"Low Impedance" vs "Low ESR"

[clearchris]

From my research, "low impedance" are pretty much the same as "low esr" caps except the "low esr" caps come in a smaller package. Am I reading this wrong? "Low impedance" caps seem to be much more commonly available (and cheaper) than "low esr" caps. I'm not afraid to lean over some caps if I have to make them fit because of size.

I'm about to pull the trigger on a pretty large cap order (for me) and want to make sure I'm not buying the wrong stuff. I'm stuck in the house, busy working through my electronics projects, and it would be nice to not have to order caps on a project by project basis.

Edit: Also, are there any nichicon series caps that are best avoided? They seem to be the most competitive "good manufacturer" caps in the "low impedance" space.

[budm]

Re: "Low Impedance" vs "Low ESR"


Look at table 2.

[clearchris]

Re: "Low Impedance" vs "Low ESR"

According to that table, if I am reading it right, is that "low impedance" caps(Low Z) have lower ESR and higher ripple current tolerance. So that makes "low impedance" caps better than low ESR?

Edit: Or maybe the answer is: depends on the capacitor. A "low ESR" designation might not mean anything.

[Curious.George]

Re: "Low Impedance" vs "Low ESR"

From my research, "low impedance" are pretty much the same as "low esr" caps except the "low esr" caps come in a smaller package. Am I reading this wrong? "Low impedance" caps seem to be much more commonly available (and cheaper) than "low esr" caps. I'm not afraid to lean over some caps if I have to make them fit because of size.

An ideal capacitor (which only exists "in theory") has no resistive component. It is a perfect energy storage component; everything that goes in (can) eventually come back out.

In practice, a capacitor is an ideal capacitor with several other "parasitic" characteristics that alter its behavior from the ideal.

E.g., the fact that a capacitor can't hold a charge indefinitely implies that there is some "load" across the capacitor that is bleeding off (consuming) that charge.

Similarly, the fact that a capacitor can't absorb all of the charge pushed into it implies that there is something "consuming" some of the charge as it tries to get INTO the (ideal) capacitor -- i.e., in series with that ideal capacitor.

Both represent "losses". But, they have different consequences to the circuit in which they reside.

A high(er) ESR means the ideal capacitance is less coupled to the circuit node to which it is attached -- changes at it's input are NOT absorbed by the capacitance as well as they could be.

A low(er) parallel (leakage) capacitance means the cap holds its charge for less time than ideal.

This is why you will often see multiple capacitors "in parallel" instead of a single LARGER capacitor -- the behavior of the GROUP of smaller caps is better (in some regard) than that of a single larger cap.

[The ESRs of each of the small caps look like they are in parallel with each other so the EFFECTIVE resistance is much smaller]

Note that even these parasitic elements are dynamic, in nature. A cap can perform "well" at one frequency and poorly at another (caps a physical devices so how they are built has an impact on how they perform)