| A |
TOP |
| Absolute
Maximum Ratings |
Specifications
that, if exceeded, could cause permanent damage to the converter. These
are not continuous ratings, and proper operation is not implied. |
| AC
Front-end |
That
part of a distributed power system that converts the AC line voltage to a
semiregulated DC voltage level. Typically, the AC front-end will provide
power factor correction and a universal (~85VAC to 265VAC) AC input. the
output of an AC front-end is normally 350VDC to 400VDC. See Power
Factor Correction. |
| Aging |
Operating
a converter under controlled conditions for a predetermined time in order
to screen out failures. See Burn-in. |
| Ambient
Air |
An
operating environment in which the air surrounding a power system has
sufficient mass and flow to prevent heat regeneration and subsequent
thermal runaway because of the heat dissipated by the power modules. |
| Amplifier |
See Error Amplifier. |
| Apparent
Power |
The
product of input RMS voltage times input RMS current. In AC input,
switch-mode power systems, where the input current is distorted, high RMS
values result in high apparent power.
|
| B |
TOP |
| BABT |
(British Approvals Board for Telecommunications)
An independent
organization that has approval authority for telecommunications equipment
sold into the UK market. BABT grants approvals and accredits testing
laboratories. |
| Back
Ripple Current |
See Reflected Ripple Current. |
| Balun
Filter |
A type
of input line filter often used within power systems/converters that
includes a differential wound transformer. Balun filters present a low
impedance to differential mode signals and a high impedance to common mode
signals. |
| Base
Plate |
A
substrate to which circuit components are mounted or, a metal plate to
which the power converter is attached. Normally used to draw heat away
from critical circuit components. See Heat Sink. |
| Base
Plate Temperature |
See Case Temperature. |
| Battery
Backup |
A
subsystem for electronic equipment that provides power in the event of
input power loss. Battery backed systems are a common application area for
DC/DC converters and UPS (uninterruptible power supplies). |
| Bead |
A
small ferrite core typically used in the construction of high frequency
inductors. |
| Bench
Power Supply |
A
cased power supply that includes displays and controls that can be used to
precisely adjust the operating characteristics to fit a particular
application. Typically an AC input device, bench supplies are often
referred to as laboratory supplies. |
| Bleeder
Resistor |
A
resistor added to a circuit to provide a path for current drain. Typically
used to insure capacitors discharge when a circuit is turned off. Bleeder
resistors are often used in AC-input filter circuits. |
| Bobbin |
A
component used in the winding of transformers and inductors. The bobbin
provides a physical frame that supports the transformer/inductor windings.
Fabricated from nonconductive materials, the bobbin also keeps the
windings isolated from the core. |
| Boost
Regulator |
A
basic switching converter topology in which an input inductor is used to
store energy. This energy is transferred to the output when the shunt
switch is turned off. The boost regulator will take an unregulated input
voltage, and produce a higher, regulated output voltage. See Buck Regulator, Bridge Converter,
Flyback Converter,
Forward Converter,
Push-Pull Converter, and
Resonant Converter. |
| Booster |
See Slave. |
| Breakdown
Voltage |
The
maximum AC or DC voltage that can be applied from the input to output (or
chassis) or output to output of a power converter without causing damage. |
| Bridge
Converter |
A
switching converter topology that employs four switching elements (full
bridge) or two switching elements (half bridge). This topology is more
often used in off-line supplies than DC/DC converters. Bridge converters
provide high output power and low ripple, but are significantly more
complex than other types of converter topologies and thus are more
expensive and prone to failure. See Boost Regulator, Buck
Regulator, Flyback Converter, Forward Converter, Push-Pull
Converter, and Resonant Converter. |
| Brown-out |
A
reduction or sag in the AC power line. AC input power systems must be
protected against input line sags (by extended input ranges or hold-up
time) to avoid inadvertent shutdown. |
| Brute
Force Supply |
A very
basic power supply that provides an output that is unfiltered and
unregulated. |
| B.S.I. |
(British Standards Institution)
An organization that develops standards
and test products/systems for compliance. An organization associated with
B.S.I. called Technical Help to Exporters (T.H.E.) provides reference
material on world wide standards. |
| Buck
Regulator |
A
basic switching converter topology, in which a series switch chops the
input voltage and applies the pulses to an averaging LC filter. The buck
regulator will only produce an output voltage that is lower than the input
voltage level. See Boost Regulator, Bridge Converter, Flyback
Converter, Forward Converter, Push-Pull Converter, and Resonant
Converter. |
| Buck-Boost
Converter |
See Flyback
Converter. |
| Buck-Derived
Converter |
See Forward
Converter. |
| Burn-in |
The
operation of newly manufactured power converters for a period of time
prior to shipment. The intent is to stabilize the converter and eliminate
infant mortality by aging the device. The time period and conditions
(input power cycling, load switching, temperature, etc.) will vary from
vendor to vendor. However, the less stringent the conditions, the less
likely it is that potential problems will be caught by the vendor. |
| Bus |
The
primary conductor path (wires, cables, etc.) used for routing power to
various components within a (sub)system.
