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Power Supplies A to Z : "F"

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 of farad.

Failure Mode

The way in which a device does not meet specified requirements.

Fall Time

The time required for a Pulse to decrease from 90% to 10% of its maximum positive (or negative) amplitude.

Fan Cooled

A method of forced-air cooling used to maintain design temperatures.


Unit of measurement of Capacitance. Written as 'farad'. Abbreviation is 'F'

Faraday Cage

A conducting screen completely surrounding a space to exclude electromagnetic fields. Often put to a dual purpose: to block electric fields and to block electromagnetic radiation (RF shielding).

Faraday Shield

An electrostatic shield between input and output windings of a transformer. This can be used to reduce coupling capacitance which in turn reduces output common mode noise. See also Electrostatic Shield.

Fault Tolerant

System redundancy to provide continued operation following specified failures.


Abbreviation for Federal Communications Commission.

Federal Communications Commission (FCC)

FCC - An independent US government agency. Regulates the use of the radio spectrum and telecommunications within (or originating in) the USA.


SI prefix multiplier. Multiplies by 10-15. So 100 fF = 100 x 10-15 F. Written as 'femto'. Abbreviated to 'f'.


A ceramic, soft magnetic material with low loss at high frequencies and which contains iron oxide mixed with oxides or carbonates of one or more metals such as manganese, zinc, nickel or magnesium. Invented by TDK's founder, Dr. Yogoro Kato and Dr. Takeshi Takeiin. TDK Corporation was founded to commercialize this material in 1935.


Abbreviation for Field Effect Transistor.

Field Effect Transistor (FET)

A transistor that relies on an electric field to control the conductivity of a 'channel' in a semiconductor material. They are sometimes used as voltage-controlled resistors. All FETs, [except J-FETs (Junction Field Effect Transistors)] have four terminals (gate, drain, source and body/base). J-FETs have no body. Enhancement FETs are normally off (a voltage applied between the source and gate increases the current from source to drain), depletion FETs are normally on (a voltage applied between the source and gate decreases the current from source to drain).

Schematic Symbol for a FET


A generic term for any circuit which performs some type of signal processing. Normally this is to remove/attenuate unwanted signals (noise). Noise filters for power supply (PSU) outputs (and inputs) are generally passive.

Floating Output

An output of a power supply (PSU) that is not connected to any other output or earth, usually denotes full galvanic isolation. Usually, they can be used as either positive or negative outputs.

Flyback Converter

A simple switched mode power supply topology. In most cases, it uses one switch and only needs one magnetic element - the transformer. Energy is transferred during the off-time of the primary circuit. They are generally limited to outputs of less than 200 watts.

Foldback Current Limiting Circuit

Current limiting circuit that gradually decreases the output current under overload conditions until some minimum current level is reached under a direct short circuit. See Current Limit.

Forward Converter

An isolated form of the Buck Regulator which is capable of producing output voltages higher or lower than the input voltage.


A low cost Printed Circuit Board material. Construction is from paper impregnated with phenolic resin.


A Printed Circuit Board material. Construction is from woven fibreglass mat impregnated with a flame resistant epoxy resin. It is much stronger than FR-2 but more expensive.

Free Wheel Diode

A diode used to provide a path for current to flow from an inductive device. See also Catch Diode.


The measurement of the number of times that a repeated event occurs per unit of time. The unit of measurement is hertz (Hz) which is repetitions per second (cycles per second – cps).

Front End Power Supply

A power supply intended for use in Distributed Power Architecture systems to provide the ac/dc conversion. It will usually provide 12V output to supply Point of Load Converters directly. Lambda's range of front end power supplies includes the FPS1000 (1kW up to 3kW) and NV-350FEP (up to 350W).

Full Brick

Industry standard footprint for dc-dc converters. Dimensions are 116.8mm x 61mm (4.6in x 2.4in). See also Half Brick, Quarter Brick, Eighth Brick, Sixteenth Brick. Lambda's PAF range of dc/dc converters are examples of full bricks.

Full-Wave Rectifier

A circuit element, such as a bridge-rectifier, that rectifies both halves of the input ac wave to produce a varying dc output. Compare with Half-Wave Rectifier.


Abbreviation of 'fusible link'. An overcurrent protection device. See External Fusing.

Schematic Symbols for a Fuse

Fusible Link

See Fuse

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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