Glossary
Glossary of terms: Power Supplies
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A
AC (Alternating Current): A
current (or voltage) which reverses polarity on a periodic basis
AC-to-AC converter: A power converter which changes an AC input supply into a different form of AC output supply. e.g. 415V 50Hz 3-phase input, 30kHz 600V output
AC to-DC converter: A power converter which changes an AC input supply into one or more DC output supplies
Active ripple rejection: Feature which enables a power converter to control the ripple content of its output voltages using its closed loop control to counteract or suppress ripple, usually only at frequencies well below the switching frequency
Ambient temperature: The still air temperature of the immediate environment around the power converter
Arc discharge: An uncontrolled high current breakdown (flashover) which takes place in air, between circuit nodes with a potential difference between them which is large enough to cause ionisation of the air in between. Normally associated with high voltage power supplies, although damaging arc discharges can also occur in low voltage supplies where large stored energies and low circuit impedances are present. See Corona discharge
Battery back-up: Feature whereby a battery is incorporated into a power converter to enable operation of the outputs for a substantial period of time, without prime supply
Battery charger: A power converter designed for the specific purpose of charging a rechargeable battery
Bulk DC supply: The DC supply derived by rectifying an AC prime supply, which is used to provide power to an off-line converter switching circuit
Burn in: A test process, which operates new power converters at or near full load for an extended period to precipitate the occurrence of early failure due to manufacturing defects. See ESS
Clearance: The spacing, in air, between circuit elements intended to be isolated from one another
Closed loop control: Technique which regulates the output voltage (or current) of a power converter by comparing the voltage to be controlled with a precision reference and using the difference (error) signal to drive a corrective action at the power circuit.
Common mode noise: Noise voltages which are common to both the “supply” and “return” lines at either the input or the output of a power converter, usually measured with respect to ground
Constant current: A power supply that regulates output current level regardless of changes in load resistance
Constant voltage: A power supply that regulates voltage level regardless of changes in load resistance
Corona discharge: A controlled current breakdown, which takes place in air, between circuit nodes with a potential difference between them which is large enough to initiate ionisation of the air in between. Normally an unwanted problem in high voltage power supplies but can be created deliberately as part of a process
e.g. electrostatic ozone generation. See Arc discharge
Cross regulation: The effect of a load change to one output of a multiple output power converter on the regulation of another output
Crowbar: A protection circuit which rapidly places a low impedance path across the power supply output terminals whenever a fault condition is detected
Creepage: The spacing, across or through insulation materials, between circuit elements intended to be isolated from one another.
Current-fed: Term applied to power converter circuits where the power being switched is at a constant current, normally derived from using an inductor in series with the DC voltage source
Current limiting: A feature designed to prevent overload of a constant voltage power supply by enforcing a maximum limit on the output current delivered to the load
Current mode control: Power converter regulation technique which monitors and controls power circuit current as well as output voltage
D
DC (Direct Current): A unidirectional current or fixed-polarity voltage
DC bus: The DC supply from which the switching circuit in a power converter draws power
DC to-DC converter: Power converter that changes a DC input supply into one or more DC output supplies, normally at different voltages to the input and possibly isolated from it
De-rating: Operating a power converter at reduced output power (or with some other specified reduction in parameters) to improve reliability
Differential mode noise: Noise voltages which can be measured between the “supply” and “return” lines at either the input or the output of a power converter
Dynamic load: A load that changes from one level to another on a periodic or random basis
Efficiency: The ratio of total output power to total input power, normally expressed as a percentage
EMC (Electro-Magnetic Compatibility): Refers to electromagnetic interaction between power converters and their loads/input supplies. Includes conducted and radiated effects. Most applications require that these effects be reduced to insignificant levels, conforming to internationally agreed technical standards
EMC filter: A filter circuit designed to control conducted EMI and to enable conformance with EMC requirements
EMI (Electro-Magnetic Interference): Also called radio frequency interference (RFI). EMI is unwanted conducted or radiated emissions from a power converter which leads to unacceptable interactions with load or input supply circuits
ESS (Environmental Stress Screening): A test process, which subjects new power converters to thermal or mechanical stresses to precipitate the occurrence of early failure due to manufacturing defects. See Burn-in
Filter: A frequency sensitive network, consisting normally of inductors and capacitors, that attenuates noise and ripple components of a DC rectified output, or EMI components which might affect an input supply
Flyback converter: A switching power converter using a single semiconductor switch in conjunction with an inductor or transformer. Operates by storing energy during the switch conduction time and releasing it when the switch is not conducting
Forward converter: A switching power converter using a single semiconductor switch in conjunction with a transformer. Operates by passing energy to the load during the switch conduction time
Full bridge converter: A switching (forward) power converter using 4 semiconductor switches configured as a bridge circuit. Operates by commutating an input DC supply to produce an AC drive voltage, with a peak-to-peak value equal to twice the DC supply voltage, to the primary of a transformer
Full wave rectifier: 2-diode or 4-diode rectifier circuit that permits utilisation of the positive and negative half-cycles of an AC voltage
Flashover: An arc discharge through air around or over the surface of insulating materials, between parts at different potential or voltage. See Arc discharge
Half bridge converter: A switching (forward) power converter using 2 semiconductor switches in conjunction with 2 capacitors or 2 diodes. Operates by commutating an input DC supply to produce an AC drive voltage, with a peak-to-peak value equal to the DC voltage, to the primary of a transformer
Half wave rectifier: Single diode rectifier circuit that permits utilisation of only positive OR only negative half-cycles of an AC voltage
Harmonic distortion: The presence of any unwanted frequencies which are harmonically related to the intended fundamental frequency in an AC voltage or current
Holdup time: The time for which a power converter’s output voltage can be maintained following the loss or removal of input power. Usually achieved using energy stored in capacitors. See Battery back-up
Input voltage range: The range of input supply voltage for which the power supply meets its specifications
Inrush current: The greater-than-normal surge of input current that occurs in off-line switching power converters at initial power-up. Caused by the charging of the input filter capacitors
Inverter: A power converter which changes DC input power into AC output power
Isolation: Electrical separation between two circuits, or circuit elements
Isolated converter: A power converter configured to isolate its prime supply from its output voltages, usually achieved using a transformer.
