Relay coil parallel diode welding reliability detection circuit

Abstract

This invention discloses a welding reliability testing circuit for a relay coil connected in parallel with a bidirectional diode. The circuit includes the coil of the relay under test and a bidirectional diode connected in parallel across its two ends. The bidirectional diode is welded and fixed to the coil pins. A key feature is the inclusion of a back EMF detection and indication module, comprising a light-emitting diode (LED), a Zener diode, an optocoupler, and an NPN power switching transistor. The anode of the LED is connected to the second terminal of the coil, the cathode of the LED is connected to the first pin of the optocoupler, the second pin of the optocoupler is connected to the cathode of the Zener diode, and the anode of the Zener diode is connected to the first terminal of the coil. The fourth pin of the optocoupler is connected to the base of the NPN power switching transistor, and the fifth pin of the optocoupler and the collector of the NPN power switching transistor are connected to the positive terminal of a DC power supply. The emitter of the NPN power switching transistor is the pulse signal output terminal. The advantage is that it utilizes the high-voltage back EMF generated by the coil's self-induction when de-energized as the detection energy source, enabling intuitive and reliable welding quality judgment.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic relay testing technology, and in particular to a welding reliability testing circuit for a relay coil connected in parallel with a bidirectional diode. Background Technology

[0002] A relay is an automatic switching element with IN / OUT isolation function, widely used in remote control, telemetry, communication, automatic control, mechatronics, and power electronic equipment, and is one of the most important basic control components. Because the relay coil is an inductive load, when the coil is de-energized, the energy stored in the coil generates a reverse electromotive force pulse, the peak value of which can reach tens of times the rated voltage, easily damaging the IC module or transistor driving the relay coil. To solve this problem, a diode is usually connected in parallel across the coil to form a discharge circuit, thereby suppressing overvoltage.

[0003] However, connecting a regular diode in parallel across the coil can affect the relay's pull-in and release times. Therefore, a solution using a bidirectional diode (such as a transient voltage suppressor (TVS) in parallel can be adopted. Bidirectional diodes have symmetrical breakdown characteristics in both forward and reverse directions, and connecting them in parallel across the coil does not affect the relay's operating time, making it a superior overvoltage suppression solution.

[0004] In actual production, bidirectional diodes are connected in parallel across the relay coil via soldering. The quality of the soldering directly determines whether the bidirectional diode can effectively connect to the circuit and perform its protective function. If the soldering is good, when the coil is de-energized and generates a back EMF, the bidirectional diode breaks down and clamps the voltage, forming a discharge circuit. If the soldering is poor (such as cold solder joints, missing solder joints, or solder joint detachment), the bidirectional diode is actually in an open circuit state and cannot connect to the circuit. The back EMF pulse generated by the coil will have no way to discharge and will directly impact the driving component, causing damage.

