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Electronics => Projects, Designs, and Technical Stuff => Topic started by: rrn on December 03, 2021, 04:03:35 am

Title: True RMS and Duty cycle calculation
Post by: rrn on December 03, 2021, 04:03:35 am

Can someone help with calculating modified sine wave true RMS value and also how to Control PWM dutycycle to maintain fixed output.
Example: input volatge 100Vdc.
Need to maintain fixed Vrms 50VAC
Frequency = 50hz
Modified sine wave same as in the picture

Title: Re: True RMS and Duty cycle calculation
Post by: gcewing on December 03, 2021, 07:22:00 am

For PWM with duty cycle d,

Vrms = sqrt(d * Vin**2) = sqrt(d) * Vin

so

sqrt(d) = Vrms / Vin

or

d = (Vrms / Vin) ** 2

So for Vin = 100V and Vrms = 50V, you want d = 1/4.

The frequency doesn't come into it.