[TriEmbed] PWM to Analog 0 to 5 VDC?

[Jon Wolfe]

Yeah an rc low pass filter is the way to go.  I've done it that way many 
times. The unity gain op amp could give you a buffer on the filter output, 
but I think ADCs are usually high impedance inputs. Depending on how fast 
you need the signal to change could impact what op amp you would need to 
use. You could play around in LT spice with different frequencies and 
component values to find something that works.  Pete would know better than 
me, but I think the downside to higher frequency might be higher power 
draw, since more of the signal is going through the cap in the filter.

On June 29, 2020 10:32:55 PM Pete Soper via TriEmbed 
<triembed at triembed.org> wrote:
> The classic way to do this is with a low pass filter. If you google "PWM 
> DAC" you'll find what you need. But the performance is going to be a 
> function of the PWM frequency and how precisely you can change the duty cycle.
> Pete
>
> -------- Original message --------
> From: Charles A via TriEmbed <triembed at triembed.org>
> Date: 6/29/20 10:23 PM (GMT-05:00)
> To: triembed at triembed.org
> Subject: [TriEmbed] PWM to Analog 0 to 5 VDC?
>
> Anyone have a favorite circuit or chip to convert a PWM signal to a 0 to 5 
> VDC signal?  The resulting voltage needs to be very stable.  It feeds an 
> ADC input.  I've looked at an RL circuit into an OpAmp that also has a cap 
> to ground at the OpAmp input.  The DVM says it's stable but the ADC reading 
> the voltage says it's not. I'm measuring 100 mV deviations.  Would like to 
> get to a 10 mV deviation. I've tried changing cap values on the input as 
> well as adding caps on the output side of the OpAmp.  Made improvements but 
> still not good enough.  So looking for suggestions please.
>
> Thanks,
> Chuck
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