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PWM Pulse width modulation

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Pulse Width Modulation (PWM) is a technique used to control the average voltage or current of a signal by modulating the width of the pulses in a periodic waveform. It is commonly used in various applications, such as motor control, power regulation, and communication systems. PWM provides a way to efficiently control the power delivered to a load while using digital signals.

To understand PWM, let's break down the process step by step:

  1. Waveform: PWM operates with a periodic waveform, typically a square wave. The waveform consists of a repeating cycle with two states: ON and OFF. The ON state represents a high or logical 1 level, while the OFF state represents a low or logical 0 level.
  2. Duty Cycle: The duty cycle of a PWM signal refers to the percentage of time the signal is in the ON state compared to the total period of the waveform. It determines the average power or voltage delivered to the load. The duty cycle is expressed as a ratio or percentage. For example, a 50% duty cycle means the signal is ON for half of the period and OFF for the other half.
  3. Control Signal: A control signal, typically generated by a microcontroller or dedicated PWM controller, determines the duty cycle of the PWM waveform. The control signal can be analog or digital, depending on the application. The desired output or control value, such as motor speed or LED brightness, is mapped to a corresponding duty cycle.
  4. Pulse Generation: To generate a PWM signal, a comparison is made between a reference value and a varying ramp signal. The ramp signal starts at the beginning of the period and increases linearly until it reaches the end of the period. The reference value is compared to the ramp signal at each point in time. When the ramp signal is below the reference value, the PWM signal is set to the ON state. When the ramp signal exceeds the reference value, the PWM signal switches to the OFF state.
  5. Modulating the Duty Cycle: By adjusting the reference value or the slope of the ramp signal, the duty cycle of the PWM waveform can be modulated. A higher reference value or steeper slope leads to a longer ON time and a higher duty cycle. Similarly, a lower reference value or shallower slope results in a shorter ON time and a lower duty cycle.
  6. Filtering: After generating the PWM waveform, it is often passed through a low-pass filter to remove high-frequency components and smooth out the signal. This filtering helps to obtain a more continuous output voltage or current.
  7. Load Response: The load, such as a motor or LED, responds to the average voltage or current determined by the duty cycle. For example, in motor control, a higher duty cycle delivers more power to the motor, resulting in increased speed. Conversely, a lower duty cycle reduces the average power and slows down the motor.

PWM offers several advantages, including high efficiency, precise control, and easy interfacing with digital systems. It allows for analog-like control using digital signals, making it widely used in applications that require accurate and adjustable power delivery.