A Pulse-Width Modulation (PWM) circuit is an electronic circuit used to control the amount of power delivered to a load by rapidly switching it on and off at a fixed frequency. The term "pulse-width modulation" refers to the technique of varying the width of the pulses while keeping the frequency constant. This method allows for precise control of the average voltage or current supplied to the load.
PWM is commonly used in various applications, including motor control, LED dimming, power regulation, audio amplification, and more. The key components of a PWM circuit are:
Comparator: The heart of the PWM circuit is a comparator that compares a reference voltage (or a sawtooth wave) with a varying control signal (often from a microcontroller or a dedicated PWM generator). The output of the comparator is a digital signal.
Reference voltage: This voltage sets the maximum value for the duty cycle, representing the highest power level applied to the load. The duty cycle is the ratio of the ON time to the total period of one PWM cycle.
Control signal: The control signal determines the duty cycle of the PWM waveform, and thus the average voltage or current applied to the load.
PWM Generator: In some cases, a dedicated PWM generator or microcontroller with built-in PWM functionality is used to generate the control signal.
When the control signal is below the reference voltage, the comparator output is low, and the load is turned off (0% duty cycle). When the control signal rises above the reference voltage, the comparator output goes high, and the load is turned on (100% duty cycle). By varying the control signal between these extremes, the duty cycle is adjusted, allowing for continuous control of the load's power level.
The frequency of the PWM signal is typically much higher than what the load can respond to, which means the load effectively "sees" a constant average voltage or current, even though it is being rapidly switched on and off.
In summary, a PWM circuit provides a method to control the power delivered to a load by adjusting the duty cycle of a high-frequency square wave, making it a versatile and widely used technique in electronics and control systems.