Overvoltage protection for current brake switch

Abstract

A method comprising: providing a welding current to a welding zone; monitoring a voltage of a current brake switch during a welding current ramp-down period of a given short-arc welding process cycle, the current brake switch being in an open state and causing the welding current provided to the welding zone to decrease; and closing the current brake switch prior to the end of the welding current ramp-down period of the given short-arc welding process cycle when the voltage of the current brake switch in the open state reaches a first predetermined voltage threshold.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Patent Application Serial No. 17 / 228,761, filed April 13, 2021, entitled “OVERVOLTAGE PROTECTION FOR CURRENT BRAKING SWITCH”, pursuant to 35U.SC119(e). The entire disclosure of that application is incorporated herein by reference for all purposes. Background Technology

[0003] Metal Inert Gas (MIG) welding and Metal Active Gas (MAG) welding are both welding processes in which electrodes are continuously fed towards the workpiece. A power source generates the welding voltage and welding current. During welding, the workpiece is primarily heated by the electric arc generated by the power source. The electrode is heated partly by the power generated in the electrode as the welding current flows through the electrode stickout, and partly by the heat generated by the arc itself. This electrode stickout is the section between the free wire end and the contact tip, where the current is transferred to the electrode. An inert or active gas is introduced through the welding torch, surrounding the weld pool and the arc, thus preventing oxygen and any associated byproducts from contaminating the weld. A fundamental control objective of the welding process is to match the electrode melting rate with the electrode feed rate. Another fundamental control objective is to ensure that the welding process operates in the desired metal transfer mode. A further objective of this control could be, for example, to influence the heat transferred to the workpiece.

[0004] MIG / MAG welding is performed using one of three basic droplet transfer methods: short arc, mixed arc, and spray. In short arc welding, material is transported from the electrode to the workpiece via a short-circuit droplet.

[0005] When the power supply increases, the welding process enters a mixed arc form, where material is transported through a mixture of short-circuit and non-short-circuit droplets. The result is an unstable and difficult-to-control arc, potentially producing excessive welding spatter and fumes. This type of welding should generally be avoided.

[0006] With sufficiently high power, the welding process enters a spray mode, where material is transported through fine, dispersed droplets without short circuits. The amount of spatter is lower than in short-arc welding. This mode provides greater heat to the base material and is primarily suitable for thicker workpieces.

[0007] Let's discuss the short-arc droplet transfer mechanism. Following the short-circuit welding cycle are the arc phase. During the short-circuit phase, the molten metal ball formed at the tip of the traveling wire engages with the molten metal pool on the workpiece, causing a high current to flow through the molten wire and the molten metal ball. This short-circuit phase is terminated by an electrical pinch action, causing the metal forming the molten metal ball on the wire to electrically contract and then explosively detach from the wire, commonly referred to as the "fuse." The current in the short-circuit portion of the welding cycle is controlled by a power supply control circuit. A premonition circuit is typically provided, where a specified increase in dv / dt (the change in voltage over time) indicates that fuse formation is imminent. Therefore, the welding current can be reduced to background levels or lower immediately before melting occurs. This significantly reduces the energy of the fuse in each welding cycle, which in turn reduces spatter at the termination of the short-circuit phase.

[0008] To rapidly reduce the current at the appropriate moment (i.e., before the fuse blows), a switch located on the normal current path leading to the welding area can be turned off, forcing the current through a resistor that increases the voltage drop across the entire welding circuit, thus causing the welding current to decrease to a lower level more quickly. This switching method is known as "currentbraking."

[0009] The implementation schemes described in this article improve upon current braking technology. Summary of the Invention

[0010] This document discloses a technique for protecting a current-braking switch from overvoltage conditions. One method includes: supplying a welding current to a welding zone; monitoring the voltage of a current-braking switch, which is in an open state and reduces the welding current supplied to the welding zone, during a welding current descent period of a given short-arc welding process cycle; and closing the current-braking switch before the end of the welding current descent period of the given short-arc welding process cycle when the voltage of the open current-braking switch reaches a first predetermined voltage threshold.