[0005] Currently, there is a lack of effective dedicated testing methods for the soldering reliability of bidirectional diodes connected in parallel with relay coils. Conventional multimeter or low-voltage testing methods cannot determine whether the bidirectional diode is truly and reliably soldered into the circuit, because the bidirectional diode is in a cutoff state under low voltage, making its electrical behavior indistinguishable from that of an open circuit. Furthermore, visual inspection or contact testing methods often require damaging the relay casing or exposing the internal structure, making online testing in a fully enclosed state impossible. This results in only sampling inspection being possible in actual production, making it impossible to perform full inspection on every relay. Ultimately, this poses a risk that defective soldered products may enter the market, causing damage to the drive components. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a detection circuit that can quickly and accurately detect the reliability of the parallel bidirectional diode welding of the relay coil in a fully enclosed state of the relay housing, so as to solve the problem that the existing technology can only use sampling inspection due to the lack of dedicated detection methods, and there is a risk that defective welding products will enter the market and cause the driving components to break down and be damaged.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: A circuit for testing the welding reliability of a relay coil with a bidirectional diode connected in parallel includes the coil of the relay under test and a bidirectional diode connected in parallel across its two ends. The bidirectional diode is soldered and fixed to the coil pins. The circuit also includes: The power supply control unit is connected to both ends of the coil and is used to apply a detection pulse to the coil to detect when it is powered on and then powered off. The back EMF detection and indication module, connected in parallel across the coil, includes a light-emitting diode, a Zener diode, an optocoupler, and an NPN power switching transistor. The anode of the LED is connected to the second end of the coil, the cathode of the LED is connected to the first pin of the optocoupler, the second pin of the optocoupler is connected to the cathode of the Zener diode, and the anode of the Zener diode is connected to the first end of the coil. The fourth pin of the optocoupler is connected to the base of the NPN power switching transistor, the fifth pin of the optocoupler and the collector of the NPN power switching transistor are connected to the positive terminal of the DC power supply, and the emitter of the NPN power switching transistor is the pulse signal output terminal. The breakdown voltage of the Zener diode is set to be higher than the clamping voltage of the bidirectional diode and lower than the peak value of the reverse pulse voltage generated when the coil is de-energized. When the coil is energized first and then de-energized, a reverse pulse voltage is generated: If the welding is good, the generated reverse pulse voltage breaks down the bidirectional diode to form a discharge circuit. The voltage is clamped to a level lower than the breakdown voltage of the Zener diode. The back EMF detection and indication module does not conduct, the LED does not light up, and the optocoupler has no output. If the soldering is faulty, the generated reverse pulse voltage exceeds the breakdown voltage of the Zener diode, causing the back EMF detection and indication module to conduct, and the LED to light up to indicate the soldering fault. At the same time, the emitter of the NPN power switching transistor outputs a pulse signal that indicates the soldering fault.

[0008] The power supply control unit includes a power supply and a pulse switch; the positive terminal of the power supply is connected to the first end of the coil, the second end of the coil is connected to one end of the pulse switch, and the other end of the pulse switch is connected to the negative terminal of the power supply; the control terminal of the pulse switch is connected to a controller, which controls its on / off state to apply a detection pulse that indicates energization followed by de-energization to the coil.

[0009] It also includes a signal processing module, which is used to receive the pulse signal and process the pulse signal to drive the subsequent actuator.

[0010] The signal processing module includes a pulse transformer, an operational amplifier, a clamping diode, a driver transistor, a first resistor, a second resistor, a freewheeling diode, and an output relay. The pulse transformer is provided with a primary winding and a secondary winding; one end of the primary winding is connected to the emitter of the NPN power switching transistor, and the other end of the primary winding is connected to the system common ground; the secondary winding is a signal output terminal, one end of the secondary winding is connected to the inverting input terminal of the operational amplifier, and the other end of the secondary winding is connected to the system common ground, for isolating and transmitting the pulse signal to the operational amplifier. The negative power supply pin of the operational amplifier is connected to a -12V DC power supply, and the positive power supply pin of the operational amplifier is connected to a +12V DC power supply; the non-inverting input terminal of the operational amplifier is connected to one end of a first resistor, and the other end of the first resistor is connected to the system common ground; the second resistor is connected between the signal output terminal and the non-inverting input terminal of the operational amplifier to form a positive feedback loop, so that the operational amplifier constitutes a Schmitt comparator. The signal output terminal of the operational amplifier is connected to one end of the clamping diode and the base of the driving transistor, and the other end of the clamping diode is connected to the system common ground. The emitter of the driving transistor is connected to a +12V DC power supply, and the collector of the driving transistor is connected to one end of the coil of the output relay; the other end of the coil of the output relay is connected to the system common ground; the freewheeling diode is connected in reverse parallel across the coil of the output relay, the anode of the freewheeling diode is connected to the system common ground, and the cathode of the freewheeling diode is connected to the collector of the driving transistor. The exposed contacts of the output relay serve as the output port for the final judgment result, and are used to send a welding failure signal to the controller.

