the delay circuit and the relay cut-off control signal command are respectively connected to the two input terminals of the software redundancy control circuit. The output terminal of the software redundancy control circuit and the reset RESET are respectively connected to the two input terminals of the reset protection circuit. The output terminal of the reset protection circuit and the short-circuit protection command are respectively connected to the two input terminals of the hardware fast short-circuit protection circuit. The output terminal of the hardware fast short-circuit protection circuit is connected to the input terminal of the overheat relay cut-off circuit. The output terminal of the overheat relay cut-off circuit is used to output an overheat relay turn-off command.

[0006] Further, the three-way sensor temperature acquisition circuits are the same and are all temperature sensors.

[0007] Further, the three-way high-low overheat hysteresis comparator circuits are the same. The first high-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. Among them, the non-inverting input terminal of comparator IC1A is connected to the voltage division 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, serving as the output of the low overheat hysteresis comparator. The inverting input terminal of comparator IC1A is connected to the anode of diode D1, the cathode of diode D2, one end of resistor R5, and one end of capacitor C2. The cathode of diode D1 is connected to the power supply. The other end of resistor R5 is connected to the output terminal of the sensor temperature acquisition circuit. The other ends of diode D2 and capacitor C2 are grounded. The non-inverting input terminal of comparator IC1B is connected to the voltage division of the high overheat bridge circuit and one end of resistor R9. The other end of resistor R9 is connected to the output terminal of comparator IC1B, serving as the output of the high overheat hysteresis comparator. The inverting input terminal 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] Further, the low overheat bridge voltage division circuit includes: resistor R1, resistor R2, and resistor R3. Among them, one end of resistor R1 is connected to one end of resistor R2 and one end of resistor R3; the other end of resistor R1 is connected to the power supply; the other ends of resistor R2 and resistor R3 are grounded.

[0009] Further, the high overheat bridge circuit includes: resistor R6, resistor R7, and resistor R8. Among them, 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 the power supply; the other ends of resistor R7 and resistor R8 are grounded.

[0010] Further, the three-way high and low temperature overheat judgment circuits have the same structure. The first-way high and low temperature overheat judgment circuit includes an exclusive-OR gate IC2 and a capacitor C1. Among them, the two input terminals of the exclusive-OR gate IC2 are respectively connected to the output terminals of the corresponding high overheat hysteresis comparator and the low overheat hysteresis comparator; one end of the capacitor C1 is connected to the power supply of the exclusive-OR gate IC2, and the other end of the capacitor C1 is connected to the ground of the exclusive-OR gate IC2.

[0011] Further, the overheat logic judgment circuit includes: a NOR gate IC4A and a NOR gate IC4B. Among them, the four input terminals of the NOR gate IC4A are respectively connected to the output terminals of the three-way high and low temperature overheat judgment circuits and the BIT online injection command; the output terminal of the NOR gate IC4A is connected to the input terminal of the NOR gate IC4B, and the output terminal of the NOR gate IC4B is used as the output of the overheat logic judgment circuit.

[0012] Further, the delay circuit includes resistor R14, resistor R17, diode D5, and capacitor C5. Among them, one end of resistor R14 is connected to the cathode of diode D5 as the input terminal of the delay circuit; the other end of resistor R14 is connected to one end of resistor R17 and one end of capacitor C5 as the output terminal of the delay circuit; the other end of resistor R17 is connected to the anode of diode D5; the other end of capacitor C5 is grounded.

[0013] Further, 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] Further, the overheat relay cut-off circuit includes: diode D3, resistor R16, capacitor C4, and MOS transistor Q1. Among them, the anode of diode D3 is used as the input terminal of diode D3, and the cathode of diode D3 is connected to one end of resistor R16, one end of capacitor C4, and the gate of MOS transistor Q1; the drain of MOS transistor Q1 is used as the output terminal of the overheat relay cut-off circuit, and the other ends of resistor R16, capacitor C4, and the source of MOS transistor Q1 are grounded.

[0015] Beneficial effects:

[0016] Aiming at the disadvantages of traditional overheat protection technologies, such as low reliability, single protection method, and long protection time, the present invention provides a high-reliability multi-stage overheat protection method with rich overheat protection margins and a 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 overheats, there is no power output from the product, improving the stability and safety of the electric heating system. It greatly improves the reliability of the aircraft's electric heating system and ensures flight safety. The entire circuit design, calculation process, and control logic method of the present invention meet the requirements of forward design for aviation airborne products. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic block diagram of a high-reliability multi-stage overheat protection circuit.