|
| C |
TOP |
| CSA |
(Canadian Standards Association)
An independent organization that
establishes and tests safety standards for electronic components and
systems for the Canadian marketplace. |
| Case |
See Enclosure. |
| Case
Temperature |
The
temperature of the case when the converter (and surrounding system) are
operating normally. Often used as a specification for DC/DC converters
with extended temperature ranges, case temperature is at times referred to
as base plate temperature. |
| CEN/CENELEC |
(Comite pour European de Normalisation Electronic (European Commitee for
Electrotechnical Standardization)) A technical committee that recommends
standards for adoption by the European Community (EC). These standards
(referred to in the applicable EC directive issued by the committee) cover
EMI/RFI interference, intrinsic safety, immunity, etc. |
| Central
Power System |
A
system in which all power supply components are contained in one box (or
on one card). Typically, this type of system consists of a medium/high
power switching power supply that takes an AC input and provides multiple,
regulated DC outputs. The DC outputs are then used around the system (via
a wiring harness or back-plane) to provide power to various system
components. |
| CFM |
(Cubic
Feet per Minute) A measure of the volume of air flowing in a system. See LFM. |
| Channel |
An
isolated output section of a power system. A channel may consist of one or
more outputs. |
| Chassis |
See Enclosure. |
| Chassis
Ground |
The
voltage potential of the chassis or enclosure surrounding a power system. |
| Circulating
Current |
See Ground Loop. |
| Clearance
Distance |
The
shortest distance (through air) separating two conductors or circuit components.
See Creepage Distance. |
| Clock |
Timing
pulses used within a system or circuit to synchronize the operation of
components. In a power converter, these pulses are generated by the pulse width modulation
(PWM) chips. |
| Common |
A
conductive path used as a return for two or more circuits. Common is often
used interchangeably with ground, which is not technically correct unless
it is connected to earth. See Ground. |
| Common
Mode Noise |
Noise
component common to both power system output and return lines with respect
to input common. |
| Compliance
Voltage |
The DC
output voltage of a constant current power converter. |
| Conduction
Cooling |
The
transfer of heat through a solid material. Used to cool a power converter
by adding a heat sink or attaching the module to the system chassis. This
effectively increases the module case surface area, lowering the case
thermal resistance. Thermal resistance is proportional to the resistivity
and length of a material and inversely proportional to its surface area. See Cooling,
Convection Cooling,
Free Convection
and Forced Air Cooling. |
| Constant
Current |
A
power converter that regulates its output current to within a specified
range regardless of changes in output load, input line and ambient
temperature. |
| Constant
Voltage |
A
power converter that regulates its output voltage to within a specified
range regardless of changes in output load, input line and ambient
temperature. |
| Continuous
Shield |
See Six-Sided Shielding. |
| Convection
Cooling |
The
transfer of heat via a fluid motion (typically air). In distributed power
systems this is accomplished by the movement of air over the module or
heatsink surface. See Cooling,
Conduction Cooling, Free
Convection and Forced Air Cooling. |
| Converter
(DC/DC) |
A
device that accepts a DC input voltage and produces a DC output voltage.
Typically the output produced is at a different voltage level than the
input. However, converters sometimes have the same input/output, and are
used to provide isolation, power bus regulation, ground loops elimination,
etc. |
| Cooling |
The
transfer of heat from a power system into the ambient air mass surrounding
the system. See Convection Cooling, Conduction Cooling, Free
Convection and Forced Air Cooling. |
| Creepage
Distance |
The
shortest distance between two conductors (typically, one primary, one
secondary). |
| Crest
Factor |
The
ratio of peak to RMS value of an AC waveform. For a pure sinusoidal
waveform, this value is 1.414. Crest factor was once used to approximate the
current stress in an AC mains circuit. Today, the use of power factor is
more common. See Power Factor. |
| Crest
Value |
The
maximum value of a waveform (excluding transients). |
| Cross
Regulation |
For a
multiple output power converter, the change in voltage on one output
(expressed as a percent) caused by a load change on another output. |
| Crowbar |
A
circuit that crowbars or rapidly shuts down a power converter's output if
a preset voltage level is exceeded. The circuit places a low resistance
shunt across the output when an overvoltage condition exists. (For
non-isolated converters with a crowbar output over voltage protection
circuit, a fuse must always be used in the input lines.) |
| Cuk
Converter |
A
variation of the "buck-boost" converter that produces very low
output ripple. Used primarily in applications that do not require input to
output isolation. See Flyback Converter. |
| Current
Foldback |
See Foldback Current Limiting. |
| Current
Limiting |
A
feature that protects the power converter (or load) from damage under
overload conditions. The maximum power converter output current is
automatically limited to a predetermined, safe value. If the converter is
specified for auto restart, normal operation is automatically restored
when the overload condition is removed. See Foldback Current Limiting
and Current Limit Knee. |
| Current
Limit Knee |
On a
plot of output voltage vs. current, the point at which current begins to
limit or foldback. See Current Limiting
and Foldback Current Limiting. |
| Current
Mode Control |
A
control method used with switching converter topologies. A dual loop
control circuit--a current loop within a voltage loop--adjusts the PWM operation in response to a measured output
current and output voltage. |
| Current
Sharing |
Multiple
power converters are often connected redundantly (to increase system
reliability) or in parallel (to increase system power). When connected in
this way, their outputs are strapped together and each power converter
supplies approximately an equal "share" of the load current.
