low frequency PM

After the bridge rectifier, you may want to consider the buck-boost solutions that we have. Please try to check this link: https://www.analog.com/en/parametricsearch/11503#/p5362=Buck-Boost

If the link won't work, please search in ADI website these generics: LTC3119, LTC3106, LTC3331, LT8490, LTC3129.

Thank you!

I assume you refer to a bridge without smoothing capacitor.  Can these buck-boost solutions handle the large time between impulses?

I think that you will still need bit of capacitance after the bridge rectifier.

Thank you Fil,

If the frequency is 25Hz and the matched resistance is say ~20 ohm then for 10% ripple the capacitor is ~20mF.  These are typically super-capacitor.  Do they behave the same as standard capacitors? 

If I understand what you are saying, we don't need a 10% smoothness at the input to the PM in order to get stable voltage at the output of the PM.  Maybe 30% ripple is still good enough.  Is this what you have in mind?

The ripple should be able to go by how much the buck-boost can take as low voltage as possible. You have to check that when the voltage goes to minimum, the current goes high & rating of the parts are still ok.

The ripple should be able to go by how much the buck-boost can take as low voltage as possible. You have to check that when the voltage goes to minimum, the current goes high & rating of the parts are still ok.