Primary feedback control welding power supply circuit and inverter welding machine using the same

Abstract

The present invention discloses a primary feedback control welding power supply circuit, comprising: an inverter unit, the input end of the inverter unit is connected to direct current; a buck rectifier filter unit, the input end of the buck rectifier filter unit is connected to the output end of the inverter unit, and the output end of the buck rectifier filter unit is connected to an external welding electrode; a feedback unit, the feedback unit is connected to the input end of the buck rectifier filter unit; a comparison control unit, provided with a first comparison input end, a second comparison input end and a control output end, the first comparison input end is connected to the feedback unit, the second comparison input end is connected to a reference voltage, and the control output end is connected to the control end of the inverter unit. By obtaining a feedback signal from the input end of the buck rectifier filter unit, the interference of the welding environment on the feedback signal can be reduced, thereby making the final output direct current, that is, the load current, more stable, and improving the reliability of welding.

Description

Technical Field

[0001] The invention relates to the field of power supplies, in particular to a welding power supply circuit and an electric welder using the same. Background Art

[0002] Welding, as a common processing method to achieve connection, has the advantages of good connection performance, high welding structure rigidity and good integrity. Among welding equipment, inverter welding machines are widely used due to their small size, simple operation and high work efficiency.

[0003] The general output characteristic of the inverter welding machine is constant current output. In order to make the output current constant, current negative feedback is required. In the prior art, the current feedback signal is sampled from the load current, usually the output current of the welding electrode. However, the output current of the welding electrode is easily affected by the interference from the welding environment, resulting in unstable output current and affecting the welding effect. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a primary feedback control welding power supply circuit and an inverter welding machine using the same, which can avoid interference from the welding environment and make the output current more stable.

[0005] A technical solution provided by the present invention to solve the technical problem is:

[0006] Primary feedback controlled welding power supply circuit, comprising:

[0007] An inverter unit, wherein an input end of the inverter unit is connected to direct current;

[0008] A buck rectifier and filter unit, wherein the input end of the buck rectifier and filter unit is connected to the output end of the inverter unit, and the output end of the buck rectifier and filter unit is connected to an external welding electrode;

[0009] A feedback unit, the feedback unit is connected to an input end of the step-down rectifying and filtering unit;

[0010] The comparison control unit is provided with a first comparison input terminal, a second comparison input terminal and a control output terminal, wherein the first comparison input terminal is connected to the feedback unit, the second comparison input terminal is connected to a reference voltage, and the control output terminal is connected to the control terminal of the inverter unit.

[0011] Preferably, the feedback unit includes a current transformer and a rectifier module, the current transformer is coupled to the input end of the step-down rectifier and filter unit, the output end of the current transformer is connected to the input end of the rectifier module, and the output end of the rectifier module is connected to the first comparison input end.

[0012] Preferably, it further includes a ramp compensation unit, the comparison control unit includes an oscillation module, the ramp compensation unit is connected to the oscillation module to generate a ramp signal, and the ramp compensation unit is respectively connected to the output end of the rectifier module and the first comparison input end.

[0013] Preferably, the ramp compensation unit includes a transistor Q5, a resistor R10 and a resistor R12;

[0014] The collector of the transistor Q5 is connected to an external power supply, the base of the transistor Q5 is connected to the oscillation module, and the emitter of the transistor Q5 is connected to one end of the resistor R10;

[0015] The other end of the resistor R10 is respectively connected to the output end of the rectifier module, the first comparison input end and one end of the resistor R12;

[0016] The other end of the resistor R12 is grounded.

[0017] Preferably, it also includes a voltage compensation unit and a superposition unit, the voltage compensation unit is connected to the comparison control unit to generate a voltage compensation signal, the input end of the superposition unit is respectively connected to the voltage compensation unit and a reference voltage, and the output end of the superposition unit is connected to the second comparison input end.

[0018] Preferably, the comparison control unit includes a comparator and a complementary output module, the comparator non-phase input terminal is connected to the first comparison input terminal, the comparator inverting input terminal is connected to the second comparison input terminal, the complementary output module is connected to the output terminal of the comparator to generate two complementary PWM control signals, and the complementary output module is connected to the control terminal of the inverter unit.

[0019] Preferably, the complementary output module comprises a T trigger, the input end of the T trigger is connected to the output end of the comparator, and the positive phase output end and the negative phase output end of the T trigger are both connected to the control end of the inverter unit.