[0011] The present invention also discloses an apparatus. The apparatus may include: a power supply configured to provide welding current to a welding zone; and a braking switch voltage monitoring circuit configured to: monitor the voltage of a current braking switch during the ramp-down period of a given short arc welding process cycle, the current braking switch being in an open state and reducing the welding current supplied to the welding zone; and, when the voltage of the open current braking switch reaches a first predetermined voltage threshold, close the current braking switch before the end of the ramp-down period of the given short arc welding process cycle.

[0012] Brief description of the attached figures

[0013] Figure 1 This is a schematic diagram of a welding power supply having a current braking switch controlled by a switch control circuit, according to an exemplary embodiment.

[0014] Figure 2 This is a block diagram of a switch control circuit according to an exemplary embodiment.

[0015] Figure 3 This is a schematic diagram of a switch control circuit according to an exemplary embodiment.

[0016] Figures 4A-4D This is a graph showing various circuit parameters of a switch that does not cause the switch control circuit to close with a current braking switch according to an exemplary embodiment.

[0017] Figures 5A-5D This is a graph showing various circuit parameters that cause the switch control circuit to close and brake the switch according to an exemplary embodiment.

[0018] Figure 6 It is a flowchart describing a series of operations of operating a switch control circuit according to an exemplary embodiment.

[0019] Throughout the accompanying drawings, the same reference numerals denote the same elements. Detailed Implementation

[0020] Figure 1This is a schematic diagram of a welding power supply with a current-braking switch controlled by a switch control circuit, according to an exemplary embodiment. Power supply 100 includes a power source 110, a current brake (i.e., a current-braking switch 120 or a simpler switch 120), and a welding zone 130. Power supply 110 may be an inverter and / or a transformer. The output of power supply 110 can be rectified by diode D1. Inductor L1 represents the internal inductance of power supply 100. Resistor R1 and capacitor C1 are connected in parallel and in series with diode D2. This combination is connected in parallel with switch 120. R1 is used to discharge capacitor C1, but those skilled in the art will understand that an alternative form of energy recovery circuit can replace resistor R1. Inductor L2 represents the inductance of welding cables 150 and 152. Resistor R2 represents the resistance of welding zone 130, that is, the resistance between the molten welding wire and the workpiece (not shown).

[0021] Switch 120 can be a metal oxide semiconductor field-effect transistor (MOSFET) with a drain (D) terminal, a source (S) terminal, and a gate (G) terminal. As shown in the figure, the switch control circuit 200 controls the gate G of switch 120, thereby controlling the operation of switch 120 (driving it to open or close).

[0022] Switch 120, connected in series with the welding current, increases the non-zero voltage drop even when in the ON state, thus causing power loss to power supply 100. Therefore, switch 120 should ideally have the lowest possible conduction loss. The switch control circuit 200 described herein can better optimize the rated voltage and conduction loss of switch 120. It will be apparent to those skilled in the art that implementing switch control circuit 200 and its associated advantages help keep the heat sink associated with switch 120 relatively small and also help keep the efficiency of power supply 100 relatively high (due to lower conduction losses).

[0023] Adding extra voltage margin to a semiconductor switch to handle worst-case load conditions typically results in a higher voltage drop when the switch is on; that is, a higher voltage rating usually means greater conduction losses. By using the switch control circuit 200 described herein, a lower voltage-rated MOSFET-based transistor switch 120 can be selected, thereby improving (reducing) overall conduction losses. This is achieved by protecting switch 120 from overvoltage under worst-case load conditions, rather than selecting switch 120 for the highest peak voltage that might occur on it without such overvoltage protection.

