Mains variable Delay circuit

Posted on Nov 27, 2012

The circuit shown will switch on and off a resistive or inductive load up to 800VA with the possibility to adjust both the on and off period. Switching takes place during the zero crossing of the sine wave. The switch on point is around the zero crossing but pinpoint accuracy is not guaranteed due to the analogue nature of the circuit. The on period is adjustable between 0.3 to 4sec while the off period is adjustable between 0.2 and 10sec.

Mains variable Delay circuit
Click here to download the full size of the above Circuit.

The chosen SCR has a sensitive gate: this avoids the use of a large electrolytic capacitor. Frequency of operation is fairly stable although it is slightly affected by temperature, supply voltage and loading conditions.

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