[0020] Preferably, the voltage compensation unit includes a switch tube Q7, a switch tube Q8, an inductor L1, a diode D15 and an adjustable resistor R15;

[0021] The input end of the switch tube Q7 is respectively connected to the input end of the switch tube Q8 and the external power supply, the control end of the switch tube Q7 is connected to the positive phase output end of the T trigger, and the output end of the switch tube Q7 is respectively connected to the output end of the switch tube Q8, the cathode of the diode D15 and one end of the adjustable resistor R15;

[0022] The control end of the switch tube Q8 is connected to the reverse output end of the T trigger;

[0023] The adjusting end of the adjustable resistor R15 is connected to the input end of the superposition unit, and the other end of the adjustable resistor R15 and the anode of the diode D15 are grounded.

[0024] Preferably, the superposition unit includes an operational amplifier U2, a resistor R13, a resistor R4 and a resistor R8;

[0025] One end of the resistor R13 is connected to the reference voltage, and the other end of the resistor R13 is respectively connected to one end of the resistor R4, one end of the resistor R8 and the inverting input end of the operational amplifier U2;

[0026] The other end of the resistor R4 is connected to the voltage compensation unit;

[0027] A non-inverting input terminal of the operational amplifier U2 is grounded, and an output terminal of the operational amplifier U2 is connected to the other end of the resistor R8 and the second comparison input terminal respectively.

[0028] Another technical solution provided by the present invention is:

[0029] Inverter electric welding machine: includes the above-mentioned welding power supply circuit, and also includes a rectifier filter circuit and a welding electrode, the input end of the rectifier filter circuit is connected to the external mains, the output end of the rectifier filter circuit is connected to the input end of the inverter unit, and the output end of the step-down rectifier filter unit is connected to the welding electrode.

[0030] The beneficial effects of the present invention are as follows: the feedback unit is connected to the input end of the step-down rectifier and filter unit, the feedback unit generates a feedback signal and transmits it to the first comparison input end, the comparison control unit compares the feedback signal and the reference voltage to generate a PWM control signal, the comparison control unit transmits the PWM signal to the inverter unit to control the inverter unit to generate suitable alternating current, the alternating current is converted into direct current suitable for welding after being processed by the step-down rectifier and filter unit, and by obtaining the feedback signal from the input end of the step-down rectifier and filter unit, the interference of the welding environment on the feedback signal can be reduced compared to the method of obtaining it from the load current, thereby making the final output direct current, that is, the load current, more stable, thereby improving the reliability of welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0032] Figure 1 It is a principle block diagram of one embodiment of the present invention;

[0033] Figure 2It is a circuit diagram of a comparison control unit, a rectifier module, a ramp compensation unit, a voltage compensation unit and a superposition unit;

[0034] Figure 3 It is the circuit diagram of the inverter unit, the step-down rectifier filter unit and the current transformer;

[0035] Figure 4 It is a graph showing the relationship between load current and PWM control signal duty cycle without voltage compensation;

[0036] Figure 5 This is a graph showing the relationship between load current and duty cycle of PWM control signal with voltage compensation. DETAILED DESCRIPTION

[0037] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it should not be understood as a limitation on the scope of protection of the present invention.

[0038] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0039] Reference Figures 1 to 3 The primary feedback control welding power supply circuit provided by the present invention comprises:

[0040] An inverter unit 10, wherein an input end of the inverter unit 10 is connected to direct current;

[0041] A buck rectifying and filtering unit 20, wherein the input end of the buck rectifying and filtering unit 20 is connected to the output end of the inverter unit 10, and the output end of the buck rectifying and filtering unit 20 is connected to an external welding electrode;

[0042] A feedback unit 30, the feedback unit 30 is connected to the input end of the buck rectifying and filtering unit 20;

[0043] The comparison control unit 40 is provided with a first comparison input terminal, a second comparison input terminal and a control output terminal. The first comparison input terminal is connected to the feedback unit 30 , the second comparison input terminal is connected to the reference voltage, and the control output terminal is connected to the control terminal of the inverter unit 10 .

[0044] The feedback unit 30 is connected to the input end of the buck rectifier and filter unit 20. The feedback unit 30 generates a feedback signal and transmits it to the first comparison input end. The comparison control unit 40 compares the feedback signal and the reference voltage to generate a PWM control signal. The comparison control unit 40 transmits the PWM signal to the inverter unit to control the inverter unit 10 to generate suitable alternating current. The alternating current is converted into direct current suitable for welding after being processed by the buck rectifier and filter unit 20. By obtaining the feedback signal from the input end of the buck rectifier and filter unit 20, the interference of the welding environment on the feedback signal can be reduced compared to the method of obtaining it from the load current, thereby making the final output direct current, that is, the load current, more stable, thereby improving the reliability of welding.

