Question

Explain why the phase of the input AC signal is varied in SCR circuits. Also what is the result of varying the phase?

Answer 1

The phase of the AC signal is varied in SCR circuits so that the SCR circuits can be turned ON & turned OFF.

The result of varying the phase is that when the signal is positive half cycle and the when the anode voltage is present and gate voltage is sufficient to turn ON the SCR. Once triggered SCR will be ON. And as phase varies at one anode - cathode voltage is not sufficient and SCR will turn OFF. And in negative cycle the voltage polarity is reversed so SCR will not conduct.