[0011] The controller is a programmable logic controller or a microcontroller.

[0012] The pulse switch is either a relay switch or a transistor switch.

[0013] Compared with the prior art, the advantages of the present invention are as follows: (1) By connecting a detection branch consisting of a light-emitting diode and a Zener diode in series in parallel across the two ends of the coil, the high voltage back electromotive force generated by the coil when it is de-energized is used as the detection energy source, thus realizing the accurate judgment of the welding status and filling the gap in this technical field. (2) The voltage difference between the breakdown characteristics of the Zener diode and the clamping characteristics of the bidirectional diode is used for judgment: when the soldering is good, the back EMF is clamped to a low voltage by the bidirectional diode, the detection branch is not conducting, and the LED does not light up; when the soldering is poor, the back EMF exceeds the breakdown voltage of the Zener diode, the detection branch is conducting, and the LED lights up; the judgment logic is clear, the result is intuitive and visible, and the detection result can be obtained without complicated signal processing or manual interpretation. (3) The detection process is completed entirely by electrical means. The detection pulse can be applied and the response signal can be obtained simply by contacting the exposed coil pin of the relay with the test spring. There is no need to remove the relay housing or expose the internal structure. It does not rely on visual inspection or manual contact. Rapid detection can be achieved in the fully enclosed state of the relay. It is suitable for online full inspection of automated production lines and overcomes the defect that the existing technology can only perform sampling inspection. (4) The introduction of optocouplers realizes electrical isolation between the high-voltage side of the detection branch and the low-voltage side of the subsequent signal processing circuit, preventing the high-voltage back EMF generated by the coil de-energization from damaging the subsequent low-voltage devices; at the same time, the optocoupler converts the conduction state of the detection branch into a standard electrical pulse signal, which is convenient for subsequent automated equipment (such as PLC) to identify and process, realizes the electrical signal output of the detection results, and provides a signal basis for automated sorting. (5) The entire detection circuit has a small number of components, a simple structure, and is easy to integrate into existing relay testing equipment or automated production lines. It has low manufacturing costs and is easy to promote and apply. At the same time, the NPN power switching transistor amplifies the weak signal output by the optocoupler and outputs a pulse signal with sufficient driving capability to ensure that the subsequent circuit can respond reliably. (6) Through this detection circuit, the welding reliability of each relay can be fully inspected, the defective products can be accurately identified and removed, avoiding the risk of drive component breakdown due to poor welding of bidirectional diodes, and improving the product qualification rate and overall reliability of relays. Attached Figure Description

[0014] Figure 1 This is the circuit schematic diagram of the present invention. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0016] like Figure 1 As shown, the reliability testing circuit for a relay coil with a parallel bidirectional diode includes a coil T1 of the relay under test and a bidirectional diode D3 connected in parallel across its two ends. The bidirectional diode D3 is soldered and fixed to the pin of the coil T1. It also includes: The power supply control unit is connected to both ends of the coil T1 and is used to apply a detection pulse to the coil T1 to detect when the power is turned off after being turned on. The back EMF detection and indication module is connected in parallel across the two ends of the coil T1 and includes a light-emitting diode LED2, a Zener diode D5, an optocoupler U2, and an NPN power switching transistor Q2. The anode of LED2 is connected to the second end of coil T1, the cathode of LED2 is connected to the first pin of optocoupler U2, the second pin of optocoupler U2 is connected to the cathode of Zener diode D5, and the anode of Zener diode D5 is connected to the first end of coil T1. The fourth pin of optocoupler U2 is connected to the base of NPN power switching transistor Q2, the fifth pin of optocoupler U2 and the collector of NPN power switching transistor Q2 are connected to the positive terminal of DC power supply, and the emitter of NPN power switching transistor Q2 is the pulse signal output terminal. The breakdown voltage of Zener diode D5 is set to be higher than the clamping voltage of bidirectional diode D3 and lower than the peak value of the reverse pulse voltage generated when coil T1 is de-energized. When coil T1 is energized first and then de-energized, a reverse pulse voltage is generated: If the welding is good, the generated reverse pulse voltage breaks down the bidirectional diode D3 to form a discharge circuit. The voltage is clamped to a level lower than the breakdown voltage of the Zener diode D5. The back EMF detection and indication module does not conduct, the LED2 does not light up, and the optocoupler U2 has no output. If the soldering is faulty, the resulting reverse pulse voltage exceeds the breakdown voltage of the Zener diode D5, causing the back EMF detection and indication module to conduct. The LED2 light-emitting diode illuminates to indicate the soldering fault, and at the same time, the emitter of the NPN power switching transistor Q2 outputs a pulse signal that indicates the soldering fault.

