Circuit Description

The circuit diagram of simple lamp dimmer is given here. This circuit is based on BT 136 Triac and can be also used as a fan regulator circuit.  The working principle of this circuit is the use of different firing angles for fan speed regulation. The resistors R1, R2 and capacitor C2 are used to vary the firing angle of Triac. Firing angle of Triac changes when the value of any one of the above mentioned passive components changes.

In this circuit, resistor R1 is used as variable element for giving various firing angles for Triac. This changes the load power and the firing pulses are given to the gate of Triac T1 by means of Diac D1.

Parts List

Resistors: R1 (10 K 1 Watt Resistor), R2 (100 K Potentiometer)

Capacitors: C1 (0.1 uF)

Active Elements: T1 (BT 136 Triac), D1 DB2 Diac

Circuit Diagram

Simple Lamp Dimmer Circuit

Simple Lamp Dimmer Circuit

BT 136Triac Datasheet

BT 136 Triac Datasheet

BT 136 Triac Datasheet


  • Use a good quality PCB or common board to assemble this particular circuit.
  • The load whether lamp, fan or any thing, should be less than 200 Watts. To connect higher loads replace the Triac BT 136 with a higher Watt capacity Triac.
  • All parts of the circuit are active with potential shock hazard.