A control circuit for a direct current motor driven welding torch

Abstract

The application discloses a control circuit of a direct-current motor driving type welding gun, which comprises a main circuit, a main circuit driving circuit and a current regulating circuit, the main circuit is a loop formed by connecting a power supply and a welding gun control line in series, the main circuit driving circuit comprises resistors R1 and R2 and a switch tube Q2, and the current regulating circuit comprises a current sampling circuit a, a comparator U1, a large current circuit, a small current circuit and a delay circuit. The control circuit provided by the application can not only realize the driving work of the welding gun under the direct-current power supply, but also can be applied to a wide working voltage range, especially can realize large current promotion and small current maintenance, can effectively avoid the welding gun work heating problem, can effectively solve the voltage drop problem caused by the long welding gun line, and avoids the defects of weak signal and non-sensitive control. The control circuit only needs common simple components, has the advantages of low cost, easy realization and reliable working performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a control circuit of a direct current motor driven welding gun, and belongs to the technical field of welding gun circuit. BACKGROUND

[0002] Arc stud welding is a high-efficiency and high-quality stud welding method. The welding gun is a direct execution mechanism for realizing stud welding, and the performance of the welding gun has a great influence on the quality of stud welding.

[0003] The traditional welding gun used for arc stud welding is mainly an electromagnetic welding gun. The main shaft body driving mechanism of this type of welding gun is an electromagnet-spring structure. A moving iron core, an electromagnetic coil and a static iron core are arranged in the cavity of the welding gun shell. The attraction and separation between the moving iron core and the static iron core are realized by changing the current of the electromagnetic coil, so as to drive the lifting movement of the welding gun main shaft body and realize the lifting and releasing operation of the welding stud. Since heat is generated in the process of generating the attraction force of the electromagnet, the surface of this type of welding gun will have a phenomenon of excessively high temperature rise after being used continuously for a certain period of time, which will cause the following problems: 1) it is easy to cause the risk of scalding for the operator; 2) it is easy to cause deformation or burning of the electromagnetic coil, so that the welding gun main shaft body is stuck and the welding gun is damaged; 3) the excessively high temperature rise will increase the resistance of the electromagnetic coil, which will reduce the current of the electromagnetic coil, thereby greatly reducing the lifting force of the welding gun, so that the welding stud cannot be lifted, which is particularly obvious when welding large-diameter or super-long welding studs; 4) when the welding stud is lowered, the attraction force between the moving iron core and the static iron core is too large, so that an oil pressure buffer is used for main shaft buffering when the welding gun returns to avoid the safety risk of molten metal splashing when the welding stud is lowered.

[0004] In order to overcome the above-mentioned defects of the electromagnetic welding gun, there is an arc stud welding gun in the prior art which uses a direct current motor to drive the main shaft body to move up and down. The driving mechanism includes a motor and a driving circuit, and usually includes a voltage regulating circuit connected with the driving circuit. Although this direct current motor driven stud welding gun can effectively avoid the defects of short service life, low welding quality and low efficiency of the existing electromagnetic driving mechanism, the voltage signal of the voltage regulating circuit will be affected by the length of the welding gun power line. The long welding gun power line will cause a significant voltage drop, so that the control signal is weak and cannot achieve sensitive control. In addition, the voltage regulating circuit is limited by the working voltage range and cannot be applied to a wide range of working voltage requirements. SUMMARY

