PFC EVM as 390V + 6.3V tube supply

[kenpeter]

UCC28061 300W PFC Pre-Regulator Evaluation Module - UCC28061EVM - TI Tool Folder

Above EVM appears very similar for purpose of discussion,
not exactly same as the newest one on my bench.
We aren't talking night and day difference, just newer.
I'll link exact one later, whenever details get released.

I found that I can easily slip 6 extra turns of wire onto
each donut core without having to "modify" anything.
And with 2 Schottky's and a 220uF, I get a DC voltage
suitable to drive filaments... I think same would be true
of the old EVM if they had the same number of turns?

I am assuming the 390V regulation loop must be what
keeps my 6.3VDC constant? I'm only driving a resistor,
not real filaments in this experiment.

I mean, there is PFC ripple of course. A compromise
between long time constant attempt to regulate 390V,
and short time constant attempt to shape currents in
phase and proportion to input voltage.

But PFC ripple still looks better than 1st cap fed only by a
diode bridge. Way better...

If I got one of these PFC's to play with at home (I'd have
to buy one, just like anybody else). I got no isolated Agilent
supply at home. I'd need some sort of isolation transformer.

But secondary could be anything from 85-265. And only 300VA.
PFC meaning no need to scale up for poor conduction angle?
I'm imagining what might be weight savings for 390V @ 770mA!

Filaments don't really need PFC, do they? But DC is nice extra,
and I don't need limit my search for isolation to those with a
filament winding... Board offers some smart protections too.

I need like 12.6 or 13VDC at roughly 20mA to wake up the
smart part of it. Its just a dumb diode bridge untill then...
I don't think I can tap that from the donuts, cause they
aren't doing anything till after PFC has kicked in. But there
is at least 100VDC diode bridged to the output even with
the lowest rated input and the PFC asleep... Enough to
bleed 12V across a Zenier and get the ball rolling?

[kenpeter]

AC/DC and DC/DC Power Supply - Power Factor Correction - UCC28063 - TI.com
Look in the User's Guide. That's the exact board I'm talking about!
If you find an EVM test signed off in blue "K", that would be me...

Anyways, them donuts got room for extra winding is all I'm saying.
I'll be buying some for unauthorized experiments at home, soon as
they get the darn thing out of preview status...

I don't usually get excited about the sorta stuff I have to test.
But this one impressed me with possibilities for my own projects.

[luka]

yea 390v is regulated, 6.3 would just be there for a ride... if you don't draw too much, this is all ok, but as far as I remember, it won't be constant

[kenpeter]

I thought diodes on 390 would forward conduct, and therefore limit 6.3V?
It seemed to work in my quickie test. With only three turns per donut,
Schottkys, 220uF, and a modest load, I measured about 1.1VDC per turn.
Minus diode drop of course... So I figure 6 turns might be about right.

I didn't have time to try anything more. Wasn't supposed to be doing
personal stuff off procedure anyway. When I own one good and proper,
I'll beat it up thoroughly and tell you whatever happens.

I noticed those final caps were 450V too! I don't yet know if output is
easily adjusted by a divider? There were at least two more feedbacks.
One from each donut, having something to do with current. I have to
make sure I don't mess up the function of those feedbacks.

[luka]

well there are more feedbacks, but only one for output voltage

One is input voltage sense, then there is current sense, V2 seems to be output voltage sense, then you have also V1 which seems to me, to be another output sense, but I don't know the IC to know why it has that

In every regulated supply, which this is, I know I got sag on unregulated secondary. Only thing saving you is that, you have very low voltage compared to main voltage, and you probably won't draw few amps from 6.3v... what I would do, it use this voltage, but make it higher, and use some low dropout regulator, to bring it down to regulated 6.3v