[0024] For a short-arc current braking circuit, the peak voltage on switch 120 is highest when switch 120 turns off the peak current and the inductance (L1 plus L2) in the welding circuit is high (e.g., due to the length and / or winding of welding cables 150, 152). In this case, according to an exemplary embodiment, switch control circuit 200 detects that the voltage of switch 120 has reached the trigger level or threshold voltage, and then switches 120 operates to turn on switch 120 within a given short-arc current braking cycle, thereby protecting switch 120 from overvoltage conditions. In this example, due to the overvoltage protection provided by switch control circuit 200, switch 120 is turned on for a period of time (i.e., switch 120 is turned on), during which time capacitor C1 connected in parallel with switch 120 discharges, and then switch control circuit 200 turns off switch 120 (within the same given short-arc current braking cycle) until the current in the welding circuit slopes down to the desired level.

[0025] Figure 2This is a block diagram of a switch control circuit 200 according to an exemplary embodiment. As shown, consistent with the above description, the switch control circuit 200 includes a brake switch voltage monitoring circuit 210, a capacitor voltage monitoring circuit 220, and a brake switch control signal generating circuit 230. The brake switch voltage monitoring circuit 210 is configured to detect an overvoltage condition on switch 120 when switch 120 is open and to perform current braking in each individual cycle of the short arc welding process. Simultaneously, the capacitor voltage monitoring circuit 220 detects when the voltage of capacitor C1 is sufficiently low to allow switch 120 to open again (and resume current braking). The switch control signal generating circuit 230 receives the outputs of the brake switch voltage monitoring circuit 210 and the capacitor voltage monitoring circuit 220, and generates a control signal that is provided to the gate of switch 120. Those skilled in the art will appreciate that the switch control circuit 200 can also be configured to respond, for example, to the slope of dv / dt on R2 in the welding zone 130, to precisely determine when to initially disconnect the switch 120 to reduce spatter during short-arc welding. Therefore, the technique described herein can be considered to surpass the conventional current-brake opening and closing time of the switch 120. That is, the switch control circuit 200 is configured to sensitively protect the switch 120 from sporadic overvoltage conditions that may occur during normal operation in short-arc welding, particularly due to the length / winding of the welding cable.

[0026] Figure 3 This is a schematic diagram of one possible implementation of a switch control circuit 200 according to an exemplary embodiment. Those skilled in the art will understand that other circuit topologies, including those more reliant on digital technology, can be used to implement the switch control circuit 200 described herein. Furthermore, alternatives may be made to… Figure 3Different component values ​​are selected to achieve a more robust output 250, namely the gate control signal described below. As shown, the brake switch voltage monitoring circuit 210 includes a first comparator U2, whose inverting input is connected to the drain D of switch 120 via several series resistors R2, R12, R13, and R14. The inverting input of comparator U2 is also connected to a capacitor C2 and a resistor R10 in parallel, which are connected to the source S of switch 120. The non-inverting input of comparator U2 is connected to a voltage divider including resistors R15 and R16, which is powered by a pull-up resistor R11, which is connected to a voltage source (e.g., +15V). One terminal of resistor R16 is connected to a reference voltage Vref, for example, +5V. Capacitor C3 filters the output of comparator U2.

[0027] The output of comparator U2 is fed to the non-inverting input of comparator U4, and a reference voltage Vref (e.g., +5V) is provided to the inverting input of comparator U4. The output 310 of comparator U4 is the output of the brake switch voltage monitoring circuit 210. (The last sentence appears to be incomplete and possibly refers to a different circuit.) Figure 3 The selected component values ​​shown include a maximum rated voltage of, for example, 200V for switch 120. When switch 120 is open, Vds (drain-to-source voltage) reaches approximately 180V, and the output of switch control circuit 200 is configured to turn on switch 120, thereby mitigating potential overvoltage conditions.

