# Converting a PWM wave into pure DC

Discussion in 'Power Electronics' started by YASH VERMA, Mar 21, 2018.

1. ### YASH VERMA

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Mar 21, 2018
Hello all,

I want to convert a PWM wave into pure DC with DC value as the peak value of PWM wave. I have tried using a peak detector circuit which has a diode, a capacitor, and a resistor. Although, I am not getting strictly peak value of PWM as DC. I have also tried using a low pass filter with a smoothing capacitor, that also does not get me my result. I again do not get peak value of PWM signal.

Best regards,
Yash Verma

2. ### duke37

5,364
769
Jan 9, 2011
The diode and capacitor will give a value of the peak minus the diode voltage drop.
To get better than this, you will need an ideal diode which can be simulated with an op-amp but will need a higher voltage power supply to drive it.

A low pass filter will give the average voltage which is of course always less than the maximum.

Why do you want the peak voltage? This can be estimated from the applied voltage.

3. ### kellys_eye

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Jun 25, 2010
I was thinking the same - most queries of this type are looking for a DC voltage proportional to the PWM signal ratio....

4. ### hevans1944Hop - AC8NS

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Jun 21, 2012
The peak value of PWM wave is CONSTANT. The only thing that varies is the pulse width, and possibly the pulse repetition frequency.

Please post either an oscilloscope screen-capture of your "PWM wave," or a hand-drawn sketch showing what kind of wave you want to "convert into pure DC." Your question does not make any sense.

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
I would suggest that you look at the power supply to the PWM controller. It will be DC having a value equal to the peak value of the PWM output.

Cannonball likes this.
6. ### YASH VERMA

7
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Mar 21, 2018
I am actually trying to amplify a PWM signal which in some mVolts to some volts by a gain factor of 38. I have a big circuit with a common supply and this supply is supposed to vary from 8 to 16 Volts. So i want the peak of the amplified PWM signal.

7. ### duke37

5,364
769
Jan 9, 2011
You can look up Wikipedia "Precision rectifier". The article is taken from Horowitz and Hill "The art of electronics".

I still do not understand what you want. The PWM signal is used to vary the average output voltage. The signal should be sufficient to turn on the switching transistors , say 10 to 20 Volts and the exact level of this will not affect the output voltage.

Please show us a schematic of what you have.

8. ### BobK

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Jan 5, 2010
Why would you want to follow the peak voltage? The signal in a PWM signal is not the peak voltage (which typically would remain constant), the signal is in the duty cycle. If you have reproduced the duty cycle at a higher voltage, you have reproduced the PWM signal.

Perhaps you are using the term PWM incorrectly.

Bob

9. ### hevans1944Hop - AC8NS

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Jun 21, 2012
Quite likely. This is the same poster who believes all actuators are inductive.
Probably not the sharpest knife in the drawer either, if this isn't a language translation problem. Still waiting for a schematic and some sort of explanation of WTF he wants to DO.