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Power Supplies A to Z : "C"

We've included this handy glossary to help with the terminology & abbreviations relating to power products. Pick a letter below to begin.

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 #

C

Abbreviation for capacitance, capacitor and coulomb.

Canadian Standards Association (CSA)

CSA - An organisation chartered to test and evaluate products and to set applicable safety standards in Canada.

http://www.csa.ca/

Capacitance

Inherent property of an electric circuit or device that opposes change in voltage. The size of a capacitor (in farads).

Capacitive Coupling

Coupling resulting from the capacitive effect between circuit elements.

Capacitive Reactance (XC)

Opposition to ac due to capacitance.

Capacitor

A charge storage device. A simple capacitor consists of two conductors separated by a dielectric.

Schematic Symbol for an Electrolytic Capacitor (polarised) and non polarised Capacitor

Catch Diode

See Free Wheel Diode. 

CB Report

Abbreviation of Certification Body's (or Bodies') Test Report.

CB Scheme

Abbreviation of Certification Bodies' Scheme. An international scheme to facilitate international trade in electrical equipment, primarily intended for use in homes, offices, workshops, healthcare facilities and similar locations, for benefit of consumers, industries, authorities etc., and to provide convenience for manufacturers and other users of the services provided by various National Certification Bodies (NCBs). It is operated by the IECEE. See http://www.iecee.org/ for more details.

CB Test Certificate

Abbreviation of Certification Body's (or Bodies') Test Certificate. It is is a formal CB Scheme document issued by an authorized NCB (National Certification Body) to inform other NCBs that a sample of the product tested was found to be in compliance with the applicable requirements. CB Test Certificates should not be used for advertising purpose, however reference to the existence of a CB Test Certificate is permitted. A manufacturer utilizing a CB test certificate issued by one of the accepted National Certification Bodies (NCBs) can obtain certification marks of the latter, within their scope of adherence, in the countries where the accepted NCBs are located. See http://www.iecee.org/ for more details.

CB Test Report

Abbreviation of Certification Body's (or Bodies') Test Report. A test report issued by an Issuing and Recognizing NCB (National Certification Body).is a standardized report in a clause by clause checklist format referencing, the requirements of the relevant IEC Standard. The Test Report provides clear and unambiguous results of all the required tests, measurements, verifications, inspections and evaluations. It also contains photographs, electrical diagrams, artwork drawings as well as a description of the product. Under the rules of the CB Scheme, a CB Test Report is considered valid only if accompanied by its CB Test Certificate. See http://www.iecee.org/ for more details.

Celsius

The SI derived unit of temperature. Written as 'degrees Celsius'. Abbreviate to °C.

CEN

Abbreviation for Comité Européen de Normalisation. See European Committee for Standardisation.

CENELEC

Abbreviation for Comité European Committee for Electrotechnical Standardization.Européen de Normalisation Electrotechnique. See European Committee for Electrotechnical Standardization. https://www.cencenelec.eu/

Centi

SI prefix multiplier. Multiplies by 10^-2. So 100 cF = 100 x 10^-2 F = 1F. Written as 'centi'. Abbreviated to 'c'.

Centigrade

The previous name for Celsius (changed in 1948). Written as 'degrees centigrade'or '°C'.

Centimetre-Gram-Second System (CGS)

Obsolete system of physical units. Replaced by SI units.

Centre Tap

An electrical connection made at the centre of a transformer or inductor winding, with an equal number of turns on either side of the tap.

CGS

Abbreviation of centimetre-gram-second system. 

Charge

The potential energy stored in a capacitive electrical device. Unit is coulomb.

Chassis

The structure supporting or enclosing the power supply (PSU).

Chassis Ground

If the product is earthed, the protective earthing point or potential for the chassis of the product. If the product is not earthed then chassis ground is the voltage potential of the chassis.

Choke, Choke Coil

An Inductor.

Choke, RF

A choke with a high impedance at radio frequencies.

Circulating Current

See Ground Loop.

Clamp Circuit

A circuit that limits a voltage waveform so that it cannot exceed a specific level.

Clamp Diode

A diode in a clamp circuit.

Class A (EMC)

See Curve A.

Class B (EMC)

See Curve B. 

Clearance Distance

The shortest path, through air, separating two conductors or two circuit components.

Clock

An oscillator producing timing pulses to synchronise various elements of a system.

CMOS

Abbreviation for Complementary Metal-Oxide Semiconductor. Complementary because the design uses 2 transistors for logic functions, only one being switched on at a time.

Coercivity

A measure of the reverse field needed to drive the magnetisation to zero after being saturated. See also Hysteresis Loop, Remanence.

Commercial off the Shelf (COTS)

A term used for standard (not custom) systems. This is most often used in military but also computer and occasionally robotic systems.

Common Point

The output/sense terminal which is designated 'common' to which load, reference and external programming signal all return.

Common Return

A return conductor to two or more circuits.

Common-Mode Noise

Noise that appears equally and in phase on conductors relative to a common reference.

Common-Mode Output

The electrical output supplied to a load connected between the terminals of the ungrounded floating output of a power supply (PSU) and the ground point to which the source power is returned.

Communications Port

(Comms port) A standard communications interface, such as IEEE488 (GPIB), RS-232, RS-485,I²C, Ethernet or USB, that provides information flow from a processor to a peripheral device, such as a power supply (PSU).