Load regulation: The change in output voltage due to the load current varying over its specified limits
Line voltage: RMS voltage of the AC prime supply used to power an off-line converter
Line regulation: The change in output voltage due to the input voltage varying over
its specified limits
Linear regulator: A form of voltage regulator where a dissipative active device such as a transistor is placed in series or parallel with the load. See Series regulator, Shunt regulator
Mains supply: Any prime supply which comes directly from the available power utility supply network e.g. 220V 50Hz in Europe, 110V 60Hz in the US
Multiple output supply: A power supply that delivers two or more output voltages
Noise: Noise is any unwanted periodic or random deviation in the output voltage (or the supply current) of a power converter. See Ripple
Non-isolated converter: A power converter designed with a direct connection between its prime supply and its output voltages.
Off-line converter: Generic term for any power converter taking its input power directly from the utility (mains) supply network
Overshoot: The amount by which an output exceeds its intended value at initial power-up or in response to a step change in load or input voltage
PARD (Periodic and Random Deviation): The total variation in the output of a power supply encompassing, ripple, load and line regulation, temperature coefficient and stability. Sometimes used to specify power supply performance instead of individually specifying the parameters concerned.
Polarity: Defines whether the output voltage of a DC power supply is “positive” or “negative” going with respect to its return
Post regulator: An additional voltage regulator circuit, usually a linear regulator, that provides improved regulation performance for the output(s) of a power converter
Power factor: Conventionally taken to be the ratio of actual power (watts) to the apparent power (VA product) in an AC circuit. When related to power converters, power factor is used as a measure of the extent to which AC input supply currents are maintained in phase with the supply voltage. Power factor of 1 means that input supply current and voltage are exactly in phase and of the same form.
Power factor correction: Any power converter technique which ensures that the current drawn by an AC-input converter from its input supply, is always in phase with the supply voltage and of the same form, normally sinusoidal
Power converter: Electronic circuit designed to change electrical power from one
form into another e.g AC-to-DC, low voltage to high voltage etc
Power density: Indicative “figure of merit” relating the total power output capability of
a power converter to its packaged volume, often in watts per cubic inch. Can provide
an easy comparison between power converters of similar capability but can be very
misleading if used to compare units whose capabilities are very different.
