Re: Feedback for low frequency PWM regulator

On Mon, 14 Jul 2008 09:06:25 -0400, legg <legg@xxxxxxxxxxxxxxx> wrote:

On Mon, 14 Jul 2008 12:45:59 GMT, "JMini"
<j.minihane@xxxxxxxxxxxxxxxx> wrote:


As the input voltage falls, the PWM needs to increase to keep the RMS voltage
the same. I've tried regulating Average voltage. It doesn't work.

This is one of the few applications where the average and rms voltage
are identical.If you averaged the voltage before it hit the resistive
load, there would be an issue. You're not doing this.

In both cases regulation is possible.

If you can't get the simpler arrangement working using an RC filter in
the feedback path, adding an rms converter will not improve the
situation.


It's funny, considering the number of times I've gone through the
procedure of explaining RMS and average relationships, over the years,
to have to re-train myself on this matter. Sort of refreshing.

The formula Epk x rootD is so automatic that I seldom give it a second
thought. Just set me down with a pencil and paper, however, and I seem
to be able to prove to myself that the moon is made of green cheese.

Wonder why wasn't there wasn't more response, reacting to this
(temporary....?) lunacy? I suspect that spending too much time typoing
large databases must atrophy regular thought processes.

Sorry for the diversion.

RL
.

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