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Glossary

AC
Alternating Current
 
A
AMPERE
This unit indicates the rating of an electric current. One ampere is the current, which is produced by a potential difference between lines of one Volt at a Resistance of one Ohm.
 
AMPERE-HOUR (Ah)
A current flow of one Ampere during one period of one hour.
 
CONSTANT CURRENT LIMITING CIRCUIT
Current-limiting circuit that holds output current at some maximum value whenever an overload of any magnitude is experienced.
 
CONSTANT CURRENT POWER SUPPLY
A power supply that regulates its output current, within specified limits, against changes in line, load, ambient temperature, and time.
 
CROSS REGULATION
In a multiple output power supply, the percent voltage change at one output caused by the load change on another output.
 
CROWBAR
an electrical circuit used to prevent an overvoltage condition, by putting a short circuit or low resistance path across the voltage source.
 
CSA
Canadian Standards Association.
An independent Canadian organization concerned with testing for public safety.
 
CURRENT LIMITING
An output protection feature which limits the output current to a predetermined value in order to prevent damage to the power supply or the load under overload conditions. The supply is automatically restored to normal operation following removal of the overload.
 
DC
Direct Current

 

DERATING
The specified reduction in an operating parameter to improve reliability. Generally for power supplies, it is the reduction in output power at elevated temperatures.
 
DRIFT
The change in output voltage of a power supply over a specified period of time, following a warm-up period, with all other operating parameters such as line, load, and ambient temperature held constant.
 
DYNAMIC LOAD REGULATION
See Output Impedance.
 
EFFICIENCY
The ratio of output power to input power. It is generally measured at full-load and nominal line conditions. In multiple output switching power supplies, efficiency can be a function of total output power and its division among the outputs.

 

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.
 
FUNCTION MANAGER
The function manager is a feature which provides the opportunity to let a power supply run automated sequences in a function according to DU/Dt. The user just has to define steps, also called points, by set values for voltage, current and time. The resulting function is run by the device and result in ramps of the output voltage between two steps (if the set value changes) and the given time.

 

HI-POT TEST
High Potential Test. A test to determine if the breakdown voltage of a transformer or power supply exceeds the minimum requirement. It is performed by applying a high voltage between the two isolated test points.
 
HOLD-UP TIME
The time during which a power supplies output voltage remains within specification following the loss of input power.
 
HYBRID TECHNOLOGY
The use of ceramic based substrates to support and interconnect components in power supplies. Resistors and interconnections are screen printed on the substrate using various inks. These are then fixed (fired) in place by a high temperature process.
 
I
Current
 
INPUT LINE FILTER
A low-pass or band-reject filter at the input of a power supply which reduces line noise fed to the supply. This filter may be external to the power supply.
 
INPUT VOLTAGE RANGE
The high and low input voltage limits within which a power supply or DC/DC converter meets its specifications.
 
INRUSH CURRENT
The peak instantaneous input current drawn by a power supply at turn-on.
 
INRUSH CURRENT LIMITING
A circuit which limits the inrush current during turn-on of a power supply.
 
INVERTER
A power converter which changes DC input power into AC output power.
 
ISOLATION
The electrical separation between input and output of a power supply by means of the power transformer.
 
ISOLATION VOLTAGE
The maximum AC or DC voltage which may be continuously applied from input to output and/or chassis of a power supply.

 

LEAKAGE CURRENT
Current flowing between the output buses and chassis ground due to imperfections in electronic components and designs. It must be tightly controlled to satisfy safety regulations such as UL and VDE.
 
LINE REGULATION
The variation of an output voltage due to a change in the input voltage, with all other factors held constant. Line regulation is expressed as the maximum percentage change in output voltage as the input voltage is varied over its specified range.
 
LOAD REGULATION
Variation of the output voltage due to a change in the outputs load from no load to full load, with all other factors held constant. It is expressed as a percent of the nominal DC output voltage.

 

MOSFET
Metal Oxide Semiconductor Field Effect Transistor. The device of choice for the main switch in switched mode power supplies having much better switching characteristics than Bipolar Transistors.
 
MTBF
Mean Time between Failure. The failure rate of a power supply, expressed in hours, established by the actual operation or calculation from a known standard. 

 

NOISE
Noise is the aperiodic, random component of undesired devitions in output voltage. Usually specified in combination with ripple.
 
NOMINAL VALUE
The stated or objective value for a quantity, such as output voltage, which may not be the actual value measured.

 

OCP
Overcurrent Protection
A feature that indicates the exceedance of an (usually) adjustable current threshold, which switches the DC output off, contrary to the constant current limitation which only limits the output current to the adjusted value.

 

OPERATION TEMPERATURE
The still-air temperature in the immediate vicinity of a power supply, measured a minimum of 4 inches (100 mm) from the supply.
 
OPP
Overpower Protection
A feature that limits the output or input power of a device to a fixed or adjustable value. This limitation is additionally to voltage or current limitation. If signalized on the device, it is usually described as “CP” (constant power).
 