Compliance Range

Range of voltage needed to sustain a given constant current throughout a range of load resistance.

Compliance Voltage

The output dc voltage of a constant current supply.

Component

An element in an electric circuit.

Conductance (G)

The ability to conduct current. It is equal to amperes per volt, or the reciprocal of resistance, and is measured in siemens (metric) or mhos (English) (1 siemens = 1 mho).

Conductor

Material which allows an electric current to pass through it (usually metal).

Configurator

An automatic product selection tool. It will ensure that the product selected best matches the requirements placed upon it. An example configurator can be seen at https://www.emea.lambda.tdk.com/uk/products/quick-product-finder.aspx

Conformal Coating

An insulating layer often applied by spraying or dipping that covers and protects the components on a circuit board. Used to provide protection against dust or other contaminants.

Conformance

Manufacturer’s commitment that product meets specified standards.

Connector

A mechanical device used to link conductors.

Constant Current Limiting

Current-limiting circuit that holds output current at a maximum value whenever an overload is experienced. For most power supplies, the performance is not truly constant current but reflects the curve shown in the Current Limiting definition. 

Constant Current Load

An electronic load with a control loop to regulate the current drawn from the power supply (PSU).

Constant Current Power Supply

A power supply (PSU) that regulates its output current, within specified limits, against changes in load and other factors.

Constant Voltage Power Supply

A power supply (PSU) that regulates its output voltage within specified limits, against changes in load and other factors.

Constant Voltage Transformer

A power conditioning device which maintains approximately constant voltage ratio over the range from zero to rated output. It is a low maintenance device with few components but is generally large.

Continuous Duty

Operation at almost constant load for an indefinitely long time. See also Intermittent Duty. 

Control Resolution

The smallest controlled increment of the stabilised output signal (usually applies to output voltage or current).

Convection

The transfer of heat in a gas or liquid (usually refers to air in power supplies).

Convection Cooled Power Supply

A power supply (PSU) cooled only by the convection (usually air) over the surfaces of heat dissipating elements.

Converter

A device / power supply that changes power from one form or level to another. Examples: DC-DC; a device that delivers dc power when energised from a dc source. Fly-back converter, Forward Converter - types of switching power supply circuits.

Cooling

The process of removing heat dissipated by a power supply (PSU).

Copper Loss

Heat loss in components or conductors as the result of wire resistance. Calculated using the equation:

Cord Set

A flexible cord terminated at one end with an attachment plug and a second connector at the other (usually for ac input to the power supply).

Core

Material (usually ferrous eg Ferrite or iron) serving as a path for magnetic flux usually in an inductor.

Core Loss

Power dissipated by a magnetic core due to hysteresis and eddy currents.

Core Saturation

The tendency of molecules in a core to orient in one direction due to excess magnetic flux densities. In most applications, core saturation is an undesirable effect which is avoided through good design: engineering the windings and core so that magnetic flux densities remain well below the saturation levels. Saturation has several causes: operating the core at a different/lower frequency, presence of DC current in the winding, overloading the winding with excess applied voltage.

COTS

Acronym for Commercial off the shelf. 

Coulomb

(abbreviation C) the SI unit of electric charge. It is the amount of charge carried by a current of 1 ampere flowing for 1 second.

Counter Electromotive Force (Counter EMF or CEMF)

The voltage developed in an inductor by an alternating or pulsating current. The polarity of this voltage is at every instant opposite that of the applied voltage. Sometimes called Back EMF.

Creepage Distance

The shortest distance separating two conductors as measured along a surface touching both conductors.

Crest Value

Maximum value of a waveform excluding transients (also called Peak Value).

Cross Regulation

The change of one output voltage as the load is changed on another output with all other factors constant. Usually expressed as a percentage of the nominal output. See also Regulation. 

Crowbar

An overvoltage protection circuit which will rapidly place a low resistance shunt across the power supply (PSU) output terminals if a predetermined voltage is exceeded. Not usually used in switched mode power supplies as they have more sophisticated overvoltage protection methods.

Overvoltage Crowbar Circuit

CSA

Abbreviation for Canadian Standards Association. 

Current (I)

The rate of transfer of electrical charge measured in amperes (amps).

Current Foldback

See Foldback Current Limiting. 

Current Limit Knee

The point on the plot of current v voltage of a supply at which the current starts to foldback, or limit.

Foldback Current Limiting and 'Constant' Current Limiting

Current Limiting

An electronic overload protection circuit which limits the maximum output current to a preset value. Please note that power supplies incorporate current limiting usually to protect the power supplies. Care must be taken to ensure that connecting leads and any PCB tracks are designed to allow for the maximum current possible from the power supply (or supply additional protection circuitry / fusing for protection).

Current Sensing Resistor

A resistor placed in series with the load to develop a voltage proportional to load current.

Current Source

A power source that delivers constant current at a specified level.

Curve A (or Class A)

See Curve B.

Curve B (or Class B)

Relates to conducted or radiated EMC performance, usually EN55022 which specifies two levels.

Level/Class/Curve A which is for equipment designed to operate in EMI tolerant environments such as industrial locations.

Level/Class/Curve B which is for equipment installed in EMI sensitive areas (such as domestic, commercial and light industrial).

Products which achieve curve B will always achieve curve A also it allows higher levels of conducted or radiated noise than curve B.

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