[0045] refer to Figure 3 The step-down rectifier and filter unit 20 generally includes a transformer T1, a diode D1, a diode D2, an inductor L0 and a resistor Rf. The primary coil of the transformer T1 is connected to the output end of the inverter unit 10. The secondary coil of the transformer T2 and the diode D1 and the diode D2 form a full-wave rectifier circuit. The inductor L0 and the resistor Rf form an RL filter circuit. The output end of the full-wave rectifier circuit is connected to the RL filter circuit, and the RL filter circuit is connected to the external welding electrode.

[0046] According to the working principle of transformer T1, the primary coil current of transformer T1 is proportional to the secondary coil current, and after the secondary coil current of transformer T1 is rectified and filtered, the final load current, i.e., the welding current, is also proportional to the primary coil current of transformer T1, specifically, the average value of the load current is proportional to the peak value of the primary coil current of transformer T1. Therefore, the feedback unit 30 generates a feedback signal by connecting to the input end of the step-down rectifier and filter unit 20, i.e., the primary coil of transformer T1. The feedback signal can reflect the change of the load current, thereby achieving an effect similar to that of generating a feedback signal by sampling the load end. At the same time, the feedback signal is less affected by the interference of the welding environment, which is conducive to stabilizing the load current.

[0047] refer to Figure 3 As a preferred embodiment of the inverter unit 10, the inverter unit 10 adopts a full-bridge inverter circuit. The comparison control unit 40 is connected to the control ends of the four switch tubes in the full-bridge inverter circuit. Compared with the half-bridge inverter circuit, the full-bridge inverter circuit has a higher output power and is more suitable for welding. As a further preferred embodiment, the switch tube in the full-bridge inverter circuit uses an IGBT tube, which has the advantages of fast response speed and high efficiency. In the case where the control output end of the comparison control unit 40 cannot directly drive the IGBT tube, the control output end can be connected to the control end of the inverter unit 10 through an IGBT driver chip.

[0048] refer to Figures 1 to 3As a preferred implementation of the feedback unit 30, the feedback unit 30 includes a current transformer 31 and a rectifier module 32. The current transformer 31 is coupled to the input end of the step-down rectifier and filter unit 20, the output end of the current transformer 31 is connected to the input end of the rectifier module 32, and the output end of the rectifier module 32 is connected to the first comparison input end.

[0049] The current transformer 31 samples the input current of the step-down rectifier filter unit 20, specifically the primary coil current of the sampling transformer T1. The primary coil current of the transformer T1 is the alternating current output by the inverter unit 10. The sampled current signal is also an alternating current signal. The rectifier module 32 is required to process the sampled current signal to form a feedback signal and transmit it to the first input end of the comparator 42. Then the comparator 42 generates a PWM signal based on the feedback signal and the reference voltage. The feedback unit 30 can also be an implementation method including a Hall current sensor and a rectifier bridge. The Hall current sensor samples the primary coil current signal of the transformer T1, and the current signal is rectified by the rectifier bridge to form a feedback signal; the feedback unit 30 can also be an implementation method including a shunt, an amplification module and a rectifier bridge. The current signal is sampled by the shunt, amplified by the amplification module and rectified by the rectifier bridge to form a feedback signal.

[0050] refer to Figure 2 As a preferred embodiment, it also includes a ramp compensation unit 50, the comparison control unit 40 includes an oscillation module 41, the ramp compensation unit 50 is connected to the oscillation module 41 to generate a ramp signal, and the ramp compensation unit 50 is respectively connected to the output end of the rectifier module 32 and the first comparison input end.

[0051] In the current PWM control mode, when the duty cycle of the PWM signal output by the comparison control unit 40 exceeds 50%, an oscillation problem may occur, resulting in an unstable PWM signal. In order to prevent oscillation, the ramp compensation unit 50 is connected to the oscillation module 41 to generate a ramp signal, and the ramp compensation unit 50 is connected to the output end of the rectifier module 32, so that the ramp signal is superimposed on the feedback signal to achieve ramp compensation of the feedback signal, and the superimposed signal is transmitted to the first comparison input end, so that the oscillation can be suppressed by ramp compensation, making the output PWM signal more stable.

