PWM LED dimmer circuit using IC 555

PWM LED light dimmer circuit

PWM ( Pulse Width Modulation) is a modulation technique in which the width of the pulse is varied based on the modulating signal. This possess wide variety of applications including motor speed control which is the most famous application of the PWM. This PWM led dimmer circuit uses IC 555 to generate PWM  which is employed to dim the LED’s connected to the IC.


555 timer IC a widely used one was used to generate the PWM signal here. Here the IC was wired as an Astable Multivibrator which gives square wave pulses as output in pin 3. The output frequency of the the Multivibrator was governed by the values R2, RV1 and C2. Here change in resistance value of the RV1 alters the width of the output pulse thereby generating a PWM signal in the pin 3.

The generated PWM signal is fed into the base of the transistor  since the 555 cannot source sufficient current for the working of LED’s. In the above circuit we have used white LED’s which consume 30mA and forward voltage of 3.5v. The above dimmer circuit can be used for two purposes here one is to produce dimming effect in the LED’s whereas another one is to save power consumed by the LED’s.

Using PWM signal we can reduce the on time of the LED in the above circuit which makes the circuit to consume less power. Around 70% – 80% PWM duty cycle it will switch as fast so that the human eye cannot see the flickering in the LED’s. The duty cycle of the PWM signal can be adjusted by varying resistance in RV1 and should be altered till no flickering is observed through our eyes. So through this way we can obtain desired luminescence with less power consumption.

Dimming of LED’s works the same way as above and should be done manually. You should vary the Resistance through the RV1 and this create an interesting dimming effect in the LED’s because of the varied on and off time of the PWM signal.


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Frank Donald

Frank Donald

Junior Network Engineer at Tata Communications
Frank Donald is an Electronics and Communication Engineer who loves building stuff in his free time. Video games, blogging and programming are the things he loves most
Frank Donald

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8 Comments on "PWM LED dimmer circuit using IC 555"

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What is diode number???

amman hussain

can any one share this ckt layout for pcb…?


how do i know that duty cycle of output pulse is 70-80%

Frank Donald

Adjust the pot until until there is no flicker in the LED’s or you can also determine the duty cycle using the below formula
Duty Cycle = (R2+RV1)/(R2+2RV1)


can i use this circuit used for any pwm application?

Frank Donald

Of course you can PWM has tons of applications.