[0028] The capacitor voltage monitoring circuit 220 is configured to monitor the voltage of capacitor C1 by monitoring the voltage of the anode 190 of diode D2 relative to the source S of switch 120 when switch 120 is turned on. The capacitor voltage monitoring circuit 220 includes several series resistors R5, R8, and R9 connected between the anode 190 and the non-inverting input of comparator U1. A reference voltage Vref (e.g., +5V) is also applied to the non-inverting input of comparator U1 through resistor R6, with capacitor C4 acting as a filter. Diode D4 protects the non-inverting input of comparator U1 from excessively negative input values. The inverting input of comparator U1 is connected to the source S of switch 120 and the output 320 of comparator U1 through resistor R21, with capacitor C5 acting as a filter at output 320. Output 320 is the output of the capacitor voltage monitoring circuit 220.

[0029] The outputs 310 of the brake switch voltage monitoring circuit 210 and 320 of the capacitor voltage monitoring circuit 220 are combined (e.g., added) and effectively used as input to the OR circuit (brake switch control signal generation circuit 230). When either output 310 or output 320 is low, causing node 325 to be low, switch 120 is turned on, resulting in transistor Q1 being turned off. This causes output 250 to go high, thus turning on switch 120 and protecting itself. It should be noted that the outputs of comparators U1 and U4 are open collectors, meaning they can sink current but cannot output current. The combined signal 327 is provided to the base of transistor Q1 and the collector of transistor Q2, i.e., the base of transistor Q1 and the collector of transistor Q2 are connected together. +15V is applied to the collector of transistor Q1 through resistor R17 and to node 325 through resistor R18. The emitters of transistors Q1 and Q2 are connected together, with a fixed voltage of -5V. The base of transistor Q2 is fed by a normal brake control signal, which controls current braking within a given short arc period. That is, V4 in the brake switch control signal generation circuit 230 controls this normal brake control signal. For braking (under normal conditions), transistor Q2 is turned off (e.g., pulse turn-off), and transistor Q1 receives its base current through resistor R18 and turns on. The output 250 of the switch control circuit will then go low and turn off switch 120, thus achieving current braking. The output 250 of the switch control signal generation circuit 230 is taken from the collector of transistor Q1 and applied to the gate G of switch 120.

[0030] like Figure 3 As shown, the voltage rails of comparators U1, U2, and U4 are -5V and +15V, respectively. Therefore, in the following discussion, the "low" and "high" outputs of comparators U1, U2, and U4 can be interpreted as corresponding to these voltage levels. In operation, assume that the drain voltage of switch 120 is in an overvoltage state (i.e., at or above 180V in this example). This state forces the output of comparator U2 to go low, which in turn causes the output of comparator U4 to go low, thereby turning off transistor Q1 and causing the output 250 of switch control circuit 200 to go high (given the +15V supply voltage provided through R17), thus turning on switch 120 and alleviating the overvoltage state. During non-braking operation, when an overvoltage state is detected, the voltage on anode 190 is approximately -180V. In this state, the output 320 of comparator U1 is also low (just like the output 310 of comparator U4), ensuring that switch 120 is closed (i.e., turned on) and alleviating the overvoltage state.

[0031] Since this overvoltage condition is only occasional, and it is likely to be cleared once switch 120 is closed, it is still necessary to re-brake (close or open switch 120) within the same short arc welding process cycle in which the overvoltage condition first occurs. According to an exemplary embodiment, this can be achieved by monitoring capacitor C1 (…). Figure 1 This is achieved by adjusting the voltage across the anode 190. When an overvoltage condition is detected (e.g., reaching or exceeding 180V), the voltage across the anode 190 is approximately -180V relative to the source S of the switch 120. When the switch 120 is closed, the voltage across the anode 190 will increase, i.e., the negative value of the voltage decreases. Figure 3 In this embodiment, once the voltage of capacitor C1 drops to a predetermined level, the output 320 of the capacitor voltage monitoring circuit 220 will be high. Both outputs 310 and 320 need to be high to turn on transistor Q1. Since switch 120 is on and short-circuiting the voltage on its drain D, output 310 is already high. High outputs 310 and 320 cause transistor Q1 to turn on, making output 250 (which controls the gate of switch 120) low, thus causing switch 120 to turn off again (and re-brake the welding current). This cycle of switch 120 can occur multiple times during a given short arc welding process cycle (more specifically, during the welding current descent period of that cycle).