Current sharing can be achieved with
external passive circuits (by synchronizing multiple converters and
trimming their outputs to within a tight error band) or active circuits
(converters that feature internal circuits to monitor and adjust output
load current). The most popular redundant topology is the "N+1"
circuit. See Master/Slave Operation,
N+1
and Dual-Redundant.
|
| D |
TOP |
| dB |
(Decibel)
Logarithmic
gain unit. Derived by the
equation: dB = 20 Log (V2/V1) |
| DC/DC
Converter |
See Converter (DC/DC). |
| Density |
See Power Density. |
| Derating |
For a
power converter, the specified reduction in output power required for
operation at elevated temperatures. The most common operating temperature
range specified for commercial grade converters is 0°C to +70°C without
derating. See Cooling, Convection Cooling, Conduction
Cooling, Free Convection and Forced Air Cooling. |
| Dielectric |
A
material used to prevent two points in an electrical circuit from becoming
conductively connected. Sometimes referred to as a dielectric barrier. |
| Dielectric
Strength Test |
See High Potential Test. |
| Dielectric
Withstand |
The
maximum voltage an insulating material can withstand before breaking down
(suffering punch through Voltage or arcing). See Breakdown
Voltage and High Potential Test. |
| Differential
Mode Noise |
The
noise component measured between two points with respect to a common point
(minus common mode noise). |
| Differential
Voltage |
The
difference in voltage levels measured at two points. The measurement is
made with respect to a common reference point. |
| Distributed
Power |
A
system level architecture in which power converters operating off an
intermediate power bus (i.e. 24 or 48 VDC) provide localized power (and
various voltage levels) to individual subassemblies and/or
components. The type of power distribution system used is highly dependent
upon the needs of a particular application. |
| Drift |
The
change in the output voltage of a power converter over a specified period
of time. All other operating parameters (load, line, etc.) are assumed to
be held constant. Often specified as starting after a warm-up period. |
| Driver |
See Master. |
| Dual-Redundant |
A
topology that provides full power system redundancy. Sometimes referred to
as a "100% redundant" system, the circuit consists of two
complete power systems connected in parallel to the load. One system
supplies all the load current, while the second power system runs
"cool" (disconnected from the load via oring diodes). If the
"hot" power system fails, the oring diodes forward bias and the
second power system starts to supply full load current. While expensive,
the dual redundant system allows separate input power sources to be used.
See Master/Slave Operation
and N+1. |
| Duty
Cycle |
The
ratio of "on" time to "off" time for an electronic
component or signal. In a power system duty cycle is typically used in
reference to the semiconductor switch (in PWM controlled systems) or clock
signal. |
| Dynamic
Load |
An
output load that changes rapidly. Normally specified as a load change
value as well as a rate of change. |
Dynamic
Response
(Transient Response) |
The
output overshoot/undershoot that occurs when the output load of a power converter is
turned on/off or abruptly changed. This overshoot/undershoot gives the high frequency
output impedance of the converter. See Output Impedance.
|
| E |
TOP |
| Efficiency |
The
ratio of total output power to input power expressed as a percentage.
