Low-low-load voltage circuit and lithium battery welding machine

Abstract

The invention relates to the technical field of welding, and provides a low-load voltage circuit and a lithium battery welding machine. The circuit comprises a main control module, a voltage detection unit, a switching circuit, a pulse modulation unit and a current sampling feedback unit. The voltage detection unit monitors the end voltage of a welding gun of a welding machine in real time, the switching circuit limits the output voltage to be smaller than a safety threshold value of 36 V in a no-load mode, and a built-in bidirectional thyristor achieves isolation of a high-voltage loop and a low-voltage loop. The pulse modulation unit adjusts the on-off frequency of a main power loop, and the current sampling feedback unit dynamically adjusts the pulse duty ratio so as to accurately control the welding current. The lithium battery welding machine integrates the circuit and is provided with a welding gun assembly, a main transformer and a power supply module, the electric shock risk is effectively reduced, and the welding quality and efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of welding, and in particular to a low no-load voltage circuit and a lithium battery welding machine. Background Art

[0002] During welding operations, traditional welding machines may maintain high voltages even when unloaded, increasing the risk of electric shock and potentially wasting energy. This is particularly true for delicate operations like lithium battery welding, which place even higher demands on voltage control accuracy and safety. While existing technologies offer some voltage control methods, they still struggle with precisely limiting the no-load voltage, safely isolating high and low voltage circuits, and dynamically regulating the current during welding. These limitations make them difficult to meet the stringent safety and efficiency requirements of modern welding operations. Summary of the Invention

[0003] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a low no-load voltage circuit and a lithium battery welding machine to solve the problems of excessively high no-load voltage, insufficient safety isolation and inaccurate current control in the prior art.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a low no-load voltage circuit, comprising a main control module, a voltage detection unit, a switching circuit, a pulse modulation unit, and a current sampling feedback unit; The main control module is electrically connected to the voltage detection unit, the switching circuit, the pulse modulation unit and the current sampling feedback unit respectively; The voltage detection unit monitors the voltage at the welding gun end of the welding machine in real time and generates a detection signal which is transmitted to the main control module; The voltage detection unit includes a voltage-dividing resistor network and a filter capacitor to detect low-noise transmission of the signal; The switching circuit includes a no-load mode and a welding mode. The main control module controls the switching circuit based on the detection signal to limit the output voltage to a safety threshold of less than 36V in the no-load mode; The switching circuit has a built-in bidirectional thyristor and a drive isolation circuit to achieve safe isolation of high and low voltage circuits; The pulse modulation unit receives the driving instruction of the main control module and generates a high-frequency pulse signal to adjust the on-off frequency of the main power circuit; The pulse modulation unit integrates a PWM generator and a totem pole amplifier circuit to drive the fast response of the power switch tube; The current sampling feedback unit collects the output current in real time and dynamically adjusts the pulse duty cycle.

[0005] Preferably, in a possible implementation manner of the first aspect, the voltage detection unit includes a voltage-dividing resistor network connected in series and a filter capacitor connected in parallel; The first end of the voltage divider resistor network is connected to the welding gun output terminal, and the second end is grounded; The two ends of the filter capacitor are connected between the middle node of the voltage divider resistor network and the ground, forming a detection signal output path that attenuates high-frequency interference; The total resistance of the voltage divider resistor network is configured to proportionally reduce the voltage at the welding gun terminal to a recognizable range of the main control module.

[0006] Preferably, in a possible implementation of the first aspect, the output end of the voltage detection unit is connected to the main control module through an isolation optocoupler, the primary side of the isolation optocoupler is connected in series with a current limiting resistor and receives the detection signal after voltage division, and the secondary side outputs the isolated analog voltage signal to the ADC port of the main control module, thereby realizing electrical isolation between the high-voltage detection circuit and the low-voltage control circuit.

