220V Light Dimmer

This simple 220V light dimmer circuit can be used to adjust the brightness of mains lights. It also can be used to adjust the speed of AC motors. It uses a triac, diac and has a radio-frequency interference (RFI) noise suppression circuit built into it as well.

Schematic diagram:

Components List:
R1 = 10K
R2 = 2K2
R3 = 180K
Potentiometer 250K
C1 = 150nF/400V dipped polyester
C2 = 47nF/630V  dipped polyester
C3 = 220nF/250V AC dipped polyester
Triac = 2N6075 or BT136-500D
Diac = HT-32
FUSE 2A or 3A

How the circuit works:

The circuit here controls the average power to a load through the triac by phase control. The ac supply is applied to the load for only a controlled fraction of each cycle. The triac is held in an OFF condition for a portion of its cycle then is triggered ON at a time determined by the circuit. The main problem with this circuit is radio frequency interference (RFI).

RFI. Each time the triac is turned on the load current changes very quickly – a few micro seconds – from zero to a value determined by the lamp resistance and the value of the mains voltage at that instant in time. This transition generates RFI. It is greatest when the triac is triggered at 90^o and least when it is triggered at close to zero or 180^o of the mains AC waveform.

Since there may be long lengths of mains wire between the triac and the lamp load which will radiate this RFI an L-C RFI suppression network is usually built into these types of circuits. You may detect this RFI by bringing an FM radio close to the dimmer circuit. Short out the choke coil and notice that the RFI increases. The wire-wound coil and C1 provide the RFI suppression network.

Download the circuit documentation of 220V Light Dimmer. The kit of this circuit is available at kitsrus.com, please visit the website to purchase the kit.