Pulse-Width Modulation (PWM) is a modulation technique used in electronics and digital control systems to generate analog-like signals using digital components. It's a way to encode analog information in a digital signal by varying the width of the signal's pulse while keeping the frequency constant.
In a PWM signal, the period (T) of the signal remains constant, but the duty cycle (D) changes. The duty cycle is the ratio of the ON time (time the signal is high) to the total period. It's often expressed as a percentage.
A high-duty cycle means the signal is ON for a larger portion of the period, and a low-duty cycle means the signal is ON for a smaller portion of the period.
PWM signals are commonly used in applications like motor speed control, LED dimming, power regulation, and generating analog-like signals for various purposes. The key advantage of PWM is that it can control the average power delivered to a load without dissipating much power in the control device itself.
Here's how a PWM signal is generated:
Comparison: The system generates a reference voltage or signal and compares it to a ramp signal. The ramp signal is a continuously increasing signal that resets once it reaches the period T. The comparison determines whether the PWM signal should be high or low during a particular period.
Modulation: Based on the comparison, the PWM generator decides whether the signal should be high (ON) or low (OFF) for that specific interval. If the reference signal is higher than the ramp signal, the PWM output is high; otherwise, it's low.
Duty Cycle Control: To change the duty cycle, the rate at which the ramp signal increases is adjusted. A higher rate results in a shorter time to reach the reference signal, leading to a higher duty cycle, and vice versa.
Filtering: In applications like motor control or audio, a low-pass filter might be used to smooth out the PWM signal and obtain an analog-like output.
The resulting PWM waveform is a square wave with varying pulse width. By adjusting the duty cycle, you can effectively control the average voltage or current delivered to a load, allowing for precise control over the load's behavior.
For example, in LED dimming, a higher duty cycle results in brighter light, and a lower duty cycle leads to dimmer light. Similarly, in motor speed control, a higher duty cycle can increase the speed of the motor.
PWM signals are commonly generated using microcontrollers, digital signal processors (DSPs), dedicated PWM generator ICs, and FPGA (Field Programmable Gate Array) devices.