PWM understanding

pwm

I am giving PWM to a MOSFET (50% duty). It switches about 8.5V to be fed to a phase of a motor. There are 3 such phases.

Now, I am looking at voltage measured from these phases as well. I have 3KΩ and 10KΩ resistors acting as a voltage divider which steps down the voltage to about 1.96V. This will be measured by the ADC.

Now, will the value of 1.96V vary with respect to the PWM duty cycle? Will this voltage be lower at lower duty cycles and so on and so forth?

Best Answer

The duty cycle of the signal effectively gives the percent of the amplitude that will be seen by the circuit having it applied. That is,

V = Vo*D

Where D is the duty cycle.

This can seen as very intuitive if you consider the definition of duty cycle. Namely, the signal is ON (HIGH) for what percent of the time? For a duty cycle of 50% we have that half of the time the output is high and half of the time the output is low. So if you average this then we have

Vo = (V + 0)/2 = V/2

Or for a duty cycle of 25% we have:

Vo = (V + 0 + 0 + 0)/4 = V/4

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