Resistance welding using Triac - Diac circuit

  • The power circuit for the resistance welding using TRIACDIAC 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.
resistance welding using triac and diac

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