[0007] Preferably, in a possible implementation manner of the first aspect, the switching circuit includes a bidirectional thyristor and a drive isolation circuit; The two main terminals of the bidirectional thyristor are connected in series in the secondary winding loop of the welding machine's main transformer. The drive isolation circuit receives the mode switching instruction from the main control module and applies a trigger pulse to the gate of the bidirectional thyristor. When in no-load mode, the bidirectional thyristor is turned off to form a high-impedance loop through the secondary winding through the current-limiting resistor. When in welding mode, the bidirectional thyristor is turned on to bypass the current-limiting resistor.

[0008] Preferably, in a possible implementation manner of the first aspect, the pulse modulation unit includes a PWM signal generator and a totem pole driving circuit; The PWM signal generator generates a reference square wave signal according to the duty cycle instruction of the main control module. The totem pole drive circuit increases the voltage amplitude of the reference square wave signal to the driving requirement level of the power switch tube and transmits it to the gate of the power switch tube through the magnetic isolation device.

[0009] Preferably, in a possible implementation manner of the first aspect, the main power circuit includes an energy storage inductor and a freewheeling diode connected in series, one end of the energy storage inductor is connected to the drain of the power switch tube, and the other end is connected to the output terminal of the welding gun, the anode of the freewheeling diode is grounded, and the cathode is connected to the connection node between the energy storage inductor and the power switch tube, so as to maintain the continuity of the inductor current when the power switch tube is turned off.

[0010] Preferably, in a possible implementation manner of the first aspect, the current sampling and feedback unit includes a Hall current sensor and a signal conditioning circuit; The Hall current sensor is mounted on the welding machine output bus and generates a voltage signal proportional to the instantaneous current; The signal conditioning circuit amplifies, filters and offset-adjusts the voltage signal and then inputs it into the feedback port of the main control module to form a closed-loop control circuit.

[0011] Preferably, in a possible implementation of the first aspect, the main control module has a built-in no-load judgment algorithm, and when the detection signal is continuously lower than a preset threshold for more than a set time, it is determined to be a no-load state and outputs a mode switching instruction to the switching circuit.

[0012] Preferably, in a possible implementation of the first aspect, the main control module is further connected to a soft start module, which is composed of an adjustable resistance network and a MOS tube. When the no-load mode is switched to the welding mode, the equivalent resistance of the current limiting resistor is gradually reduced, so that the output voltage of the secondary winding of the main transformer rises to the operating voltage in a ramp form.

[0013] In a second aspect, the present invention provides a lithium battery welding machine, comprising the low no-load voltage circuit, welding gun assembly, main transformer and power supply module described in the first aspect; The main control module of the low no-load voltage circuit is connected to the rectifier output end of the power supply module, the primary winding of the main transformer is connected to the power supply module through the power switch tube, and the secondary winding is connected to the welding gun assembly through the switching circuit; The welding gun assembly includes an electrode clamping mechanism and a cooling water channel. The two ends of the electrode clamping mechanism are respectively connected to the output positive and negative poles of the low no-load voltage circuit. The cooling water channel is arranged around the electrode to reduce the temperature rise during welding. The power supply module is a high-frequency inverter power supply that outputs a DC bus voltage to the primary side of the main transformer.

[0014] The beneficial effect of the present invention is that the risk of electric shock is effectively reduced by monitoring the voltage at the welding gun end of the welding machine in real time and limiting the output voltage to below a safety threshold in no-load mode.

[0015] At the same time, the bidirectional thyristor and drive isolation circuit built into the switching circuit achieve safe isolation of high and low voltage circuits, further improving the safety of the equipment.

[0016] In addition, the coordinated work of the pulse modulation unit and the current sampling feedback unit enables the welder to dynamically adjust the pulse duty cycle according to the actual current demand during the welding process, thereby achieving precise control of the welding current and improving welding quality and efficiency.

[0017] Overall, the present invention effectively solves the problems existing in the prior art such as excessively high no-load voltage, insufficient safety isolation, and inaccurate current control, and has significant technological progress and practical value for the manufacture of welding equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A low no-load voltage circuit structure diagram is provided for this application.