Derived by the equation:
Efficiency(%) = (Output
Power / Input Power) * 100
Efficiency is normally measured at full
rated output power and nominal input line conditions at room temperature. |
| Electrolytic
Capacitor |
A type
of capacitor used in power converters that consists of two plates (or
electrodes) separated by an electrolyte. |
| Electrostatic
Shield |
See Faraday Shield. |
| EMI
- Conducted |
(Electromagnetic
interference) Noise generated by a power system (typically by the
switching action of the more popular power converter topologies) and
reflected back onto the input power bus. Acceptable limits for conducted
EMI are set by various agencies (FCC, VDE, etc.). Switch-mode power
converters typically include input filters to reduce noise to within
agency limits. |
| EMI
- Radiated |
(Electromagnetic
interference) Noise generated by a power system (typically by the
switching action of the more popular power converter topologies) and
emitted into the area surrounding a power system. Radiated EMI, consisting
of broadband radio frequencies and narrow band emissions is set by
various agencies (FCC, VDE, etc.) and is controlled by
shielding. |
| Enclosure |
The
case or container used to package a power converter. Often, power
converters are packaged in small plastic or metal cases that protect the
internal components from the outside environment; and also improve thermal
and noise performance. |
| Error
Amplifier |
An
operational or differential amplifier used in the control feedback loop of
a power converter. The amplifier produces an error voltage when the sensed
output (tapped off a voltage divider network) differs from a reference
voltage. This error voltage is used to adjust the operation of the PWM so
as to correct the sensed output voltage. Sometimes called a reference
amplifier. |
| ESD |
(Electrostatic
discharge) The current produced by two objects having a static
charge when they are brought close enough to produce an arc or discharge. |
| ESL |
(Equivalent
Series Inductance) The inductance in series with an
"ideal" capacitor. ESL sources could include terminals,
electrodes, etc. |
| ESR |
(Equivalent
Series Resistance) The resistance in series with an
"ideal" capacitor. ESR sources include lead resistance, terminal
losses, etc. ESR is an important specification for high frequency
applications.
|
| F |
TOP |
| Failure
Mode |
The
reason for which a converter either does not meet or stops meeting its
specified parameters. |
| Fan
Cooled |
See Forced
Air Cooling. |
| Faraday
Shield |
An
electrostatic shield that reduces coupling capacitance in transformers.
The shield, which reduces output common mode noise, is placed between the
primary and secondary windings of a transformer and connected to either
input or output common. |
| Fault
Mode Current |
The
input current drawn by a power converter when the output is shorted. |
| Fault
Tolerant |
A
power system configuration optimized for continuing operation without
shutdown. Typically involves the use of a redundant topology (i.e. N+1,
etc.) and the ability to remove and replace power modules without
disturbing system operation (hot-plug capability). Thus, the failure of
any one power module will not cause a system failure or shutdown. |
| FCC |
(Federal Communications Commission)
A US government agency that sets
standards for, and governs the testing of conducted and radiated
emissions. These are system level standards, but they are typically used
in specifying converters. See EMI - Conducted
and EMI - Radiated. |
| Feedback |
The
process of returning a portion of the output signal of a system to its
input. |
| Feed
Forward |
A
method of improving line regulation by directly sensing the input voltage
of the power converter. See Line Regulation. |
| Ferroresonant |
A
transformer in which part of the core is driven into saturation by a
resonant tank circuit. The output of the transformer, taken from the
saturated portion, is relatively immune to variations in input voltage.
Used in ferroresonant power converters. |
| Filter |
See Input Line Filter,
Balun Filter, Pi Filter
and Output Filter. |
| Flag
Signal |
An
alarm or status signal generated by a power system. Typical, would be a front
panel LED that indicates "Power Good." "Power On,"
"Overtemperature," etc. or output logic signals (normally TTL/CMOS
compatible). |
| Floating
Output |
A
converter output that is ungrounded and not referenced to another output.
Typically, floating outputs are fully isolated and may be referenced
positive or negative by the user. Outputs that are not floating share a
common return and as such, are referenced to one another. |
| Flyback
Converter |
The
off time (flyback) during which power is transferred to the output of the
primary switch. This
technique is cost effective because of the minimum number of components
required. See Boost Regulator, Buck Regulator, Bridge
Converter, Forward Converter, Push-Pull Converter and Resonant
Converter. |
| Foldback
Current Limiting |
A
power converter protection technique. The circuit is protected under
overload conditions by reducing the output current as the load approaches
short circuit. This minimizes internal power dissipation under short
circuit conditions. See Current Limiting and Current Limit Knee. |
| Forced
Air Cooling |
The
use of a fan (or other air moving equipment) within a (sub)system to move
air across heat producing components in order to reduce the ambient
temperature. See Convection Cooling, Free Convection and
Forced Convection. |
| Forced
Convection |
An
operating environment in which air movement induced by a fan, blower, etc.
is used to maintain power modules within operating limits. See Convection Cooling,
Free Convection, and Forced Air Cooling. |
| Forward
Converter |
Also
called a "Buck-Derived" converter, this topology, like the
flyback converter, typically uses a single transistor switch. Unlike the
flyback converter, energy is transferred to the transformer secondary
while the transistor switch is "on," and stored in an output
inductor. See Boost Regulator, Buck Regulator, Bridge
Converter, Flyback Converter, Push-Pull Converter and Resonant
Converter. |
| Free
Convection |
An
operating environment in which the natural movement of air (unassisted by
fans or blowers) is sufficient to maintain the power module within its
operating limits. Also called "natural convection." See Convection
Cooling, Forced Air Cooling and
Forced Convection. |
| Frequency
of Operation |
See Switching Frequency. |
| Full
Bridge Converter |
A
converter topology that typically operates as a forward converter but uses
a bridge circuit, consisting of four switching transistors, to drive the
transformer primary. See Bridge Converter. |
| Full
Load |
The
maximum value of output load specified for a converter under nominal operating conditions. |
| Full
Wave Rectifier |
A
circuit (bridged or center tapped) that rectifies both halves of an AC
waveform.
