Re: Need input on high voltage regulator design

From: Scott Miller (scott_at_3xf.com)
Date: 11/29/04 

Date: Sun, 28 Nov 2004 18:04:27 -0800

> What does the ADC use as a reference?

The MCU's supply, which is provided by a 5-volt linear regulator in this
case. It's fixed internally, can't select a different reference.

> How good does the regulator have to be?

500 volts, -50/+150 according to the GM tube's spec ***. So not very. =]

> You could sample the primary windings voltage some time after the MOSFET
> is switched off. The waveform will look like this:

> The voltage you want for this sort of feedback is the one at (C). The one
> at (B) is almost as good. From (B) to (C) is almost a straight line.
>
> You should be able to get fairly good regulation. The tricky bit is that
> the micro needs to fiddle with the ADC timing to get the right point for
> the feedback. The nice thing is that the load doesn't change much so the
> software can take a bit of time.

Sounds kind of tricky. With the voltage doubler stage after the secondary,
how sure can I be that what I see on the primary will reflect the actual
output voltage?

> The ADC will give a zero output up to some voltage and then go up towards
> full scale as the volatge increases above that point. This allows the
> ADCs bits to be put to better use since you know that the voltage must be
> near 500V

This is more like what I was looking for. Fred Bloggs posted something
similar. Between the two examples, I ought to have enough to keep me busy
experimenting for a bit. Just need to check my parts bins for an
appropriate op amp, or go pick one up.

Thanks...

Scott