Simple Light Dimmer Switch Circuit

In this post we learn through two examples how to build a simple light dimmer switch circuit for controlling light intensity with pot, using the principle of triac phase chopping.

We have already seen in many of my earlier articles how triacs are used in electronic circuits for switching AC loads.

Triacs are basically devices which are able to switch ON a particular connected load in response to an external DC trigger.

Though these may be incorporated for complete switch ON and complete switch OFF procedures of a load, the device is also popularly applied for regulating an AC, such that the output to the load may be reduced to any desired value.

For example triacs are very commonly used dimmer switch applications where the circuit is designed to make the device switch in such a manner that it conducts only for a particular section of the AC sine wave and remains cut OFF during the remaining parts of the sine wave.

This result is an corresponding output AC which has an average RMS value much lower than the actual input AC.

The connected load also responds to this lower value AC and is thus controlled to that particular consumption or resultant output.

This is what exactly happens inside electrical dimmer switches which are normally used for controlling ceiling fan and incandescent lights.

Simple Light Dimmer Switch Circuit

Simple and the Best Triac Dimmer Switch Circuit

The circuit diagram shown above is an classic example of a light dimmer switch, where a triac has been utilized for controlling the intensity of light.

When AC mains is fed to the above circuit, as per the setting of the pot, C2 charges fully after a particular delay providing the necessary firing voltage to the diac.

The diac conducts and triggers the triac into conduction, however this also discharges the capacitor whose charge reduces below the diacs firing voltage.

Due to this the diac stops conducting and so does the triac.

This happens for each cycle of the mains AC sine wave signal, which cuts it into discrete sections, resulting in well tailored lower voltage output.

The setting of the pot sets the charge and the discharge timing of C2 which in turn decides for how long the triac remains in a conducting mode for the AC sine signals.

You might be interested to know why C1 is placed in the circuit, because the circuit would work even without it.

It’s true, C1 is actually not required if the connected load is a resistive load like an incandescent lamp etc.

However if the load is an inductive type, the inclusion of C1 becomes very crucial.

Inductive loads have a bad habit of returning a part of the stored energy in the winding, back into the supply rails.

This situation can choke up C2 which then becomes unable to charge properly for initiating the next subsequent triggering.

C1 in this situation helps C2 to maintain is cycle by providing bursts of small voltages even after C2 has completely discharged, and thus maintains the correct switching rate of the triac.

Triac dimmer circuits have the property of generating a lot of RF disturbances in the air while operating and therefore an RC network becomes imperative with these dimmer switches for reducing the RF generations.

The above circuit is shown without the feature and therefore will generate a lot of RF which might disturb sophisticated electronic audio systems.

The light dimmer switch circuit illustrated below incorporate the necessary precautions for subsiding the above issue.

Parts List for the above enhanced fan dimmer circuit

C1 = 0.1u/400V
C2, C3 = 0.022/250V,
R1 = 15K,
R2 = 330K,
R3 = 33K,
R4 = 100 Ohms,

VR1 = 220K, or 470K linear
Diac = DB3,
Triac = BT136
L1 = 40uH

200 Replies to “Simple Light Dimmer Switch Circuit”

  1. Dear swagtam, I am looking for a fan dimmer switch, mostly a light dimmer are available. A light dimmer cannot work properly if we control a ceiling fan. Can you please give me some suggestions.

  2. Hello Swagatam

    I have a 20 liter electric storage water heater which has a 230V AC, 2KW electric heating element. The heating element is failing frequently primarily due to bad quality of water inducing faster corrosion of heating element. I decided to experiment with the current to increase the life of heating element. I want to limit the heating to about 80% of normal so that heating element runs at slightly cooler temperatures.

    I have BTA41-600B 41Amp Triac available to me. This triac has sufficiently high current rating for a 2KW coil. Two options come to my mind.

    1. Buy a electric fan speed regulator. These are available cheap and in plenty. Open the enclosure, identify the triac in the circuit and just replace the triac with BTA41-600B. The question is will this work? I am an electrical Engineer and I do build small electronic circuits on my own, but I have never built a circuit involving Triac.

