Pulse Width Modulation (PWM - Pulse Width Modulation)

Pulse Width Modulation (PWM - Pulse Width Modulation)

Pulse width modulation (PWM) is a technique that regulates the average voltage or current sent to an electrical device (such as an LED or a motor) by rapidly switching it on and off. PWM is widely used in lighting to dim LEDs without sacrificing efficiency.

How does PWM work?

PWM rapidly switches the power to an LED on and off at a specific frequency (usually a few kHz to tens of kHz). The ratio of the on-time (T $_aan$ ) and the total period (T $_totaal$ ) determines the brightness of the LED.

This ratio is expressed as the duty cycle and is shown as a percentage:

• 100% duty cycle → LED lights up at full brightness (continuously on)
• 50% duty cycle → LED burns at half brightness (equal amounts of on and off)
• 10% duty cycle → LED is dimly lit (short on, long off)

Humans cannot perceive these rapid switching cycles, which is why the LED appears to dim instead of flashing to us.

Benefits of PWM dimming on LEDs

✅ Efficiency : The LED always receives the full voltage, so no energy is lost as heat (as with analog dimming).
✅ Precise dimming control : It is possible to dim LEDs very precisely, often to <1% of maximum brightness.
✅ Colour consistency : With PWM the colour temperature remains stable, unlike analogue dimming where colour shifting can occur.
✅ Long lifespan : Because there is less heat development, LEDs and drivers can last longer.

Disadvantages of PWM dimming

⚠ Flicker : If the PWM frequency is too low (<1 kHz), the user may experience flickering, which can be tiring to the eyes and possibly cause health problems.
⚠ EMC interference : High switching frequencies may cause electromagnetic interference in other electronic equipment.
⚠ Not compatible with all LED drivers : Some LED drivers do not support PWM and require analog (voltage or current controlled) dimming.

Applications of PWM

🔹 LED lighting : Dimming of LED strips, LED lamps and industrial lighting.
🔹 Screens : Brightness control of LCD and OLED screens.
🔹 Motor control : Speed control of DC motors.
🔹 Electronics : Power control in power supplies and circuits.

Conclusion

PWM is an efficient and precise way to dim LEDs without losing brightness or color quality. It's widely used in lighting, displays, and motor control, but must be applied carefully to minimize flicker and electromagnetic interference.