[0032] Figures 4A-4D This is a graph showing various circuit parameters that, according to an exemplary embodiment, will not cause the switch control circuit to close and brake the switch current. More specifically, with Figure 3 Associated with an exemplary embodiment, at 0.3ms, due to current braking, switch 120 is opened, and the current through L2 (i.e., the welding current) decreases. Figure 4A At the same time, the voltage across capacitor C1 (drain to anode 190°) rises rapidly. Figure 4B The same applies to the voltage of switch 120. Figure 4C However, these voltages did not exceed the 180V threshold, at which point the overvoltage protection of the switch control circuit 200 activates in this example. Approximately 0.6ms later, switch 120 closes after its descent period, causing the voltage at anode 190 to drop rapidly before ramping up again. Figure 4D As shown. In the context of the embodiments described herein, a portion of a given short-arc welding process cycle (i.e., arc time + short-circuit time, approximately 8–10 ms) can be considered as a time period from, for example, 0.3 ms to 1.1 ms, which is Figure 4AThe example shows the time interval between the peak welding current output of approximately 440A. Furthermore, the welding current descent period caused by current braking in a given short arc welding process cycle can be considered as a period from, for example, 0.3ms to approximately 0.48ms, i.e., when the welding current reaches a predetermined level (e.g., Figure 4A The time of 80A in the middle.

[0033] Figures 5A-5D This is a graph showing various circuit parameters that cause the switch control circuit 200 to close the switch 120 according to an exemplary embodiment. More specifically, with Figure 3 Associated with the example embodiment, at 0.3ms, switch 120 opens to brake the current, thus reducing the current through L2 (i.e., the welding current). Figure 5A At the same time, the voltage across capacitor C1 (drain to anode 190°) rises rapidly. Figure 5B The voltage of switch 120 also rose rapidly. Figure 5C In this example, these voltages reach the 180V over-protection threshold or trigger; therefore, the switch control circuit 200 operates to close switch 120 and mitigate the overvoltage condition. Given that switch 120 is closed, Figure 5B and Figure 5C This will show a rapid drop in the voltage across capacitor C1 (drain to anode 190) and switch 120. When the voltage across anode 190 rises and reaches, for example, -45V (from -180V)... Figure 5D The switch control circuit 200 causes switch 120 to open again (and brakes the welding current). This action will cause the voltage (from drain to anode 190) of capacitor C1 to decrease. Figure 5B ) and the voltage of switch 120 ( Figure 5C The voltage rose rapidly again. As can be seen from the graph, the overvoltage protection was activated twice. Figure 5A It can be seen that the welding current continues to decrease during the overvoltage protection period (switch closed), but at a slower rate.

[0034] Therefore, those skilled in the art will understand that the switch control circuit 200 described herein is configured to monitor overvoltage conditions of the current-braking switch 120 and, during the current descent period of a given short arc welding process cycle, rapidly switch the switch 120 to avoid damage to the switch 120, while still providing current braking functionality. Since overvoltage conditions are rare, the switch control circuit 200 can be used to help protect current-braking switches with rated voltages lower than those otherwise selected, thereby improving power supply efficiency.

[0035] Figure 6This is a flowchart describing a series of operations of a switch control circuit according to an exemplary embodiment. At 610, a power supply provides welding current to the welding zone. At 612, during the welding current descent period of a given short arc welding process cycle, an operation monitors the voltage of a current braking switch, which is in an open state and reduces the welding current supplied to the welding zone. Furthermore, at 614, when the voltage of the open current braking switch reaches a first predetermined voltage threshold, an operation closes the current braking switch before the end of the welding current descent period of the given short arc welding process cycle.

[0036] In general, in one form, a method is provided that includes supplying a welding current to a welding zone; monitoring the voltage of a current braking switch during a welding current descent period of a given short arc welding process cycle, the current braking switch being in an open state and reducing the welding current supplied to the welding zone; and closing the current braking switch before the end of the welding current descent period of the given short arc welding process cycle when the voltage of the open current braking switch reaches a first predetermined voltage threshold.