    2. The other option is to build a simple circuit with a preset resistance connected to the gate. But what should be the rating of this preset resistance?

    There is one more question. Should I need to use a heat sink for this application?

    1. Hello Jaydeep,

      Modifying a fan speed controller would be a better idea. However you will need to replace the diac also along with the triac. The diac also needs to be equally powerful in order to support the triac gate current.

      Heatsink is a MUST for your application, make it as big as possible.

  3. Hi Swagatam,

    I want to use the dimmer circuit above to to dim a LED light bulb. I will have
    120 v as input and want to control the dimmer with software through an Electric
    imp device which puts outputs 3.3v max as a trigger. I have this currently
    working with a relay that is triggered with the 3.3v output. My question is where
    can I put my 3.3 v trigger leads from the imp in your circuit?

    Thanks

    Charlie

    1. Hi Charlie,

      I am afraid you cannot use a triac dimmer for controlling an LED bulb because it's an capacitive/inductive load, not recommended to be used with triac dimmers.

      Any way there's no harm in trying, you will have to employ a handmade LED/LDR opto-coupler sealed inside a light proof box.

      The LED terminals should be connected to the 3.3V source possibly through a series resistor,and the LDR terminals should be connected across RV1 points, RV1 may be removed completely (in the first diagram).

      The series resistor value with the LED will decide the intensity of the LeD bulb, in other words,the intensity of the LED will be directly proportional to the intensity of the LED bulb.

    2. Actually, the circuit will work with LEDs, but you need to make a modification.

      LEDs are *** NOT *** capacitive (beyond a few picofarads) or inductive loads. But they ARE DC devices. If you use them in an AC circuit, you'll only drive them about half the time. So instead of driving the LEDs directly, drive a rectifier bridge and use the rectified output to drive the LEDs. Note that the voltage drop across the LEDs must (reasonably) match the source voltage. If you stick a 1.3V LED in line, all the smoke will leak out. There are LEDs in the 20W to 100W range with forward operating voltages in the 25V-30V range. If you're on a 120V circuit, putting ~4 of these in series will give you the correct voltage range. If you're on 220V power, you can use ~8 in series.

      Note that LEDs are about 7-8 times brighter than a corresponding incandescent lamp of the same wattage. This means you can do cool things like replace a 500W bulb with 4 series 100W LEDs and get the equivalent of 2800-3200W incandescent… good for outdoor flood lights… 6 times the light for 20% less power. I'm in the process of replacing my INDOOR torchiere halogens with 4 series 20W LEDs. At 100 lumens/watt, that will give me about 8000 lumens… about the same as a 500W incandescent. Not only that, but the LEDs won't heat up a room like a 500W incandescent or halogen!

      If you want to get fancy, you can even adjust the color temperature by using various combinations of LEDs… maybe a couple soft with with a couple cool white. Or a red or green LED with 3 cool whites.

      Do

      *****NOT****

      use a series resistor with the LEDs. That's just wasted energy. For example, if you wanted to run a 20W LED from 120V power (assuming a 30V forward voltage), you would need to drop 90 volts across the resistor. Since the LED will need to draw .67A for operation, your resistor would have to be about 135 ohms – meaning you'd dissipate nearly 60W in the resistor – three times what your LED is using (which would reduce light efficiency by ~75%). You might as well use a halogen.

      If you only want to drive a small module (not multiple 20W+ units) then your best option is a step-down transformer.

    3. I was referring to a LED bulb unit, which includes a switching driver inside and therefore it has to be a capacitive/inductive load….if it would be only a LED then the issue would be different.

  4. hi sir, can i use this cercuit for charger trasformar praimary ac volt control, because the ac line voltage is up and down.i want to fix this problem by this cercuit. i want to charge my led battery conostant volt by controling ac volt. please solv my problem.oh my transformar is 15volt dc,210volt ac, 50amp. thank you

    1. Hi Rahamania,

      Yes you may do it….but that's not the right way of getting constant DC, in fact it won't help…. you should use voltage regulator IC with your transformer power supply such as LM317 or LM338.

