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Signal noise in Boost PFC?

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Faringdon:
Hi,
{EDIT....if you are a top  power supply  consultant, seeking interesting posts to enhance your horizons, then this post is not for you..this is just a PCB layout issue....END OF EDIT}

Doing 1kW Boost PFC  with UCC28070A. (390vout, 220vac, 60kHz) The current sense is via 50:1 Current sense transformer (CST).

{EDIT-----I suspect the PCB layout is bad, and wish to confirm this with a mod wire.....prior to getting the PCB re-layed out.....---END_OF_EDIT}


The CST (and its reset/rectifier circuit) is some 15cm away from the Control PCB containing the UCC28070A (burden resistor is near controller). To save complexity, I just routed the Current sense current to the controller with a PCB trace over its ground plane. On second thoughts, the power stage switching currents flow in this ground plane aswell, so it’ll be noisy. As such, I think I will “augment” the current sense tracking with a twisted pair kynar wire from the CST reset circuit, to the controller. (ie, some 15cm).
Do you think this will cause more noise issues?
I can’t find out by scoping it, since all I have to probe the burden resistor with is a Micsig DP10007 diff probe…..and with its two huge “dangling clips”, the waveform from it is obviously just common mode trash filled.
I really need an isolation transformer, but it would need to be rated  for 1KVA and they are expensive. AYK, With isol  tran I could use a coax probe direct into the scope and get a great waveform.

Though anyway, what about the twisted pair kynar?
Surely just as good as if i had used star grounding of the CST output/GND on the PCB , back to the controller?

UCC28070A
https://www.ti.com/lit/ds/symlink/ucc28070a.pdf?ts=1660244875404&ref_url=https%253A%252F%252Fwww.google.com%252F

jonpaul:
sorry entire post and project makes little sense.

Why do you waste our time?

jon

Faringdon:
OK, thanks anyway,

I suspect the PCB layout is bad, and wish to confirm this with a mod wire.....prior to getting the PCB re-layed out.....

Its talking about taking the output feedback divider resistor point back to the controller with a twisted pair. (instead of PCB tracks).
On the PCB, the feedback divider point wasnt taken back to the controller as a star-grounded pair....so i am thinking of doing it with an externally added twisted pair wire.
(ie fixing a layout issue with a mod wire , to confirm it works, prior to getting the PCB re-layed out, with the preferred  star-grounding method.)
What i am wondering is, will the twisted pair mod wire bring loads of noise issues of itself.?

(i am actually  thinking of having mod wires for all three feedback signals, VINACP, VOUT and Current sense. At the moment, the ground of these signals is just the ground plane, going back to the controller. -I thought that would be sufficient, but  it seems not.).

(Learned Info for anyone doing 1kW Boost PFC for the first time.....just do a single board first, containing just the Boost PFC on its own, so that you can get that bit right first....the size of the power components at 1kW, mean that you cant get tight layout like you can with a much lower powered converter, so PCB layout things, like  having a separate star ground for the feedback signals, apply......ie, not possible to just rely on the ground plane.)


--- Quote ---Why do you waste our time?
--- End quote ---
Apologies Jon Paul, i have edited the top post now, so that top consultants such as yourself, no longer waste their time here.

jonpaul:
Farrington your PCB note needs photos of layout and schematics to get any cogent response

j

Faringdon:

--- Quote ---Farrington your PCB note needs photos of layout and schematics to get any cogent response
--- End quote ---
Thanks Jon Paul,
If anyone wants, i will send them the Layout/Schem  file for the 4 layer main PCB,  and the three daughter PCBs (2 x double sided, 1 x 4 layer)......then the kind person would have to work out how they fit together, (which is certainly possible due to lots of helpful silkscreen annotation), then they would have to  evaluate, after they have downloaded an Eagle Pro 7.4.0 viewer. Sorry, i dont believe anyone would want to bother with all that, as such, the above question of the principle, but please pass  it up if its too much time, or not felt appropriate..
In any case, for the next PCB, i have decided to take the current and voltage feedback signals back to the controller using dedicated ground/signal pairs, instead of just relying on using the two ground planes.

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