Reply 20 of 54, by PCBONEZ
I agree with what you said except this part.
wrote:If you reduce the ESR, you reduce the amount of power which must be removed from the capacitor casing.
When you lower the ESR you raise Irip through the cap and that results in greater heating of the cap.
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People forget there is a load in parallel with the cap(s).
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The caps do not control the total amount of ripple ( in WATTS ) in the circuit.
That is controlled by the activity of the switchers, VR, MOSFET or whatever. I'll just say the IC for all since this is general.
The IC is in turn controlled by the DC at or near the load by some kind of feedback. (Usually controlled by DC voltage but could be DC current.)
Thus the DC needs of the load determine IC activity and the IC activity creates a corresponding amount of ripple - regardless of what the caps are doing.
The caps do not control the total amount of ripple *put in* - they only control what path it takes after it's created.
For ripple the ESR of the cap is (or caps are) one side a of a voltage divider with the load being the other side.
So, if you lower ESR you direct more ripple current through the cap and less ripple current goes through the load.
- With more ripple current passing through it the cap is heated more, not less.
- And the load (other side of the voltage divider) sees less ripple current and is heated less - which is the actual goal of all this.
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