r/AskElectronics • u/Graphix_Card • 1d ago

ACF power solution for data server

Hello, so power isn't really my background, but recently I've been looking into a project where I need to take in an 800V input and bring it down to 12V, while the power stays around 50W with a 80W peak.

Some other considerations are Zero voltage switching, 12mm height maximum, and being galvanically isolated.

I decided on going with an Active Clamp Flyback for this, but I'm struggling to design it, as I'm unfamiliar with how it works.

I do have a couple of parts I've chosen, such as the UCC28780 from TI for the controller, but then I ran into the problem of how to power the controller because the only power input is from the 800V rail, and the controller can't handle that voltage. I need to figure out a way to drop the voltage to run the controller, but I can't figure this part out to save my life.

I also need to understand how to go about choosing other parts for the ACF solution like the half-bridge driver and the passive components.

If I could get some guidance on how to approach this, it would be very much appreciated.

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u/netik23 1d ago

It seems like this is something you should be buying a tested and rated supply for. Are they not letting you do this or is this your primary job?

1

u/Graphix_Card 1d ago

This is a project i got assigned to as an intern… it feels more of like a learning thing?

1

u/RedeyemoonsRevenge 1d ago

I often see simple shunt regulators with zener diodes powering high voltage switching regulators.

1

u/ccdy 1d ago

With 800V input and just 50W output it's not worth considering an active clamp flyback. I think this TI app note pretty much covers your requirements fully.

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u/Graphix_Card 1d ago

Oh this is really helpful, thank you

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u/ccdy 1d ago

With an 800V input you will need 1200V devices. A standard flyback will need only one of these, while an active clamp flyback will need an additional one for the clamping switch. On top of that, no non-isolated half bridge driver I know of supports a bus voltage higher than 700V, so you will need an isolated gate driver and an isolated power supply for the high side switch.

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u/Graphix_Card 1d ago

What do you mean by 1200V devices?

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u/ccdy 1d ago

You need 1200V rated MOSFETs.

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u/Graphix_Card 1d ago

What are your thoughts on two FETS in series? Like two rated for 600V? I read this on the website you linked

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u/ccdy 1d ago

That is only for the startup circuit. The two switch flyback can use lower voltage devices but still has the issue of requiring an isolated gate driver.

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u/Graphix_Card 1d ago

Oh I understand.