Power conditioner: Another term for power converter
Power supply: Another term for power converter
Pre regulator: An additional voltage regulator circuit that provides a controlled input supply to a power converter. Used where the regulation performance of the basic power converter is inadequate for the application
Prime supply: The input supply, of any form, which provides power to the converter, and from which all other voltages are derived
PWM (Pulse Width Modulation): A control technique for switching power converters where the conduction time (pulse width) of the semiconductor switches is modulated to control power transfer and thus regulate output voltage(s)
Push pull converter: A switching (forward) power converter using 2 semiconductor switches to alternately drive the opposing primaries of a centre-tapped transformer
Ratings: Specified values delineating the absolute maximum capabilities of a power converter
Rated output current: The maximum continuous load current a power supply is designed to provide
Rated supply voltage: The range of input supply over which a power converter is
designed to operate
Rated power: The maximum continuous output (or input) power a power converter is designed to supply
Rectifier: Circuit using semiconductor diodes to change an alternating (AC) current into a direct (DC) current
Regulation: 1. The control of power converter output voltage(s). 2. Changes in output voltage due to changes in input supply or load. See Line regulation, Load regulation
Remote sensing: A technique for monitoring the output voltage of a power converter at the load rather than at the output terminals. Improves regulation by compensating for voltage drops in the wiring between the power converter and the load
Renewable energy sources: Prime power sources generated using environmentally acceptable processes e.g wind turbines, solar cell arrays, wave power generators, fuel cells etc
Resonant converter: A switching converter whose operating frequency is not fixed but is controlled by the natural zero-crossings of voltage or current taking place in its power circuit. The technique eliminates much of the switching loss associated with fixed-frequency converters by enabling switching at either near-zero voltage or near-zero current
Ripple: Any periodic AC component present in the output of a DC power supply which is related either to the input AC supply or to switching frequencies within the power supply itself. See Noise
RFI (Radio Frequency Interference): Another term for EMI
Semi regulated output: An output from a multiple output power supply that is not regulated by closed loop control although it is subject to the effect of closed loop control acting on another output
Series regulator: A linear regulator in which the active control element (transistor) is connected in series with the load. Regulation is achieved by the control element sustaining a voltage whilst carrying the load current and results in dissipation
Short circuit: A direct connection that provides an almost zero resistance path for current
Short circuit protection: Circuit feature that limits the output current of a power supply to prevent damage when loaded with a short circuit
Shunt regulator: A linear regulator in which the active control element (transistor) is in parallel with the load. Regulation is achieved by the control element sinking a current whilst carrying the load voltage and results in dissipation
Soft-start: Circuit features which gradually increase the power output from a converter when it is powered-up. Minimises stresses on the power circuit components by eliminating uncontrolled voltage or current surges.
Stability: The change in output voltage of a power supply over a specific period of time, following a warm up period, with all other operating parameters held constant
Static inverter: A power converter designed specifically to produce an AC output meeting the specifications for utility line supplies e.g 240V 50Hz in Europe or 110V 60Hz in the USA. Input supplies normally derived from renewable energy sources
Switching regulator: A regulator utilising semiconductor switches which open and close as necessary to regulate power output and thus control the voltage across a load
Switching converter: Generic term for any form of power converter which achieves power transfer and regulation using semiconductor switches alternating between full conduction and full blocking, normally at high frequency. The technique eliminates much of the (dissipative) loss associated with linear regulation and enables physical shrinkage of transformers and filter components due to the high operating frequency.
Switch-mode converter: Another term for switching converter
Switching frequency: The rate at which a switching power converter or regulator operates its switches
Temperature coefficient: The sensitivity of output voltage to changes in the temperature of a power converter
Temperature range: The range of ambient (or mounting surface) temperatures over which a power converter will meet its specifications
Thermal protection: A protective feature that shuts down a power supply if its internal temperature exceeds a predetermined limit
Topology: The classification of circuit configurations of power converters into clearly identifiable and characteristic types, usually based on the way the power circuit switching semiconductors and magnetic components are connected. Examples of circuit topologies are Flyback, Push-Pull, Half-Bridge etc
Tracking: A specified relationship between the outputs of a multiple-output power converter where any changes due to line, load, temperature (or other parameters) are proportional across all outputs
Transformer: The key magnetic component in most power converters. Consists of a magnetic “core” wound with 2 or more “windings”. An AC voltage applied to the “primary” (input) winding will cause an alternating flux swing in the core which will induce AC voltages in the “secondary” (output) windings, all in proportion to the number of turns in the respective windings. Thus a transformer is the fundamental voltage-changing element in most power converters
Transient: A temporary and brief change in a given parameter. Typically associated with input voltage or output loading parameters
Transient recovery time: The time interval between a step change in the loading or supply conditions for a power converter to the time when the outputs return to within specification
Transient response: Specifications defining a power converter’s behaviour during and following a transient. See Transient recovery time, Overshoot, Undershoot
Undershoot: The amount by which an output falls short of its intended value at initial power-up or in response to a step change in load or input voltage
Universal input: Term describing a power converter designed to operate from any available AC mains supply, worldwide, without user adjustment or settings
UPS (Uninterruptible Power Supply): A power converter designed to supply output power in the event of temporary loss of AC line power. Usually configured as battery-backed off-line converters with integrated battery charging circuits and automatic changeover between off-line and battery-backed operation
Voltage-fed: Term applied to power circuits where the power being switched is at a constant voltage, such as across the terminals of a capacitor
Voltage mode control: Power converter regulation technique based only on monitoring and control of output voltage
Zero current switching (ZCS): The synchronising of the operation of semiconductor switches in (resonant) power converters with the natural zero-crossing of the current flowing in the converter’s power circuit. Results in near-lossless switching, permitting increases in switching frequency required to enable reduction in transformer and filter component sizes. This facilitates the design of high efficiency power converters with very high package power density
Zero-voltage switching (ZVS): Similar to ZCS, but using the voltage zero-crossings in the power circuit to synchronise the switches
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