[0017] In this specific embodiment, the power supply control unit includes a power supply V1 and a pulse switch J1. The positive terminal of the power supply V1 is connected to the first end of the coil T1, the second end of the coil T1 is connected to one end of the pulse switch J1, and the other end of the pulse switch J1 is connected to the negative terminal of the power supply V1. The control terminal of the pulse switch J1 is connected to a controller (not shown in the figure), which controls its on / off state to apply a detection pulse that is energized and then de-energized to the coil T1. The pulse switch J1 controlled by the controller achieves automated on / off control, eliminating the need for manual operation, and providing fast detection speed and good repeatability. The connection relationship of the power supply module is matched with the polarity of the light-emitting diode LED2 and the Zener diode D5 in the subsequent detection branch to ensure that the back electromotive force is correctly applied to the detection branch.

[0018] In this specific embodiment, taking an electromagnetic relay with a coil excitation voltage of 12V as an example, the power supply V1 uses a 12V DC power supply, the bidirectional diode D3 is a P6KE33CA (clamping voltage approximately 34V), and the Zener diode D5 is an IN4756A (regulated voltage 47V). When the coil is de-energized, the peak value of the generated back EMF is approximately 120V. By properly matching the above parameters, accurate detection of welding reliability can be achieved.

[0019] However, the detection circuit of this invention is not limited to a 12V relay. For electromagnetic relays with a coil excitation voltage of 24V, the power supply V1 can be adjusted to 24V accordingly, and a Zener diode D5 with a higher breakdown voltage (such as 56V or 68V) can be selected. Simultaneously, it should be ensured that the breakdown voltage of Zener diode D5 is higher than the clamping voltage of bidirectional diode D3 and lower than the peak value of the back EMF. The following table provides recommended configurations for different coil excitation voltages:

[0020] It should be noted that, apart from the power supply voltage V1 and the Zener diode D5 model needing to be configured according to different excitation voltages, all other components in the detection circuit (including LED2, optocoupler U2, NPN power switching transistor Q2, pulse transformer T2, operational amplifier U3, driver transistor Q1, output relay K1, etc.) do not need to be changed. The solution adopted in this invention has good versatility and scalability. By only replacing the power supply and the Zener diode, it can be adapted to relay detection of different voltage levels from 5V to 48V, while the other components remain unchanged, greatly reducing the adaptation cost.

[0021] It also includes a signal processing module, which receives and processes pulse signals to drive subsequent actuators. Employing a modular design approach, the isolation, shaping, amplification, and output functions of the pulse signal are integrated into a single signal processing module, facilitating circuit expansion and portability. It can output standardized switching signals for interface with industrial controllers.

