Monday, September 8, 2014
Courtesy Light
Obviously, users will be able to find different applications for this schema in order to suit their needs.
Parts:
R1____________470R 1/2W Resistor
R2____________100K 1/4W Resistor
R3______________1M5 1/4W Resistor
R4______________1K 1/4W Resistor
C1____________330nF 400V Polyester Capacitor
C2____________100µF 25V Electrolytic Capacitor
C3,C5__________10nF 63V Polyester or Ceramic Capacitors
C4_____________10µF 25V Electrolytic Capacitor
D1,D2________1N4007 1000V 1A Diodes
D3_________BZX79C10 10V 500mW Zener Diode
D4__________TIC206M 600V 4A TRIAC
Q1____________BC557 45V 100mA PNP Transistor
IC1____________7555 or TS555CN CMos Timer IC
SW1____________SPST Mains suited Switch
Due to the low current drawing, the schema can be supplied from 230Vac mains without a transformer. Supply voltage is reduced to 10Vdc by means of C1 reactance, a two diode rectifier cell D1 & D2 and Zener diode D3. IC1 is a CMos 555 timer wired as a monostable, providing 15 seconds on-time set by R3 & C4. When SW1 is closed, IC1 output (pin 3) is permanently on, driving Triac D4 which in turn feeds the lamp. Opening SW1 operates the monostable and, after 15 seconds, pin 3 of IC1 goes low switching off the lamp.
Notes:
* The schema is wired permanently to the mains supply but current drain is negligible.
* Due to transformerless design there is no heat generation.
* The delay time can be varied changing R3 and/or C4 values.
* Taking C4 = 10µF, R3 increases timing with about 100K per second ratio. I.e. R3 = 1M Time = 10 seconds, R3 = 1M8 Time = 18 seconds.
* Low Gate-current Triacs are recommended.
* Use a well insulated mains-type switch for SW1.
* Warning! The schema is connected to 230Vac mains, then some parts in the schema board are subjected to lethal potential!. Avoid touching the schema when plugged and enclose it in a plastic box.
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