  5. ok thank you sir for your coments, but sir i want to control dc side voltage from transformar ac input side for my project benifite. plese help me sir, if i control transformar ac side input then i shine my project.make any diagram for me and my project. please answer me shortly. thank you sir.

  6. Sir, please see the cercuit diagram of Indian Bimtex invarter cercuit diagram then publish their only charge option. how can charge that cercuit to battery conostantly.Please Sir, that diagram is very importat for me. i am waiting for your answer. thank you.

  7. Sir, what is face control battery charger? Bimtex is apply this formula. Sir, i have no link for Bimtex diagram. Just i bought that cercuit from market and use. So i want to make same cercuit. i make drivar and power section but can not draw their chargeing site. So you are my last direction. Bimtex apply face contro system for charge led acid battery and it is very nice because i use this cercuit. I think they use scr tyn612m + 4n35 etc. please make any diagram like this for me. thank you

    1. I researched about phase control battery charger circuit but could not find any such circuit online. There are scr controlled battery charger circuits available but they require transformer and bridge rectifier for stepping down the mains AC.

      I'll try to design a compact one…. if it's feasible I'll inform you.

  8. Hi Swagatam,

    can you do a circuit using triac and incorporate it to a 24 hrs timer to turn off the airconditon 1Hp?

    Regards,
    Mike L

    1. Hi Mike,

      I have discussed a few long duration timer circuits in this blog, these can be simply used with a triac for acquiring the required functions….I may possibly discuss it in a new post soon.

      Regards.

  9. Hi

    Im trying to build a circuit that can dimm LED lamps from 230 mains voltage. The triacs leading edge I have found causes overshoots and spikes in voltage and current which destroy LEDS due to the sharp rise times in voltage.
    I was using inductive, capacitive and resistive Ballasts to drop the voltage down enough to rectify and smooth.
    The only circuit that looks like working is the resistive ballast, Im using 1 smoothing capacitor after rectification.
    From simulation in LTspice the current drops nicely and almost linearly as i change the firing times of the triac.

    Would you have any ideas on how to get around the problems with the inductive/capacitive ballasts ?

    I thought your circuit would work until I read the comments

    thanks for your time

    best

    sct

  10. Hi Swagatam Majumdar

    that's a very good circuit, i was looking for a cheap method to reduse speed of a washing machine motor. The motor is AC with bruses there is no label on it, i need it for other use (Easter in Greece to be rotated five lambs) for example as i calculate it must have 30 rpm maybe less. So i need help if this is possible and what i will need to built it.
    Thank's in advance.

    1. Hi Nick, thanks!

      you may build the first circuit, if your motor is mains AC operated then the circuit will surely work with it.

      You may use a BT136 triac if the shown type is unavailable.

  11. Hi Swagatam
    i was thinking how can i reduse speed of a washing machine motor i need it for other use (Εaster in Greece, it will turn lambs) so i need very low speed 30 rpm or less. Can i use this circuit, is this possible and what i will need to use

    Thanks in advance

    1. Dear Swagatam,
      Thanks for the quick reply.
      I implemented your first circuit, with the following changes:
      – The potentiometer is 200K (two 100K in series) instead of 220K.
      – I didn't put a inductor.
      Unfortunately, it doesn't work.
      The DIAC is DB3TG 32V.
      I tried two TRIAC models: The Phillips BT131 800V 1A TRIAC, and the Littlefuse Q6012LH1LED HiCom (snuberless) TRIAC.
      In both cases, the TRIAC always conducts, and the sine wave on the oscilloscope is always full. I also tried different combinations of resistance.
      Moreover, I tried the simple circuit with only one firing capacitor. In this case, when I connect the power plug to the power socket correctly (L-L / N-N), the TRIAC is always ON. When I connect the power plug in reverse (L-N, N-L), the TRIAC is always OFF.
      Have you any idea of what might go wrong?
      The load is a simple 15W incandescent lamp. I implement the circuit on a breadboard. All connections tested extensively.
      Thank you in advance.

    2. Dear Dimitris,

      Try the second circuit, it has been tested by me not once, but many times.

      R1 = 15K
      R2 = 330K
      R3 = 22K
      VR1 = 220K
      diac resistor = 47 ohm
      diac = DB-3
      Triac = BT136 or equivalent.
      C2, C3 = 0.1uF/250V
      C1 = 0.1uF/400V

      The first circuit is also correct and should have worked… anyway you may try the second one, will 100% work.

    1. Try the second circuit given in the above article.

      Use the following parts:

      R1 = 15K
      R2 = 330K
      R3 = 22K
      VR1 = 220K
      diac resistor = 47 ohm
      diac = DB-100
      Triac = BTA41/600.
      C2, C3 = 0.1uF/250V
      C1 = 0.1uF/400V

  12. Very interesting article..
    I would like to know, how are the values calculated for R & C in case of ac motor dimmer? Please provide some link or doc which explains the calculation part in detail, if you have..

    Thanks..

    1. thanks, i don't know about the formula, but the diac is the center of focus here.

      It requires around 30V to fire….by determining how quickly it reaches the 30V mark alternately, we decide for how long the triac can remain switched ON for each cycle.

      the firing timing of the diac is controlled by the various timing components in the form of resistors and capacitors whose vales are appropriately chosen for the implementations.

  13. Hi Swagatam, I want to create a dimmer switch for 3 series light bulbs 50W each, can I use this same circuit? Thanks in advance. By the way, this is a very good article, I've been searching for other circuit, and this is the best and very informative one.

    1. yes putting them in parallel would be the correct approach, however the triac won't hold more than 200 watts without heatsink, and 500w with heatsink attached, so be careful about that.

      if the above parameter is taken care of then it would be a permanent thing, no issues 😉

  14. Hi Sir –

    I would like to use a dimmer type switch to control the input from the main of a transformer which is rated at 2500W at 20amps.

    Would this circuit work & how would I spec out the components properly? Any help would be greatly appreciated.

    1. Hi Brad,

      You can try the second circuit, with the following pats:

      R1 = 15K
      R2 = 330K
      R3 = 22K
      VR1 = 220K
      diac resistor = 47 ohm
      diac = 100mA big diac
      Triac = BTA41/600.
      C2, C3 = 0.1uF/250V
      C1 = 0.1uF/400V

      Use a large heatsink for the triac.

  15. Hello,
    I would like to implement your dimmer switch circuit but on an 120 V AC line at 60 hz for incandescent bulbs. What values should I use for the resistors, pot and capacitor?

    Thank You

  16. I burned 5 Triacs because of miss rate of C1. It works fine in 110v (if it's not working, you are doing something wrong, or your triac is already fried). But in 220v, I believe that C1 must be 600v or above.

  17. First off please pardon my ignorance.

    I am trying to build dimmer for a 220 v 16 amp resistive heating coil. But I think I would like to add the noise suppression of the motor circuit (the extra capacitor and induction coil) but I am not finding induction coils that are rated that high. Can a pair be run in parallel? Or some other arrangement?

    And one other request. What amperage ratings do the resistors need? 1 amp seem like that would be fine.

    Thanks for any input.

    John

  18. Hi, my name is Luca and I have some questions for you please…

    1) by use of the rectifier bridge, can I use the controller with DC motor?
    2) are there problems if I use the controller in series with a mag-thermic switch?

    Thanks

    Luca

  19. Hi there.
    Let me ask you a question.
    If we have a circuit that controls the speed of an AC motor through a diac-triac scheme like your designs. Basically it has the Q4008LT IC which is the same thing. When switching on the circuit on a preset speed the motor builds up its speed on a veeeery veeery slow rate… If the preset speed is set to low the motor doesnt start at all…. If the speed is set on high values the motor starts the building process I have mentionted…
    What do you think the problem could be?
    Thank you in advance for your time.

    1. Hi, you can test the response by replacing the AC motor with a 100 watt incandescent bulb, if the bulb illuminates gradually as per the normal specs it would indicate a proper dimmer switch, if it behaves identically as the motor, you could assume a faulty dimmer switch….if the dimmer switch is good then probably there's nothing you can do to correct the motor response.

  20. Can you please tell me how to design a circuit for different load and inputs? More specifically what specifications and rating of components to be used (resistor, capacitor, diac, triac). Thank you.

