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would it be possible design any psu without any electrolytic capacitors?
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chris_leyson:
I once designed a 6W 48V to 5V converter with nothing but X7R ceramic caps on the primary and secondary side. It was designed to run in an 85C+ environment 24 hours a day and I didn't want to use electrolyics. Doable but expensive.
chris_leyson:
It was DC so I guess it doesn't count  :(
SiliconWizard:
Whereas it's certainly relatively easy (if a bit expensive) for a DC/DC converter, as was mentioned earlier, PS from single-phase mains for anything but very low power are much trickier, and unless you're ready to design something ridiculously expensive and bulky, it's often a compromise with the power factor (which in turn may make it not compliant with current regulations.)
David Hess:

--- Quote from: T3sl4co1l on March 02, 2020, 05:16:30 pm ---
--- Quote from: David Hess on March 02, 2020, 04:55:09 pm ---An active PFC stage is a great way to lower the required input bulk capacitance by increasing the conduction angle however using it this way compromises the power factor.
--- End quote ---

You can get the best of both worlds using an active capacitor multiplier -- essentially, use a smaller capacitor at a higher ripple fraction, by application of a synchronous buck converter (controlled to act as, I think, a step-up transformer relative to a virtual midpoint).

In combination with poled ceramics (e.g. Ceralink), this enables record low volumes (e.g. Google Little Box inverter from some years ago).
--- End quote ---

I have never had to take advantage of it but for a given size of capacitor, doubling the working voltage while halving the capacitance doubles the energy storage (0.5CV^2).  So stepping the AC input voltage up further allows for a physically smaller input capacitor but also requires handling a higher ripple voltage.

A couple years ago I looked into this for SSD power loss protection and while it would work, it is not necessary because the energy density of existing non-super capacitors is sufficient for SSDs and in some you can see a bank of solid tantalum capacitors just for this purpose.
schmitt trigger:
A rotary converter?
https://www.nycsubway.org/wiki/Rotary_Converter_Power_Technology

Now seriously, like others have mentioned, it is feasible but impractical because of size and cost constraints.
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