Low ESR vs Low Impedance

[bigbeark]

I note that Mouser has selections for "Low ESR" and "Low Impedance" capacitors on their site. The caps they identify as "Low ESR" are Panasonic FR series.

When I look at the spec sheet, it states "FR has same low impedance as FM".

I have read elsewhere that "Low ESR" caps are to be used in power supplies as they are less sensitive to high frequencies.

I note that most catalogs and spec sheets are likely to have a "max Impedance" column but ESR data are often not shown.

I generally go for low-impedance high-riplle caps.

Does Low Impedance = Low ESR?

[Th3_uN1Qu3]

Originally Posted by bigbeark

Does Low Impedance = Low ESR?

Yes.

[mockingbird]

Here is what PCBONEZ will answer you:

Originally Posted by PCBONEZ

Not ~really~ but close enough at 100kHz.

Lets run an example cap through the math so everyone finally gets it:
I chose a 1500uF 6.3v MBZ with ESR = 0.026 Ohms
[Middle of the normal range of caps on mobos and Rubycon gives actual ESR in data sheet vs Impedance.]

Z = Impedance
C = 1500 uF = 0.0015 F
ESR = .026 Ohm [squared = 0.000676 Ohm]
ƒ = 100 kHz = 100,000 Hz [Data sheet standard.]
p = PI = 3.14159
10 nH = 0.00000001 H
-- nH guessed as reasonable based on other reading. Is physical size dependent.
-- Lytics range from 4 nF for an itty bitty to 34 nF for a beer can cap.]

XC= 1 ÷ 2pƒC
2pƒC = 2 x 3.14159 x 100000Hz x 0.0015F = 942.477
XC = 1 ÷ 942.477 = 0.001061
XC = 0.001061

XL = 2pƒL
XL = 2pƒL = 2 x 3.14159 x 100000Hz x 0.00000001H = 0.006283
XL = 0.006283

(XL - XC) = 0.005222
(XL - XC)² = 0.0000273

Z² = ESR² + (XL - XC)² = 0.000676 + 0.0000273 = 0.0007033
Z² = 0.0007033
Z = 0.0265

Z is only 0.0005 different from ESR at 100kHz
That's less than 2% different.
.