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Power Supplies A to Z : "O"

We've included this handy glossary to help with the terminology & abbreviations relating to power products. Pick a letter below to begin, or download the glossary to refer to it whenever you like.

A B C D E F G H I J K L M N O P Q R S T U V W X-Z #


Abbreviation for Open-Circuit Voltage

Off-Load Voltage

See Open-Circuit Voltage.

Ohm (O)

Unit of measurement of Resistance and Reactance. Written as 'ohm'. Abbreviated to Ω.

Ohm’s Law

The fundamental mathematical relationship between current (I), voltage (E) and resistance (R) discovered by George Simon Ohm. The passage of one ampere through one ohm produces one volt.


Abbreviation for Operational Amplifier.

Open-Circuit Voltage (OCV)

The voltage when the circuit is open (no-load condition). See No Load Voltage.

Open-Frame Construction

A construction technique where the power supply (PSU) is not provided with an enclosure. Particular care needs to be exercised when installing an open frame power supply to ensure that adequate spacings and shock protection is maintained. Additional care needs to be taken to ensure that the unit is installed to meet the EMC standards and thermal performance.

Operating Temperature Range

The range of temperatures (ambient, baseplate or case) over which a power supply (PSU) is specified to operate safely and to perform within specified limits. See also Ambient Temperature, Storage Temperature

Operational Amplifier (OP-AMP)

A high gain differential input semiconductor device that measures the error voltage and produces at its output an amplified version of this.

Schematic Symbol for an Op-Amp (often the +V and -V are omitted)


A package that contains a light emitter and a photoreceptor used to transmit signals between electrically isolated circuits. Used in power supplies to ensure that the Status Signals  presented by the PSU and control signals with the PSU are isolated from the outputs.

Schematic Symbol for an Opto-Coupler


See Opto-Coupler.


The energy provided by the power supply or the terminals on the power supply which provide the output power.

Output Choke

The inductor in the output L-C Filter.

Output Current Limiting

A protective feature that keeps the output current of a power supply (PSU) within predetermined limits during overload to prevent damage to the supply or the load. Power supply current limiting is usually designed to protect the power supply, not the load and it is advisable that the system designer ensures that the system is protected in the event of excess current.

Output Filter

Components used to attenuate output ripple and noise.

Output Filter Capacitor

The capacitor(s) across the output terminals of a power supply (PSU).

Output Impedance

See Internal Impedance.

Output Inductance

See Output Choke.

Output LC Filter

The low pass filter in the output of a power supply (PSU) that smooths the rectified output to its average value. Also called an averaging filter.

Output Range

The specified range over which the value of an output (voltage or current) can be adjusted.

Output Ripple and Noise

See Periodic and Random Deviation.

Output Voltage

The voltage measured at the output terminals of a power supply (PSU).

Overcurrent Protection

See Output Current Limiting.

Overload Protection

A feature that senses and protects the power supply from current or power overload conditions. See also Output Current Limiting.


A transient change in output voltage in excess of specified output regulation limits, which can occur when a power supply (PSU) is turned on or off, or when there is a step change in line or load.

Overshoot, Undershoot & Transient Recovery Time


A voltage that exceeds specified limits.

Overvoltage Protection (OVP)

A feature that detects a high voltage condition and protects the circuit as necessary. See also Overvoltage, Crowbar.


Abbreviation for Overvoltage Protection.

A B C D E F G H I J K L M N O P Q R S T U V W X-Z #

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