[0037] The aforementioned first predetermined voltage threshold may be lower than the rated voltage of the current braking switch.

[0038] The method may also include setting the current braking switch to the off state again before the end of the welding current descent period of a given short arc welding process cycle.

[0039] The method may also include monitoring the voltage of a clamping capacitor connected in parallel with the current braking switch, and causing the current braking switch to be turned off again when the voltage of the clamping capacitor reaches a second predetermined voltage threshold.

[0040] The closing and opening of the current braking switch may include a gate that controls the current braking switch.

[0041] The method may further include determining whether a first output of a first comparator representing the voltage of a current braking switch and a second output of a second comparator representing the voltage of a clamping capacitor are both high, and generating a control signal for the gate to disconnect the current braking switch when both the first and second outputs are high.

[0042] The method may also include closing and opening the current braking switch more than once before the end of the welding current descent period of a given short arc welding process cycle.

[0043] The second predetermined voltage threshold may be approximately 45V on the clamping capacitor, while the first predetermined voltage threshold may be approximately 180V.

[0044] In one embodiment, the method is performed in a welding power source.

[0045] In another form, an apparatus is provided comprising a power supply configured to supply welding current to a welding zone, and a braking switch voltage monitoring circuit configured to: monitor the voltage of a current braking switch during the welding current descent period of a given short arc welding process cycle, wherein the current braking switch is in an open state and reduces the welding current supplied to the welding zone; and close the current braking switch before the end of the welding current descent period of the given short arc welding process cycle when the voltage of the open current braking switch reaches a first predetermined voltage threshold.

[0046] The first predetermined voltage threshold may be lower than the rated voltage of the current braking switch.

[0047] The device may also include a capacitor voltage monitoring circuit configured to disconnect the current braking switch again before the end of the welding current descent period of a given short arc welding process cycle.

[0048] The capacitor voltage monitoring circuit can be configured to monitor the voltage of the clamping capacitor connected in parallel with the current braking switch, and to disconnect the current braking switch again when the voltage of the clamping capacitor reaches a second predetermined threshold.

[0049] The device can be configured to close and open the current braking switch by controlling the gate of the current braking switch.

[0050] In one embodiment, the device further includes a first comparator having a first output representing the voltage of a current braking switch and a second comparator having a second output representing the voltage of a clamping capacitor, and the device is further configured to combine the first and second outputs to obtain a combined output for a control signal for driving the gate.

[0051] The device can also be configured to close and open the current braking switch more than once before the end of the welding current descent period of a given short arc welding process cycle.

[0052] In another form, the device includes: a power supply configured to provide welding current to a welding zone; a braking switch voltage monitoring circuit configured to: monitor the voltage of a current braking switch during the welding current descent period of a given short arc welding process cycle, wherein the current braking switch is in an open state and reduces the welding current supplied to the welding zone; and close the current braking switch before the end of the welding current descent period of the given short arc welding process cycle when the voltage of the open current braking switch reaches a first predetermined voltage threshold; and a capacitor voltage monitoring circuit configured to keep the current braking switch open again before the end of the welding current descent period of the given short arc welding process cycle.

[0053] The device may also include a switch control signal generation circuit that communicates with the brake switch voltage monitoring circuit and the capacitor voltage monitoring circuit, and is configured to output a gate control signal to control the operation of the current brake switch.

[0054] The device can also be configured to close and open the current braking switch more than once before the end of the welding current descent period of a given short arc welding process cycle.

[0055] Although the technology of the invention has been described in one or more specific embodiments, the specific details of each embodiment are not intended to limit the scope of the invention, as various modifications and structural changes can be made within the scope of the invention. Furthermore, various features of one embodiment discussed herein may be incorporated into any other embodiment. Therefore, the appended claims should be interpreted broadly and in accordance with the scope of the invention.

