February 2, 2012 AT 7:46 am

EEBookshelf: Capacitors Demystified

This useful lecture handout (from a Stanford electronics course) comes courtesy the always insightful johngineer.  While something inside me died when I read that aesthetics “is a foreign term to EE’s anyway”, it’s a great summary of some of the issues that need to be kept in mind choosing the right capacitor for the right situation, and describes some common situations where you’d use a capacitor and helps you select the right tool for the job. Read Capacitors Demystified for more.



  1. Not all ceramic capacitors are poor at high frequencies. In fact, they are often used for RF bypassing, coupling and resonating at frequencies well up into the GHZ range. The high voltage “door knob” capacitors used in amateur transmitter circuits with voltage ratings of 20KV (or more) are ceramic.

  2. That high-speed comment did strike me as odd thought these notes are a bit old. Look at the range … 22µF max. Today you can get MLCC caps well beyond that. Still some good information in there, though.

  3. More on ceramic caps:
    They have been used at RF since before WWII. Many war surplus radios have used small “dog bone” type ceramic caps for RF coupling and resonant circuits. Ceramic caps are available in values below 1pf, especially in SMT packages. Ceramic capacitors in the uf range are used for bypassing and audio coupling. I suspect that the comment on ‘not good for hf’ may apply to caps above .1 uf, though the monolithic types in this range are used for hf bypassing in digital circuits.

    Not mentioned were ‘paper’, ‘mylar’, and other ‘plastic’ dielectric types. Most of these are not suitable for HF use as these are constructed of foil/dielectric layers wound tightly which may have considerable inductive reactance.

  4. Circuit Cellar INK for Feb. 2012 has an article by Ed Nisely about bypass caps. Self-resonance — basically the inductance hidden in the leads and the rest of the structure of the cap — has some amazing effects.

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