Thyristor & Power Control Circuits Unit 7 – TRIAC AC Power Control
Exercise 1 – TRIAC Half-Wave Phase Control
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to describe half-wave phase control by
using a typical triac ac power control circuit. You will verify your results with an oscilloscope.
EXERCISE DISCUSSION
- The circuit shows a half-wave triac phase control.
- Diode CR2 blocks the negative half-cycle of source voltage (Vac) from reaching the triac
gate. - R1, R2, and C1 form a phase shift network. Adjusting R1 controls the phase angle of the
triac’s gate trigger voltage. - The triac continues to conduct until the MT2 current falls below the holding current level of
the device.