Zero-voltage switching Triac trigger/driver ciruits which facilitate RFI-free power regulation of resistive loads.

The number of complete mains cycles during fixed repeating periods (typically 1 to 10 seconds) is varied, thus altering the duty cycle or on-/off-time ratio. Trigger pulses coincide with the zero-crossing times of the mains supply thus ensuring no RFI is produced when using resistive loads.