|
| G |
TOP |
| Galvanic
Isolation |
Two
circuits which have very high resistance (several gigaohms) are considered to be
"galvanically isolated" from each other. Galvanic isolation
(separation) is achieved by using a transformer, opto-coupler, etc. |
| Ground |
An
electrical connection that is made to earth (or to some conductor that is
connected to earth). A power converter "common" is not actually
ground unless it is somehow connected to earth. See Common. |
| Ground
Loop |
A
condition caused when two or more system components share a common
electrical ground line. A ground loop is unintentionally induced,
causing unwanted voltage levels. |
| Ground
Plane |
A
conductive layer on the printed circuit board upon which a power converter
is mounted that is at ground potential. Primarily used to shield system
components from possible RFI noise generated by the power converter.
|
| H |
TOP |
| Half
Bridge Converter |
A
converter topology that typically operates as a forward converter but uses
a bridge circuit, consisting of two switching transistors, to drive the
transformer primary. See Bridge Converter. |
| Half
Wave Rectifier |
A
single diode circuit that rectifies one-half of an AC waveform. |
| Harmonic
Distortion |
For
sinusoidal AC current waveforms, the distortion characterized by the
presence of multiple harmonics of the fundamental frequency. This
distortion is caused by the switching action of the power converter. |
| Heat
Flux |
The
flow rate of heat across or through a material. Typically given in units
of W/cm2. |
| Heat
Rise |
The
increase in component/subassembly temperature caused by self-heating or
heat absorption. |
| Heat
Sink |
A
metal plate, thermally conductive potting material, extrusion, case, etc. that is used to transfer heat away from
sensitive components and/or circuits. See Base Plate. |
| Heatsink
Temperature |
Average
temperature of a heatsink attached to a power system module during normal
operation. Typically, the heatsink temperature will be lower than the
baseplate (or case) temperature. |
| Hiccup
Mode |
An
operating mode triggered by an output fault condition (short-circuit) in
which the converter cycles on and off. The duty cycle of on time to off
time maintains the internal power dissipation at a safe level until the
fault condition is corrected. |
| High
Line |
The
maximum value of input line voltage specified for normal converter
operation. See also Low Line
and Input Voltage Range. |
| High
Potential Test |
(Hi-Pot
Test) A test used to determine whether a converter passes its minimum
breakdown isolation voltage specification. See Breakdown
Voltage. |
| Hold-Up
Capacitor |
A
capacitor added to the input of a distributed power system. This capacitor
is intended to "hold-up" or maintain the input voltage to the
power system in the event a fault causes a momentary loss of the input bus
voltage. |
| Hold-Up
Time |
The
period of time that a converter output will remain operating within
specification following the loss of input power. This is a more common
specification for AC/DC supplies. |
| Hot-Plug |
The
ability to insert or remove a power converter from a system while the
system is powered and operating. Power converters must be specifically
designed to allow this without disturbing other modules or subassemblies
connected to the system power bus. Often used in redundant power systems
to achieve fault tolerant operation. |
| Hot-Swap |
See Hot-Plug.
|
| I |
TOP |
| IEC |
(International
Electrotechnical Commission) An organization based in
Switzerland that sets standards for electronic products and components. IEC does not conduct any testing, however, their standards have been
adopted by many of the national safety/standards agencies. |
| Inhibit |
See Logic Inhibit/Enable. |
| Input
Current |
The
current drawn from the input power bus by a power converter when operating
under nominal conditions. |
| Input
Line Filter |
A
low-pass or band-reject filter on the power converter input (internal or
external) that attenuates noise introduced into the power bus from
the power converter. See Balun Filter and Pi Filter. |
| Input
Reflected Ripple Current |
The AC
component (typically generated by the switching circuit) measured at the
input of a power converter. Given as a peak on the power bus. See Balun Filter
and Pi Filter. |
| Input
Surge Current |
See Inrush Current. |
| Input
Transient |
A
spike or step change in the input line to a power converter. Input
transient protection circuits are used to shield sensitive components
(such as the MOV, high-voltage zener diode, etc.) from possible damage due to transients. |
| Input
Voltage Range |
The
minimum and maximum input voltage limits within which a power converter
will operate to specifications. Often given as a ratio of high line to low
line (i.e. a range of 9VDC to 18VDC is 2:1). |
| Inrush
Current |
The
maximum, instantaneous input current drawn by a power converter at turn
on. Also called input surge current. (Typically the charging current of
the input capacitance.) |
| Inrush
Current Limiter |
A
protection circuit that limits the current a power system draws at turn
on. |
| Insulation |
A
non-conductive material used to protect and separate electronic components
or circuits. |
| Insulation
Resistance |
The
resistance offered by an insulating material to current flow. |
| Internal
Power |
The
power dissipated (as heat) within the power converter during normal
operation. Primarily a function of the power handling capability and
efficiency of the power converter. Internal power dissipation is normally
given as a maximum specification that cannot be exceeded without risking
damage to the power converter. |
| Inverter |
A
power conversion circuit that converts DC power to AC power. |
| Isolated
Output |
See Floating Output. |
| Isolation |
The
electrical separation between the input and output of a power converter.
