Circuit diagram:
Parts:
R1____________470R 1/2W Resistor R2_____________10K 1/4W Resistor R3,R4_________100K 1/4W Resistors R5______________1K 1/4W Resistor C1____________330nF 400V Polyester Capacitor C2____________100µF 25V Electrolytic Capacitor C3____________100nF 63V Polyester or Ceramic Capacitor C4_____________10µF 25V Electrolytic Capacitor D1,D2________1N4007 1000V 1A Diodes D3_________BZX79C12 12V 500mW Zener Diode D4__________TIC206M 600V 4A TRIAC IC1____________4011 Quad 2 Input NAND Gate CMos IC P1_____________SPST Pushbutton
Comments:
Due to the low current drawing, the circuit can be supplied from 230Vac mains without a transformer. Supply voltage is reduced to 12Vdc by means of C1 reactance, a two diode rectifier cell D1 & D2 and Zener diode D3. IC1A, IC1B, R2, R3 and C3 form a reliable bounce-free toggle switch operated by P1. R4 and C4, wired to pin #6 of IC1B reset the circuit (lamp off) when power supply is applied. IC1C and IC1D wired in parallel act as a buffer, driving the Gate of the Triac through R5.
Notes:
- The circuit can be wired permanently to the mains supply as current drain is negligible.
- Due to transformerless design there is no heat generation.
- Low Gate-current Triacs are recommended.
- Obviously, other appliances can be powered in place of a lamp, provided their power dissipation does not exceed about 400W @ 230V
- 110-120Vac operation is easily obtained by simply changing C1 value to 680nF 250V. No further changes are necessary.
- In some cases, e.g. when the controlled device is far from the toggle switch, a pilot LED could be necessary for monitoring purposes. If so, disconnect pin #10 of IC1C from pin #11 of IC1D and wire a LED and its 1K series current limiting resistor across pin #10 of IC1C and negative supply.
- Warning! The circuit is connected to 230Vac mains, so some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged in and enclose it in a plastic box.