[0020] Figure 2 A structural diagram of a lithium battery welding machine is provided for this application. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] Example 1: Figure 1 As shown, the present invention provides a low no-load voltage circuit, including a main control module, a voltage detection unit, a switching circuit, a pulse modulation unit and a current sampling feedback unit.

[0023] The main control module is electrically connected to the voltage detection unit, the switching circuit, the pulse modulation unit and the current sampling feedback unit respectively.

[0024] In this embodiment, the main control module achieves coordinated control through multiple signal channels: the ADC sampling port receives the voltage-divided signal from the voltage detection unit via an isolated optocoupler, monitoring the voltage status at the welding torch in real time. Two independent GPIO output channels respectively transmit mode commands to the switching circuit's driver isolation circuit and duty cycle parameters to the pulse modulation unit's PWM generator. Simultaneously, the module receives the conditioned digital current signal from the current sampling and feedback unit via an SPI interface. Shielded cables connect each unit, and slots are used in the PCB layout to isolate the high- and low-voltage traces, ensuring interference resistance in signal transmission.

[0025] The voltage detection unit outputs a voltage divided signal that is filtered out of high-frequency interference by an RC filter network and then undergoes potential isolation conversion via a linear optocoupler. When the voltage at the welding gun terminal exceeds the preset threshold, the analog voltage signal output by the optocoupler secondary side triggers the ADC sampling interrupt of the main control module, at which point the main control module sends a cutoff instruction to the switching circuit. The bidirectional thyristor drive isolation circuit in the switching circuit uses a magnetic coupling isolation chip to isolate the main control module. Logic level conversion Gate drive pulse. In no-load mode, the drive circuit stops outputting trigger pulses to turn off the bidirectional thyristor, and the secondary winding current forms a voltage divider loop through the current limiting resistor, clamping the output voltage at Safety value.

[0026] After receiving the PWM duty cycle instruction from the main control module, the pulse modulation unit increases the signal amplitude to , and then isolated by a pulse transformer to drive the MOSFET switch tube of the main power circuit. When the current sampling feedback unit detects that the welding current deviates from the set value, the differential voltage signal output by the Hall sensor is amplified 100 times by the instrument amplifier, and the ADC of the main control module collects it in real time and dynamically adjusts the PWM duty cycle to form a closed-loop control. At the moment of switching from no-load to welding mode, the main control module starts the slow-start algorithm and controls the adjustable resistor network of the slow-start module through the DAC output ramp voltage, so that the operating voltage is within Internal Ramp up smoothly to rated welding voltage.

[0027] The voltage detection unit monitors the voltage at the welding gun end of the welding machine in real time and generates a detection signal to be transmitted to the main control module. The voltage detection unit includes a voltage divider resistor network and a filter capacitor to ensure low-noise transmission of the detection signal.

[0028] In this embodiment, the voltage divider resistor network is composed of precision metal film resistors connected in series. The high voltage end is directly connected to the welding gun output terminal, and the low voltage end is grounded at a single point through the copper foil grounding area. The signal extraction point is set at the middle node of the voltage divider network. The node is connected in parallel with a multilayer ceramic filter capacitor to form a first-order RC low-pass filter with a cutoff frequency of 1kHz to suppress high-frequency switching noise. The voltage divider ratio is set to , when the welding gun end appears At peak voltage, the intermediate node output Detect the signal and match the ADC range of the main control module.

[0029] The divided voltage signal is filtered and input to the primary side of the linear optocoupler. The current limiting resistor in series in the primary loop controls the operating current to The optocoupler secondary side uses an adjustable feedback resistor network to adjust the isolated analog voltage signal to The analog signal is transmitted to the ADC input port of the main control module through a twisted shielded pair cable. In the PCB layout, the optocoupler device spans the slotted isolation strip between the high-voltage detection area and the low-voltage control area to achieve A bidirectional TVS diode is connected in parallel on the high-voltage side of the voltage divider network. When a transient overvoltage occurs at the welding gun end, the TVS diode clamps the voltage at the voltage divider node to a safe value within nanoseconds.

