Electronic – How to tell if a capacitor is still good

If a datasheet just says 'low ESR' without specifying a value, you are usually fine with any style of capacitor with a relatively low ESR. All this really means that you should avoid cheap unrated aluminum electrolytic capacitors, since their ESR is terribly high and can be several ohms.

In this case it wants a 'low-ESR' capacitor for the 1000 µF output capacitor. I don't think I've ever seen a ceramic 1000 µF capacitor and a 1000 µF tantalum capacitorwould probably cost US$50, so you are going to have to track down a low-ESR aluminum capacitor for this application. The output ripple will decrease linearly with the ESR of the capacitor, so lower is better up to whatever price you want to pay.

As an aside, that is a ridiculously high required output capacitance for a switching regulator in that voltage range. You may want to take a look around for a regulator that meets your needs, but is stable without such a requirement. Don't get me wrong, usually the more capacitance the better, but 1000 µf is really high for a 1.5 A power supply.

The voltage rating is generally a parameter for the maximum voltage which the component can withstand. This maximum voltage could be

• the absolute maximum
• the the typical maximum, or what the component manufacturers' tests found over repeated tests
• a conservative figure well below a threshold expressed in the previous

By testing for the voltage in a given component, you stand to destroy the component when testing. This is certainly not recommended, especially if you have a limited number of components.

If you need to test the components, maybe consider placing the components in an area of the circuit well below the specified threshold and test the component instead for the typical and maximum operating values.