[SI-LIST] Re: ESR of caps
- From: "Reams, William" <William.Reams@xxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 9 Oct 2009 13:54:02 -0600
I recall that Istvan Novak had a "simple" spreadsheet intended to show
impedance of parallel capacitors. It would show this impedance v
frequency quite well in the graph it generates.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Doug Brooks
Sent: Friday, October 09, 2009 1:29 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: ESR of caps
Sorry. It ain't that simple.
You have ESR impedance (resistance) in series with capacitive impedance
(reactance)(which is frequency dependent) and maybe additional Impedance
(reactance) from the inductance, if significant.
You have two RLC circuits in parallel. You must solve for the parallel
IMPEDANCE of the circuit. Then the equivalent ESR is the real part of
that impedance.
In more simple terms, if you have two ESRs in parallel, one with a large
capacitor and one with a small capacitor, the ESR of the large capacitor
will dominate at any given (and indeed at all) frequencies
--- at least until the frequency is high enough that the capacitive
impedance is negligible.
Doug Brooks
At 11:24 PM 10/8/2009, you wrote:
>Hi All
> I need help to understand calculating the equivalent ESR of
>capacitors in parallel. For example if we have tant capacitor with
>65mOhm ESR and a ceramic cap with 10mOhm ESR, whether the equivalent
>ESR is simply the parallel of these two ESRs? If it is so simple then
>we can always keep one ceramic and tantalums in parallel to achieve low
>ESR as ceramic always will have low ESR?
>
>
>Thank you,
>Sree
>
>
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