PWM Controlled Fan Dimmer Switch

In this article we look into a simple 220V mains PWM controlled fan or light dimmer circuit which does not require a microcontroller or costly triac drivers for the intended operations.

Capacitive Phase Chopping

All Ordinary types fan dimmers which rely on capacitive phase chopping technology have one drawback in common, these generate a lot of RF noise and require bulky inductors for controlling them partially.

Furthermore, the switching or the phase chopping being done using ordinary capacitor diac technology lack accuracy and sharpness.

The proposed mains transformerless PWM controlled fan dimmer circuit designed by me is free from all such possible issues normally accompanied with traditional fan or light dimmers since it uses an advanced CMOS IC based circuit and an accurate zero crossing detector stage.

No MCUs Used

The best thing about this circuit is that it does not require microcontrollers and programming, and also a triac driver has been eliminated making the circuit extremely easy to build even for the new hobbyists.

Let's learn the configuration in detail, which is rather too straightforward:

Referring to the circuit, IC1 which is a 4060 timer chip is configured to produce a delayed positive pulse for the triac each time the phase crosses the zero line of its phase angle.

The entire circuit is powered from an ordinary capacitive power supply using C1, D5, Z1 and C3.

IC1 is configured in its standard form for generating a delayed switch ON or a high every time its pin12 goes through a reset action.

Zero Crossing Switching for the Triac

The dimming action or the phase control action is achieved by making the triac to conduct after a predetermined delay each time a zero crossing is detected.

If this delay is short, it means the triac gets an opportunity to conduct for a greater amount of time for the phase angles, causing the connected fan to spin faster or the light to shine to brighter.

As this delay is increased, the triac is forced to conduct for proportionately shorter durations across the phase angles producing a proportionate amount of reduction over the speed or the brightness of the connected fan or the light respectively.

The zero crossing operation is simply enforced by using an ordinary opto coupler, as can be witnessed in the given diagram.

The bridge D1---D4 transforms the alternating phase angle into equivalent 100 Hz positive pulses.

The LEd and the transistor inside the opto coupler responds to these positive 100Hz pulses and stays switched ON only for so long as the pulses are 0.8V above the zero mark and switches OFF instantly as the pulses reach the zero crossing point.

While the opto transistor is in the conducting phase, the IC pin12 is held at ground level allowing a delay or a predetermined negativestarting pulse for the triac gate.

However at the zero crossing levels the opto switches OFF, resetting the pin12 of the IC such that the IC pin3 restarts a fresh or a new delay for the triac to respond for that particular phase angle.

PWM Phase Control

The length or the pulse width of this delay pulse can be varied by suitably adjusting VR1 which also becomes the speed control knob for the discussed PWM controlled fan dimmer circuit.

VR1 and C2 must be selected such that the maximum delay produced by these should not exceed the 1/100 = 0.01 second timing in order to ensure a linearly incrementing 0 to full calibration over the given control knob.

The above could be implemented by some trial error or by using the standard formula for IC 4060.

For the above you may also experiment the other outputs of the IC.

 Circuit Diagram

Parts List

R1, R5 = 1M
R2, R3, R4 R6 = 10K
C1 = 0.22uF/400v
C3 = 100uF/25V
D1---D5 = 1N4007
Z1 = 12V
IC1 = 4060

Waveform Simulation

The delay waveform image below shows how the phase for the fan may be delayed at every zero crossing, for the various settings of VR1 and C2.


Need Help? Please send your queries through Comments for quick replies!


oliver oliveros said…
Hi Swagatam,

i want to ask on how can i reduce a line AC voltage from 230V to 200V? is ithere a circuit for this? i have a contactor witch the coil is 200V and my grid is 230V. i hope you can help me for this to use of my contactor.

Thanks in advance,
Swagatam said…
Hi Oliver,

you will need a 25-0-25V /5amp/230V step down transformer which you can wire up to get a reduced voltage upto 205 or 200V as per your requirement.

the wiring instructions can be found in the following article:
oliver oliveros said…
thank you swagatam... your an angel
Swagatam said…
you are welcome dear!!
Arpan ASR said…

please help me to make a circuit...
i want to make a micro-controller less,MOC3041 opto base heater dimmer...
Swagatam said…
Hi Arpan, you can find plenty of such circuits on the web, please type the keywords and you will come across many.
Arpan ASR said…
I google about this circuits in web...but it result aurdino or any microcontroller base dimmer..i can't find any MOC3041 opto and op-amp ic base dimmer..
Swagatam said…
Arpan, why don't you try the above circuit, I have eliminated the use of MOC3041 and made the design even simpler.
Swagatam said…
...or you can try the following circuit:

MOC3021 has a built-in zero crossing detector so you won't need to worry about that...the pWM input could any square wave signal having pulse timing of 0.01 seconds

the inverter output may be replaced with 220v AC mains input at extreme right of the circuit
Arpan ASR said…
Thank you swagatam sir..thank you..
oliver oliveros said…
Hi Swagatam,

what is the best value of Rt and Ct?