Claims

1. A method for controlling short-arc welding process, characterized in that, It includes: Provide welding current to the welding zone; During the current descent period of a given short arc welding process cycle, the voltage of the current braking switch is monitored, which is in the open state and reduces the welding current supplied to the welding zone. In response to determining that the voltage of the current braking switch in the open state reaches a first predetermined voltage threshold, the current braking switch is closed before the end of the welding current descent period of the given short arc welding process cycle. as well as The current braking switch is brought back to the open state before the end of the welding current descent period of the given short arc welding process cycle. The welding current descent period of the given short arc welding process cycle begins when a predetermined increase in the arc voltage between the welding wire tip and the workpiece is detected over time, and ends when molten metal from the welding wire tip is detected.

2. The method according to claim 1, characterized in that, The first predetermined voltage threshold is lower than the rated voltage of the current braking switch.

3. The method according to claim 1, characterized in that, It also includes monitoring the voltage of a clamping capacitor connected in parallel with the current braking switch; and When the voltage of the clamping capacitor reaches the second predetermined voltage threshold, the current braking switch is returned to the open state.

4. The method according to claim 3, characterized in that, Closing and opening the current braking switch includes controlling the gate of the current braking switch.

5. The method according to claim 4, characterized in that, It also includes determining whether a first output of a first comparator representing the voltage of the current braking switch and a second output of a second comparator representing the voltage of the clamping capacitor are both high; and When the first output and the second output are high, a control signal is generated for the gate to disconnect the current braking switch.

6. The method according to claim 4, characterized in that, It also includes closing and opening the current braking switch more than once before the end of the welding current descent period of the given short arc welding process cycle.

7. The method according to claim 3, characterized in that, The second predetermined voltage threshold is 45V.

8. The method according to claim 1, characterized in that, The first predetermined voltage threshold is 180V.

9. The method according to claim 1, characterized in that, It also includes performing the method in a welding power source.

10. An apparatus for controlling a short-arc welding process, characterized in that, It includes: A power source, configured to supply welding current to the welding zone; and The switch control circuit includes a brake switch voltage monitoring circuit and a capacitor voltage monitoring circuit, and the switch control circuit is configured as follows: During the current descent period of a given short arc welding process cycle, the voltage of the current braking switch is monitored, which is in the open state and reduces the welding current supplied to the welding zone. In response to determining that the voltage of the current braking switch in the open state reaches a first predetermined voltage threshold, the current braking switch is closed before the end of the welding current descent period of the given short arc welding process cycle. as well as The current braking switch is brought back to the open state before the end of the welding current descent period of the given short arc welding process cycle. The welding current descent period of the given short arc welding process cycle begins when a predetermined increase in the arc voltage between the welding wire tip and the workpiece is detected over time, and ends when molten metal from the welding wire tip is detected.

11. The device according to claim 10, characterized in that, The first predetermined voltage threshold is lower than the rated voltage of the current braking switch.

12. The device according to claim 10, characterized in that, The capacitor voltage monitoring circuit is configured to return the current braking switch to the open state before the end of the welding current descent period of the given short arc welding process cycle.

13. The device according to claim 12, characterized in that, The capacitor voltage monitoring circuit is further configured to monitor the voltage of the clamping capacitor connected in parallel with the current braking switch; and When the voltage of the clamping capacitor reaches the second predetermined voltage threshold, the current braking switch is returned to the open state.

14. The device according to claim 13, characterized in that, The device is configured to close and open the current braking switch by controlling the gate of the current braking switch.

15. The device according to claim 14, characterized in that, It also includes a first comparator having a first output representing the voltage of the current braking switch, and a second comparator having a second output representing the voltage of the clamping capacitor, and, The device is further configured to combine the first output and the second output to obtain a combined output of control signals for driving the gate.

16. The device according to claim 14, characterized in that, The duration of the welding current descent period in the given short arc welding process cycle is less than 0.3 ms.

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