[0018] Figure 2 It is a circuit diagram of a high-reliability multi-stage overheat protection. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Such as Figure 1 , a high-reliability multi-stage overheat protection circuit applied to airborne products, including: 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.

[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 one of the sensors overheats or fails, the redundant design can reliably and effectively ensure the cut-off of the overheat relay. The BIT online injection command CPU_BIT can perform online self-check and periodic self-check on the circuit to monitor the circuit state, improving the reliability of the product. 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) participates in the control first. 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 redundant protection reliably ensures that there is no three-phase 115V AC PHA, 115V AC PHB, 115VAC PHC AC power output from the product, ensuring the safety of the aircraft's electric heating system.

[0021] First-level software overheat protection logic: The temperature sensor values collected are processed by the CPU processor. By executing the software overheat logic, when overheating is determined, an overheat relay shutdown command is output. The entire software overheat protection time cycle is about 2S. After 2S, if any software determines that the overheat exceeds 60°C, software overheat protection is executed, an 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 one of the three sensors overheats, the overheat protection logic can be directly executed through a highly reliable multi-level overheat protection circuit to cut off the overheat relay. The hardware overheat protection time is about 5S. After the highly reliable multi-level overheat protection circuit recognizes that any one sensor overheats for 5S, the overheat relay is cut off. The above hardware overheat protection logic does not need to go through the CPU processor and does not need to execute the software overheat protection logic to directly shut down the overheat relay. When the CPU processor fails or the software crashes, the hardware overheat protection logic can also complete the shutdown of the overheat relay to ensure that the product has no power output.

[0023] The third-level fault reset protection logic (RESET): When the product is fault reset, it improves the safety margin ability of the first two levels of overheat protection, increases the reliability of the product. At the same time, this 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 recognizes a short circuit, the hardware short-circuit protection logic quickly realizes the cut-off of the overheat relay in microseconds, effectively ensuring the safety of the system.

[0025] To make the purpose, content, and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] As Figure 1 The principle block diagram of the highly reliable multi-level overheat protection circuit, the control logic method is as follows:

[0027] ① The first-level software overheat protection logic method is as follows: The software overheat protection logic is to collect the temperature sensor values, process them through the CPU processor, execute the software overheat logic, and when overheating is determined, then execute the software overheat protection and output an overheat relay shutdown command. The entire software overheat protection time cycle is about 2S. After 2S, if any software determines that the overheat exceeds 60°C, software overheat protection is executed, and an overheat relay shutdown command is output to cut off the overheat relay.

[0028] ②The second-level hardware overheat protection logic is as follows: The voltage values of the three input sensors are collected and compared with the high and low overheat hysteresis comparators. When the temperature of the input sensor exceeds the threshold reference temperature of the hysteresis comparator, the hysteresis comparator outputs a low level. When the temperature of the input sensor is lower than the threshold reference temperature of the hysteresis comparator, the hysteresis comparator outputs a high level. The output results of the upper and lower comparators corresponding to 55°C and 100°C are fed to the XOR 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 XOR 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 XOR gate is the same. Taking the first-way high and low overheat logic analysis as an example, when the temperature T° of the input sensor ≤ 55°C, the output of the XOR gate is low level 0, and the product considers the sensor normal. When the temperature of the input sensor 60°C < T° ≤ 100°C, the output of the XOR gate is high level 1, and the product considers the sensor to be in low overheat. When the temperature of the input sensor 100°C < T°, the output of the XOR gate is low level 0, and the product considers the sensor to have a broken circuit, 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 XOR 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 the 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, which is 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 it non-overheated. The drain output of the NMOS is low level 0, the relay coil circuit is turned on, the AC relay contact is attracted, 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 it overheated. The drain output of the NMOS is high level 1, the relay coil circuit is not turned on, the AC relay contact is disconnected, 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 AND gate logic is executed to effectively cut off the overheat relay.

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

[0035] As described in Table 1, the overheat protection logic control table, the specific execution logic mainly includes 9 working conditions in Table 1. This electric heating overheat 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 working states of the product mainly include the above 9 working conditions. This electric heating overheat logic protection method has a high - reliability redundant design, rich logic, and comprehensive control methods.