[0005] In view of the above-mentioned problems existing in the prior art, the purpose of the present application is to provide a control circuit of a direct current motor driven welding gun which has control performance not affected by the length of the welding gun power line and can be applied to a wide range of working voltages.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] A control circuit of a direct current motor driven welding torch, comprising a main circuit, a main circuit driving circuit and a current regulating circuit, the main circuit is a loop formed by connecting a power supply and a welding torch control line in series, a switch tube Q1 and a sampling resistor R are connected in series on the circuit between the output end of the welding torch control line and the negative pole of the power supply, the main circuit driving circuit comprises resistors R1 and R2 and a switch tube Q2, the current regulating circuit comprises a current sampling circuit a, a comparator U1, a large current circuit, a small current circuit and a delay circuit; wherein: the current sampling circuit a is connected in parallel across the sampling resistor R, and the current sampling circuit a is electrically connected to the V+ pin of the comparator U1, the resistor R1 and the collector of the switch tube Q2 are connected in parallel at the base of the switch tube Q1, the resistor R2 and the base of the switch tube Q2 are connected in parallel at the Vout pin of the comparator U1, and the emitter of the switch tube Q2 is connected to the negative pole; the large current circuit comprises resistors R3 and R4 and a switch tube Q3, the small current circuit comprises resistors R5 and R6 and a switch tube Q4, one end of the resistor R3 is electrically connected to the welding signal input end, and the other end is electrically connected to the base of the switch tube Q3, one end of the resistor R4 is electrically connected to the V- pin of the comparator U1, and the other end is electrically connected to the collector of the switch tube Q3, one end of the resistor R5 is electrically connected to the welding signal input end, and the other end is electrically connected to the base of the switch tube Q4, one end of the resistor R6 is electrically connected to the V- pin of the comparator U1, and the other end is electrically connected to the collector of the switch tube Q4, and the emitters of the switch tubes Q3 and Q4 are both connected to the negative pole; one end of the delay circuit is electrically connected to the circuit between the resistor R3 and the base of the switch tube Q3, and the other end is electrically connected to the circuit between the resistor R5 and the base of the switch tube Q4; and the resistance value of the resistor R4 is greater than that of the resistor R6.

[0008] A preferred scheme further comprises a stabilized power supply, which is connected in series with the power supply and is electrically connected to the main circuit driving circuit and the power input end of the comparator U1.

[0009] A further preferred scheme, the input voltage of the stabilized power supply is 20-190V, and the output voltage of the stabilized power supply is 10-40V.

[0010] A preferred scheme, the main circuit is provided with a unidirectional diode, a capacitor filter circuit and a freewheeling diode.

[0011] An embodiment, the current sampling circuit a is composed of resistors R7 and R8 and a filter capacitor C1, wherein the resistors R7 and R8 are connected in series and then connected in parallel across the sampling resistor R, the filter capacitor C1 is connected in parallel across the resistor R8, and the input end of the filter capacitor C1 is electrically connected to the V+ pin of the comparator U1.

[0012] A preferable scheme is that a light-emitting indicating circuit is connected in series with the circuit between the resistance R1 and the base of the switch tube Q4.

[0013] A preferable scheme is that a light-emitting indicating circuit is connected in series with the circuit between the resistance R5 and the base of the switch tube Q4.

[0014] An embodiment is that the delay circuit is any one of a capacitor charging delay circuit, a single-chip microcomputer delay circuit or a digital circuit delay circuit.

[0015] An embodiment is that the delay circuit is a capacitor charging delay circuit, which comprises charging capacitors CA and CB and a switch tube Q5, wherein the input ends of the charging capacitors CA and CB and the base of the switch tube Q5 are all connected to the output end of the resistance R5, the output ends of the charging capacitors CA and CB and the emitter of the switch tube Q5 are all connected to the negative electrode, and the collector of the switch tube Q5 is connected to the circuit between the resistance R3 and the base of the switch tube Q3.

[0016] A preferable scheme is that a light-emitting indicating circuit is connected in series with the circuit between the input ends of the charging capacitors CA and CB and the base of the switch tube Q5.

[0017] A preferable scheme further comprises a short-circuit protection circuit, which comprises a current sampling circuit b, a photoelectric switch U2, resistances R9 and R10 and a unidirectional thyristor Q, the current sampling circuit b is composed of resistances R11 and R12 and a filter capacitor C2, wherein the resistance R11 is connected in series with the resistance R12 and then connected to the two ends of a sampling resistance R, the filter capacitor C2 is connected to the two ends of the resistance R12, the input end of the filter capacitor C2 is electrically connected to the V+ pin of the photoelectric switch U2, the resistances R9 and R10 are connected in series to the output end of the photoelectric switch U2, the control electrode of the unidirectional thyristor Q is connected to the circuit between the resistances R9 and R10, the anode of the unidirectional thyristor Q is electrically connected to the base of the switch tube Q1, and the cathode of the unidirectional thyristor Q and the other end of the resistance R10 are both connected to the negative electrode.

