- The power circuit for the resistance welding using TRIAC – DIAC is shown in the figure A.
- The current passes through transformer primary winding when TRIAC is turned on.
- As soon as the alternating supply is on, the charging of capacitor is done through path AC supply – R – C.
- When the voltage across capacitor becomes equal to DIAC break over voltage, the DIAC turns on.
- Now the gate of the TRIAC gets pulse and resulting TRIAC turns on.
- The current starts to flow through primary winding of the transformer.
- The control of current is done by variable resistor R.
- The firing angle of the TRIAC increases when the setting of variable resistor is made at higher value.
- The current passes through transformer primary winding decreases as the firing angle of the TRIAC increases.
- The transient voltage generated due to switching on the TRIAC and this voltage may damage the transformer primary winding.
- The thyride resistor is connected across transformer primary winding in order to suppress transient voltage.
- The resistor of the thyride resistor decreases as the voltage increases and this will protect the transformer primary.
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