Understanding Pulse Width Modulation (PWM)

Pulse Width Modulation (PWM) is a powerful technique used in electronics to control the amount of power sent to a device. Instead of varying the voltage level directly (like using a dimmer knob that adds resistance), PWM works by switching the power fully ON and fully OFF in a rapid sequence.

How it Works:

Imagine a light switch you can flick on and off very quickly. PWM does something similar, but electronically, hundreds or thousands of times per second (this is the frequency). The key is controlling how long the switch stays ON compared to how long it stays OFF within each cycle.

This ratio of ON-time to the total cycle time is called the Duty Cycle, usually expressed as a percentage.

• 0% Duty Cycle: The power is always OFF.
• 50% Duty Cycle: The power is ON for exactly half the time and OFF for the other half.
• 100% Duty Cycle: The power is always ON.

By changing the duty cycle, you change the average power delivered to the device. A higher duty cycle means more average power, while a lower duty cycle means less. The device (like an LED or motor) often responds to this average power level due to its physical properties or the rapid switching speed.

Why Use PWM?

• Efficiency: It's often more efficient than analog control methods (like using resistors), which dissipate excess power as heat.
• Digital Control: PWM signals are digital (either fully ON or fully OFF), making them easy to generate and control with microcontrollers and digital circuits.
• Versatility: It's used in countless applications.

Common Applications:

• Dimming LEDs: Varying the duty cycle changes the average brightness.
• Motor Speed Control: Adjusting the duty cycle controls the average voltage sent to a DC motor, thus controlling its speed.
• Servo Motor Control: Specific pulse widths within a PWM signal are used to set the angle of servo motors.
• Audio Synthesis & Amplifiers: Class-D audio amplifiers use PWM to create efficient sound reproduction.

Explore with the Simulator:

Our interactive simulator lets you visualize how changing the frequency and duty cycle affects the PWM waveform (the green line) and the resulting effective voltage (the orange dashed RMS line). See firsthand how these changes impact the brightness of a virtual LED and the speed of a virtual motor!

More Labs To Love:

Interactive Logic Gate Simulator Lab
Kirchhoff’s Laws Virtual Lab

More on UART: Wikipedia