    1. except the triac everything can be left as is….just the triac will need to be upgraded depending upon the load current, example if you intend to operate a 10 amp load you could opt for a 16 amp triac such as a BTA16/600 etc. and so on.

    2. This is the scenario Sir Swagatam:

      i want to build a dimmer to control our 18 W, 105 mA lamp and another dimmer for 60 W, 262 mA fluorescent lamp. i want the circuit to be permanently installed. i also want to be as efficient as possible. by the way i am just student and has limited knowledge about these for now.. thank you for your appreciation Sir Swagatam

    3. Hi Jerven, for the 18w lamp (180V) you can try the circuits presented in the above article, however for the fluorescent I won't be able to suggest any circuit since it's difficult to make a light dimmer for fluorescent lights unless it's made using special ICs.

    4. for my 18 W lamp, my input will be 220 VAC. is it still ok to use the above circuit efficiently? and final thing, can you give me some possible reason why the circuit above is not good to use for the 60 W fluorescent lamp (also for 220 VAC input)? thanks again Sir Swagatam. you really help me to understand this topic.

    5. yes the above circuits can be used for the 18 watt application.

      fluorescent tubes with electronic or inductive ballasts will not respond properly to a triac based dimmer….the dimming response might be erratic and non linear.

  21. Sir Swagatam you said that above circuit will work with 18 W lamp with 180 VAC as input. I became confused when you also said that it will also work for 220 VAC. I thought that the 180 VAC is the maximum voltage that can be applied to the circuit?

    another thing Sir is can you teach me how do you calculate or assumed the values of all resistors and capacitors in the circuit? So that if I can build a dimmer circuit with my own. Thank You Sir!

    1. Jereven, 180V or 220V are the extreme ranges so it doesn't make any difference for the circuit, for a 180V input the circuit would produce a zero to 180V control and for a 220V it would be from zero to 220V. The maximum limit is around 300V

      The above circuits are not mine, the component values were calculated and positioned by the original designer.

  22. Your helps are very much appreciated Sir! Thanks alot for providing me details regarding this circuit. Do you have any idea for calculating or assumptions of the values of resistors and capacitors? if none, it's ok Sir. You really help me alot to understand this. Thanky you so much 🙂

    1. Thanks Jerven, the part combinations are simple RC networks so the formulas would be also based on RC timing formulas.

      It's easier to solve it through practical analysis.

      Basically, if the pot value is more, the capacitor values should be proportionately less and vice versa so that the extreme zero end of the pot generates a voltage just above zero and not zero, because at zero the load will suddenly die and will not revive until the pot is moved back substantially……example for a 220K pot the capacitors could be 0.1uF, for 330K pot it could be 0.068uF, for 680K pot 0.047uF and so on.

    1. hello Gururaj, yes you can use it for controlling a soldering iron.

      I couldn't find any complimentary negative voltage regulator rated at 5amps compatible with LM338…will have to do some more searching.

    1. the circuit will not produce different results for different watt loads on a given pot setting, because the circuit is designed to control voltage not current so the net result will be the proportionately the same for both the irons

      the same pot setting can be used for both the irons.

  23. Hello,
    LM317 and LM337 addresses my need as presently i dont have need for high current psu but i asked in case i need such high current in future i know about pass transistors to increase current but LM338 would decrease components layout for the same result.

  24. That is not for two irons but one and same iron i just wanted to incorporate two presets in place of pots and add toggle switch between them so that i can select between two voltage levels hence 50w iron would become 25 watt iron as that would be easier to control than the pot.

    1. outboard pass transistors only help to increase current output by allowing an additional path for the current to pass, however it has to ultimately depend on the transformer for the current….so 2 amp will not give 3amps. 2amp will give less than 2amps but never more unless voltage is compromized

  25. hi sir,
    i am vishnu.sir i am in need of an illumination control circuit that could controll the brightness of 5 incandecent lamps connected in parellel,each pf 200watts,can i use the above circuit for that???i am afraid the above circuit cant withstand that much of power .please help me sir

  26. sir
    i was wrong with the triac number in the previous question, sorry for that.i was trying to ask you that is it possible for me to use the first circuit by changing only the triac bt136 by bt 139.

    sir your posts are very much useful for beginers like me more over your kindness in replay to our doubts are appreciable.