Swagatam said…
Hi Oliver, if you are referring to the above 4060 circuit, it can be identified best through some trial and error....ideally the range should be within 1/100 = 0.01 second..... meaning within 0 to 0.01 second
oliver oliveros said…
do i have to add the R4 to VR1 for the computation?

R4=10k, VR1=5k = Rt=15k

f = 1/(2.3*15*0.01) = 2.89
t = 1/2.89*16 = 5.5sec

16 is pin7 or Q4

correct me if i'm wrong...

Swagatam said…
VR1 is a pot or a variable resistor, R4 is for making sure that even at minimum pot value the IC does not stall.

It would be difficult to identify the exact values of the pot and the capacitor...

pin 16 is the supply pin of the IC which joins with D5, C3, R3, mistakenly not shown in the diagram.
AlFa said…

Dear Sir Swagatam

The ground plane PWM regulator circuit is the negative you get the rectifier bridge D1-D4, I mean where is the negative of Z1, C3 and IC1.

Thank you very much for your reply

Best regards
Swagatam said…
Dear AIFa,

the bridge is only for the opto and for implementing the zero crossing detection....the actual ground of the circuit the line which connects with pin8 of the iC 4060
AlFa said…
Thank you very much dear Swagatam.
Rakesh Maurya said…
Dear sir can i use MOC3021 with BTA41 600V for light dimmer or motor speed controller
Swagatam said…
Dear Rakesh, yes you can use them together
Rakesh Maurya said…
Dear sir

what is voltage value of 0.05uf and 0.01uf in your circuit diagram

Swagatam said…
Dear Rakesh, It's 400V for both
Rakesh Maurya said…
Ok and thank you sir
Rakesh Maurya said…
Dear sir MOC3021 it's not proper work with BTA41 for light dimmer circuit
this is on and than off, not a dimming condition

so please sir solve this problem
Swagatam said…
you must apply varying pwm at the input side of MOC3021, only then it will respond with the dimming effect
Rakesh Maurya said…
Dear sir please एक last question है

आप के दिए हुवे circuit में (जिसका address नीचे दिया हुवा है) 470R के दो resistance लगे हुवे है
अगर मै BTA41 की जगह पे BT139 use करता हूँ तो उन 2 जगहों पे कितने value के resistance की जरुरत पड़े ही जहा 470R के 2 resistance लगे हुवे है
please sir
Swagatam said…
Dear Rakesh, no need to change the resistor values, you can use the same values for BT139 also.
Samrat said…
Hello Swagatam, Appreciate your help and documenting these design for new comers like me.

I am trying to find a fan speed controller without a POT/VR1 and instead use Arduino software to control the speed of the fan. I did see you other image-

Do you think that circuit would help in controlling the inductive fan speed just with PWM from Arduino?

Appreciate your guidance.


Swagatam said…
Thank you Samrat,

No, the picture that you have shown was designed on a mistaken assumption, triacs can never be controlled through PWM, except the method explained in the above article or as implemented in triac dimmer circuits.
AliGul said…
sir i want to make Ac fan speed controlling .i want seketch of arduino for controlle the speed of through serial monitor of arduino IDE
Randy Aspen said…
Hi Swagatam,

I have built your PWM Controlled Fan Dimmer Switch Circuit (as shown above) - running on 60Hz 120 volts. I am using a 100k pot for VR1 and a C2 capacitor of .1uF which does not work.

How can I calculate the value of C2?
Or can you give me a guess of what might be close?


Swagatam said…
Hi Randy, calculating C2 with respect to VR1 can be quite difficult unless you do it through an oscilloscope or with some relentless experimentation. I'll explain how it is supposed to work

the optocoupler will switch ON as soon as the mains phase has crossed the zero crossing point, and will remain switched ON until the phase has reached back to the next zero crossing......since this may happen 60 times per second (in your country), and after rectification 120 times, the period for which the opto remains ON can be calculated as 1sec/100 = 0.01 second

the 0.01 second is the time range for which the IC pin#12 stays grounded and allows the IC to initiate the counting of it timimng cycle.

Therefore we have this 0.01 sec range in which the RC timing components must be adjusted such that the triac gate triggers after a certain delay inside this 0.01 second slot.

For example suppose the VR/C2 are adjusted such that the IC triggers the gate after a period of 0.005 second would imply that the triac is allowed to conduct for the next 0.005 second within the stipulated 0.01 second...that's 50% conduction and would allow the fan to rotate at 50% speed....and so on.

therefore in short the VR/C2 have a time slot of 0.01 second range under which these have to decide after how much delay the triac could be switched ON until the next zero crossing, which would go repeating for every phase causing that much amount of speed on the fan.

I'll possibly try to update another circuit using two 555 IC and by implementing a "time proportional" control theory...that will hopefully be easier to understand and execute than the above theory.
Swagatam said…

sorry...the period for which the opto remains ON can be calculated as 1sec/120 = 0.0083 second
Glory said…
Please, how can I reduce the power wattage of my plasma TV 440w. Any circuit.
Glory said…
Please, how can I reduce the power Consumption for wattage of my plasma TV 440w. Any circuit.
Swag said…
sorry, no ideas

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