Normally determined by transformer characteristics and component spacing,
isolation is specified in values of resistance (typically megohms) and
capacitance (typically picofarads). |
| Isolation
Capacitance |
See Isolation. |
| Isolation
Resistance |
See Isolation. |
| Isolation
Voltage |
The
maximum voltage (AC or DC) that can be continuously applied between
isolated circuits without a break-down occurring. On converters, this is
normally specified as input-output or input-case isolation. Minimum
isolation voltage levels must be maintained to meet most safety
regulations. See Breakdown
Voltage, High Potential Test and
Isolation.
|
| L |
TOP |
| L-C
Filter |
A
low-pass input filter consisting of a series inductor and a parallel
capacitor (series and parallel being referenced to the input). Used in
power converters to reduce input reflected ripple current. |
| Leakage
Current |
The
current flowing from input to output or input to case of an isolated power
converter at a specified voltage level. |
| LFM |
(Linear
Feet per Minute) A measure of the velocity of air. Used in distributed
power systems to give the air flow over a baseplate or heatsink surface
area. LFM is equal to m/s multiplied by 196.8. |
| Life
Test |
A
reliability test in which a power system is operated (typically under
accelerated conditions) over some period of time in order to approximate
its life expectancy. |
| Line |
The
bus used to deliver power to the input (terminals, pins, etc.) of a power
converter. See Bus,
High Line,
Mains
and Low Line. |
| Line
Effect |
See Line
Regulation. |
| Line
Regulation |
The
percentage change in output voltage caused by varying the input voltage
over a specified range (with output load, temperature, etc. remaining
constant). |
| Line
Transient |
See Input Transient. |
| Line
Voltage |
The AC
input voltage (off the mains) to a power subsystem. |
| Linear
Regulation |
A
power supply regulation technique in which the regulating device
(typically a transistor) is placed in series or parallel with the load.
Voltage variations across the load are controlled by changing the
effective resistance of the regulating device to dissipate unused power.
See Series Regulator,
Shunt Regulator and Post Regulation. |
| Load |
The
electronic components or circuitry connected to the outputs pins of a
power system. The characteristics (resistance, reactance, etc.) of the
load determine the amount of power drawn from the power system. |
| Load
Decoupling |
The
placement of filter components (typically µF capacitors) at the power
terminals of the load in order to reduce noise. |
| Load
Regulation |
The
change in the output voltage of a power converter (expressed as a
percentage) caused by varying the output load over a specified range (with
input line, temperature, etc. remaining constant). |
| Load
Sharing |
See Current Sharing. |
| Local
Sensing |
Using
the output terminals of the power converter to provide feedback to voltage
regulation circuits. See Remote Sensing. |
| Logic
Inhibit/Enable |
A
signal (typically TTL/CMOS compatible) used to turn a power converter
output on/off. Also called a remote on/off. |
| Long
Term Stability |
The
change in output voltage of a power system over time with all other
factors (line, load, temp, etc.) remaining constant. Expressed as a
percent, the output change is primarily due to component aging. |
| Low
Line |
The
minimum value of input line voltage specified for normal converter
operation. See High Line and Input Voltage Range.
|
| M |
TOP |
| Mains |
The AC
power distribution lines provided by a power utility. |
| Margining |
Adjusting
the output of a power converter up and down (typically by 5%) to test
system performance. Generally used to verify the resilience of a system to
fluctuations in supply voltage. |
| Master |
The
intelligent power converter (or subsystem) in a master/slave connection.
