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Low ESR vs Low Impedance

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    Low ESR vs Low Impedance

    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?

    #2
    Re: Low ESR vs Low Impedance

    Originally posted by bigbeark View Post
    Does Low Impedance = Low ESR?
    Yes.
    Originally posted by PeteS in CA
    Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
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      #3
      Re: Low ESR vs Low Impedance

      Here is what PCBONEZ will answer you:
      Originally posted by PCBONEZ View Post
      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.
      .
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      -Leonid Brezhnev (On the Yom Kippur War)

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