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PWM Fan Controller by LM2902N or LM324N

Project Summary

This circuit is a fan controller which is using the pulse width modulation (PWM) method. It is tiny (33.78mm x 54.76mm) and easy to build. Functions of the circuit parts are listed below;

Project Description


Figure 1 

VR1: 10 K Variable resistor adjusts the fan speed.

R9: This sets the minimum speed. With the 10k pot, a 1k resistor will give 0–100% control which is OK for model motors or lighting, 10k will give around 5v–12v range, more suitable for cooling fans.

C2: This is the timing capacitor, and with the 47k timing resistor R1 and wave amplitude control resistors R2 (22k) & R3 (10k) gives a PWM frequency of around 117Hz according to the formula

Frequency = R2 / (4 x R3 x R1 x C1)

Don’t change R2 or R3, but you can alter R1 and/or C1 if you want to try different frequencies.Fan controller by LM2902

Q1: For load currents up to about 600mA a 2N2222A NPN transistor is recommended. It comes in a TO-18 metal can.


Figure 2 

For higher loads go for a darlington power transistor such as the TIP120, 121 or 122, rated to 5A, or a power mosfet. The IRF530 is easy to find, not expensive, and can carry up to 14A. Providing you take the usual precautions for handling CMOS, static electricity is not going to zap it. Most n-channel MOSFETs will do, look for a low RDS and adequate current-handling ability. Both darlingtons and mosfets are in the TO-220 case.

Using the 2N2222A bipolar transistor you might lose 200-400mV from the 12v supply to the fan, double that for one of the darlington types; with the IRF530 I measured the loss at only 40mV with a 200mA fan.

Check the transistor or mosfet pin-outs, base or gate to R9, emitter or source to ground, collector or drain to the fan negative. A heatsink is not necessary at moderate loads.

D1: The diode prevents back-emf from inductive loads such as brushed motors from damaging the switching transistor. With “brushless” computer fan motors it’s not necessary to fit this diode across the load, as they have any needed protection already in-fan.

Project Files

File NameFile Size
pwm_fan_controller.rar1.46 MB
Tags: PWM, fan controller,

Comments on this Project:

By Jeremy Byington -1Score: 

6 years ago:  Is there a way to alter this circuit to allow for changing the frequencies?

By Komeil Bahmanpour -1Score: 

6 years ago:  I think the "Description" is mistaken. In C2's description,

1. by R1 you meant R4 (47k timing resistor)
2. by R2 you meant R3 (22k wave amplitude control 1)
3. by R3 you meant R5? (10k wave amplitude control 2)
4. by C1 you meant C2 (in the formula only)

So, the correct formula would be: Frequency = R3 / (4 * R5? * R4 * C2)

using this new formula,

22000/(4*10000*47000*0.0000001)=117.0 Hz (correct, as stated)

using site's formula,

10000/(4*22000*10000*0.0000001)=113.6 Hz

Finally, which exact components needed to be modified to affect the frequency? Would it be R4 and/or C1?

By zsa zsa zaturna 0Score: 

5 years ago:  Thanks komeil for clearing out the values. I had some confusions but you were able to solve my queries. Wish you all the best...

By jeff teaque 0Score: 

5 years ago:  the circuit looks very simple to construct! thanks for this!!!

By Jan 0Score: 

5 years ago:  is it possiblewith this circuit to control a fan that use 9,5 v??

By Geezer 1Score: 

4 years ago:  do fans using this circuit suffer from the low frequency growl sometimes found on 555 timer circuits.

Also can i replace the lm324n with an lm339n or lm3900n.

is the schematic correct in the fact that Komeil Bahmanpour was just wondering about altering the frequency in an earlier post.

By eddy -1Score: 

3 years ago:  I would like to know if you can get the outup of a 555 go into an Lm324 IC to exxpand the Freq range..

ahsan niaz
By ahsan niaz (0) 0Score: 

3 months ago:  can you please tell me that is this circuit working properly or not? if yes please comment thanks

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