Glossary of power supplies (2)

AC: Alternating current. Describes voltage and current that varies in amplitude, usually in a sinusoidal waveform with respect to time. AC power is almost universally used for distributing electrical power.

Blackout: Loss of AC electrical power.

Brownout: A planned AC voltage reduction by the power company to counter excessive demand.

Capacitive coupling: Two separated conductors always form a capacitor. The closer they are, the more it’s possible for voltage variations on one conductor to be electrostatically induced on the other conductor (contrast to inductive coupling).

Inductive coupling: When a changing current is flowing in one wire, a voltage is induced in a nearby wire because of the magnetic field caused by the current (contrast to capacitive coupling).

Crest factor: In an AC waveform, crest factor is the ratio of the peak value to the RMS value.

DC: Direct current. Used to describe an unchanging voltage, current, or electrical power.

Drift: The change in time of an output voltage or current.

Electronic load: A type of instrument that serves as a load, usually dynamic, and can be used for testing power supplies and sources.

ESR: Equivalent series resistance. The simple “series” model of a capacitor or
an inductor places the pure reactance in series with a pure resistor, whose value is usually called the ESR. Often measured on larger electrolytic capacitors and a high value of ESR generally indicates a bad capacitor.

Ground: Electrical ground in an AC power system is a wire that is connected to the earth, hence the name “ground”. The reason for such connection stems from the need to protect users of electrical equipment from shock hazards. Power is delivered to the utilization site using a pole mounted or other type of transformer. The output of such a transformer consists essentially of two lead wires, with the utilization voltage available between the leads. For a variety of complicated reasons involving safety, one of these transformer lead wires is connected to the earth using a copper bar driven into the ground.

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