What Is PWM (Pulse Width Modulation)?
PWM (Pulse Width Modulation) sets the average power delivered to a load by varying how long a signal stays on within each cycle — its duty cycle. The frequency stays fixed; only the pulse width changes. A 25% duty cycle delivers a quarter of full power. It is widely used for LED brightness, motor speed and servo control.
PWM (Pulse Width Modulation) is a technique for adjusting average power by switching a signal on and off very quickly. Instead of reducing the voltage, it changes "how long the voltage stays on."
What Is the Duty Cycle?
The duty cycle is the percentage of a period the signal stays on. 100% is fully on, 0% fully off, and 50% is half and half. This ratio is the heart of PWM.
Average Voltage Calculation
The average voltage is simply: V_avg = V_max × duty cycle. For example, if a 5 V signal runs at 40% duty cycle, the load sees an average of 5 × 0.40 = 2 V. This way you set the "effective" voltage without lowering the source.
Where Is It Used?
- LED brightness control: the eye perceives fast blinking as steady light; the duty cycle sets the brightness.
- Motor speed control: in motor driver circuits, speed is efficiently set with PWM.
- Servo and signal generation: a servo motor's angle is set by the PWM pulse width.
Why Does Frequency Matter?
The PWM frequency must be high enough so there's no flicker in an LED or audible hum in a motor. Microcontrollers usually generate PWM in hardware at a high frequency.
Why PWM Instead of Directly Lowering the Voltage?
Lowering the voltage with a resistor dissipates energy as heat (inefficient). PWM, by keeping the switch fully on/fully off, works with very little loss — which is why it's preferred in power electronics.
Frequently Asked Questions
What is duty cycle?+
Why use PWM?+
Does PWM produce a real analog voltage?+
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