[0018] Compared with the prior art, the control circuit has the following beneficial technical effects:

[0019] The control circuit provided by the application can not only realize the driving work of the welding gun under the direct current power supply, but also can be applied to a wide range of working voltages of 20-190V, especially can realize the large current promotion and the small current maintenance, and can effectively avoid the welding gun work heating problem; the key is that the control circuit adopts the current regulation control instead of the existing voltage regulation control, which can effectively solve the voltage drop problem caused by the long welding gun line, and avoid the defects of weak signal and insensitive control; in addition, the structure of the control circuit is simple and ingenious, and can be realized only by using common simple components, which is low in cost, easy to realize, and reliable in working performance; therefore, the application has significant progress and practical value compared with the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A structure schematic diagram of a control circuit of a DC motor driven welding gun provided by the embodiment of the present application is provided.

[0021] Figure 2 A structure schematic diagram of a short circuit protection circuit provided by the embodiment of the present application is provided.

[0022] Figure 3 A circuit principle diagram of the control circuit for realizing the on-off of the main circuit provided by the embodiment of the present application is provided.

[0023] Figure 4 A circuit principle diagram of the control circuit for realizing the work in large current boosting provided by the embodiment of the present application is provided.

[0024] Figure 5 A circuit principle diagram of the control circuit for realizing the work in small current maintaining provided by the embodiment of the present application is provided.

[0025] Figure 6 A circuit principle diagram of the short circuit protection circuit for realizing the short circuit protection provided by the embodiment of the present application is provided.

[0026] The labels in the drawings are as follows: 1, main circuit; 1-1, power supply; 1-11, positive pole of the power supply; 1-12, negative pole of the power supply; 1-2, welding gun control line; 1-21, input end of the welding gun control line; 1-22, output end of the welding gun control line; 1-3, unidirectional diode; 1-4, capacitor filter circuit; 1-5, freewheeling diode; 2, main circuit driving circuit; 2-1, light indicating circuit; 3, current regulating circuit; 3-1, current sampling circuit a; 3-2, comparator U1; 3-3, large current circuit; 3-4, small current circuit; 3-41, light indicating circuit; 3-5, delay circuit; 3-51, light indicating circuit; 4, stabilized power supply; 5, short circuit protection circuit; 5-1, current sampling circuit b; 5-2, photoelectric switch U2. DETAILED DESCRIPTION

[0027] The technical solutions of the present application are described in further detail below in combination with the drawings and embodiments.

[0028] EMBODIMENT

[0029] Please refer to Figure 1 as shown:

[0030] The control circuit of the DC motor driven welding gun provided by the embodiment comprises a main circuit 1, a main circuit driving circuit 2, a current regulating circuit 3 and a stabilized power supply 4.

[0031] The main circuit 1 is a loop formed by connecting the power supply 1-1 and the welding gun control line 1-2 in series, and is provided with a unidirectional diode 1-3, a capacitor filter circuit 1-4 and a freewheeling diode 1-5. The unidirectional diode 1-3 is connected in series between the positive electrode 1-11 of the power supply and the input end 1-21 of the welding gun control line; the capacitor filter circuit 1-4 and the freewheeling diode 1-5 are connected in parallel between the positive electrode 1-11 of the power supply and the negative electrode 1-12 of the power supply; and the switching tube Q1 and the sampling resistor R are connected in series between the output end 1-22 of the welding gun control line and the negative electrode 1-12 of the power supply. The switching tube Q1 can be an IGBT tube (i.e., an insulated gate bipolar transistor), a field effect tube, a common triode, a silicon carbide tube or other semiconductor capable of switching current, and the embodiment takes the common triode as an example, but is not limited to this example.

