PWM (pulse Width Modulation) Power LED Dimmer




About: Music: my profession for over 40 years... Electronics: my beloved hobby always.

This LED dimmer is built around the CD 4093 CMOS chip. PWM technique (pulse width modulation) is a very efficient way of controlling the brightness of LEDs with minimum energy waste. Instead of varying the brightness by varying the supply current with a variable resistor or transistor it is accomplished by varying the ratio of ON time vs OFF time. This when done at a high frequency rate is perceived by the eye (POV) as a smooth change in brightness.

Step 1: How It Works

The "heart" of the circuit is the SCHMITT trigger inverter multivibrator. Very simple: when output is high (Vdd) capacitor C charges through resistor R until input reaches the HIGH threshold voltage. Then, output inverts to 0v(Vss) and now C discharges through R. When voltage at gate input reaches the LOW threshold voltage output of gate inverts again to High (Vdd) and this cycle repeats to form a 50:50 square wave.

Step 2: Schmitt Trigger Inverter Multivibrator

see animation in video (last step)

Step 3: Varying the Pulse Width (pwm)

separate capacitor charge time and discharge time with a resistor and a diode and you can alter the DUTY CYCLE of the multivibrator. Replace resistors with a potentiometer, and you have a continuously variable duty cycle multivibrator .

Step 4: The Circuit Diagram

CD 4093 integrated circuit contains 4 identical SCHMITT trigger input NAND gates. Joining the 2 inputs of each gate they form Inverters or NOT gates. This dimmer circuit uses only 2 of the 4 gates. The other 2 gates can be used for a second dimmer channel. Cmos IC CD40106 contains 6 identical Schmitt trigger inverters and can be used for a full single chip 3 channel RGB controller.The specific FET and supply for the LEDs will depend on the required current-voltage of the led array. Supply can be a constant current source or constant voltage one with a small value series resistor, and with an output voltage slightly above the total led forward voltage drop.

Step 5: Circuit Operation Details

Step 6: Waveforms

Step 7: For Details, Watch the Video. Thank You !



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    5 Discussions


    1 year ago

    can you tell me how to make a dimmer for 220v 12w led bulb?


    2 years ago

    Nice circuit. Simple, low part count and does the job. I usually built such PWM circuits around the famous 555 timer chip, but this is even less part count. Nice...


    2 years ago

    I wander if the power LED can be replaced by an electro motor. I am looking for a solution for my pump. I want to control the speed of the pump. Replacing the potentiometer by an Arduino analog line (all my pwm lines are already used).


    2 years ago

    Wow. This was a great read. Well thought out with alot of explainaintions and


    2 years ago

    Even with PWM, unless you're using a constant current generator, a resistor is needed in the Led circuit. Without limitation, current will usually exceed the max forward current of the Led. This kind of schematics is well known, I made lighting mixers in the 80s with the same principle but with opamps and comparators, because, for these applications, a stable frequency was needed.