    1. sorry sir i have no idea about the load voltage .kindly pardon my little knowledge.i intented to controll the brightness of 5 incandecent lamps each having 200 watts ,my input is 230 volt 50 hz

    1. the current does not split, it completely passes through the resistors, causes the capacitors to get charged and the triac to fire in a controlled manner so that the lamp can illuminate accordingly….

  27. Hi sir…could you tell me the component to controlling the speed of bench grider 220v/250Watt.
    and which type of schema diagram for that controller? thanks sir

  28. Hi Swagatam,
    I was trying to do switching ckt using BTA16-600BW and MOC3061 to replace mech relay.My intention is to do a dimmer to control Direct AC driven led module with MC.
    I have connected 330 ohm between pin 6 of moc and A2 of triac, A2 connected to hotline. Pin 4 to Gate and pin 4 to 330 ohm to A1. A1 to load to nuetral. Note: I have not connected MC until now. Just directly using 5v supply thru 39 ohms to pin 1.
    Issue 1: When load is CFL, ckt works perfect. But when LED light is connected i can see little current flowing through and led lights up with little intensity. How to avoid this?. LED module is Direct AC driven. I can see smd L1 component on the led module.
    Issue 2: When LED lights up, after few seconds it starts to flicker. How to avoid this? Do i require a snubber here?
    Issue 3: I tried 39 ohm and 103k 400v brown ceramic capacitor across A1 and A2. But the LED was ON even before i could trigger gate.
    Issue 4: I also noticed CFL lamp flickering once in a while after some time.
    Issue 5: MOC is getting very hot within few seconds. Any thing wrong in connection? I have used 39 ohms in series with + 5v to pin 1.
    Please help me in getting this LED light up(flicker free).

    1. Hi Sham, LED and CFL lights don't work properly with phase chopper dimmer circuits.

      I think you should try a PWM controller circuit for achieving perfect dimming response from these lights.

    1. Dear Imanul, I am not sure about the formula, but the capacitor is related with the pot value….the two must be selected and matched such that the minimum adjustment of the pot should not force the lamp or the load to completely shut off rather enable a minimum possible dimming…….if the load shuts off then the pot will need to be rotated back upto the center of the dial to regain the actions….so this can be a little inefficient and shabby…therefore the two values must be appropriately selected and matched.

    1. Hi Shruthi, you can eliminate L1/C1 from the circuit, if RF noise is a not a concern for you, and you can use a fuse if you wish to…the value could be around 60/220 = 0.27 or 300mA.

  29. Hai sir,
    Recently I tried to make a dimmer circuit for microscope lamp.unfortunately I couldn't get any output.I skip the inductor part and 100 ohm resistoralso I used a pot 470 k instead of 220 k.is this affect the output of circuit?pls rply…hoping ur favorable rply

  30. https://lh3.googleusercontent.com/-e_xqQfr9NvU/Vs2pvulBRtI/AAAAAAAAAJs/9kqty3z4Uwg/w1060-h460-p-rw/IMG_20160224_183010.jpg

    Dear sir please ऊपर दिए हुवे link को open कर के ये बताय की इस circuit में अगर input LED को मैं उसके DC voltage requirement के हिसाब से देता हूँ या उस से कम voltage देता हूँ तो क्या TRIAC का output भी 240AC voltage या उसे कम मिलेगा
    मेरा कहने का मतलब है अगर input कम देने पर output भी कम मिले और बराबर देने पर output बराबर मेले please sir yas या no में जवाब दे sir please

    1. Dear Rakesh,

      first of all the triac will not produce 220V., this volatge will need to be fed from the right side and the triac will switch ON the 220V whenever the LED is switched ON. The triac should be connected with a load in series as shown in this circuit

      http://3.bp.blogspot.com/-4dY_nPZyFGk/VXveLFjql3I/AAAAAAAAKbc/mJzqWjJt2xg/s1600/triac%2Bpwm%2Bdriver.png

      the input LED intensity will not change the triac 220V conduction but if the LED intensity is too low then the triac will just shut off completely.

