Filament Light Dimmer Circuit

filament light dimmer using bt136 triac DB3 diac

Filament Light Dimmer Circuit

This simple triac dimmer can be used to control incandescent filament lamps up to 200W. The circuit operates on the phase-control principle.

filament light dimmer circuit using bt136 triac DB3 diac

R1 10kΩ 0.5W
R2 100Ω 0.5W
VR1 500kΩ Potentiometer
C1 330n (0.33µF)
C2 100n (0.1µF)
D1 DB3 Diac
Q1 BT136 Triac
L1 Filament Light

The main control is provided by VR1. This determines the rate at which C1 charges and hence the point along the mains waveform at which the voltage on C2 reaches the breakdown voltage  of the diac (D1), which is when the triac is triggered.

BT136 triac pin configuration Passivated, sensitive gate triac DB3 Diac trigger diode
BT136 Triac pin configuration DB3 Diac

Interference suppression is provided by R2 and C2.

This light dimmer is directly connected to mains. So be careful.

The potentiometer should have a plastic spindle.

Please send your ideas, which are very important for our success…

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22 comments on “Filament Light Dimmer Circuit
  1. Great site. A lot of useful information here. I’m sending it to some friends!

  2. Pretty nice post. I just stumbled upon your blog and wanted to say that I have really enjoyed browsing your blog posts. In any case I’ll be subscribing to your feed and I hope you write again soon!

  3. roclafamilia says:

    Helpful blog, bookmarked the website with hopes to read more!

  4. Andrew P. says:

    The cheapest commercial light dimmers omit C2 and R2. The best interference-suppressed triac dimmers add a choke — 20 to 30 turns of heavy Formvar insulated solid copper wire wound on a ferrite slug — in series with the dimmer. The purpose of the choke is to slow down the fast switching edges and reduce radio frequency interference (RFI) that can wipe out radio reception on the AM band for radios in the same room or adjacent rooms. At 2011 prices, the cheapest dimmers can be purchased for $6 to $10. The better interference-suppressed dimmers can cost $25 to $30. Choosing a triac with slower switching characteristics will greatly reduce radio frequency generation at the expense of requiring a larger heat sink.

  5. Robert says:

    Is Dimmable CFL (Compact FLuorescent Lamp) Ballast applicable for this circuit instead of incandescent filament lamps?

  6. Deebwebs says:

    Great site with awesome projects, thanks and keep going.

    I’ve got a question, can we use this circuit to control the speed of a motor, like simple drilling machine (about 750 W)?

    Thanks again..

  7. abhi says:


  8. Lsener says:

    very good project

  9. OHMark says:

    Please help me. Is it ok if i replace the filament light to LED light? And what type of capacitor did you use in the circuit? Thanks. 🙂

  10. skytipsbd says:

    Thank you very much. Please need an idea when i go to the shop they don’t know diac or triac, just give me another named. which is known the shopper?

  11. ghorbani says:

    nice post , thank you

  12. enhassan says:

    very good

  13. Malihe says:

    Thank you very much

  14. sergio says:

    esta bueno todo pero no anda este proyectoooo, esta mal puesta la carga

  15. Nsuh Christain says:

    thanks very much. helping me take electronic to my village.
    God bless you.

  16. mithun says:

    t1 t2 which terminal where connected?

  17. alex says:

    sir, i have 0.36uf/400v capacitor, what are the changes needed to the circuit

  18. hamed says:

    i need a circuit to control the heater 1000w

    i use bta 40 and need 100 ma for gate drive to turn on

    but this circuit dont work
    pleas help me

  19. mukesh prajapti says:


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