Power Supply Terminology @
These definitions should be considered
relevant to a SMPS, and may not apply identically to other technical areas.
While definitions already available in other
publications (standards, dictionaries, manufacturer's data books, technical
notes, manuals) were considered, the following terminology represents the
personal view of the author, and might be slightly different from what a
particular user of this document may be used to.
- Absolute Maximum Ratings,
- Specifications which, if exceeded,
could cause permanent damage to the component. These are not
continuous ratings, and proper operation is not implied.
- For a magnetic core with a given
geometry, is the magnetic cross-sectional area of a hypothetical
toroidal core of the same material that will be the magnetic
equivalent to the given core.
- Ambient Temperature (1):
- The temperature of the objects and
of the still air surrounding the SMPS, measured at a minimum of 4"
(100mm) from the supply.
- Ambient Temperature (2):
- According to MIL-STD-810E: The
test unit shall be surrounded by an envelope of air, except at
necessary support points. The gradient throughout this envelope
shall be within 2°C of the test temperature and shall not exceed
1°C per meter.
- Ampere Turns (NI):
- The product of current flowing in
a winding times number of turns.
- Acceptance Test Procedure.
- The British Approvals Board for
Telecommunications. An independent organization that approves
telecom equipment for UK market. BABT grants approvals and
accredits testing laboratories.
- Behavioral Model:
- Model of a circuit block expressed
in mathematical relationship. The highest level of simulation
- Bipolar Junction Transistor.
- Bill of Material.
- A basic SMPS topology in which
energy is stored in a inductor when a switch is ON, and is
transferred to the output when the switch is OFF. It converts an
unregulated input voltage to a regulated output voltage higher
than the input.
- The first physical implementation
of a circuit. It may be incomplete and may have no resemblance to
the final product.
- British Standard.
- British Standards Institution
(United Kingdom). A institution that develops standards and tests
products for compliance.
- A basic SMPS topology in which a
series switch chops the input voltage and applies the pulses to an
averaging LC filter. The Buck regulator will produce a lower
output voltage than the input.
- See Flyback.
- The procedure of operating a SMPS
for some period of time with the intent to eliminate the infant
mortality and stabilizing the SMPS by aging. Temperature cycling
and power cycling may also be applied during burn-in.
- C1, Core Constant:
- The summation of the magnetic path
length of each section of the circuit divided by the corresponding
area of the same section.
- Comite pour Europeen de
Normalisation Electronic (European Committee for Electrotechnical
Standardization). An organization that includes 17 European
countries, and develops standards that are published as EC
- CE Mark:
- Indicating compliance with all
relevant European Union directives.
- Cubic Feet per Minute.
- Committee International Special
des Perturbations Radioelectriques.
- A conductive path used for more
than two circuits. Also known as Return. Not to be used for
defining the Ground terminal.
- Constant Current:
- A mode of operation when the
Output Current is regulated for changes in output load.
- Constant Voltage:
- A mode of operation when Output
Voltage is regulated for changes in output load.
- A heat transfer mode that occurs
at the interface between a solid surface and surrounding still
- Convection, Natural:
- When a warm surface is surrounded
by cooler natural moving air.
- Convection, Forced:
- When a air flow is created around
and along the warm surface by a fan or other mechanical means.
- Converter (DC/DC):
- A SMPS that converts a DC input
voltage to a different DC output voltage.
- Cross Regulation:
- In a multiple output power supply
is the percentage in voltage change at one output caused by a load
change at another output.
- An overvoltage protection circuit
which places an almost short circuit is placed across the points
where the overvoltage was detected.
- Canadian Standards Association. A
independent organization that set standards and conducts safety
testing for Canadian market.
- CSA 22.2 No. 950:
- See UL1950.
- A buck-boost derived SMPS topology
that can produce very low output ripple.
- Curie Temperature:
- The transition temperature above
which a ferromagnetic material becomes diamagnetic.
- Current Mode Control:
- A control method which is using a
dual loop circuit to adjust the PWM operation.
- Current, Maximum Rated Output:
- The maximum output current which a
SMPS was designed to provide at a specified set of conditions,
such as: ambient temperature, intake air temperature, elevation,
airflow restrictions, heat radiated by other components of the
environment, output voltage, output power.
- Dansk Electroteknisk Komite.
- The specified reduction in an
operating parameter to improve reliability. Generally for a SMPS,
it is the reduction in maximum available output power at
temperature above the ambient, input voltages below the nominal,
- Dissipation Factor.
- Department of Health and Human
- The change in output voltage of a
SMPS over a specified period of time, following a warm-up period,
with all other operating parameters such as input voltage, load
and ambient temperature held constant.
- Engineering Change Order.
- The ratio of total output power to
the active input power, expressed as a percentage. This is
normally specified at full load, nominal input voltage and 25C
- EMC, Electromagnetic
- The ability of a device to
function satisfactorily in its electromagnetic environment without
introducing intolerable disturbances to that environment or to
other devices therein.
- Electromagnetic Interference.
Unwanted energy, generated from the SMPS which may be conducted or
- Euro Norme.
- Equivalent Series Inductance. The
value of a inductance in series with an ideal capacitor , which
duplicates the performance of a real capacitor.
- Equivalent Series Resistance. The
value of a resistance in series with an ideal capacitor, which
duplicates the performance of a real capacitor.
- Equipment Under Test.
- Faraday Shield:
- An electrostatic shield between
input and output windings of a transformer. This is used to reduce
primary to secondary coupling capacitance, which in turn will
reduce output common mode noise.
- Federal Communications Commission
- Feed Forward:
- A control technique whereby the
line regulation of a SMPS is improved by directly sensing the
- Field Effect Transistor.