  31. Dear Rakesh,

    I use Firefox and your link opens in chrome so it becomes difficult for me to check.

    upload the image on any free image hosting side and give me the link, I'll check

  32. https://lh3.googleusercontent.com/-5ytd6csNdOE/VtCRI2Tz5xI/AAAAAAAAANg/sXNnVTv0VL8/w1060-h558-p-rw/IMG_20160226_231911.JPG

    Sir i repeat again

    Dear sir please ऊपर दिए हुवे circuit link को open करे और क्रप्या बतायें इस circuit में SCR से Triac को communicate कर ने के लिए किस किस components की आवशकता पड़ेगी
    please sir complete this circuit

    1. Dear sir RV1 की जगह पर LDR लगा के देखा पर वो लगातार जलता ही जारहा है LDR को चाहे रौशनी मिले या ना मिले पर ये circuit, dimmer की तरह काम नहीं कर रहा

      कोई नया idea हो तो sir बताइए

    2. Dear Rakesh, if a 220K pot works at RV1 then an LDR will also work…first test it with a 220K pot, then try it LDR….it has to work…
      more light on ldr will cause more brightness on the lamp ad low light on the LDR will cause lower illumination on the lamp. If still it does not work check the LDR with ohm meter….it should show a varying resistance from 10K to 2M in response to the various light intensities

    3. Daer sir मैं आपके इस नए idea को भी check कर चूका हूँ और नया LDR भी लगा के देख चूका हूँ और LDR को multimeter से check भी कर चूका हूँ पर इस बार light थोड़ी कम जल रही थी 220k की वजह से लेकिन LDR का response अभी भी वही है LDR और 220k लगाने के बाद LIGHT जलती ही जा रही है LDR पर रौशनी पड़े या ना पड़े कोई फर्क नहीं पड़ रहा है
      बताइए क्या करू
      ध्यान रहे सर ये मैं BTA41 के साथ कर रहा हूँ

    4. maine 220k ko alag se test karne ko kaha tha, LDR ke sath me nahi lagana hai….agar 220K alag se kaam karta hai to LDR bhi kaam karna chahiya..

      maine test kiya hai …it works.

      agar yeh nahi jum raha hai to PWM wala difficult circuit try karna padega.

    5. हा किया था sir जैसा आप कह रहें है दोनों को अलग अलग और एक साथ भी लगा कर देखा था

      PWM वाला पे भी मैंने try किया वो कामयाब हो गया पर उसमे light जरा सा डीम होते ही अचानक से light बंद हो जाती है मतलब पूरी तरह से धिरे धीरे डीम नहीं होती जबकि मैंने LDR पे
      Led के जरिये धीरे धीरे flash मारा है

      अब बताइए sir इसका कोई उपाय है ??

  33. Dear sir अपने first circuit बोला है पर उसमे TRIAC TIC226 लगा हुवा है और मुझे BTA41 लगाना है तो क्या मैं उसकी जगह BTA41 लगा सकता हूँ कोई परेशानी तो नहीं होगी और बाकि components वही रहेगे

  34. Dear sir ,
    Good day to you . I have used above the Triac Dimmer Switch I can regulate the ceiling fan At the moment it got little bit of noise from fan. How can I regulate the fan speed smoothly without noise?

    Thank you

    1. Dear Satheesh, use L1 with higher number of turns, wind it over an iron core such as an iron bolt or rod. use around 300 turns or more

      make sure the 0.1/400V capacitor is not faulty.

  35. Dear Swagatam

    Nice to say hello, I have intentions to use the circuit of the second image, this would help me to control engine speed from a desktop drill press Black & Decker 1/3HP – 250W.

