Construct a 220/240V AC Light Dimmer Circuit

Introduction To Light Dimmer Circuit

This is a standard 220-240 VAC circuit which can be used to adjust the brightness of mains lights. It uses a triac, diacand has a radio-frequency interference (RFI) noise suppression circuit built into it as well.

Caution: This project connects directly to mains power supply. You must know what you are doing. The completed project mustbe put in a suitable enclosed box before using.

Light Dimmer Circuit Schematic Description

This is a standard text-book circuit. A triac may be considered as two SCR's (Silicon Controlled Rectifiers)connected in opposite directions. A diac is a gate trigger device. Triacs, diacs & SCR's are different types ofThyristors.

A triac is a 3 terminal AC semiconductor switch which is triggered ON when a low energy signal is applied to itsGate. Switching is fast. The low energy of switching means that a wide range of low cost control circuits canbe used. Since the triac is bilateral (2 SCR's connected in opposite directions) the terms anode and cathode have no meaning. So the terms Main Terminal 1 and 2 (MT1, MT2) are used. It is standard to use MT1 as a reference point.

The circuit 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.

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 Radio Frequency Interference. It is greatest when the triac is triggered at 90 degree and least when it is triggered at close to zero or 180 degree of the mains AC waveform. L-C suppression network is thus used to suppress these electrical noise.

Light Dimmer Circuit Parts List

The parts list of the project is as shown below.

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