[0032] The main circuit driving circuit 2 includes resistors R1 and R2 and a switching tube Q2. The switching tube Q2 can be an IGBT tube (i.e., an insulated gate bipolar transistor), a field effect tube, a common triode, a silicon carbide tube or other semiconductor capable of switching current, and the embodiment also takes the common triode as an example, but is not limited to this example.

[0033] The current regulating circuit 3 includes a current sampling circuit a 3-1, a comparator U1 3-2, a large current circuit 3-3, a small current circuit 3-4 and a delay circuit 3-5. Wherein:

[0034] The current sampling circuit a 3-1 is composed of resistors R7 and R8 and a filter capacitor C1. The resistor R7 is connected in series with the resistor R8, and then connected in parallel with the two ends of the sampling resistor R. The filter capacitor C1 is connected in parallel with the two ends of the resistor R8. The input end of the filter capacitor C1 is electrically connected with the V+ pin (i.e., the 5 pin of U1 in the figure) of the comparator U1 3-2. The resistor R1 and the collector of the switching tube Q2 are connected in parallel with the base of the switching tube Q1. The resistor R2 and the base of the switching tube Q2 are connected in parallel with the Vout pin (i.e., the 7 pin of U1 in the figure) of the comparator U1 3-2. The emitter of the switching tube Q2 is connected with the negative electrode.

[0035] The large current circuit 3-3 includes resistors R3 and R4 and a switch tube Q3, the small current circuit 3-4 includes resistors R5 and R6 and a switch tube Q4, one end of the resistor R3 is electrically connected with the welding signal input end, the other end is electrically connected with the base of the switch tube Q3, one end of the resistor R4 is electrically connected with the V- pin (i.e. the 6 pin of U1 in the figure) of the comparator U1 3-2, the other end is electrically connected with the collector of the switch tube Q3, one end of the resistor R5 is electrically connected with the welding signal input end, the other end is electrically connected with the base of the switch tube Q4, one end of the resistor R6 is electrically connected with the V- pin (i.e. the 6 pin of U1 in the figure) of the comparator U1 3-2, the other end is electrically connected with the collector of the switch tube Q4, the emitters of the switch tubes Q3 and Q4 are both connected with the negative pole, and the resistance value of the resistor R4 is greater than that of the resistor R6;

[0036] One end of the delay circuit 3-5 is electrically connected with the circuit between the resistor R3 and the base of the switch tube Q3, the other end is electrically connected with the circuit between the resistor R5 and the base of the switch tube Q4; the delay circuit 3-5 can adopt any one of a capacitor charging delay circuit, a single-chip microcomputer delay circuit or a digital circuit delay circuit, and the embodiment takes the capacitor charging delay circuit as an example, the delay circuit 3-5 includes charging capacitors CA and CB and a switch tube Q5, wherein: the input ends of the charging capacitors CA and CB and the base of the switch tube Q5 are both connected with the output end of the resistor R5, the output ends of the charging capacitors CA and CB and the emitter of the switch tube Q5 are both connected with the negative pole, and the collector of the switch tube Q5 is electrically connected with the circuit between the resistor R3 and the base of the switch tube Q3;

[0037] The voltage stabilizing power supply 4 is connected in series with the power supply 1-1, and is electrically connected with the power input ends of the main circuit driving circuit 2 and the comparator U1; the input voltage of the voltage stabilizing power supply is 20-190V, the output voltage of the voltage stabilizing power supply is 10-40V, and a switching power supply or a transformer can be adopted to obtain the voltage stabilization from the commercial power supply.

