pwm to voltage convertor filter analysis

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Hi every one . I had found this circuit in internet . it converts pwm of mcu to analog voltage up to 10 V . i need the second part filter parameters . i think so tha second part is a three stage filter and the opamp side is a lowpass MFP filter . most the samples circuits on internet had input side into opamp on inverting pin . but this one has an input signal on non inverting pin .



i need to know , filter type , Transfer function , Q factor , Cut-off frequency . could some one help me please ?
 

Hi,

I don't think it is a classical MFP. And I don't think it's a really calculated design.
I rather say it is some kind of random filter 3rd order with low Q. Maybe 0.4.

Klaus
 
According to SapWin, the filter has three almost real poles and a real zero, respectively it's not better than a low Q second low-pass.

If you want optimal filter behavior, use a standard MFB or Sallen-Key design.


 
These might help, ap notes on PWM filtering, attached.


Regards, Dana.
 

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  • slyt076[1].pdf
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  • spraa88a.pdf
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  • Cancel PWM DAC ripple with analog subtraction _ EDN.pdf
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Im agree with you . i must use a standard MFB or Sallen-Key design.
 

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