Electronics notes/Capacitors

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Intro

The symbols used in circuits

Capacitors (regularly abbreviated as caps) take an electrostatic charge, which (ignoring leakage) will remain until discharged.

When you put DC across them, they charge to that voltage. They work as a sort of battery - with tiny capacity, but enough for a number of practical uses.

When you put AC across them, limited charging speed means they work more like frequency-dependent resistors, as in oppose some frequencies more than others, which is why they help build signal conditioning, noise reduction, filtering, and resonant circuits.

Some theory and behaviour

Charging and discharging

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

See also:

• http://en.wikipedia.org/wiki/RC_time_constant
• http://www.electronics-tutorials.ws/rc/rc_1.html

Capacitor marking

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Rating considerations

Voltage

You'll often know the maximum voltage a capacitor will be exposed to, though you may wish to consider your circuit's ripple current, peak current, fault current, possible voltage reversal, and more.

The voltage spec seems a nominal one, in that it can probably handle more, but you may shorten its lifespan, and with significantly more you will make it fail.

Dielectrics / types / designs

Electrolytic capacitors (type)

Some electrolytic capacitors - various radial lead (both leads on one end) and some axial lead (both ends), and SMD variants ( top left)

• polarized - reverse biasing these will cause an electrochemical reaction in the electrolyte, causing it to heat, expand, vent, and likely short in the process. The common cylinder shape has indentations on the top that will bulge and fold open (a safety feature, and one that makes failed electrolytic caps easy enough to identify)

• higher inductance than many other types, so not so useful for high-frequency applications

• cheap, so common wherever the frequency or stability limitations are not a problem

• often can-shaped, and regularly black, grey, blue, and with a stripe indicating its negative lead

• Capacitors with more than ~1µF are regularly electrolytic capacitors because of cost. Other types are also used, but often when electrolytic's polarization or lower stability is a problem.

Ceramic capacitors (type)

Various types of ceramic capacitors

http://en.wikipedia.org/wiki/Ceramic_capacitor

Tantalum capacitors (type)

• http://en.wikipedia.org/wiki/Tantalum_capacitor

• http://images.google.com/images?q=tantalum%20capacitors
• http://commons.wikimedia.org/w/index.php?title=Special%3ASearch&search=tantalum+capacitor
• http://images.google.com/images?q=SMD+tantalum+capacitor

Silver mica capacitors (type)

http://en.wikipedia.org/wiki/Silver_mica_capacitor

Variable Capacitor (design)

Adjustable capacitors, often looking similar to potmeters (and frequently like trimpots).

More applied

Capacitive dropper (application)

See Electronics_notes/Changing_voltage#capacitive_dropper

See also

• http://en.wikipedia.org/wiki/Capacitor
• http://en.wikipedia.org/wiki/Types_of_capacitor

• http://www.interfacebus.com/Design_Capacitors.html

• http://www.faqs.org/docs/electric/AC/AC_8.html

• http://en.wikipedia.org/wiki/Capacitor_plague

• http://www.educypedia.be/electronics/capacitorstypes.htm
• http://www.satcure-focus.com/tutor/page6.htm