[0022] In this specific embodiment, the signal processing module includes a pulse transformer T2, an operational amplifier U3, a clamping diode D4, a driver transistor Q1 (PNP type), a first resistor R2, a second resistor R3, a freewheeling diode D1, and an output relay K1; The pulse transformer T2 is equipped with a primary winding and a secondary winding; one end of the primary winding is connected to the emitter of the NPN power switching transistor Q2, and the other end of the primary winding is connected to the system common ground; the secondary winding is the signal output terminal, one end of the secondary winding is connected to the inverting input terminal of the operational amplifier U3, and the other end of the secondary winding is connected to the system common ground, which is used to isolate and transmit the pulse signal to the operational amplifier U3. The negative power supply pin (pin 4) of operational amplifier U3 is connected to a -12V DC power supply, and the positive power supply pin (pin 7) of operational amplifier U3 is connected to a +12V DC power supply. The non-inverting input (pin 3) of operational amplifier U3 is connected to one end of the first resistor R2, and the other end of the first resistor R2 is connected to the system ground. The second resistor R3 is connected between the signal output (pin 6) and the non-inverting input (pin 3) of operational amplifier U3 to form a positive feedback loop, so that operational amplifier U3 can function as a Schmitt comparator. The signal output terminal (pin 6) of operational amplifier U3 is connected to one end of clamping diode D4 and the base of driving transistor Q1, and the other end of clamping diode D4 is connected to the system common ground; The emitter of the driver transistor Q1 is connected to the positive terminal of the 12V DC power supply, and the collector of the driver transistor Q1 is connected to one end of the coil of the output relay K1; the other end of the coil of the output relay K1 is connected to the system common ground; the freewheeling diode D1 is connected in reverse parallel across the coil of the output relay K1, the anode of the freewheeling diode D1 is connected to the system common ground, and the cathode of the freewheeling diode D1 is connected to the collector of the driver transistor Q1. The exposed contacts of output relay K1 serve as the output port for the final judgment result, used to send a welding failure signal to the controller. Pulse transformer T2 provides further electrical isolation of the signal, enhancing anti-interference capability; operational amplifier U3 forms a Schmitt comparator with hysteresis characteristics, capable of removing edge jitter and noise glitches from the pulse signal; clamping diode D4 protects the base of driver transistor Q1 from overvoltage damage; freewheeling diode D1 absorbs the reverse electromotive force when the output relay coil is de-energized, protecting driver transistor Q1; the exposed contacts of output relay K1 output a passive switching signal, which can be easily interfaced with industrial controllers such as PLCs and microcontrollers.

[0023] In this specific embodiment, the controller is a programmable logic controller (PLC) or a microcontroller. PLCs have strong anti-interference capabilities and high reliability, making them suitable for industrial automated production lines; microcontrollers are low-cost and small in size, making them suitable for embedded testing equipment. The controller not only controls the on / off timing of pulse switches but also receives contact signals from output relays for logical judgment and outputs sorting instructions.

[0024] In this specific embodiment, the pulse switch J1 is either a relay switch or a transistor switch. Relay switches provide complete electrical isolation and have extremely low on-resistance; transistor switches offer fast switching speeds, no mechanical contacts, and long lifespans. Users can flexibly choose based on factors such as actual detection frequency, coil current, and cost budget.

[0025] In this specific embodiment, the optocoupler U2 is a 4N35, the pulse transformer T2 is an NLT_PQ_4_10, the operational amplifier U3 is a 741, the clamping diode D4 is a 15CLQ100, the driver transistor Q1 is a 2N1132A, the freewheeling diode D1 is a 1N4007, and the output relay K1 is an NT73AS5DC12V.

[0026] The working principle of the detection circuit in this embodiment is as follows: First, the controller controls the pulse switch J1 to close, and the power supply V1 energizes the coil T1, which then establishes a magnetic field. Then, the controller controls the pulse switch J1 to open, the coil T1 is de-energized, the magnetic field in the coil disappears quickly, and according to the law of electromagnetic induction, the coil T1 generates a reverse pulse voltage with a direction opposite to the original voltage and an amplitude of about 120V (taking a 12V relay as an example). The reverse pulse voltage is applied to two branches connected in parallel across the two ends of coil T1: one is a protection branch consisting of bidirectional diode D3, and the other is a back EMF detection and indication module consisting of LED2, optocoupler U2, and Zener diode D5 connected in series.

