ESR and regular caps?

[jleon92f]

Hi, Are ESR and regular caps interchangable? Is it important to use ESR caps?

Thanks,
John.

[mariushm]

Re: ESR and regular caps?

Why would low esr exist if they weren't important?

Low ESR is an important characteristic of capacitors when these capacitors are used in particular circuits that are designed to require capacitors with low esr.

In most cases, you can use low esr capacitors in regular circuits that don't require low esr, but it doesn't work the other way around. Circuits that need low esr capacitors mayl be overloaded, may be "stressed", may overheat some components in the circuit, may be "unstable" etc with regular capacitors.

[jleon92f]

Re: ESR and regular caps?

Why would low esr exist if they weren't important?

Low ESR is an important characteristic of capacitors when these capacitors are used in particular circuits that are designed to require capacitors with low esr.

In most cases, you can use low esr capacitors in regular circuits that don't require low esr, but it doesn't work the other way around. Circuits that need low esr capacitors mayl be overloaded, may be "stressed", may overheat some components in the circuit, may be "unstable" etc with regular capacitors.

OK, so if I use Low ESR all the time I am OK. I do not have the schematic for the HG281D monitor to tell me what caps are being used.

Thanks,
John.

[mariushm]

Re: ESR and regular caps?

No, if you use Low ESR all the time you're not OK.

In some places, capacitors with not so low ESR are used to take advantage of the R in the ESR ("Equivalent Series Resistance") - in combination with other parts of the circuit that ESR value can keep the circuit stable.
If that circuit expects a particular ESR and you use a low ESR capacitor, the circuit may become unstable.

For example, here's a simple linear regulator, LM2941 : https://cdn.badcaps-static.com/pdfs/...ddde41b832.pdf
See page 7.
In order to be stable, this IC requires a capacitor on the output that's at least 22uF in size, but you can use bigger capacitors.

It has however one quirk : at under 200mA of load, the regulator will be unstable with very low ESR capacitors, whatever capacitor you use needs to have 0.1 ohm or more ESR.

200mA can be a lot, a microcontroller, a lcd display etc all use 10-50-100 mA so you can't just ignore this and assume the regulator will use more than 200mA all the time.

So if I make a 5v linear regulator, I could use any capacitor bigger than 22uF and with at least 6.3v rating, but it's smart to use 10v or even more rating, as larger capacitors handle heat better.

I can't just put a 1000uF 16v Nichicon HM capacitor for example, with about 0.025 ohm ESR because it's much lower than 0.1 ohm. This is a very-low ESR capacitor.

But I could use a Nichicon HD capacitor, a 100uF 25v capacitor in this series will have about 0.13 ohm ESR, above the 0.1ohm esr required by the IC to get stable output but low enough to not waste too much energy in the capacitor.

This is technically classified still as an low esr capacitor, but compared to newer series of capacitors, more modern, nowadays it's barely considered low esr.

Just the same, I couldn't use ceramic capacitors (some kinds, most of the good ones, have esr below 0.1 ohm) or polymer capacitors (most are ultra low esr, usually 0.01 ohm esr or even less).

You have to search for datasheets of the capacitors you plan to replace, determine what kind of capacitor is, and replace with suitable capacitors.

Once you repair lots of hardware and you have some practice you start to understand how some circuits you repair work and can determine easily if that capacitor needs to be Low ESR or not so low esr.

[imp]

Re: ESR and regular caps?

An interesting post from you mariushm, as usual It answered several questions I also had about low ESR capacitors and when NOT to use them ...

[ratdude747]

Re: ESR and regular caps?

Moved from FAQ.

[Paddan1000]

Re: ESR and regular caps?

I replaced all the caps at 100uF and lower (I left the 220uF:s) on a V-smile game console PCB with low-ESR caps. Now the game console won't start any games but just shows a blank screen. Could the problem be the low ESR of the new caps?
The PCB looks like this: