Low ESR vs Low Impedance

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  • bigbeark
    Badcaps Veteran
    • Jan 2010
    • 661
    • Canada

    #1

    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?
  • Th3_uN1Qu3
    Believe in
    • Jul 2010
    • 6031
    • Romania

    #2
    Re: Low ESR vs Low Impedance

    Originally posted by bigbeark
    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.
    A working TV? How boring!

    Comment

    • mockingbird
      Badcaps Legend
      • Dec 2008
      • 5484

      #3
      Re: Low ESR vs Low Impedance

      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.
      .
      "We have offered them (the Arabs) a sensible way for so many years. But no, they wanted to fight. Fine! We gave them technology, the latest, the kind even Vietnam didn't have. They had double superiority in tanks and aircraft, triple in artillery, and in air defense and anti-tank weapons they had absolute supremacy. And what? Once again they were beaten. Once again they scrammed [sic]. Once again they screamed for us to come save them. Sadat woke me up in the middle of the night twice over the phone, 'Save me!' He demanded to send Soviet troops, and immediately! No! We are not going to fight for them."

      -Leonid Brezhnev (On the Yom Kippur War)

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