[0038] In addition, please refer to Figure 2 as shown:

[0039] As a preferred scheme, the control circuit of the welding torch driven by the direct current motor in the embodiment further comprises a short circuit protection circuit 5, the short circuit protection circuit 5 comprises a current sampling circuit b 5-1, a photoelectric switch U2 5-2, resistors R9 and R10 and a unidirectional thyristor Q, the current sampling circuit b 5-1 is composed of resistors R11 and R12 and a filter capacitor C2, the resistor R11 is connected in series with the resistor R12 and then connected in parallel with both ends of a sampling resistor R, the filter capacitor C2 is connected in parallel with both ends of the resistor R12, an input end of the filter capacitor C2 is electrically connected with a V+ pin (i.e., a 1 pin of U2 in the figure) of the photoelectric switch U2, the resistors R9 and R10 are connected in series in sequence at an output end (i.e., a 4 pin of U2 in the figure) of the photoelectric switch U2, a control electrode (i.e., a G level in the figure) of the unidirectional thyristor Q is electrically connected to a circuit between the resistors R9 and R10, an anode (i.e., an A level in the figure) of the unidirectional thyristor Q is electrically connected with a base of the switch tube Q1, and a cathode (i.e., a K level in the figure) of the unidirectional thyristor Q and another end of the resistor R10 are both connected with a negative electrode; the photoelectric switch U2 can adopt an optical coupling or a triode.

[0040] As a preferred scheme:

[0041] A light-emitting indication circuit 2-1 is connected in parallel with both ends of the resistor R1, the light-emitting indication circuit 2-1 is composed of a resistor R13 and a light-emitting diode D1 connected in series, and is used to display the on-off of the switch tube Q1.

[0042] A light-emitting indication circuit 3-41 is connected in series in a circuit between the resistor R5 and a base of the switch tube Q4, the light-emitting indication circuit 3-41 is composed of a resistor R14 and a light-emitting diode D2 connected in series, and is used to display the on-off of the switch tube Q4.

[0043] A light-emitting indication circuit 3-51 is connected in series in a circuit between input ends of the charging capacitors CA and CB and a base of the switch tube Q5, the light-emitting indication circuit 3-51 is composed of a resistor R15 and a light-emitting diode D3 connected in series, and is used to display the on-off of the switch tube Q5.

[0044] Figure 3 The control circuit provided by the embodiment of the present application realizes the circuit principle diagram of the on-off of the main circuit, as shown in the figure: Figure 3

[0045] When a V+ pin (i.e., a 5 pin of U1 in the figure) of U1 has a voltage lower than that of a V- pin (i.e., a 6 pin of U1 in the figure) of U1, a Vout pin (i.e., a 7 pin of U1 in the figure) of U1 outputs a low level, so that the resistor R2 cannot trigger the Q2 to be turned on, thereby causing the resistor R1 to trigger the Q1 to be turned on.

[0046] ​When the voltage of the V+ pin of U1 (i.e. the 5 pin of U1 in the figure) is higher than the voltage of the V- pin of U1 (i.e. the 6 pin of U1 in the figure), the Vout pin of U1 (i.e. the 7 pin of U1 in the figure) outputs high level, causing the resistance R2 to trigger the conduction of Q2, so that Q1 is turned off;

[0047] The conduction and turn-off of Q1 determines whether the main circuit has current, and realizes the chopper circuit of the main circuit, so that the main circuit can form the precise current control in conformity with the driving of the direct current motor, i.e. at the beginning of welding, there is large current to realize rapid lifting, and after the lifting is realized, small current is maintained.

[0048] Figure 4 The control circuit provided by the embodiment of the present application realizes the circuit principle diagram of large current lifting work, as shown in Figure 4 The control circuit provided by the embodiment of the present application realizes the circuit principle diagram of large current lifting work, as shown in

[0049] When the welding start signal arrives, Q3 is turned on by R3, and the resistance R4 works. Because the resistance value of R4 is large, the voltage of the 6 pin of U1 is high, and the main circuit has large current, so that the voltage of the two ends of the sampling resistance R is high, and then the voltage of the 5 pin of U1 is divided by the current sampling circuit a. Once the voltage of the 5 pin of U1 is higher than the voltage of the 6 pin of U1, Q1 will be turned off. When the voltage of the 5 pin of U1 is lower than the voltage of the 6 pin of U1, Q1 will be turned on repeatedly, so as to realize the chopper circuit of the main circuit under large current, until the delay circuit 3-5 starts to work and changes to small current work. The required lifting current can be obtained by adjusting the resistance value of R4.

[0050] Figure 5 The control circuit provided by the embodiment of the present application realizes the circuit principle diagram of small current maintenance work, as shown in Figure 5 The control circuit provided by the embodiment of the present application realizes the circuit principle diagram of small current maintenance work, as shown in

[0051] When Q5 in the delay circuit is turned on, Q3 will be turned off, so that the large current in the main circuit disappears. At this time, the resistance R5 makes Q4 conduct, and the resistance R6 works. Because the resistance value of R6 is small, the voltage of the 6 pin of U1 is low, and the main circuit has small current (the required small current can be obtained by adjusting the resistance value of R6). When the voltage of the 5 pin of U1 is higher than the voltage of the 6 pin of U1, Q1 will be turned off. When the voltage of the 5 pin of U1 is lower than the voltage of the 6 pin of U1, Q1 will be turned on repeatedly, so as to realize the chopper circuit of the main circuit under small current, until the welding control signal is turned off.

[0052] Figure 6 The short circuit protection circuit provided by the embodiment of the present application realizes the circuit principle diagram of short circuit protection, as shown in Figure 6 The short circuit protection circuit provided by the embodiment of the present application realizes the circuit principle diagram of short circuit protection, as shown in

[0053] When the welding torch control line is short-circuited, the voltage across the sampling resistor R rises rapidly due to no load motor in the main circuit, so that the current sampling circuit b 5-1 triggers the photoelectric switch U2 5-2 to turn on, the photoelectric switch U2 5-2 triggers the unidirectional thyristor Q to turn on through the resistor R9, so that Q1 is triggered without current and is turned off, and then the main circuit is also turned off, avoiding the risk of burning the main circuit caused by the short circuit of the welding torch, and ensuring the safety of the operator and the welding equipment.

[0054] As can be seen from the above: the control circuit provided by the application can not only realize the driving work of the welding torch under the direct current power supply, but also can be applied to a wide range of working voltages (can be applied to a wide range of working voltages of 20-190V), especially can realize large current lifting and small current maintenance, and can effectively avoid the welding torch work heating problem; the key is that the control circuit described in the application can effectively solve the voltage drop problem caused by the long welding torch line by using current regulation control instead of the existing voltage regulation control, avoiding the defects of weak signal and insensitive control; in addition, the structure of the control circuit described in the application is simple and ingenious, and can be realized only by using common simple components, which not only has low cost and is easy to realize, but also has reliable working performance; therefore, the application has significant progress and practical value compared with the prior art.

[0055] Finally, it is necessary to point out here that: the above description is only the preferred specific embodiment of the application, but the protection scope of the application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the application, which should be covered within the protection scope of the application.

Claims

1. A control circuit for a DC motor-driven welding torch, characterized in that: The circuit includes a main circuit, a main circuit drive circuit, and a current regulation circuit. The main circuit is a loop formed by connecting the power supply and the welding torch control line in series. A switching transistor Q1 and a sampling resistor R are connected in series between the output terminal of the welding torch control line and the negative terminal of the power supply. The main circuit drive circuit includes resistors R1 and R2 and the switching transistor Q2. The current regulation circuit includes a current sampling circuit a, a comparator U1, a high-current circuit, a low-current circuit, and a delay circuit. Specifically: the current sampling circuit a is connected in parallel across the sampling resistor R, and is electrically connected to the V+ pin of the comparator U1; resistor R1 is connected in parallel with the collector of the switching transistor Q2 and in parallel with the base of the switching transistor Q1; resistor R2 is connected in parallel with the base of the switching transistor Q2 and in parallel with the Vout pin of the comparator U1; the emitter of the switching transistor Q2 is connected to the negative terminal; the high-current circuit includes resistors R3 and R4.

