Patent ID: 7193404

Claim:
A load control circuit having first and second terminals for connection in series with a controlled load, the load control circuit comprising a bidirectional semiconductor switch for switching at least a portion of both positive and negative half cycles of an alternating current source waveform to the load, the bidirectional semiconductor switch having a control electrode, further comprising: a phase angle setting circuit including a timing circuit which sets the phase angle during each half cycle of the AC source waveform when the bidirectional semiconductor switch conducts; the phase angle setting circuit including a voltage threshold trigger device connected in series with the control electrode of the switch, further comprising a rectifier bridge connected in series between an output of the timing circuit and the control electrode of the semiconductor switch, and wherein the rectifier bridge has a first pair of terminals and a second pair of terminals, the first pair of terminals connected in series between the output of the timing circuit and the control electrode of the semiconductor switch, and the second pair of terminals connected to the voltage threshold trigger device; whereby acoustic noise generated in the load connected in series with the load control circuit is reduced.