Simulate a Pulse Width Modulator (PWM) in Multisim

Updated Jul 23, 2018

Reported In

Software

  • Multisim

Issue Details

In my version of Multisim there are no models for Pulse Width Modulator (PWM) in the database. Is there a way to simulate this in Multisim?

Solution

Multisim 12 has updated its components database with 92 component models that are widely used in the design of power and electromechanical devices.  This updated database includes power controllers such as models of phase angle controllers and PWM controllers.

If you are using an older version of Multisim you can simulate a PWM using the Controlled One Shot component.

The Controlled One Shot is a very versatile component which can be used to create a PWM signal. You can find this component under the Sources group and Controlled Voltage Sources family.

From left to right the pins at the top of the symbol represent:
  1. Clock
  2. Control
  3. Clear
  4. Output
All pins on the bottom of the component are usually tied to ground.

To set the Controlled One Shot component;
  1. Double click on the component and select the Value tab.
  2. The Clock Trigger Value sets the clock pin threshold value. When the voltage at this pin reaches the define value, it will trigger the component.
  3. The input voltage at the Control pin is used to determine the output pulse width. In the example circuit, the following values were entered:
Control Array      Pulse width array (sec)
         1                            0.0001
         3                            0.0003 

When the voltage to the control pin is 1V, the output pulse is 3ms. When the input is at 3V the output pulse will be 3ms. Since this table has a piecewise property, when the input to the Control pin is 2V the output pulse will be 2ms and if it is 4V the pulse will be 4ms. 

When simulating the example circuit below, please note the following:
  1. Press the space bar on your keyboard. When the input is set to high the output should be zero. When set to low, the circuit will be in operation mode.
  2. The function generator outputs a triangle wave. When it passes 0.5V, it will trigger the one shot.
  3. Pressing A on the keyboard changes the potentiometer wiper position which controls the voltage at the Control pin, controlling your pulse width.

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