Electronics > Beginners

Linear PSU and low-ESR vs normal capacitors.

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I have a Korad KKG305D bench power supply and while i was cleaning the filthy PCB:s and swapping out the noisy fan, i thought that i could also swap out those cheap chinese capacitors to a good known brand capacitors.
I know it still will be just a ~100€ power supply, but electrolytic capacitors are relatively cheap, so why not. And maybe it will even improve it's reliability and lifetime a little bit.

When i was searching for new capacitors, i read from several sites that unlike SMPS:s, the linear regukators don't like low-ESR capacitors.
So, my question is, should i buy a low-esr caps or "normal" ones? Or, does it make any difference in this case?
For example the output capacitor, or the other capacitors.



Context matters.

Where did they say linear supplies don't like them?  Who was speaking?  Are they an authority on the topic, or just repeating n-th hand information?

Where in the circuit did they say linear supplies don't like them?  Input? Output? Compensation? Bypass?  How low is "low ESR"?  Does this include polymer electrolytics or the regular kind?  Ceramic?

What kinds of linear supplies did they discuss?  There are many kinds, many ways to compensate them, whether internally or discrete.  LDOs supporting ceramic caps are a very normal thing these days, but you do have to check that you're actually buying the latest and greatest, not some cheap shovelware from the '90s back when electrolytic and tantalum were all we had.  (Even to this day, '1117s are conspicuously present.)

The reason I ask, is any unqualified, broad, blanket statement, on a subject with even a little nuance, is almost certainly wrong, and at the very least must be verified against other more authoritative sources (and so on in turn), or checked by original research (these are verifiable claims, we can measure them).  Until then, such statements are at best hearsay, let alone fact; be careful repeating, let alone internalizing, them.

Notice I've said almost nothing about the topic in question, just brought up variations of parameters, possibilities.  This is a most valuable life lesson, it generalizes to anything and everything!  particularly valuable as you have the opportunity to learn it without having even modified your power supply (implied: potentially breaking it from acting on bad advice).

As for how to know, how to do the technical evaluation; you need the schematic first, and then datasheets of candidate parts.  Also since your concern is reliability/lifetime, likely many other glaring issues can be noted -- searching for schematics or improvements on the unit in question (also check similar part numbers under clone brands; nonsense/random branding proliferates along cheap products such as this (not necessarily this product in particular, but products of this sort, at low prices) may find teardowns and reviews that are most useful.


Well there's not much information about this power supply on internet.
Can't find any schematics or anything else.
I guess it's not so popular model. And that's why i asked.
I guess i was hoping if there will be some general rule of thumb whitch kind of capacitors are used in where.
I still think it's better to replace these cheap capacitors, before they go bad and break something else.

Be careful, using ultra low ESR capacitors (such as solid state capacitors) in circuit which is designed for high ESR electrolyte capacitor may lead to circuit damage or unwanted oscillations. This is because circuit may expect high ESR capacitor to dump oscillations or don't exceed some level of current.

In other words, the circuit may expect some ESR of capacitor as a resistor which is a part of circuit. And if you replace it with ultra low ESR it removes that resistor and circuit going to unexpected mode...

It is safe and reliabe to use a general use type 105 C capacitors of a reputable brand.


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