3 ms·

We go -48 -> 48 -> 12 -> 3v3,1v8 etc etc. If you went 48 straight to POL voltages then you would have horrific converter performance.

eqvinox 6mo ago
> If you went 48 straight to POL voltages then you would have horrific converter performance. What's horrific converter performance in numbers? An isolated flyback (to 12V) should be able to hit >92% and doesn't care if it's fed -48V or +48V or ±24V. TI webench gives me 95% though I'd only believe that if I'd built and measured it. What's the performance of your -48V → +48V? [with the caveat that these frequently require custom transformers... not an issue with large runs, but finding something that can be done with an existing part for smaller runs is... meh]
- fecal_henge 6mo ago
  -48 to 48 claims something like 97% (load dependent of course). It also needs to arbitrate between two input supplies for glitchless redundancy, plus have PM bus and other spec mandated stuff. There is no technical reason why you cant go -48 -> 12 as you state with good efficiceny, but we cant get hold of a part that ticks all the boxes. Horrific performance by my definition would be 48v to say 1v. We only realistically use buck topologies for POL supplies. Such a ratio is really bad for current transients, not to mention issues like minimum on times for the controller.
  - deleted 6mo ago
    [deleted]
  - eqvinox 6mo ago
    I'm just surprised that either input isolation isn't on your spec, or it still somehow works out better with isolated to +48V than straight to 12V... but I guess if your spec requires other things, it makes sense. (Thanks for the info!)
mastax 6mo ago
I was just looking at these funny parts: https://www.vicorpower.com/products?productType=cfg&productKey=VTM48EF012T130C01 https://www.vicorpower.com/products?productType=cfg&productK... 130A, 48V -> 1.2V @ 94% efficiency! Except: - $100 ea. - Fixed 1/40 voltage ratio, regulation done by upstream regulator. - Look at the minimum specs for efficiency…
- fecal_henge 6mo ago
  This is a very strange part, what with the upstream regulator circuit. My guess is that their efficiency stats dont include losses in the upstream regulator. 100 usd per unit doesnt seem that excessive.

eqvinox 6mo ago

> If you went 48 straight to POL voltages then you would have horrific converter performance. What's horrific converter performance in numbers? An isolated flyback (to 12V) should be able to hit >92% and doesn't care if it's fed -48V or +48V or ±24V. TI webench gives me 95% though I'd only believe that if I'd built and measured it. What's the performance of your -48V → +48V? [with the caveat that these frequently require custom transformers... not an issue with large runs, but finding something that can be done with an existing part for smaller runs is... meh]

fecal_henge 6mo ago
-48 to 48 claims something like 97% (load dependent of course). It also needs to arbitrate between two input supplies for glitchless redundancy, plus have PM bus and other spec mandated stuff. There is no technical reason why you cant go -48 -> 12 as you state with good efficiceny, but we cant get hold of a part that ticks all the boxes. Horrific performance by my definition would be 48v to say 1v. We only realistically use buck topologies for POL supplies. Such a ratio is really bad for current transients, not to mention issues like minimum on times for the controller.
- deleted 6mo ago
  [deleted]
- eqvinox 6mo ago
  I'm just surprised that either input isolation isn't on your spec, or it still somehow works out better with isolated to +48V than straight to 12V... but I guess if your spec requires other things, it makes sense. (Thanks for the info!)

mastax 6mo ago

I was just looking at these funny parts: https://www.vicorpower.com/products?productType=cfg&productKey=VTM48EF012T130C01 https://www.vicorpower.com/products?productType=cfg&productK... 130A, 48V -> 1.2V @ 94% efficiency! Except: - $100 ea. - Fixed 1/40 voltage ratio, regulation done by upstream regulator. - Look at the minimum specs for efficiency…

fecal_henge 6mo ago
This is a very strange part, what with the upstream regulator circuit. My guess is that their efficiency stats dont include losses in the upstream regulator. 100 usd per unit doesnt seem that excessive.