Early capacitors or “condensers” were known as Leyden Jars. They were named after the university where they were developed.

Today’s capacitors look more like these Start Run Surface Mount Ceramic Variable Electrolytic Noise Suppression

FUNCTION Capacitors store electrical charge. They are used in timing circuits because it takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by acting as a reservoir of charge. They are used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals.

Capacitance This is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to show the smaller values. Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico): µ means 10-6 (millionth), so 1000000µF = 1F n means 10-9 (thousand-millionth), so 1000nF = 1µF p means 10-12 (million-millionth), so 1000pF = 1nF

AIR

Electrolytic Capacitors Electrolytic capacitors are polarized. They must be connected correctly. At least one lead will be marked + or -. There are two designs of electrolytic capacitors: Axial, where the leads are attached to each end. Radial, where both leads are at the same end.

ELECTROLYTIC Usually polarized (has a + and – terminal) DC use only Cheap, not very accurate Good storage capability, wide range of voltage & µF Used in ripple filters, timing circuits & other, not good for high frequency De-rate voltage by 100% (for 12 volt circuit use 24 volt capacitor) CAN EXPLODE if rated voltage is exceeded or polarity reversed!

ELECTROLYTIC FAILURE MODES What to look for

TANTALUM They are electrolytic so watch for the '+' and '-' indicators Excellent temperature and frequency characteristics Small size, reliable, common values readily available Expensive, easily damaged by spikes, large values exists but hard to find

Super Capacitors Despite the large capacitance value, its physical dimensions are relatively small. It has a diameter of 21 mm (almost an inch) and a height of 11 mm (1/2 inch). Like other electrolytics the super capacitor is also polarized so exercise caution in regards to the break-down voltage. Care must be taken when using this capacitor. It has such large capacitance that, without precautions, it would destroy part of a powersupply such as the bridge rectifier, volt regulators, or whatever because of the huge inrush current at charge. For a brief moment, this capacitor acts like a short circuit when the capacitor is charged. Protection circuitry is a must for this type.

Variable Capacitors Used in radio tuning circuits Sometimes called 'tuning capacitors'. They have very small capacitance values, typically between 100pF and 500pF (100pF = 0.0001µF).

Trimmer Capacitors Trimmer capacitors (trimmers) are miniature variable capacitors. They are designed to be mounted directly onto the circuit board and adjusted only when the circuit is built.

PARALLEL CAPACITORS  Capacitors connected in parallel have their capacitance added together, which is just the opposite of parallel resistors. It is an excellent way of increasing the total storage capacity of an electric charge: Ctotal = C1 + C2 + C3

SERIES CAPACITORS Opposite of calculating resistors in series. Capacitors in series will have total capacitance lower than the lowest value.

pF, nF, & µF A capacitor marked 105 means 10+5zeros = 10 + 00000 = 1.000.000pF = 1000 nF = 1 µF. Value is in pF (PicoFarads). The letters added to the value is the tolerance and in some cases a second letter is the temperature coefficient mostly only used in military applications. A ceramic capacitor with 474J printed on it it means: 47+4zeros = 470,000pF or 470nF or 0.47µF and J=5% tolerance.

Capacitor Number Code A number code is often used on small capacitors where printing is difficult: the 1st number is the 1st digit, the 2nd number is the 2nd digit, the 3rd number is the number of zeros to give the capacitance in pF. letters indicate tolerance and voltage rating. For example:   102   means 1000pF = 1nF   (not 102pF!) For example:   472J means 4700pF = 4.7nF (J means 5% tolerance).

CONVERSION VALUES microFarads (µF) nanoFarads (nF) picoFarads (pF) = 0.001nF 1pF 0.00001µF 0.01nF 10pF 0.0001µF 0.1nF 100pF 0.001µF 1nF 1000pF 0.01µF 10nF 10,000pF 0.1µF 100nF 100,000pF 1µF 1000nF 1,000,000pF 10µF 10,000nF 10,000,000pF 100µF 100,000nF 100,000,000pF