[0052] The oscillation module 41 can generate a working frequency signal, ie, a clock signal. The oscillation module 41 generally includes an oscillator, a timing capacitor CT, and a timing resistor RT.

[0053] refer to Figure 2 , as a preferred embodiment of the ramp compensation unit 50 , the ramp compensation unit 50 includes a transistor Q5 , a resistor R10 and a resistor R12 ;

[0054] The collector of the transistor Q5 is connected to an external power supply, the base of the transistor Q5 is connected to the oscillation module 41, and the emitter of the transistor Q5 is connected to one end of the resistor R10;

[0055] The other end of the resistor R10 is respectively connected to the output end of the rectifier module 32, the first comparison input end and one end of the resistor R12;

[0056] The other end of the resistor R12 is grounded.

[0057] The base of the transistor Q5 is connected to the oscillation module 41, specifically to one end of the timing capacitor CT. When the oscillation module 41 generates a clock signal, a ramp signal with the same frequency will be generated on the timing capacitor CT. The transistor Q5 amplifies the ramp signal on the timing capacitor CT, and then divides the voltage through the resistors R10 and R12. Finally, the ramp signal is superimposed on the feedback signal to achieve ramp compensation.

[0058] refer to Figure 4 When the reference voltage remains unchanged, that is, the voltage at the second comparison input terminal remains unchanged, due to the effects of the primary excitation current of the transformer T1 and the ramp compensation, there is an error between the actual load current and the set current value, and the error will change with the duty cycle of the PWM signal output by the comparison control unit 40. Specifically, the actual load current decreases with the increase of the duty cycle of the PWM signal.

[0059] refer to Figure 2 In order to solve the above problem and make the actual load current output constant, the system further includes a voltage compensation unit 60 and a superposition unit 70. The voltage compensation unit 60 is connected to the comparison control unit 40 to generate a voltage compensation signal ( Figure 2 Ub), the input end of the superposition unit 70 is respectively connected to the voltage compensation unit 60 and the reference voltage ( Figure 2 Ua) connection, the output end of the superposition unit 70 is connected to the second comparison input end.

[0060] The voltage compensation unit 60 generates a voltage compensation signal according to the PWM signal output by the comparison control unit 40, and the superposition unit 70 superimposes the voltage compensation signal with the reference voltage and inputs the resultant voltage to the second comparison input terminal. Since the voltage compensation signal is affected by the PWM signal, when the duty cycle of the PWM signal changes, the voltage compensation signal will also change accordingly, so that the voltage compensation signal is superimposed with the reference voltage and inputs the resultant voltage to the second comparison input terminal. The voltage at the second comparison input terminal changes with the duty cycle of the PWM signal, thereby changing the set current value curve. Figure 5 Under the action of the voltage compensation unit 60 and the superposition unit 70, the set current curve increases with the duty cycle of the PWM signal, and finally the actual load current value is stabilized.

[0061] refer to Figure 2 As a preferred embodiment, the comparison control unit 40 includes a comparator 42 and a complementary output module 43, the non-phase input terminal of the comparator 42 is connected to the first comparison input terminal, the inverting input terminal of the comparator 42 is connected to the second comparison input terminal, the complementary output module 43 is connected to the output terminal of the comparator 42 to generate two complementary PWM control signals, and the complementary output module 43 is connected to the control terminal of the inverter unit 10.

[0062] Since the two switch tubes in the same bridge arm of the inverter unit 10 are working, the inversion of direct current is achieved by turning on one switch tube and turning off the other switch tube. After the feedback signal voltage and the reference voltage input by the feedback unit 30 are compared by the comparator 42 to generate a PWM control signal, the PWM control signal is transmitted to the complementary output module 43 to generate two complementary PWM control signals, and the two complementary PWM control signals respectively control the two switch tubes in the same bridge arm of the inverter unit 10 to meet the control requirements of the inverter unit and realize the process of inverting direct current. The comparison control unit 40 can also be an implementation method including a DSP chip, the feedback unit 30 transmits the feedback signal to the DSP chip, and the DSP chip outputs a suitable PWM signal to the inverter unit 10 after calculating according to the feedback signal; the comparison control unit 40 can also be other devices or circuits that can adjust the output PWM signal according to the feedback signal.

[0063] refer to Figure 2 As a preferred embodiment of the complementary output module 43, the complementary output module 43 includes a T flip-flop, the input end of the T flip-flop is connected to the output end of the comparator 42, and the positive phase output end of the T flip-flop and the negative phase output end of the T flip-flop are both connected to the control end of the inverter unit 10. The oscillation module 41 can be connected to the clock signal input end of the T flip-flop to control the frequency of the output signal of the T flip-flop.

