PWM LED Dimmer/ Brightness Control by 555 Timer With Video Simulation

How to change the brightness of a LED? Whether led lights are dimmable? Is it possible to adjust the brightness of LEDs? LED is basically a diode, when the forward voltage exceeds 0.7 volt, it starts to glow, and if the forward voltage is less than 0.7 volt, it will be in the OFF state. What happens if we are providing a high voltage to the LED so as to increase the brightness?

Will it be a practical solution? No, it will lead to the burning of LED. So what we can do to adjust the brightness of LEDs? Here Circuits Gallery comes with a simple LED brightness control circuit using (Pulse Width Modulation) PWM method. It is also called PWM LED dimmer circuit diagram. By changing the pulse width of square wave, it is possible to control the brightness of LED. We have already discussed about the PWM signal generation before. Here NE555 timer IC is used to produce PWM signals.

LED Dimmer Circuit Schematic

Components Required for LED Dimmer Controller

  1. Resistors (4.7kΩ)
  2. Potentiometer (10kΩ)
  3. Capacitor (100nF or 0.1µF)
  4. 555 timer IC

Working of PWM LED Light Dimmer Circuit

  • Our new circuit is based on 555 timer IC. You can use this circuit as a dimmer switch for LED lights. This PWM concept is also applicable for lamp dimmer switches too. But here we are explaining about 555 led dimmer.
  • At the instant of powering ON the circuit, output will be 5V, because the voltage at the 2nd pin (trigger pin) is less than 1/3 Vcc. [Read Astale Multivibrator for getting familiarized with 555 timer].
  • At the very next moment, the output voltage will reach the capacitor via the 10kΩ potentiometer and diode D2 so that the capacitor starts charging with a time constant RdR1C (where Rd is the forward resistance of Diode D2).
  • When the capacitor voltage exceeds 2/3 Vcc, the 555 timer gets reset. Then the output will be 0V.
  • At this moment the capacitor discharges via the diode D1 and potentiometer R1 to the output pin since it is in ground potential.
  • When the capacitor voltage goes below 1/3 Vcc, the output of 555 IC again rises to 5V. This process continues.
  • Here the charging and discharging path is entirely different since it is isolated by diodes D1 and D2 (refer above images). If the potentiometer midpoint is at 50% (middle), we will able to get 50% duty cycle (square waves of equal pulse width).
  • Pulse with can be varied by changing the charging and discharging time, this is possible by adjusting the potentiometer. Thus we get PWM signal…!

Refer also:

  1. 555 Timer internal circuit during charging
  2. 555 timer internal circuit during discharging
  • This signal is applied to the LED via a 4.7kΩ resistor. The brightness of LED is proportional to the average value of the square wave.
  • For high pulse width it is possible to get huge brightness of LED. Also if it is low pulse with, brightness also decreases.
  • Please watch the design simulation video and practical implementation of the circuit given below for better understanding.

This is the video practical implementation of PWM LED dimmer circuit.

(We express our thanks to Mr. Giorgos Lazaridis for providing this video

Pinout of 555 timer IC

11 thoughts on “PWM LED Dimmer/ Brightness Control by 555 Timer With Video Simulation

  1. I have this set up currently:
    6 x high brightness LEDs in parallel each with its own 200-ohm resistor in series with the LED (resistors are between LEDs and GND)

    my question would be…. will this setup discussed in this article work with my configuration? do I really need the 4.7k-ohm resistor at the output of the 555 IC or it will be unnecessary?

  2. Hello Mr. Jaseem,
    I’ve rig up the same circuit in Multisim, but in the oscilloscope’s reading is showing a plane line. I’m not getting the PWM output. Can you please share the Multisim file or tell us the settings for oscilloscope in multisim.
    Thank you in advance.

  3. This circuit works but the frequency varies with the duty cycle, by as much as almost 1:10. It’s not a problem for some applications (such as lighting an LED) but it is for others (such as controlling the speed of a motor).

    Colin, it’s a super bright LED type 😉


  5. Would it be possible to modify this circuit to use say a 250K or 500K audio taper pot and maintain a 0-100% dim over the sweep of the pot?

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