Electronics notes/Capacitors

From Helpful
(Redirected from Bypass capacitor)
Jump to navigation Jump to search
This is for beginners and very much by a beginner / hobbyist.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.

Some basics and reference: Volts, amps, energy, power · batteries · resistors · transistors · fuses · diodes · capacitors · inductors and transformers · ground

Slightly less basic: amplifier notes · varistors · changing voltage · baluns · frequency generation · Transmission lines · skin effect

And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions

Audio notes: See avnotes

Platform specific

Arduino and AVR notes · (Ethernet)
Microcontroller and computer platforms ··· ESP series notes · STM32 series notes

Less sorted: Ground · device voltage and impedance (+ audio-specific) · electricity and humans · power supply considerations · Common terms, useful basics, soldering · landline phones · pulse modulation · signal reflection · Project boxes · resource metering · SDR · PLL · vacuum tubes · Multimeter notes Unsorted stuff

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·

See also Category:Electronics.

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 — probably a pile of half-sorted notes and is probably a first version, is not well-checked, so may have incorrect bits. (Feel free to ignore, or tell me)

See also:

Capacitor marking

This article/section is a stub — probably a pile of half-sorted notes and is probably a first version, is not well-checked, so may have incorrect bits. (Feel free to ignore, or tell me)

Rating considerations


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.

Temperature (spec / behaviour)

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


Tantalum capacitors (type)

Silver mica capacitors (type)


Plastic film

See also (types)

Variable Capacitor (design)

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


EMI/RFI suppression (spec)

Pulse capacitor

More applied

Gimmick (design)

Bypass capacitor (application)

De-coupling and coupling capacitor (application)

Power supply filtering (application)

Lowpass filter (application)

Signal generator (application)

Capacitive dropper (application)

See Electronics_notes/Changing_voltage#capacitive_dropper

Motor capacitor (application)

See also