[0064] refer to Figure 2 As a preferred embodiment of the voltage compensation unit 60, the voltage compensation unit 60 includes a switch tube Q7, a switch tube Q8, an inductor L1, a diode D15 and an adjustable resistor R15;

[0065] The input end of the switch tube Q7 is respectively connected to the input end of the switch tube Q8 and the external power supply, the control end of the switch tube Q7 is connected to the positive phase output end of the T trigger, and the output end of the switch tube Q7 is respectively connected to the output end of the switch tube Q8, the cathode of the diode D15 and one end of the adjustable resistor R15;

[0066] The control end of the switch tube Q8 is connected to the reverse output end of the T trigger;

[0067] An adjusting end of the adjustable resistor R15 is connected to the input end of the superposition unit 70 , and the other end of the adjustable resistor R15 and the anode of the diode D15 are grounded.

[0068] The switch tube Q7, the switch tube Q8, the inductor L1 and the diode D15 form a dual switch tube BUCK circuit, the adjustable resistor R15 serves as the load of the dual switch tube BUCK circuit, and the voltage on the adjustable resistor R15 forms a voltage compensation signal. The positive phase output terminal and the negative phase output terminal respectively output complementary PWM signals, and the switch tube Q7 and the switch tube Q8 work under the control of the complementary PWM signal output by the comparison control unit 40, so that the voltage compensation signal on the variable resistor R15 is associated with the PWM signal. At the same time, since the inverter unit 10 is also controlled by the PWM signal of the comparison control unit 40, the output current of the inverter unit 10 is also associated with the PWM signal, and there is a proportional relationship between the input voltage and the output voltage Uf of the buck rectifier filter unit 20, therefore, the voltage compensation signal is proportional to the output voltage Uf.

[0069] The change of the output signal can be reflected by the voltage compensation signal, and the voltage compensation signal is superimposed on the reference voltage to adjust the set current value curve. In addition, the voltage rising slope of the voltage compensation signal can be adjusted by adjusting the adjustment end of the adjustable resistor R15. When the voltage rising slope of the voltage compensation signal is the same as the slope of the ramp signal output by the ramp compensation unit 50, the load current can be kept constant and does not change with the change of the duty cycle of the PWM signal.

[0070] refer to Figure 2 , as a preferred embodiment of the superposition unit 70, the superposition unit 70 includes an operational amplifier U2, a resistor R13, a resistor R4 and a resistor R8;

[0071] One end of the resistor R13 is connected to the reference voltage, and the other end of the resistor R13 is respectively connected to one end of the resistor R4, one end of the resistor R8 and the inverting input end of the operational amplifier U2;

[0072] The other end of the resistor R4 is connected to the voltage compensation unit 60;

[0073] A non-inverting input terminal of the operational amplifier U2 is grounded, and an output terminal of the operational amplifier U2 is connected to the other end of the resistor R8 and the second comparison input terminal respectively.

[0074] The operational amplifier U2, the resistor R13, the resistor R4 and the resistor R8 form an adder, which can add the reference voltage and the voltage compensation signal in proportion and then output the result. The adder has a simple structure and is easy to implement.

[0075] The comparison control unit 40 preferably adopts a current-type PWM power supply controller 3846 chip.

[0076] The inverter electric welding machine provided by the present invention includes the welding power supply circuit in the above embodiment, and also includes a rectifier filter circuit and a welding electrode. The input end of the rectifier filter circuit is connected to the external mains, the output end of the rectifier filter circuit is connected to the input end of the inverter unit 10, and the output end of the step-down rectifier filter unit 20 is connected to the welding electrode.

[0077] The rectifier and filter circuit converts the AC power into DC power and inputs it into the inverter unit 10. The comparison control unit 40 controls the inverter unit 10 to output a suitable AC power. After being processed by the step-down rectifier and filter unit 20, the DC power is formed into welding power and output to the welding electrode for welding. The feedback signal of the feedback unit 30 is taken from the input end of the rectifier and filter unit, which can reduce the interference of the welding environment and make the output welding DC power more stable.

[0078] The above embodiments are only preferred embodiments of the present invention, and the present invention may have other embodiments. Those skilled in the art may also make equivalent modifications or substitutions without violating the spirit of the present invention, and these equivalent modifications or substitutions are all included in the scope set by the claims of this application.