[0027] Since the breakdown voltage of Zener diode D5 (47V) is higher than the clamping voltage of bidirectional diode D3 (34V), therefore: If the bidirectional diode D3 is soldered well, the reverse pulse voltage will preferentially break down the bidirectional diode D3 to form a discharge circuit. The voltage will be clamped at around 34V. The voltage across the detection branch is insufficient to break down the Zener diode D5, so the detection branch remains cut off. The LED2 will not light up, the optocoupler U2 will not conduct, and the NPN power switch transistor Q2 will have no output. If the bidirectional diode D3 is poorly soldered (open circuit), the reverse pulse voltage cannot be discharged through the bidirectional diode D3 and is entirely applied to the detection branch. When the voltage exceeds 47V, the Zener diode D5 breaks down, and the detection branch conducts. The current path is: second terminal of coil T1 → LED2 (positive → negative) → pin 1 of optocoupler U2 → internal LED of optocoupler U2 → pin 2 of optocoupler U2 → Zener diode D5 (cathode → anode) → first terminal of coil T1. This current causes LED2 to light up (indicating poor soldering) and simultaneously causes the internal LED of optocoupler U2 to light up, thus conducting on the output side of optocoupler U2.

[0028] After the output side of optocoupler U2 is turned on, the +12V DC power supply flows into the base of NPN power switching transistor Q2 through the fifth pin of optocoupler U2, the phototransistor inside optocoupler U2, and the fourth pin of optocoupler U2, turning on NPN power switching transistor Q2 and outputting a pulse signal from the emitter of NPN power switching transistor Q2.

[0029] The pulse signal is fed into the primary winding of pulse transformer T2, and after electromagnetic coupling isolation by pulse transformer T2, it is output from the secondary winding and sent to the inverting input terminal of operational amplifier U3. Operational amplifier U3, together with the first resistor R2 and the second resistor R3, forms a Schmitt comparator: the first resistor R2 biases the non-inverting input terminal close to the system common ground, and the second resistor R3 is connected between the output terminal and the non-inverting input terminal to form positive feedback, creating a hysteresis characteristic. When the amplitude of the input pulse signal exceeds the upper threshold of the Schmitt comparator, operational amplifier U3 outputs a low level (close to 0V); when the pulse signal disappears, the output of operational amplifier U3 returns to a high level.

[0030] While the operational amplifier U3 outputs a low-level signal: it is fed back to the non-inverting input through the second resistor R3 to maintain the comparator state; it is sent to the clamping diode D4, which clamps the voltage to a safe range; and it is sent to the base of the driver transistor Q1, turning on the driver transistor Q1.

[0031] After the driving transistor Q1 is turned on, the +12V DC power supply forms a current loop through the emitter-collector of the driving transistor Q1, the coil of the output relay K1, and the system common ground. The coil of the output relay K1 is energized, the output relay K1 is energized, and the state of its exposed contacts changes (normally open contacts close or normally closed contacts open), sending a welding failure signal to the controller.

[0032] After receiving a welding failure signal, the controller confirms the product as a defective product through logical judgment, and then outputs control commands to the subsequent sorting execution mechanism (such as pneumatic solenoid valve, robot, etc.) to automatically transfer the defective product to the defective product channel.

[0033] This completes a full testing cycle.

