Capacitor’s ESR

[Jonathan Rullman]

Hi Everyone, I just wanted to know what you would consider a high ESR reading for a capacitor. And also at what point would you consider replacing a capacitor because of its’ ESR?

 

[kellys_eye]

Depends on its value but certainly anything approaching single figures would be suspect. You should be able to get ESR figures for a 'good' capacitor from the manufacturers data sheet.

 

[(*steve*)]

The ESR of a capacitor is high when it becomes:

1. Higher than the maximum specified on the datasheet.
2. High enough that the circuit operation is impaired.

ESR is not always specified, and some circuits are insensitive to ESR. In these cases, the ESR may never be too high.

In other circuits there ESR might be critical. I recall a regulator which specified a range of ESR's for stability. In this case the ESR might be too high, but the cap might still be in spec (possibly a poor choice of capacitor if this happened).

Switch mode regulators are a classic user of low ESR caps. In general, the ESR is too high when the ripple on the power rail can no longer be tolerated by the circuit.

There is no hard and fast rule (especially if you don't have the datasheet).