[0030] In order to improve the detection accuracy, the voltage divider resistors are selected from a pair of resistors with matching temperature coefficients, and their total resistance is set at to The second-order active filter circuit is set at the output end of the secondary side of the optocoupler. The operational amplifier forms a Sallen-Key topology to attenuate the noise in the frequency band above 100Hz, so that the ripple voltage of the detection signal is controlled within The ADC sampling clock of the main control module is set out of phase with the welding machine switching frequency, and the sampling resolution is increased to 12-bit effective accuracy through the digital mean filtering algorithm.

[0031] The entire detection circuit adopts a triple protection design: a ring discharge tooth structure is set at the high voltage input end, the voltage divider resistor is arranged in series and parallel to increase the creepage distance, and a When the voltage at the welding gun end drops abnormally, the main control module The fault protection sequence is started internally and the hardware watchdog circuit is used to prevent the program from running away. The static power consumption of the detection unit is controlled at The voltage change is continuously monitored in no-load state without affecting the system standby characteristics.

[0032] The switching circuit includes no-load mode and welding mode. The main control module controls the switching circuit based on the detection signal to limit the output voltage to less than 0.01% in the no-load mode. The switching circuit has a built-in bidirectional thyristor and a drive isolation circuit to achieve safe isolation between high and low voltage circuits.

[0033] In this embodiment, the core function of the switching circuit is to realize the switching between the no-load mode and the welding mode of the welding machine, ensuring that the output voltage is limited to less than The circuit primarily consists of a bidirectional thyristor (TRIAC) and a driver isolation circuit. The two main terminals of the TRIAC are directly connected in series in the output circuit of the secondary winding of the main transformer, serving as the key actuator for voltage switching. The driver isolation circuit receives mode switching commands from the main control module and converts the low-voltage control signal into a high-voltage drive pulse via an optocoupler isolator. This pulse is then applied to the gate of the TRIAC, achieving electrical isolation between the high- and low-voltage circuits and preventing high voltage from entering the low-voltage control circuit, potentially creating a safety hazard.

[0034] When the main control module determines that the welding gun terminal voltage signal collected in real time by the voltage detection unit is in a no-load state (for example, the voltage continues to be lower than the preset threshold for more than a set time), it sends a cut-off instruction to the drive isolation circuit. The drive isolation circuit then stops outputting trigger pulses, putting the bidirectional thyristor in the cut-off state. At this time, the current path of the secondary winding of the main transformer is forced to flow through a current limiting resistor, forming a high-impedance loop, thereby effectively clamping the output voltage at to When welding mode is activated (e.g., the welding gun contacts the workpiece), the main control module sends a turn-on command, driving the isolation circuit to generate a high-current trigger pulse applied to the gate. The bidirectional thyristor is turned on, completely bypassing the current-limiting resistor. The secondary winding directly outputs the rated welding voltage, ensuring a stable supply of welding current.

[0035] The pulse modulation unit receives the driving instructions from the main control module and generates a high-frequency pulse signal to adjust the on-off frequency of the main power circuit; the pulse modulation unit integrates a PWM generator and a totem pole amplifier circuit to drive the fast response of the power switch tube.

[0036] In this embodiment, the core function of the pulse modulation unit is to receive the driving instructions from the main control module and generate a high-frequency pulse signal to accurately adjust the on-off frequency of the main power circuit, ensuring accurate current control and rapid response during the welding process. The unit integrates a PWM signal generator and a totem pole drive circuit, wherein the PWM signal generator directly receives the duty cycle instruction from the main control module and generates a reference square wave signal accordingly. The frequency adjustable range of the reference square wave signal is set to to to meet the needs of different welding conditions. Its duty cycle is calculated and output in real time by the main control module. The initial value is based on the preset welding parameters and can be dynamically optimized during the welding process. The totem pole drive circuit is responsible for increasing the voltage amplitude of the reference square wave signal from the logic level to the drive level required by the power switch tube. The circuit uses a complementary transistor pair (NPN and PNP types) to form a push-pull output structure to ensure that the rising and falling edge times are shortened to the nanosecond level, thereby driving the rapid response of the power switch tube. In order to isolate the high and low voltage circuits and improve the safety of signal transmission, the totem pole output signal is transmitted to the gate of the power switch tube through a magnetic isolation device. The primary side of the magnetic isolation device is connected to the totem pole output end, and the secondary side is directly connected to the gate drive resistor of the power switch tube. The isolation voltage is The above blocks the interference and risks of the high-voltage circuit.

[0037] The main power circuit is directly controlled by the pulse modulation unit and consists of a series-connected energy storage inductor and a freewheeling diode. One end of the energy storage inductor is connected to the drain of the power switch, and the other end is connected to the welding gun output. It stores energy and limits the current rise rate during the on-state of the switch, ensuring smooth welding current output. The freewheeling diode's anode is grounded, and its cathode is connected to the junction between the energy storage inductor and the power switch. When the power switch turns off, the energy storage inductor releases energy, and the freewheeling diode immediately turns on, forming a freewheeling loop. This maintains the continuity of the inductor current and prevents voltage spikes or welding instability caused by sudden current changes. During the process, the main control module outputs a duty cycle command to the PWM generator based on welding requirements. The PWM generator generates a reference square wave, which is then amplified by a totem pole circuit. The amplified signal is transmitted via magnetic isolation to the gate of the power switch, driving it to switch on and off at high frequency. The action of the switch regulates the charging and discharging of the energy storage inductor, thereby controlling the amplitude and waveform of the welding current. The current sampling and feedback unit monitors the output current in real time and provides feedback to the main control module to form a closed-loop control loop, dynamically adjusting the duty cycle to compensate for load changes.

[0038] The current sampling feedback unit collects the output current in real time and dynamically adjusts the pulse duty cycle.

[0039] In this embodiment, the current sampling feedback unit uses a Hall current sensor to monitor the instantaneous current value of the welding machine output bus. The Hall current sensor is directly mounted on the output positive and negative busbars. Its closed-loop magnetic core structure senses the current magnetic field changes in real time and outputs a millivolt differential voltage signal proportional to the instantaneous current. The signal is transmitted through a twisted pair shielded cable, which effectively suppresses common-mode interference and ensures the real-time and accuracy of the acquisition. The signal conditioning circuit consists of a high-precision instrumentation amplifier, a multi-stage filtering module and a bias adjustment unit: the instrumentation amplifier performs adjustable gain amplification on the weak differential signal output by the Hall sensor to increase the signal amplitude to the standard level; then, the signal enters the second-order Butterworth low-pass filter, and the cutoff frequency is set to , filter out high-frequency switching noise and electromagnetic interference; the bias adjustment unit applies precise DC bias through the reference voltage source and voltage divider network to shift the signal to Within the range, adapt to the input requirements of the main control module.

[0040] The conditioned analog voltage signal is input to the feedback port of the main control module and is converted by a 12-bit ADC to The sampling rate is converted into a digital signal. Based on the deviation between the real-time current sampling value and the preset welding current setting value, the main control module dynamically calculates and outputs the PWM duty cycle adjustment instruction through the PID control algorithm. When it is detected that the output current is lower than the target value, the duty cycle instruction increases linearly to increase the conduction time of the power switch tube and increase the average welding current; conversely, when the current overshoots, the duty cycle instruction decreases to suppress the current peak. The response time of this closed-loop regulation process is less than , so that the welding current fluctuation is controlled within range to ensure stable welding heat input.

[0041] The entire feedback loop operates continuously throughout the welding cycle. The wideband characteristics of the Hall effect sensor ensure accurate capture of high-frequency current transients. The signal conditioning circuit integrates common-mode rejection to eliminate ground loop interference. The main control module regularly performs a self-calibration process, using zero correction and gain compensation to offset the effects of temperature drift, maintain long-term measurement accuracy, and ultimately achieve closed-loop control of the welding current.

