Warning: Please be careful when experimenting or working on this circuit as the voltage in the circuit is 230V.
This circuit is a simple 1 step dimmer. It takes advantage that diodes only allow current to flow in one direction. Full voltage of 230V is supplied to the lamp when the switch is closed at 'A' as both halves of the supply voltage flow. On the other hand, when the switch is closed at 'B', only positive half will flows to the lamp and this gives voltage of 163V (i.e Vrms/√2 OR Vpeak/2). This reduces the brightness of the lamp.
Diode D1 is T6A100L with rating 1000 PIV and 6A is chosen in this circuit so that it can work with normal 60 watt or 100watt, 115/230V lamp.
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1 step light dimmer circuit
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Automatic street light circuit 2