PWM Power

Hi
I have a question to do with using PWM
If for example I had a 1ohm load and a voltage supply of 4JC-1, I would get a power draw of 16JS-1, now if I had a duty cycle of say 50% I should get an average power output of 8JS-1. However if i thought of it as having an average current of 2CS-1 and a average voltage of 2JC-1 then the power output comes out to be 4JS-1, which is 4 times less and not half. If it should be the half what does the actual voltage and current average out to?

Thank you very much.
 

berkeman

Mentor
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(4V)^2/1 Ohm = 16W continuous = 4A * 4V

50% duty cycle

8W = 4A * 4V * 0.5

You can't average both the current and voltage, without taking an RMS average. RMS averages give you the right answer -- can you see why?
 
I can see that it does seem work. However I thought that RMS using route 2 was for sine waves? Am i missing something?

Thank you
 

Averagesupernova

Science Advisor
Gold Member
3,514
533
Be sure to keep in mind that .707 * Vpeak is the RMS equivalent for sine waves only. But real actual RMS doesn't care what the waveform is.
 
Thank you both very much for your help. I understand it alot better now.
 

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