The light dimmer circuit or fan regulator circuit (either case, the circuit, and design are the same, the only difference is the output load to be varied, that is, fan or light) is used to control the brightness of the light or the speed of the fan according to our desire. The objective of the circuit is to vary in intensity the brightness of the light bulb or fan speed by using a fixed source. There is no need to replace the bulb with a higher wattage one to do so. A simple Triac can do the work for you. Triacs are used in this circuit as a dimmer as they are easy to design and control, and are very much economic due to their high efficiency and low buying costs.

This is the circuit diagram of the simplest lamp dimmer or fan regulator. The circuit is based on the principle of power control using a Triac. The circuit works by varying the firing angle of the Triac. Resistors R1, R2 and capacitor C2 are associated with this. The firing angle can be varied by varying the value of any of these components. Here R1 is selected as the variable element. By varying the value of R1 the firing angle of Triac changes (in simple words, how much time should Triac conduct) changes. This directly varies the load power, since the load is driven by Triac. The firing pulses are given to the gate of Triac T1 using Diac D1.


You will get a better understanding of the light dimmer circuit by learning more about Triac.


Assemble the circuit on a good quality PCB or common board. The load whether lamp, fan or anything 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. So be careful.

I advise testing the circuit with a low voltage supply (say 12V or 24V AC) and a small load (a same volt bulb), before connecting the circuit to mains.

Parts List

R1 1o K 1 Watt Resistor

R2 1o0 K Potentiometer (Variable Resistance)

C1 0.1 uF (500V or above ) Polyester Capacitor

T1 BT 136 Triac

D1 DB2 Diac

Fan Regulator Circuit Diagram

Fan speed regulator circuit and lamp or light dimmer circuit

BT 136Triac Necessary Data.

BT 136 Data sheet,Pin out diagram and specifications
BT 136 Specifications

The light dimmer circuit explained above has been modified with the addition of a snubber circuit to improve the performance of the Triac.



  1. I have the simple circuit for electrical fan regulator by resistance

  2. purnachandrasekhar

    what is the estimated cost of single phase ac voltage regulator using diac and triac?

  3. how to connect variable resistance (potentiometer)?????

  4. dera sir ,
    i have use BT 136 for operate 10uf 400v capacitor but after five time tric if burned , pl give solution

  5. Atish Palan

    May i get the relevant waveforms for the firing angle of 60 degrees? please….

  6. Is it possible to turn this to be automatic light dimmer, for example,substituting that potentiometer with LDR?

  7. and why we use particular component like resister,capacitor value is there are formula for that

  8. sir please can u send me the total documentation of the temperature controlled fan using triac thermistor. Please send me totally as early as posiible

  9. How this circuit will be interfaced with PIC16F877?

  10. Can you please give me the information about how this circuit will be interfaced with PIC16F877?

  11. please give me a circuit that can very 0 volt to 230 volt with 7amp

  12. Rishabh V Pandey

    It helped me alot in my project.

  13. please give me a common circuite control fire thyristors 3phase
    in put 3phase 50HZ 380VAC
    out put 0 – 550VDC

  14. I want to adapt this design for a 3 phase motor blower. Let me know how I can do this…

  15. eng. mohamed

    please help me to control the speed of AC 220v motor 1HP, can i use this circuit with just changing the triac with higher one?

  16. kareemulla

    Hello sir please can u send me the total documentation of the temperature controlled fan using triac, diac, thermistor. Please send me totally as early as posiible. I will be waiting for your reply.

  17. Seetharaman

    Hi Nohammed Saad The same circuit can be used if it is mains operated LED appeared on Circuits today. If it is DC operated then you can use a variable current source using LM317 or MOSFET.

  18. nohammed saad

    i would like to control a dc load like LED s what do you recommend for me??

  19. Seetharaman

    Hi Tomin Thank you very much good useful circuit

  20. i want to design light dimmer circuit.lamp brightness will be controlled based on already existing brightness in room.give information about sensor i have to use.

  21. Awadhesh Kumar

    I m a 4th year student of EEE department and i m looking 4 project based on automatic temperature controlled circuit. So i choose automatic temperature controlled fan regulator. I need of details about this circuit………..

  22. dear,
    how to modify this “simple lamp dimmer/ fan regulator” circuit to dark controlled on off switch by using LDR

  23. can any one provide efficient circuit diagram for dc fan regulator at 12v,5A .if so give me some website address

  24. This is sure way to have noise on your power lines in your home it will work but coils filtering make a real world circuit


  25. i would like to make a scr controled dc regulated power supply,can u help me

  26. pabitra mukherjee

    I would like to connect higher load like 3000watt filament lamp,pls. recommend me the appropriate triac with proper circuit to avoid potential shock hazards.

    • tell me how many watts of bulb are used in this circuit and were should we have to connect the bulb