Re: SMPS inverter voltage feedback methods

Joerg wrote:
MooseFET wrote:

On Jan 27, 7:27 am, Jamie Morken <jmor...@xxxxxxx> wrote:

Joerg wrote:

[....]

To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr, send some AC there if you can't feed the HV side
circuitry locally (toroid xfmr or something), sample, then send sample
across another toroid xfmr back to LV side. I use little #43 ferrites
for those jobs, sometimes #77. Mostly #43 because there always seems to
come a time when someone asks for even more bandwidth later.

Is this the same as what Moosefet is talking about with the VCO on the
transformer primary? Can the sampling be tied into the PWM signals sent
to the SMPS fets? So that the modulation and demodulation is done by
these signals, not sure if this would work with variable dutycycle PWM?



From my reading of it, it isn't but it is worthy of consideration. A
balanced modulator and balanced demodulator will bring DC across with
no trouble. If you pick the right sort of running frequency, it will
be quite insensitive to all the switching noise.

With a bit of trichery, you could get any imbalance between the two
sides to come across on the same transformer. The second channel
could be phase or an even harmonic.


Addendum, mostly for Jamie: "Balanced" or "synchronous" demodulator is in this sense just a glorified old-fashioned clamp circuit. Just like the one in a TV set where a correct DC black level must be gleaned from a source that cannot reliably transmit DC levels directly. Except that you don't have to fish the clamp pulse out of a noisy morass but it's already there.

IOW you clamp both sides to their respective grounds while the pulse is not present. When the pulse cometh then the source side is switched to the signal. Now you sample the value on the receiving end while the pulse is there and hold it until the next pulse. Or have a fast enough ADC log it during the pulse and stash the result. That's pretty much it.


Hi Joerg,

I cant quite picture it, would you care to cough up an ascii schematic? didnt unitrode make a chipset that did prettty much this?

Cheers
Terry
.

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