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Working Principle Of Spot Welder Circuit
Dec 12, 2018

The working principle of spot welding machine circuit spot welding machine B2 is a step-down transformer. It is also the core component of welding machine. AB2 rectifier bridge, SCR, UJT, resistance R2, R3, R4, R5, capacitance C2 and potentiometer RP constitute the stepless regulator of welding current. DC ammeter A is used to indirectly indicate the working current of welding. Just with the LED power supply indicator circuit. Small transformer B1, rectifier bridge AB1, capacitor C1 and fan M constitute the heat dissipation system. From the diagram, we can see that the circuit of the equipment is very concise. To be complex, it can only be regarded as a current regulator. The relaxation oscillator is composed of the negative resistance characteristics of the single junction transistor, which acts as the trigger circuit of the one-way thyristor. Because the power supply of the single junction transistor relaxation oscillator is derived from the full-wave pulsating DC voltage output from the bridge rectifier circuit. When SCR is not on, the capacitor C2 of relaxation oscillator is charged by R2, R5 and RP, and the voltage VC2 of capacitor ends increases exponentially. At the peak voltage VP of the unijunction transistor. The unijunction transistor UJT suddenly turns on and the base resistance RB1 decreases sharply. Capacitor C2 discharges rapidly through PN junction resistance R4, causing a positive jump of voltage Vg at both ends of R4. With the discharge of capacitor C2, VC2 decreases exponentially. When the voltage is below the trough point V_, the single junction transistor is cut off. The tip trigger pulse is output at both ends of R4 by spot welder. Make SCR turn on. There is AC current in the primary winding of B2, and the voltage drop at both ends of the thyristor becomes very small, which forces the relaxation oscillator to stop working. When the AC voltage passes zero, the thyristor is forced to turn off.  The relaxation oscillator is charged again, and the capacitor C2 is charged again, repeating the process repeatedly. Regulating potentiometer RP can change the charging time of capacitor C2, that is, the oscillation period of relaxation oscillator. It naturally changes the time when the relaxation oscillator emits the first trigger pulse after each AC voltage crosses zero. Correspondingly, the conduction control angle of SCR is changed, so that the voltage added to the two ends of B2 primary winding changes. Finally, the secondary output current can be adjusted and controlled.