Claims

1. Primary feedback controlled welding power supply circuit, characterized in that, include: An inverter unit (10), wherein an input end of the inverter unit (10) is connected to direct current; A step-down rectifying and filtering unit (20), wherein an input end of the step-down rectifying and filtering unit (20) is connected to an output end of the inverter unit (10), and an output end of the step-down rectifying and filtering unit (20) is connected to an external welding electrode; A feedback unit (30), the feedback unit (30) being connected to an input end of the step-down rectifying and filtering unit (20); A comparison control unit (40) is provided with a first comparison input terminal, a second comparison input terminal and a control output terminal, wherein the first comparison input terminal is connected to the feedback unit (30), the second comparison input terminal is connected to a reference voltage, and the control output terminal is connected to the control terminal of the inverter unit (10); The feedback unit (30) comprises a current transformer (31) and a rectifier module (32), the current transformer (31) is coupled to the input end of the step-down rectifier filter unit (20), the output end of the current transformer (31) is connected to the input end of the rectifier module (32), and the output end of the rectifier module (32) is connected to the first comparison input end; It also includes a ramp compensation unit (50), the comparison control unit (40) includes an oscillation module (41), the ramp compensation unit (50) is connected to the oscillation module (41) to generate a ramp signal, and the ramp compensation unit (50) is respectively connected to the output end of the rectification module (32) and the first comparison input end; It also includes a voltage compensation unit (60) and a superposition unit (70), wherein the voltage compensation unit (60) is connected to the comparison control unit (40) to generate a voltage compensation signal, the input end of the superposition unit (70) is respectively connected to the voltage compensation unit (60) and a reference voltage, and the output end of the superposition unit (70) is connected to the second comparison input end; The comparison control unit (40) comprises a comparator (42) and a complementary output module (43), the non-phase input terminal of the comparator (42) is connected to the first comparison input terminal, the negative input terminal of the comparator (42) is connected to the second comparison input terminal, the complementary output module (43) is connected to the output terminal of the comparator (42) to generate two complementary PWM control signals, and the complementary output module (43) is connected to the control terminal of the inverter unit (10); The complementary output module (43) comprises a T trigger, the input end of the T trigger is connected to the output end of the comparator (42), and the positive phase output end and the negative phase output end of the T trigger are both connected to the control end of the inverter unit (10); The voltage compensation unit (60) comprises a switch tube Q7, a switch tube Q8, an inductor L1, a diode D15 and an adjustable resistor R15; The input end of the switch tube Q7 is respectively connected to the input end of the switch tube Q8 and the external power supply, the control end of the switch tube Q7 is connected to the positive phase output end of the T trigger, and the output end of the switch tube Q7 is respectively connected to the output end of the switch tube Q8, the cathode of the diode D15 and one end of the adjustable resistor R15; The control end of the switch tube Q8 is connected to the reverse output end of the T trigger; the adjustment end of the adjustable resistor R15 is connected to the input end of the superposition unit (70), and the other end of the adjustable resistor R15 and the anode of the diode D15 are grounded; The superposition unit (70) comprises an operational amplifier U2, a resistor R13, a resistor R4 and a resistor R8; One end of the resistor R13 is connected to the reference voltage, and the other end of the resistor R13 is respectively connected to one end of the resistor R4, one end of the resistor R8 and the inverting input end of the operational amplifier U2; The other end of the resistor R4 is connected to the voltage compensation unit (60); A non-inverting input terminal of the operational amplifier U2 is grounded, and an output terminal of the operational amplifier U2 is connected to the other end of the resistor R8 and the second comparison input terminal respectively.

2. The primary feedback controlled welding power supply circuit according to claim 1, characterized in that: The ramp compensation unit (50) comprises a transistor Q5, a resistor R10 and a resistor R12; The collector of the transistor Q5 is connected to an external power supply, the base of the transistor Q5 is connected to the oscillation module (41), and the emitter of the transistor Q5 is connected to one end of the resistor R10; The other end of the resistor R10 is respectively connected to the output end of the rectifier module (32), the first comparison input end and one end of the resistor R12; The other end of the resistor R12 is grounded.

3. Inverter welding machine, characterized by: It comprises a welding power supply circuit as described in any one of claims 1 to 2, and also comprises a rectifier filter circuit and a welding electrode, wherein the input end of the rectifier filter circuit is connected to an external mains power supply, the output end of the rectifier filter circuit is connected to the input end of the inverter unit (10), and the output end of the step-down rectifier filter unit (20) is connected to the welding electrode.

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