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Physical / electrical concepts

ESR

Equivalent Series Resistance. A real capacitor isn't perfect; ESR is the tiny resistance in series with it. Matters for LDO stability.

How it looks

Drawing
A REAL CAPACITOR, MODELLEDESRthe ideal capacitorevery real capacitor behaves like a perfect one plus a tiny resistor in series
ESR = Equivalent Series Resistance.

How it works

  1. An ideal capacitor would hand out charge instantly. A real one has a small built-in resistance on the way in and out: its ESR.
  2. Ceramic capacitors have very low ESR; older electrolytic ones more.
  3. Some regulators (LDOs) need ESR in a certain range to stay stable; their datasheet says which capacitor to use.

Where it fits

Matters for decoupling and bulk capacitors around regulators.

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