Introduction: PWM (pulse Width Modulation) Power LED Dimmer

Picture of PWM (pulse Width Modulation) Power LED Dimmer

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

Picture of 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

Picture of Schmitt Trigger Inverter Multivibrator

see animation in video (last step)

Step 3: Varying the Pulse Width (pwm)

Picture of 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

Picture of 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

Picture of Circuit Operation Details

Step 6: Waveforms

Picture of Waveforms

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

Comments

gm280 (author)2017-01-09

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...

Chipmunk03 (author)2017-01-09

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).

Genturner (author)2017-01-09

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

rafununu (author)2017-01-09

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.

About This Instructable

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