[0040] For Figure 2The electric heating overheat protection method unfolds as follows. The signal collected by the input sensor temperature acquisition circuit participates 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 sent to the inverting input terminal of the hysteresis comparator after first-order filtering and diode protection. This middle part of the circuit consists of R5, C2, D1, D2, R15, C6, R26, C8, D7, D8. The reference level of the non-inverting input terminal of the low overheat hysteresis comparator for sensor 1 is obtained by the voltage division of the bridge composed of resistors R1, R2, and R3. The comparator is IC1A, and R4 is the feedback resistor of the hysteresis comparator. The calculated hysteresis range is 55°C ≤ T ≤ 60°C. The reference level of the non-inverting input terminal of the high overheat hysteresis comparator for sensor 1 is obtained by the voltage division of the bridge composed of resistors R6, R7, and R8. The comparator chip is IC1, and R9 is the feedback resistor of the hysteresis comparator. The calculated hysteresis range is 95°C ≤ T ≤ 100°C. Similarly, the principle of the corresponding hysteresis comparators for sensor 2 and sensor 3 is the same as that of sensor 1, and they are 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 exclusive-OR gates IC2, IC6, and IC8. The two input pins of the exclusive-OR gate are respectively connected to the outputs of the hysteresis comparators. The truth table of the logic chip 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. C1 - C3 are the decoupling capacitors of the chip. The overheat logic judgment circuit is composed of a logic chip 4-input 1-output NOR gate, IC4 chip. The output pins of the 3-way exclusive-OR gate chips are connected to the three input pins of chip IC4A. Another input pin of chip IC4A is connected to the online self-test injection test command output by the CPU processor for online and periodic BIT self-test. The output pin of IC4A is connected to the input terminal of IC4B. The output pin of IC4B goes to the delay circuit. The logic of the 4-input 1-output NOR gate is that the output is 0 when any one of the inputs is 1, and the output is 1 only when all 4 inputs are 0. When the output pin of IC4B outputs a high level, it is considered that the circuit is in an overheat state. The RC overheat delay circuit consists of R14 and C5, and the calculated charging delay is about 5S. When the output pin of IC4B outputs a low level, it is considered that the circuit is in a non-overheat state. The RC non-overheat delay circuit consists of D5, R17, and C5. The D5 diode acts as an anti-reverse function in the non-overheat state, and the calculated discharge delay is 0.Around 2S, the software redundancy control circuit is the NOR gate IC5 of the logic chip. One input terminal of the NOR gate IC5 is connected to the relay cut-off control signal command (software control) RELAY_OPEN_CMD output by the CPU processor, and the other input terminal is connected to the output of the delay circuit. The logic of the 2-input 1-output NOR gate is that the output is 0 when any one of the inputs is 1, and the output is 1 only when both inputs are 0. When the software output control command is at a low level (0), the output pin state of the NOR 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 terminal of the software redundancy control circuit IC5 is connected to the D3 anti-reverse diode, R16, and C4 to the gate control terminal of the Q1 NMOS. When the output terminal of IC5 outputs a high level, Q1 conducts and the drain output of Q1 is at a low level. The RELAY_CTL signal of the overheat relay cut-off circuit is at a low level. The drain output of the MOS transistor Q1 is connected to the overheat cut-off relay coil. When the drain of the MOS transistor Q1 is at a low level, the coil conducts and the relay contact closes, and the three-phase 115V AC power is normally output. On the contrary, when the circuit considers that it is in an overheat state and the output terminal of the NOR gate IC5 outputs a low level and the drain output of the MOS transistor Q1 is at a high level, the relay coil does not conduct and the overheat relay contact disconnects, and the three-phase 115V AC power output is disconnected, effectively ensuring that the product power is not output when the product is in an overheat state, and the product overheat protection function is effective. Two AND gates UA2 and UA3 are involved in the third-level reset protection logic and the hardware fast protection logic of the product.

