Intro: 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
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.