    Regards

  36. Hello Sir and thanks for your efforts, you site is highly educational. I built the second circuit, but get little variation between both ends of the variable resistor, both with a light or a 300w motor. I did not have all the components as recommended, so I am using a 500k variable resistor, a 68 uH inductor, the triac is an sc146d, the 33k resistor is made of paper and pencil lead scribbled on it. The 0.022 uf caps are 400v not 250.
    do you have any suggestions? thanks in advance

    1. Thanks Mark, C1 and L1 are not relevant, so those are not responsible for the full phase control.

      the capacitors, the pot and the resistors are the components which are actually used for the phase control.

      try increasing the values of the 0.022uF to 0.044uF each and then see the difference, if still there's no difference then definitely there's some other serious issue with your circuit, in that case you might want to replace the diac, or the triac or the 33K etc.

    2. Thanks for your reply, I've been tinkering all day with it, it seems I get the same rpm out of the motor with no load on it, but the power is lower, as if the circuit is actually decreasing power instrad of rpm. I need this for a lathe, so I need strong slip even at lower speeds. Not sure if I am making any sense, not an expert here…thanks!

    3. whether with load or without load, the motor should respond from minimum to max speeds when the pot is turned to and fro.

      the best way to test it is with a 100 watt lamp, if the lamp is not dimming from zero to max and vice versa, then definitely your circuit has some fault.

    4. Thanks, I need to male sure I am reading the second schematic correctly. Are all intersections also connections? I wired as such on my breadboard, but maybe I should not have connected something to something else

    5. Hi, ok created a pcb, not working. I really need to know if designing the schematics you followed standard rules in the matter of crossing lines. Usually when crosssing lines have a dot on them they are connected, otherwise they are not, or show a little bridge line. Are yours connecting at intersections or not? Thanks

    6. Hi again, it works fine with resistive loads and single phase brushed motor, however I cannot regulate a brushed universal motor, I can only increase speed but cannot decrease it afterwards. Have to switch it off then lower pot to min then switch on and increase to whichever speed desired. The motor has three coils and two brushes, with ac mains going in one brush on one side and one coil on other side, while the other brush and one other coil pin are bridged together.

    7. Hi, sorry can't figure it out…The circuit works perfectly with ceiling fans which have capacitor start motors, not sure why it's not working with your brushed universal type motor…somebody having expertise in motor electronics would be able to diagnose this correctly.

  37. Hi Swagatam.
    Thank you for the nice post, and for keeping the thread alive – awesome 😀

    I'm looking to build a dimmer-box to mount on the ceiling next to a chandelier. I just want a rotary knob on the box to be able to adjust the light level, so no fancy/smart stuff..

    The chandelier has 5 LED bulbs (4W each) which all include the needed circuitry to allow for dimming (supplier specified a SCR-dimmer).

    Do you think I can use the second schematic from your post without adjustments?
    What size resistors would you recommend? 1W or larger?
    Would it hurt if all capacitors are 500V?
    Do you have any suggestions on what variable resistor/potentiometer to use?
    I'm looking to use either BT136-600E or BT136-800E – any recommendations?
    Where should R4 go? The one next to the diac?

    Sorry, but I'm a bit of a noob in electronics 🙁

    1. Thank you Kenneth,

      Why don't you buy a readymade dimmer switch instead of taking the risk and time of building one, unless you are doing it as a hobby?

      yes second schematic will do, the first one will also work.

      however I have never seen a triac based dimmer switch being used for controlling LED modules.

      the circuit indicated in the above article will not need any kind of changes for upto 200 watt 220V applications, so for your requirement also the same circuit could be used.

      BT136 600, or 800 both are fine.

      R4 should be where it is shown in the diagram, behind the diac.

      all the resistors are 1/4 watt….L1 and C1 are optional.

      If you are a noob then you should prefer buying one ready made, ceiling fan dimmer-switches are quite cheaply variable in the market….just a couple of dollars.

  38. HI engineer, pls i got 0.1uf/400v caps for C2, C3 instead of 0.1uf/250v and also got 500k VR. but i tested it soldering iron, it came up but didnt get hot as usual. i turned the pot but no difference, pls can the caps and vr i used affect it.

    1. Hi, with soldering iron you won't be able understand the response, you should use a 100 watt bulb instead, however with 0.1uF and with 500K pot the output might show sudden shut down at some lower pot limit…therefore you must match the parameters such that the lowest pot adjustment does not allow the output to fall below a specified minimum voltage level

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