Claims

1. A reliability testing circuit for a relay coil with a bidirectional diode connected in parallel, comprising a coil of the relay under test and a bidirectional diode connected in parallel across its two ends, the bidirectional diode being soldered and fixed to the coil pins, characterized in that, Also includes: The power supply control unit is connected to both ends of the coil and is used to apply a detection pulse to the coil to detect when it is powered on and then powered off. The back EMF detection and indication module, connected in parallel across the coil, includes a light-emitting diode, a Zener diode, an optocoupler, and an NPN power switching transistor. The anode of the LED is connected to the second end of the coil, the cathode of the LED is connected to the first pin of the optocoupler, the second pin of the optocoupler is connected to the cathode of the Zener diode, and the anode of the Zener diode is connected to the first end of the coil. The fourth pin of the optocoupler is connected to the base of the NPN power switching transistor, the fifth pin of the optocoupler and the collector of the NPN power switching transistor are connected to the positive terminal of the DC power supply, and the emitter of the NPN power switching transistor is the pulse signal output terminal. The breakdown voltage of the Zener diode is set to be higher than the clamping voltage of the bidirectional diode and lower than the peak value of the reverse pulse voltage generated when the coil is de-energized. When the coil is energized first and then de-energized, a reverse pulse voltage is generated: If the welding is good, the generated reverse pulse voltage breaks down the bidirectional diode to form a discharge circuit. The voltage is clamped to a level lower than the breakdown voltage of the Zener diode. The back EMF detection and indication module does not conduct, the LED does not light up, and the optocoupler has no output. If the soldering is faulty, the generated reverse pulse voltage exceeds the breakdown voltage of the Zener diode, causing the back EMF detection and indication module to conduct, and the LED to light up to indicate the soldering fault. At the same time, the emitter of the NPN power switching transistor outputs a pulse signal that indicates the soldering fault.

2. The welding reliability detection circuit for a relay coil connected in parallel with a bidirectional diode as described in claim 1, characterized in that... The power supply control unit includes a power supply and a pulse switch; the positive terminal of the power supply is connected to the first end of the coil, the second end of the coil is connected to one end of the pulse switch, and the other end of the pulse switch is connected to the negative terminal of the power supply; the control terminal of the pulse switch is connected to a controller, which controls its on / off state to apply a detection pulse that indicates energization followed by de-energization to the coil.

3. The welding reliability detection circuit for a relay coil connected in parallel with a bidirectional diode as described in claim 1, characterized in that... It also includes a signal processing module, which is used to receive the pulse signal and process the pulse signal to drive the subsequent actuator.

4. The welding reliability detection circuit of the relay coil connected in parallel with a bidirectional diode as described in claim 3, characterized in that... The signal processing module includes a pulse transformer, an operational amplifier, a clamping diode, a driver transistor, a first resistor, a second resistor, a freewheeling diode, and an output relay. The pulse transformer is provided with a primary winding and a secondary winding; one end of the primary winding is connected to the emitter of the NPN power switching transistor, and the other end of the primary winding is connected to the system common ground; the secondary winding is a signal output terminal, one end of the secondary winding is connected to the inverting input terminal of the operational amplifier, and the other end of the secondary winding is connected to the system common ground, for isolating and transmitting the pulse signal to the operational amplifier. The negative power supply pin of the operational amplifier is connected to a -12V DC power supply, and the positive power supply pin of the operational amplifier is connected to a +12V DC power supply; the non-inverting input terminal of the operational amplifier is connected to one end of a first resistor, and the other end of the first resistor is connected to the system common ground; the second resistor is connected between the signal output terminal and the non-inverting input terminal of the operational amplifier to form a positive feedback loop, so that the operational amplifier constitutes a Schmitt comparator. The signal output terminal of the operational amplifier is connected to one end of the clamping diode and the base of the driving transistor, and the other end of the clamping diode is connected to the system common ground. The emitter of the driving transistor is connected to a +12V DC power supply, and the collector of the driving transistor is connected to one end of the coil of the output relay; the other end of the coil of the output relay is connected to the system common ground; the freewheeling diode is connected in reverse parallel across the coil of the output relay, the anode of the freewheeling diode is connected to the system common ground, and the cathode of the freewheeling diode is connected to the collector of the driving transistor. The exposed contacts of the output relay serve as the output port for the final judgment result, and are used to send a welding failure signal to the controller.

5. The welding reliability detection circuit for a relay coil connected in parallel with a bidirectional diode as described in claim 2, characterized in that... The controller is a programmable logic controller or a microcontroller.

6. The welding reliability detection circuit of the relay coil connected in parallel with a bidirectional diode as described in claim 2, characterized in that... The pulse switch is either a relay switch or a transistor switch.

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