(PWM) Pulse Width Modulation

PWM (pulse width modulation) or PDM (pulse-duration modulation) is a technique for decreasing the average power produced by an electrical signal by splitting it up into discrete portions. The average value of voltage (and current) provided to the load is regulated by rapidly switching the supply and load switches on and off.

The higher the overall power provided to the load, the longer the switch is on relative to the off times. It is one of the principal ways, along with maximum power point tracking (MPPT), of decreasing the output of solar panels to that which can be used by a battery.

PWM is a modulation procedure or technique used in most systems to encode the amplitude of one signal into the pulse width or length of another signal, generally a carrier signal, for transmission. Although PWM is employed in communications, its primary use is to manage the power provided to various sorts of electrical equipment, particularly inertial loads such as AC/DC motors.

Pulse Width Modulation

PWM has a significant advantage in that power loss is minimized. Unlike analogue potentiometers, which restrict power output by basically blocking the electrical route, resulting in power loss as heat, PWM actually turns off the power output rather than limiting it.

Important PMW signal parameters Duty Cycle of the PMW

A PWM signal, as we know, remains “ON” for a set period of time before switching to “OFF” mode. The duty cycle is the proportion of time that the signal remains “ON.” If the signal is always “ON,” it must have a duty cycle of 100 percent. The duty cycle calculation formula is as follows:

The average voltage value is affected by the duty cycle. As a result, the average value may be adjusted by varying the width of a pulse’s “ON.”

Duty Cycle

The word duty cycle refers to the ratio of ‘on’ time to regular intervals or ‘periods’ of time; a low duty cycle equates to low power because the power is off for the majority of the time. The duty cycle is given as a percentage, with 100 percent being completely on. When a digital signal is on half of the time and off the other half of the time, it has a duty cycle of 50% and looks like a “square” wave.

A duty cycle of more than 50% indicates that a digital signal spends more time in the on state than in the off state. A digital signal has a duty cycle of 50% when it spends more time in the off state than in the on state.

Take the duty cycle and multiply it by the high voltage level (which is a digital “on” or “1” state for the MCU) to get the average voltage level that the motor is experiencing at the time.

Duty Cycle x High Voltage Level = Average Voltage

When you add the word “instantaneous” to it, you get the impression that things are changing dynamically

PWM (Pulse Width Modulation) signal output voltage

Pulse width modulation circuit diagram

The PWM signal’s output voltage will be the duty cycle %. During example, if the operating voltage is 5 V for a 100% duty cycle, the output voltage will also be 5 V. If the duty cycle is set to 50%, the output voltage is 2.5 V.

There are three common forms of pulse width modulation techniques, which are as follows:

  • Trail Edge Modulation – In this approach, the lead edge of the signal is modified while the trailing edge remains constant.
  • Lead Edge Modulation – This approach fixes the signal’s lead edge while modulating the trailing edge.
  • Pulse Center Two Edge Modulation – In this technique, the pulse centre is fixed and both edges of the pulse are modulated.

Advantages and Disadvantages of Pulse Width Modulation

First, let us talk about the advantages of pulse width modulation technology before considering its disadvantages:

  • The PWM approach reduces LED overheating while retaining brightness.
  • The PWM approach is precise and offers a quick reaction time.
  • The PWM approach has a high input power factor.
  • The PWM approach allows motors to provide maximum torque even at low speeds.
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