[0042] Embodiment 2: The present invention provides a low no-load voltage circuit, wherein the main control module has a built-in no-load judgment algorithm and is also connected to a soft start module.

[0043] In this embodiment, the no-load judgment algorithm built into the main control module realizes mode switching through a three-level detection mechanism: first, the voltage detection unit continuously collects the voltage signal at the welding gun end, and transmits it to the ADC port of the main control module through the isolation optical coupler for analog-to-digital conversion; secondly, the main control module uses The digitized voltage signal is subjected to sliding mean filtering during the sampling period to eliminate instantaneous interference; finally, when the filtered voltage value is continuously lower than the preset threshold (in this embodiment, )Exceed When the set time is reached, the algorithm determines that the load is off and sends a cut-off instruction to the switching circuit. The algorithm integrates a hysteresis comparison function. When the detection voltage rises back to the threshold The above releases the no-load lock to avoid frequent switching under critical conditions.

[0044] The soft start module is composed of a digital adjustable resistor network and a MOS tube array: the adjustable resistor network includes a precision thin film resistor in series and an NMOS tube group in parallel. The gates of each MOS tube are connected to the multi-channel PWM output port of the main control module. When the main control module issues a welding mode command, its built-in DAC circuit generates The PWM generator outputs six phase-interleaved pulse signals. The MOS tube group is gradually turned on in sequence under the PWM drive, making the parallel equivalent resistance value decrease exponentially. This process continues , change the equivalent resistance of the current limiting resistor from the initial Smooth down to , driving the output voltage of the secondary winding of the main transformer from the safety threshold by The slope rises uniformly to the rated working voltage .

[0045] The soft start process adopts a closed-loop monitoring mechanism. The main control module detects the output voltage rising curve in real time through the current sampling feedback unit, and dynamically adjusts the PWM duty cycle to compensate when it deviates from the preset ramp function.

[0046] Example 3: Figure 2 As shown, the present invention provides a lithium battery welding machine, including a low no-load voltage circuit, a welding gun assembly, a main transformer and a power supply module.

[0047] The main control module of the low no-load voltage circuit is connected to the rectifier output end of the power supply module, the primary winding of the main transformer is connected to the power supply module through the power switch tube, and the secondary winding is connected to the welding gun assembly through the switching circuit; The welding gun assembly includes an electrode clamping mechanism and a cooling water channel. The two ends of the electrode clamping mechanism are respectively connected to the positive and negative output poles of the low no-load voltage circuit. The cooling water channel is set around the electrode to reduce the temperature rise during welding. The power supply module is a high-frequency inverter power supply that outputs the DC bus voltage to the primary side of the main transformer.

[0048] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A low no-load voltage circuit, characterized in that: It includes a main control module, a voltage detection unit, a switching circuit, a pulse modulation unit and a current sampling feedback unit; The main control module is electrically connected to the voltage detection unit, the switching circuit, the pulse modulation unit and the current sampling feedback unit respectively; The voltage detection unit monitors the voltage at the welding gun end of the welding machine in real time and generates a detection signal which is transmitted to the main control module; The voltage detection unit includes a voltage-dividing resistor network and a filter capacitor to detect low-noise transmission of the signal; The switching circuit includes a no-load mode and a welding mode. The main control module controls the switching circuit based on the detection signal to limit the output voltage to a safety threshold of less than 36V in the no-load mode; The switching circuit has a built-in bidirectional thyristor and a drive isolation circuit to achieve safe isolation of high and low voltage circuits; The pulse modulation unit receives the driving instruction of the main control module and generates a high-frequency pulse signal to adjust the on-off frequency of the main power circuit; The pulse modulation unit integrates a PWM generator and a totem pole amplifier circuit to drive the fast response of the power switch tube; The current sampling feedback unit collects the output current in real time and dynamically adjusts the pulse duty cycle.

