# Glossary of power supplies (3)

**Minimum load**: If specified for a power supply, it is the minimum load current that must be drawn from the power supply so that it meets its performance specifications.

**Surge**: A momentary increase in the AC power line voltage.

**Output impedance**: The ratio of a change in output voltage to a change in load current.

**Power factor**: The ratio between real and apparent power. This determines how much

current is required to produce a certain amount of power. It is always desirable to have the ratio be as close as 1. A lower power factor system would mean greater loss in power to produce the same amount of work as compared to with a higher power factor system.

**Ripple Voltage**: The portion of unfiltered AC voltage and noise present at the output of a filtered power supply, operated at full load. Typically stated in rms AC voltages (with zero ripple voltage representing a perfectly filtered power supply).

**Ripple Current**: The portion of unfiltered AC current at the output of a filtered power supply.

**RMS**: Root Mean Square. For any waveform, the RMS is square root of the average of the sum of the squares of the sampled values. For a continuous function, an analogous integral formula applies.

**Safety ground**: A circuit designed to conduct away dangerous voltages (due to a defect or accident), thus protecting people from accidental shocks. The metal covers of instruments and appliances are connected to ground (and hence called a safety ground). Thus, if an electrically “hot” wire inside the device accidentally touches the metal case, the connection to safety ground means the metal will stay near ground potential. The usual outcome of such a condition is that the circuit breaker will trip.

**Temperature range**: The range the power supply is specified to operate over. It can also designate a temperature range the supply can be stored in.

**True power**: Also referred to as real power, are usually measured in watts.

**Apparent power**: The product of RMS current and RMS voltage, usually measured in the units of VA (volt-amps)

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