Glossary of Terms

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.

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'Back Electromotive Force (Back EMF)'

An EMF that occurs in electric motors where there is motion between the armature of the motor and the external magnetic field. See also Counter Electromotive Force.

'Backup Power Supply '

A power supply (PSU) used to provide alternate system power in the event the primary power source fails or is unable to continue providing adequate system power.


Converts between balanced and unbalanced electrical signals/power. A differential wound choke used as an EMI filter component. Presents a high impedance to common-mode signals and a low impedance to differential mode signals.

'Base Transceiver Station'

A telecommunications term (usually referring to mobile phone installations) describing an installation which contains the transceivers, antennae and equipment for encrypting and decrypting communication with the Base Station Controller.


Mounting platform for power supply (PSU) (either ac/dc or dc/dc) components.

'Baseplate Temperature'

The temperature at the hottest spot on the mounting platform of the power supply.

'Basic Insulation'

The insulation applied to live parts to provide basic protection against electric shock. See also Insulation, Double Insulation, Reinforced Insulation, Supplementary Insulation.

'Battery Charger'

Electrical equipment designed to charge batteries.


A small ferrite normally used as a high frequency inductor core also a ceramic component used to space resistors from PCB's.

'Bench Power Supply'

A power source / power supply (PSU) used for bench-top use in a laboratory. Normally has adjustable voltage / current with displays showing settings. TDK-Lambda's Genesys range of supplies is designed for bench top use and has adjustable current and voltage limits.

'Bifilar Winding'

Two conductors wound side by side.

'Bipolar Junction Transistor (BJT)'

A type of Transistor with 3 terminals. Used as either a switch or amplifier.


Schematic Symbols for BJT's


Abbreviation for Bipolar Junction Transistor.


A low current drain from a power source.

'Bleed Resistor'

A resistor that allows a current drain on a power source. Usually to discharge filter capacitors or to stabilise an output. See Minimum Load.

'Bobbin '

An insulator used to support windings.


Permanently joining all non-current-carrying metal parts to ensure electrical continuity and the ability to conduct safely any current likely to be imposed on it. Often called Earth Bonding.

'Boost Converter'

A switching power supply topology. It accepts variable dc input voltage and converts it to a higher dc voltage.

'Boost Regulator '

See Boost Converter

'Breakdown Voltage'

1) The voltage level at which insulation fails.

2) The reverse voltage at which a semiconductor device changes its conductive characteristics.


See Full Brick

'Bridge Rectifier'

Full-wave rectifier circuit employing two or more rectifiers in a bridge configuration. Compare with Half-Wave Rectifier

Bridge Rectifier

'British Standards Institute'

The National Standards Body of the UK, founded in 1901, develops standards and standardization solutions to meet the needs of business and society. (


The condition created when the electricity supply (usually ac) falls below the minimum level specified for the system. Some brownouts are made intentionally to prevent a full power outage during periods of electricity demand overload.


Abbreviation for British Standards Institute


Abbreviation for Base Transceiver Station

'Buck Regulator'

A power supply topology which accepts an unregulated dc input voltage and produces a regulated lower output dc voltage.

'Bulk Capacitor'

The energy storage capacitor at the front end of a regulator.

'Bulk Voltage'

The voltage across a bulk capacitor.

'Burn In'

The operation of a newly fabricated device or system prior to application with the intent to stabilise the device, detect defects, and expose infant mortality. See also Power Cycle


Conductor which distributes power (or signals) from a power source (or signal source) to two or more separate circuits.

'Bus Converter '

A type of dc-dc converter usually used in Distributed Power Architecture which provides an isolated intermediate bus voltage to power non-isolated Point of Load Converters. Usually 48Vdc input, 12Vdc output. Lambda's range of bus converters includes the iEB and iQD ranges.

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Feel free to download the latest version of our glossary as a PDF file.

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