Capacitors

Overview

A capacitor stores energy in an electric field. In its simplest form it consists of two conductive surfaces separated by an insulating material called a dielectric. When a voltage is applied, equal and opposite charges accumulate on the two conductors.

Capacitance: C = Q / V

Capacitance is measured in farads. Most electronic capacitors are much smaller than one farad, so common values are stated in microfarads (µF), nanofarads (nF), and picofarads (pF).

Interactive capacitor models

The original LearnTronics VRML models are preserved here in one viewer. Select a type to compare the physical packages.

Electrolytic capacitor

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What capacitors do in circuits

Store and release electrical energy.
Smooth ripple in power supplies.
Bypass unwanted AC noise around a circuit node.
Couple an AC signal while blocking steady DC.
Set timing with resistors.
Form filters and tuned circuits.
Provide short bursts of current near digital and switching devices.
Suppress transients and reduce electromagnetic interference.

Important specifications

Specification	Meaning
Capacitance	The nominal charge-storage capability.
Voltage rating	The maximum continuous voltage allowed under specified conditions.
Tolerance	The allowed difference between actual and marked capacitance.
Polarity	Whether the capacitor must be connected with a particular terminal positive.
ESR	Equivalent series resistance: internal loss that causes voltage drop and heating.
ESL	Equivalent series inductance: parasitic inductance that matters at high frequency.
Leakage	Small DC current that passes through a real dielectric.
Ripple current	The AC current the part can handle without excessive heating.

Common capacitor families

LearnTronics currently has VRML examples for electrolytic, mica, and tantalum capacitors. Practical electronics also makes heavy use of ceramic, film, and variable capacitors, each of which now has its own page here. Supercapacitors occupy another region, providing extremely large capacitance for energy storage but with different voltage, leakage, and frequency characteristics.

Type	Typical strengths	Typical uses
Aluminum electrolytic	Large capacitance at moderate cost.	Power-supply filtering, bulk energy storage, low-frequency coupling.
Mica	High stability, low loss, high Q.	RF tuned circuits, oscillators, precision high-frequency work.
Tantalum	High capacitance per volume and good stability.	Compact DC filtering and decoupling when properly derated and protected.
Ceramic	Very small size, low inductance, excellent high-frequency availability.	Decoupling, filtering, RF, timing; behavior depends strongly on dielectric class.
Film	Low loss, good pulse handling, stable values.	Audio, timing, snubbers, power electronics, AC applications.
Variable	Capacitance can be adjusted mechanically or electronically.	Radio tuning, oscillators, antenna matching, calibration, and frequency control.

Stored charge can be dangerous. Large or high-voltage capacitors may remain charged after power is removed. Follow the equipment's service procedure, discharge through an appropriate resistor or approved discharge tool, and verify the voltage with a meter before touching the circuit. Directly shorting a large charged capacitor can cause a violent spark, damage the capacitor or tool, and create a burn or arc hazard.

Continue through the capacitor pages

The Basics page explains capacitance, units, series and parallel combinations, RC timing, reactance, and everyday uses. The History page follows the development from the Leyden jar to modern electronic capacitors. The Advanced page covers dielectric physics, impedance, ESR, ESL, self-resonance, losses, ripple, and design applications.

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