[0041] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several changes and deformations can still be made, and these changes and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A high-reliability multi-stage overheat protection circuit for airborne products, characterized in that Including: 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. Among them, the output terminals of the three-way sensor temperature acquisition circuit are respectively connected to the reverse input terminals of the corresponding high and low overheat hysteresis comparator circuits. The non-inverting input terminal 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 non-inverting input terminal 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 terminals of the high and low temperature overheat judgment circuit are respectively connected to the output terminals of the corresponding low overheat hysteresis comparator and the output terminal of the high overheat hysteresis comparator; the output terminals of the three-way high and low temperature overheat judgment circuit and the BIT online injection command are respectively connected to the four input terminals of the overheat logic judgment circuit; the output terminal of the overheat logic judgment circuit is connected to the input terminal of the delay circuit, and the output terminal of the delay circuit and the relay cut-off control signal command are respectively connected to the two input terminals of the software redundancy control circuit; the output terminal of the software redundancy control circuit and the reset RESET are respectively connected to the two input terminals of the reset protection circuit; the output terminal of the reset protection circuit and the short-circuit protection command are respectively connected to the two input terminals of the hardware fast short-circuit protection circuit; the output terminal of the hardware fast short-circuit protection circuit is connected to the input terminal of the overheat relay cut-off circuit; the output terminal of the overheat relay cut-off circuit is used to output the overheat relay turn-off command. The first-level software overheat protection logic: The temperature sensor values collected are processed by the CPU processor. When overheat is determined, an overheat relay turn-off command is output. The entire software overheat protection time period is about 2S. After 2S, if any one of the software judges overheat and over-temperature by 60°C, the overheat relay is cut off. The second-level hardware overheat protection logic: When any one of the three sensors overheats, the overheat protection logic can be directly executed through the high-reliability multi-level overheat protection circuit to cut off the overheat relay. Among them, the hardware overheat protection time is about 5S. When the high-reliability multi-level overheat protection circuit recognizes that any one of the sensors overheats after 5S, the overheat relay is cut off. The third-level fault reset protection logic: When the product fails and resets, it improves the safety margin ability of the first two levels of overheat protection, and at the same time has the BIT online detection function to detect in real time whether the overheat protection function of the product is operating normally. The fourth-level hardware short-circuit protection logic: When the product recognizes a short circuit, the hardware short-circuit protection logic quickly realizes the overheat relay cut-off in microseconds, effectively ensuring the safety of the system.

2. The high-reliability multi-stage overheat protection circuit applied to airborne products according to claim 1, wherein The three-way sensor temperature acquisition circuits are the same and are all temperature sensors.

3. The high-reliability multi-stage overheat protection circuit applied to airborne products according to claim 1, wherein The three-way high and low overheat hysteresis comparator circuits are the same. The first three-way 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. Among them, The non-inverting input terminal of comparator IC1A is connected to the voltage division 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, serving as the output of the low-overheat hysteresis comparator; the inverting input terminal of comparator IC1A is connected to the anode of diode D1, the cathode of diode D2, one end of resistor R5, and one end of capacitor C2; the cathode of diode D1 is connected to the power supply; the other end of resistor R5 is connected to the output terminal of the sensor temperature acquisition circuit; the other ends of diode D2 and capacitor C2 are grounded. The non-inverting input terminal of comparator IC1B is connected to the voltage division of the high-overheat bridge circuit and one end of resistor R9; the other end of resistor R9 is connected to the output terminal of comparator IC1B, serving as the output of the high-overheat hysteresis comparator; the inverting input terminal 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.

4. The high-reliability multi-stage overheat protection circuit applied to airborne products according to claim 1, characterized in that, The low-overheat bridge voltage division circuit includes resistors R1, R2, and R3. Among them, one end of resistor R1 is connected to one end of resistor R2 and one end of resistor R3; the other end of resistor R1 is connected to the power supply; the other ends of resistor R2 and resistor R3 are grounded.

5. The high-reliability multi-stage overheat protection circuit applied to airborne products according to claim 1, wherein The high-overheat bridge circuit includes resistors R6, R7, and R8. Among them, 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 the power supply; the other ends of resistor R7 and resistor R8 are grounded.

6. The high-reliability multi-stage overheat protection circuit applied to airborne products according to claim 1, characterized in that, The three-way high and low temperature overheat judgment circuits have the same structure. The first high and low temperature overheat judgment circuit includes exclusive-OR gate IC2 and capacitor C1. Among them, the two input terminals of exclusive-OR gate IC2 are respectively connected to the output terminals of the corresponding high-overheat hysteresis comparator and the low-overheat hysteresis comparator; one end of capacitor C1 is connected to the power supply of exclusive-OR gate IC2, and the other end of capacitor C1 is connected to the ground of exclusive-OR gate IC2.

7. The high-reliability multi-stage overheat protection circuit applied to airborne products according to claim 1, characterized in that, The overheat logic judgment circuit includes NOR gates IC4A and IC4B. Among them, the four input terminals of NOR gate IC4A are respectively connected to the output terminals of the three-way high and low temperature overheat judgment circuits and the BIT online injection command; the output terminal of NOR gate IC4A is connected to the input terminal of NOR gate IC4B, and the output terminal of NOR gate IC4B serves as the output of the overheat logic judgment circuit.

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

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

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

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