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Pulse width Modulation or PWM is one of the powerful techniques used in control systems today. It is used in wide range of application which includes: speed control, power control, measurement and communication. This tutorial will take you through basics of Pulse width modulation and its implementation on microcontrollers.


Basic Principal of PWM

Pulse width modulation is basically a square wave with a varying high and low time. A basic PWM signal is shown in the figure below.

center

Pulse width modulation wave

There are various terms associated with PWM:

  1. On-Time: Duration of time signal is high
  2. Off-Time: Duration of time signal is low
  3. Period: It is represented as the sum of on-time and off-time of PWM signal
  4. Duty cycle: It is represented as percentage of time signal remains on during the period of the PWM signal

Period

As shown in the the figure, Ton denotes the on-time and Toff denotes the off time of signal. Period is the sum of both on and off times and is calculated as shown in the equation below:

PWM Period

Duty Cycle

Duty cycle is calculated as on-time to the period of time. Using the period calculated above, duty cycle is calculated as:

PWM Duty cycle equation

PWM: Voltage Regulation

PWM signal when used at a different duty cycles gives a varying voltage at the output. This method is used in various areas of application like:

  • Switching regulators
  • LED dimmers
  • Audio
  • Analog signal generation
  • and many more...

Voltage regulation is done by averaging the PWM signal. Output voltage is represented by the following equation:

PWM Voltage regulation PWM Voltage regulation

As you can see from the equation the output voltage can be directly varied by varying the Ton value.

If Ton is 0, Vout is also 0. if Ton is Ttotal then Vout is Vin or say maximum.

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