OTP
Overtemperature Protection
This is an alarm condition, which indicates overheating of a device. In this condition the power stages are deactivated temporarily and it will continue to work (usually) automatically after cooling down. Then the alarm indication will be erased.
 
OUTPUT CURRENT LIMITING
An output protection feature which limits the output current to a predetermined value in order to prevent damage to the power supply or the load under overload conditions. The supply is automatically restored to normal operation following removal of the overload.
 
OUTPUT IMPEDANCE
The ratio of change in output voltage to change in load current.
 
OUTPUT VOLTAGE
The nominal value of the DC voltage at the output terminals of a power supply.
 
OUTPUT VOLTAGE ACCURACY
For a fixed output supply, the tolerance in percent of the output voltage with respect to its nominal value under all minimum or maximum conditions.
 
OVERLOAD PROTECTION
An output protection feature which limits the output current of a power supply under overload conditions so that it will not be damaged.
 
OVERSHOOT
A transient change in output voltage, in excess of specified output accuracy limits, which can occur when a power supply is turned on or off, or when there is a step change in line or load.
 
OVP
Overvoltage Protection
A feature that indicates the exceedance of an (usually) adjustable voltage threshold, which always switches the DC output off,.in order to protect an application from dangerous voltage.

 

PARALLEL OPERATION
The connection of the outputs of two or more power supplies of the same output voltage to obtain a higher output current than from either supply alone. This requires power supplies specifically designed to share the load.
 
PF
Power Fail
A feature which indicates the defect of the AC input part of a device or the condition of over- or undervoltage of AC mains input: During this condition the power output resp. input is shut off.
 
P.F.C.
POWER FACTOR CORRECTION
Standard AC/DC converters draw line current in pulses around the peaks in line voltage. This may be undesirable for several reasons. PFC circuits ensure that the line current is drawn sinusoidal and in phase with the sinusoidal line voltage.
 
PI FILTER
A commonly used filter at the input of a switching supply or DC/DC converter to reduce reflected ripple current. The filter usually consists of two parallel capacitors and a series inductance and is generally built into the supply.
 
POST REGULATION
A linear regulator used on the output of a switching power supply to improve line and load regulation and reduce output ripple voltage.
 
POWER FOLDBACK
A power supply feature whereby the input power is reduced to a low value under output overload conditions.
 
PRE-REGULATION
The regulation at the front-end of a power supply, generally by a type of switching regulator; this is followed by output regulation, usually by a linear type regulator.
 
RATED OUTPUT CURRENT
The maximum load current which a power supply was designed to provide at a specified ambient temperature.
 
REFLECTED RIPPLE CURRENT
The AC current generated at the input of a power supply or DC/DC converter by the switching operation of the converter, stated as peak-to-peak or RMS.
 
REMOTE SENSING
A technique of regulating the output voltage of a power supply at the load by means of sensing leads which go from the load back to the regulator. This compensates for voltage drops in the load leads.
 
RESOLUTION
For an adjustable supply, the smallest change in output voltage that can be realized by the adjustment.
 
REVERSE VOLTAGE PROTECTION
A feature which protects a power supply against a reverse voltage applied at the input or output terminals.
 
RIPPLE AND NOISE
The magnitude of AC voltage on the output of a power supply, expressed in millivolts peak-to-peak or RMS, at a specified band width. This is the result of feed through of the rectified line frequency, internal switching transients and other random noise.
 
STAND-BY-FUNCTION
The Power Supply can be switched on and off by the key “Stand-by”. By using it the power output of the previously set phase position will be activated or inactivated.
 
TEMPERATURE COEFFICIENT
The average percent change in output voltage per degree centigrade change in ambient temperature over a specified temperature range.
 
TEMPERATURE RANGE, OPERATING
The range of ambient or case temperatures within which a power supply may be safely operated and meet its specifications.
 
THD
Total Harmonic Distortion
Is a measurement of the Harmonic Distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. THD is used to characterize the power quality of electric power systems.
 
TRACKING
A characteristic of a dual or other multiple output power supply whereby one or more outputs follow another output with changes in line, load and temperature, so that each maintains the same proportional output voltage, within specified tracking tolerance, with respect to common.
 
TRANSIENT RECOVERY TIME
The time required for the output voltage of a power supply to settle within specified output accuracy limits following a step change in output load current or a step change in input voltage.
 
U
Voltage

 

U.L.
Underwriters Laboratories Incorporated.
An independent, non-profit U.S. organization that tests products for safety.
 
UNDERSHOOT
A transient change in output voltage, below output accuracy limits, which can occur when a power supply is turned on or off, or when there is a step change in line or load.
 
UPS
Uninterruptible Power Supply.
A power supply which continues to supply power during a loss of AC input power. This is accomplished by means of a back-up battery and a DC/AC inverter or DC/DC converter. 
 
V
Voltage

 

VDE
Verband Deutscher Elektrotechniker.
A German organization which tests equipment for public safety and emitted noise.

 

WARM-UP TIME
The time required, after initial turn-on, for a power supply to meet its performance specifications.

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