AC Power Control: Adjustable Phase Angle Control with triac using ATmega8

Here’s the output waveform with 800µs delay (all PORTB/PINB pins high : DIP-switch state = 0):

 Fig. 3 – Triac firing with 800µs delay

Green: Input AC
Yellow: AC Output after phase angle control
Pink: Gate Drive signal

You can clearly see that before the gate driving signal is applied, there is no output (illustrated by the flat yellow line).When the gate driving signal is applied, the triac turns on. There is an output and the triac stays on till the next zero crossing. After this again, there is no output till the next gate drive signal is applied.

Now I’ll show you a few more waveforms, with other initial delays.

Here, the gate is driven 1.6ms after the zero-crossing (only PORTB0/PINB0 low : DIP-switch state = 1):

 Fig. 4 – Triac firing with 1.6 ms delay

Green: Input AC
Yellow: AC Output after phase angle control
Pink: Gate Drive signal

 Fig. 5 – Triac firing with 2.4 ms delay

Green: Input AC
Yellow: AC Output after phase angle control
Pink: Gate Drive signal

Here, the gate is driven 3.2ms after the zero-crossing (PORTB0/PINB0 and PORTB1/PINB1 low : DIP-switch state = 3):

 Fig. 6 – Triac firing with 3.2 ms delay