Sometimes called a driver, the master power converter contains the
feedback loop for the power subsystem, and thus controls output
regulation. |
| Master/Slave
Operation |
The
connection of two or more power converters so one (master) controls the
operation of the others (slaves). Master/slave configurations are used to
provide higher output power, wider input voltage ranges, synchronized
operation, etc. |
| Maximum
Load |
The
highest amount of output load allowable under the continuous operating
specifications of a power converter. |
| Maximum
Operating Temperature |
The
maximum temperature at which a power converter will start and operate to
within specified operating parameters. Typically specified as either
ambient or case. |
| Mil-Specifications |
Standards
published by the US government that specify operating, test and
environmental standards for equipment to be used in military/aerospace
applications. |
| Minimum
Load |
The
minimum amount of output load required by a power converter to maintain
normal continuous operating specifications. Usually associated with PWM
(Pulse Width Modulation) controlled power converters. |
| Minimum
Operating Temperature |
The
minimum temperature at which a power converter will start and operate to
within specified operating parameters. Typically specified as either
ambient or case. |
| Module |
An
encapsulated power converter. |
| MTBF |
(Mean Time Between Failure
(MTBF)) A unit of measure, expressed in hours,
that gives the relative reliability of a converter. MTBF data is based
upon actual operating data (demonstrated) or derived per the conditions of
MIL-HDBK-217F (calculated). |
| MTTR |
(Mean
Time To Repair) For repairable power converters (encapsulated modules are
typically not repaired), the average time required to perform the repair
work.
|
| N |
TOP |
| N+1 |
A
power system topology used to achieve high reliability levels through
system redundancy. The circuit consists of a number of power converters
connected in parallel, sharing the power drawn by the system load. One
more power converter than is necessary to provide full load current is
used (i.e. for a 400W load, three 200W converters are used). Thus, if any
single power converter fails, the remaining modules will continue to
supply current to the load. See Master/Slave
Operation and Dual- Redundant. |
| N+x |
An
"N+1" redundant circuit in which more than one extra power
converter is used (i.e. N+2, N+3, ...N+x). |
| Natural
Convection |
See Free
Convection. |
| No
Load Voltage |
The
voltage level present at the output pins of a power converter when 0% load
is applied. |
| Noise |
Unwanted
variations in the power converter output that are unrelated to the
switching frequency. Normally called "Ripple and Noise" and
given as peak to peak value with a specified bandwidth. See EMI - Conducted,
EMI - Radiated,
Ripple and Noise
and Periodic And Random Deviation.
|
| Nominal
Value |
An
ideal value that is used as a reference point.
|
| O |
TOP |
| Off
Line Power Supply |
A
power supply (linear or switching) that operates directly off the AC line.
The input voltage is rectified and filtered prior to any isolation
transformer. |
| Open-Circuit
Voltage |
See No Load Voltage. |
| Operating
Temperature |
The
range of temperatures over which a power system can be operated safely to
within specified limits. Range normally specified as ambient, however, at
times case or baseplate temperature are also sued. |
| Oring
Diodes |
Diodes
that isolate a faulty power converter from the load and other power converters.
Typically, these diodes are used external of a
power converter. |
| Output
Current Limiting |
See Current
Limiting and Foldback Current Limiting. |
| Output
Filter |
A
low-pass filter (typically an L-C filter) inserted between the output
rectifiers and output pins that attenuates output noise. |
| Output
Impedance |
The
ratio of change in output voltage to a change in output load current. |
| Output
Ripple & Noise |
See Noise
and Periodic And Random Deviation. |
| Output
Voltage |
The
value of DC voltage measured at the output terminal of a power converter. |
| Output
Voltage Accuracy |
The
maximum allowable deviation the DC output of a converter from its ideal or
nominal value. Expressed as a percentage of output voltage. Often called
output voltage tolerance. |
| Output
Voltage Range |
The
minimum and maximum output voltage limits within which a power converter
will meet its operating specifications. |
| Overload
Protection |
See Current
Limiting and Foldback Current Limiting. |
| Overshoot |
A
transient change in output voltage that exceeds specified accuracy limits.
Typically occurs on converter turn on/off or with a step change in output
load or input line. |
| OVP |
(Overvoltage
Protection) A feature on select power converters in which an
output monitoring circuit is activated if a preset voltage level is
exceeded. Depending on the type of circuit used, the OVP will shut the
converter down, "crowbar" the faulty output or switch the
converter to a different operating mode.
