Half Wave Power Control

• This is similar to the DC control circuit but the thyristor turns off every half cycle because the AC voltage drops to zero.
• The switch on is timed with an adjustable RC timing circuit.
• If R is larger, it takes longer to charge C enough to trigger the thyristor.
• If R is smaller, C charges more quickly and the thyristor is triggered almost immediately.
• This is called phase control.
• This method is very simple.
• Better control can be achieved by generating the control pulses in other ways like
  • using a microcontroller to do the timing
  • using a 555 timer to position the trigger pulses with greater accuracy.

Full Wave Power Control

• By adding four diodes as a full wave or bridge rectifier, this circuit can be converted to full wave control.
• In other respects it's the same as the half wave version.