4. The low-current circuit includes resistors R5 and R6 and a switching transistor Q4. One end of resistor R3 is electrically connected to the welding signal input terminal, and the other end is electrically connected to the base of switching transistor Q3. One end of resistor R4 is electrically connected to the V-pin of comparator U1, and the other end is electrically connected to the collector of switching transistor Q3. One end of resistor R5 is electrically connected to the welding signal input terminal, and the other end is electrically connected to the base of switching transistor Q4. One end of resistor R6 is electrically connected to the V-pin of comparator U1, and the other end is electrically connected to the collector of switching transistor Q4. The emitters of both switching transistors Q3 and Q4 are connected to the negative terminal. One end of the delay circuit is electrically connected to the circuit between resistor R3 and the base of switching transistor Q3, and the other end is electrically connected to the circuit between resistor R5 and the base of switching transistor Q4. The resistance value of resistor R4 is greater than the resistance value of resistor R6.

2. The control circuit for the DC motor-driven welding torch according to claim 1, characterized in that: It also includes a regulated power supply, which is connected in series with the power supply and electrically connected to the power input terminal of the main circuit drive circuit and comparator U1.

3. The control circuit for the DC motor-driven welding torch according to claim 2, characterized in that: The input voltage of the regulated power supply is 20-190V, and the output voltage of the regulated power supply is 10-40V.

4. The control circuit for the DC motor-driven welding torch according to claim 1, characterized in that: The main circuit is equipped with a unidirectional diode, a capacitor filter circuit, and a freewheeling diode.

5. The control circuit for the DC motor-driven welding torch according to claim 1, characterized in that: The current sampling circuit a consists of resistors R7 and R8 and a filter capacitor C1. Resistors R7 and R8 are connected in series and then connected in parallel with the two ends of the sampling resistor R. The filter capacitor C1 is connected in parallel with the two ends of resistor R8, and the input end of the filter capacitor C1 is electrically connected to the V+ pin of comparator U1.

6. The control circuit for the DC motor-driven welding torch according to claim 1, characterized in that: An indicator circuit is connected in parallel across resistor R1; an indicator circuit is connected in series between resistor R5 and the base of switching transistor Q4.

7. The control circuit for the DC motor-driven welding torch according to claim 1, characterized in that: The delay circuit can be any one of a capacitor charging delay circuit, a microcontroller delay circuit, or a digital circuit delay circuit.

8. The control circuit for the DC motor-driven welding torch according to claim 1, characterized in that: The delay circuit is a capacitor charging delay circuit, including charging capacitors CA and CB and a switching transistor Q5. The input terminals of charging capacitors CA and CB and the base of switching transistor Q5 are connected in parallel to the output terminal of resistor R5. The output terminals of charging capacitors CA and CB and the emitter of switching transistor Q5 are connected to the negative terminal. The collector of switching transistor Q5 is electrically connected to the circuit between resistor R3 and the base of switching transistor Q3.

9. The control circuit for the DC motor-driven welding torch according to claim 8, characterized in that: An indicator circuit is connected in series between the input terminals of charging capacitors CA and CB and the base of switching transistor Q5.

10. The control circuit for a DC motor-driven welding torch according to any one of claims 1 to 9, characterized in that: It also includes a short-circuit protection circuit, which includes a current sampling circuit b, a photoelectric switch U2, resistors R9 and R10, and a unidirectional thyristor Q. The current sampling circuit b is composed of resistors R11 and R12 and a filter capacitor C2. Resistors R11 and R12 are connected in series and then connected in parallel with the two ends of the sampling resistor R. The filter capacitor C2 is connected in parallel across the two ends of resistor R12, and the input end of the filter capacitor C2 is electrically connected to the V+ pin of the photoelectric switch U2. Resistors R9 and R10 are connected in series with the output end of the photoelectric switch U2. The control electrode of the unidirectional thyristor Q is electrically connected to the circuit between resistors R9 and R10. The anode of the unidirectional thyristor Q is electrically connected to the base of the switching transistor Q1. The cathode of the unidirectional thyristor Q and the other end of resistor R10 are both connected to the negative terminal.

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