|
| P |
TOP |
| Parallel
Operation |
A
power system topology used to achieve high output levels. In a parallel
circuit, the output currents of two or more power converters are summed
together into a single load, providing a higher level of output power than
that available from a single converter. Parallel operation requires power
converters specifically designed to share loads. Although parallel
operation is an integral part of a redundant circuit; power system
redundancy is not necessarily achieved through a simple parallel
connection. See Redundant Operation. |
| PARD |
(Periodic
And Random Deviation) The noise and ripple voltage that is superimposed
on the DC output of a power converter. Typically specified at full load,
it is expressed in peak-to-peak or RMS volts over a given bandwidth. |
| Pi
Filter |
An
input filter consisting of two capacitors connected in parallel with a
series inductance. Often used in power converters to reduce input
reflected ripple current. A Pi Filter resembles the Greek
letter p (Pi) where the horizontal line is the
inductor and the two vertical lines are the capacitors. |
| Polarity |
The
ability of a converter to produce an output that is positive or negative
as referenced to ground. See Floating Output. |
| Post
Regulation |
An
output circuit that sues a linear regulator to improve line/load
regulation and reduce ripple and noise. In PWM-controlled converters, post
regulation adds expense and degrades converter supply efficiency. |
| Power
Density |
The
ration of converter output power to converter volume. |
| Power
Factor |
In an
AC input power converter, the ratio of true input power to apparent input
power. In these circuits, power factor is a measure of the input current
that is in phase with the input voltage (and thus contributing to the
average power). |
| Power
Factor Correction |
(PFC)
In a AC power converter, a circuit that forces the AC input current to be
approximately in phase with the input voltage. This reduces the harmonic
distortion of the power system and increases the useful power drawn from
the mains. PFC circuits can be active or passive. See Power Factor. |
| Power
Fail |
A
signal (typically a TTL output) that indicates the DC input to the power
converter has failed. Gives some warning of an input power bus failure, so
the application can execute an orderly shutdown procedure during the
hold-up time of the power converter. |
| Power
Good |
A signal
(typically a visible LED) that indicates the DC output of the primary
channel of a power converter is still present. |
| Power
Rating |
The
specified power available at the converter output pins. |
| Primary
Circuit |
The
input side of an isolated DC/DC converter. See Secondary Circuit. |
| Pulse
Width Modulation |
(PWM)
A circuit used in converters to regulate output voltage. Regulation is
achieved by varying the conduction time of the transistor switches. |
| Push-Pull Converter |
A
converter topology that typically is configured as a forward converter but
uses two transistor switches and a center tapped transformer. The
transistor switches turn on and off alternately. See Boost Regulator,
Buck Regulator, Bridge Converter, Flyback Converter and
Resonant Converter.
|
| Q |
TOP |
| Quasi-Regulation |
Multiple
output power converters often have auxiliary outputs that are regulated
via the primary output (the primary output is controlled by a direct
feedback loop). The output voltage of the auxiliary is set by the turns
ratio of the isolation transformer. Sometimes referred to as
semi-regulation, quasi-regulated outputs are significantly affected by
changes in the primary output.
|
| R |
TOP |
| Radiation
Cooling |
The
transfer of heat between two materials at different temperature levels.
Radiant heat does not play a significant role in the cooling of
distributed power systems. |
| Rated
Output Current |
The
maximum output current that can be continuously drawn from a power
converter under specified conditions. |
| Redundant
Operation |
A
parallel configuration of converters used in distributed power system to
increase system reliability. Converters are typically configured in an
"N+1," dual redundant or master/master architecture. See Master/Slave
Operation,
Dual-Redundant and N+1. |
| Reflected
Ripple Current |
See Input Reflected Ripple Current. |
| Regulation |
The
ability of a power converter to maintain an output voltage to within
specified limits under varying conditions of input line and output load.
See Linear Regulation. |
| Regulatory
Agencies |
Organizations
(both independent and government supported) that develop specifications
and/or test power converters to specifications that define product
performance or intrinsic safety. |
| Remote
Sensing |
Using
sense leads connected at the output load to provide feedback to voltage
regulation circuits within a power converter. This arrangement is used to
compensate for voltage losses caused by long leads to a load. See Local Sensing. |
| Remote
Shutdown |
See Logic
Inhibit/Enable. |
| Resonant
Converter |
A
switching power converter technology in which a resonant tank circuit
operating at high frequencies is used to transfer energy to the
output. Typically found in higher power (>100W) DC/DC applications. |
| Return |
The
common terminal on the output of a power converter. It is the return
current path for the output. See Common. |
| Reverse
Current |
Maximum
input/output current a power converter will allow to pass. If the
input/output polarity is reversed, a catastrophic failure may occur unless
the converter is specifically designed for such conditions. See Reverse Voltage. |
| Reverse
Voltage |
A
power converter feature that prevents damage to internal components if a
reverse voltage is inadvertently applied to the input or output terminals. |
| Ripple
and Noise |
See Periodic
And Random Deviation. |
| Ripple
Voltage |
The
periodic AC component imposed on the output voltage of a power converter.
Normally expressed as part of "Ripple & Noise" and given as
a peak to peak value over a specified bandwidth. See Periodic
And Random Deviation. |
| Royer
Converter |
A
self-oscillating push-pull switching circuit configuration that is
commonly used in low-cost, low-power DC/DC converter designs. Also called
the Classic Converter.
|
| S |
TOP |
| Secondary
Circuit |
The
output side of an isolated power converter. See Primary Circuit. |
| Secondary
Outputs |
In a
multiple output power converter, the outputs that are not directly
controlled by the output feedback loop. These outputs are essentially line
regulated, with the output voltage being set by the turns ratio of the
isolation transformer. Also called auxiliary outputs. |
|