2. A low no-load voltage circuit as claimed in claim 1, characterized in that: The voltage detection unit includes a voltage dividing resistor network connected in series and a filter capacitor connected in parallel; The first end of the voltage divider resistor network is connected to the welding gun output terminal, and the second end is grounded; The two ends of the filter capacitor are connected between the middle node of the voltage divider resistor network and the ground, forming a detection signal output path that attenuates high-frequency interference; The total resistance of the voltage divider resistor network is configured to proportionally reduce the voltage at the welding gun terminal to a recognizable range of the main control module.

3. A low no-load voltage circuit as claimed in claim 2, characterized in that: The output end of the voltage detection unit is connected to the main control module through an isolation optocoupler. The primary side of the isolation optocoupler is connected in series with a current-limiting resistor and receives the detection signal after voltage division. The secondary side outputs the isolated analog voltage signal to the ADC port of the main control module, realizing electrical isolation between the high-voltage detection circuit and the low-voltage control circuit.

4. A low no-load voltage circuit as claimed in claim 1, characterized in that: The switching circuit includes a bidirectional thyristor and a drive isolation circuit; The two main terminals of the bidirectional thyristor are connected in series in the secondary winding loop of the welding machine's main transformer. The drive isolation circuit receives the mode switching instruction from the main control module and applies a trigger pulse to the gate of the bidirectional thyristor. When in no-load mode, the bidirectional thyristor is turned off to form a high-impedance loop through the secondary winding through the current-limiting resistor. When in welding mode, the bidirectional thyristor is turned on to bypass the current-limiting resistor.

5. A low no-load voltage circuit as claimed in claim 1, characterized in that: The pulse modulation unit includes a PWM signal generator and a totem pole driving circuit; The PWM signal generator generates a reference square wave signal according to the duty cycle instruction of the main control module. The totem pole drive circuit increases the voltage amplitude of the reference square wave signal to the driving requirement level of the power switch tube and transmits it to the gate of the power switch tube through the magnetic isolation device.

6. A low no-load voltage circuit as claimed in claim 1, characterized in that: The main power circuit includes an energy storage inductor and a freewheeling diode connected in series. One end of the energy storage inductor is connected to the drain of the power switch tube, and the other end is connected to the output end of the welding gun. The anode of the freewheeling diode is grounded, and the cathode is connected to the connection node between the energy storage inductor and the power switch tube, which is used to maintain the continuity of the inductor current during the shutdown period of the power switch tube.

7. The low no-load voltage circuit according to claim 1, characterized in that: The current sampling feedback unit includes a Hall current sensor and a signal conditioning circuit; The Hall current sensor is mounted on the welding machine output bus and generates a voltage signal proportional to the instantaneous current; The signal conditioning circuit amplifies, filters and offset-adjusts the voltage signal and then inputs it into the feedback port of the main control module to form a closed-loop control circuit.

8. The low no-load voltage circuit according to claim 1, characterized in that: The main control module has a built-in no-load judgment algorithm. When the detection signal is continuously lower than the preset threshold for more than a set time, it is judged to be in a no-load state and outputs a mode switching instruction to the switching circuit.

9. A low no-load voltage circuit as claimed in claim 8, characterized in that: The main control module is also connected to a slow start module, which consists of an adjustable resistor network and a MOS tube. When switching from no-load mode to welding mode, the equivalent resistance of the current limiting resistor is gradually reduced, so that the output voltage of the secondary winding of the main transformer rises to the operating voltage in a ramp form.

10. A lithium battery welding machine, characterized in that: The device comprises the low no-load voltage circuit, welding gun assembly, main transformer and power supply module according to any one of claims 1 to 9; The main control module of the low no-load voltage circuit is connected to the rectifier output end of the power supply module, the primary winding of the main transformer is connected to the power supply module through the power switch tube, and the secondary winding is connected to the welding gun assembly through the switching circuit; The welding gun assembly includes an electrode clamping mechanism and a cooling water channel. The two ends of the electrode clamping mechanism are respectively connected to the output positive and negative poles of the low no-load voltage circuit. The cooling water channel is arranged around the electrode to reduce the temperature rise during welding. The power supply module is a high-frequency inverter power supply that outputs a DC bus voltage to the primary side of the main transformer.

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