SMPS: which cap should be hi-ripple?

[baritonomarchetto]

A n00b question, i know, but reading how a switch works and considering that almost all the components are subject to ripple currents (peak currents coming from the alternate component of the "wall" juice, right?) should i conclude that its mandatory (or at least highly suggested for long life) by using ALL high ripple graded capacitors in my switch? Are there caps in the switch that could be kept low-ripple cheap crappy caps ?

Thanks

[Gianni]

Re: SMPS: which cap should be hi-ripple?

Well on SMPS (SWITCH MODE POWER SUPPLY) it is important to use always good caps with low ESR and high ripple current.
All topologies need good caps: fly-back converter, buck converter, boost converter, resonant converter, half bridge, full bridge, forward, step down and step up converter...
Usually only the big caps on the input side after the rectifier bridge (input freq. 50~60Hz) can be general purpose or no LOW ESR; today most SMPS have the Power Factor Correction so almost all caps are LOW ESR.

General purpose caps can be used on linear regulators where the current ripple is very low or other circuit with no high frequency current.

Anyway it is different to use "general purpose caps" instead of "crappy caps", I should avoid the last ones if I want a reliable circuit

Ciao
Gianni

[baritonomarchetto]

Re: SMPS: which cap should be hi-ripple?

Thank you very much

ciao

[Longbow]

Re: SMPS: which cap should be hi-ripple?

In a SMPS, any capacitor or diode that operates at the switching frequency must be a high frequency part. Typcially, the secondary rectifier diodes and filter caps all have to be high frequency types. The mains filter cap obviously does not have to work at the switching frequency.