- Flux Density, Magnetic:
- The corresponding parameter for
the induced magnetic field in an area perpendicular to the flux
path. Flux density is determined by the field strength and
permeability of the medium in which it is measured.
- Flux, Soldering:
- A substance added during soldering
to a metal surface which, when heated, will prevent oxidation and
help the flowing of the solder.
- Flyback Converter:
- A isolated Buck-Boost SMPS
topology in which, during the first period of a switching cycle
the energy is stored in a inductance and during the second period
this energy is transferred to a different winding of the same
inductor and into the load.
- Foldback Current Limiting:
- An overcurrent protection circuit
where the output current decreases with increasing overload,
reducing the stress on SMPS components.
- Forward Converter:
- A Buck-derived SMPS topology in
which energy is transferred to the secondary of a transformer
winding and into the load, when the switching transistor is ON.
- Fourier analysis:
- The use of the Fourier series to
evaluate the harmonic components of a complex wave.
- Fourier Series:
- A mathematical series that shows
any periodic function to be a combination of sine and cosine
- Full Bridge Converter:
- A SMPS topology in which four
transistors are connected in a bridge configuration to drive the
primary of a transformer.
- Gallium Arsenide.
- Ground Benign:
- Ideal laboratory environment..
Applies to test and medical equipment, laboratory instruments,
- Ground Fixed:
- Less than ideal environment.
Applies to rack mount equipment, or used in a unheated building,
- Ground Mobile:
- Applies to equipment installed in
wheeled or tracked vehicles.
- Half Bridge Converter:
- A SMPS topology, similar with full
bridge, in which only two transistors are used, the other two
being replaced by capacitors.
- Highly Accelerated Life Testing.
- Highly Accelerated Stress
- Heat Sink:
- Usually a metal plate, extrusion,
etc. that is used to transfer heat away from sensitive components.
- Hiccup Mode:
- An operating mode for a SMPS
triggered by a fault condition, in which the SMPS cycles ON and
- Hi-Pot Test:
- High Potential Test. A test to
determine if the breakdown voltage of a circuit or component
exceeds the minimum requirement.
- Holdover Time:
- See Hold-Up Time.
- Hold-Up Time:
- The time during which a SMPS
output voltage remains within specifications, following the loss
of input power.
- Hot Plug-In:
- A SMPS capability of being
connected or disconnected from the power buses (input and output)
- The International Electrotechnical
Commission. An organization that sets standards for electronic
products and components. Does not conduct any testing.
- Safety agency, Italy.
- Inrush Current:
- The peak instantaneous input
current drawn by a SMPS at turn-on.
- Insulation, Basic (IEC
- Insulation, the failure of which
could cause a risk of electric shock.
- Insulation, Double (IEC
- Insulation comprising both Basic
Insulation and Supplementary Insulation.
- Insulation, Reinforced (IEC
- Insulation which provides
protection against electric shock not less than that provided by
Double Insulation. It may comprise several layers which can not be
tested singly as Supplementary Insulation or Basic Insulation.
- Insulation, Supplementary (IEC
- Independent insulation applied in
addition to Basic Insulation in order to provide protection
against electrical shock in the event of a failure of Basic
- A power source with DC input and
- International Standards
- Isolation Voltage:
- The maximum AC or DC voltage which
may be continuously applied between two section of a SMPS.
- Laplace Transform:
- A mathematical operation that
reduces the work of solving certain differential equations to
solving algebraic equations.
- For a magnetic core with a given
geometry, is the magnetic path length of a hypothetical toroidal
core of the same material that will be the magnetic equivalent to
the given core.
- Lifetime (SMPS):
- The time during which a SMPS will
maintain its electrical specifications and a reasonable MTBF.
- Line Regulation:
- The change in output voltage, in
percentage, as the input voltage is varied over its specified
limits, with all other parameters held constant.
- Line Impedance Stabilization
- Load Regulation:
- The change in output voltage, in
percentage, as the load is varied from minimum to maximum, all
other parameters held constant.
- US military standards.
- Describes the test methods for
determining a component 's resistance to the effects of natural
elements and conditions. Typically used for small components such
- MIL-STD-202F, Method 103:
- Describes Humidity Tests. 85%
relative humidity, non condensing, 85°C ambient, 240 hours.
- MIL-STD-202F, Method 107:
- Defines Thermal Shock. 200 cycles,
-40°C to 125°C, 15 minute dwell time.
- MIL-STD-202F, Method 108:
- Defines Accelerated Life. 100
hours, 60°C ambient, maximum power.
- Describes the design and
documentation requirements for electromagnetic emission and
susceptibility characteristics of electronic equipment. It covers
four areas: Conducted Emissions, Conducted Susceptibility,
Radiated Emissions and Radiated Susceptibility.
- Describes test methods used to
verify the compliance with EMC limits set by MIL-STD-461C.
- Defines the conducted electrical
power characteristics for aircraft systems at the interface
between the power system and electronic equipment. It ensures the
compatibility of aircraft equipment and ground support equipment.
- Environmental Test Methods and
- Defines the methods for testing
the effects of natural and induced environments on equipment used
in military applications.
- MIL-STD-883D, Method 2002.3:
- Defines Mechanical Shock.
Condition A, 500G, 1mSec, half sine, 5 shocks, 2 directions, 3
axes, 30 shocks total. Suitable for packaged, low power modules.
- MIL-STD-883D, Method 2007.2:
- Defines Mechanical Vibration. 4
four minute sweeps, 4 times each axis, total time 48 minute, 20 to
2000Hz logarithmically. Suitable for packaged, low power modules.
- Describes the transient voltage
characteristics and steady state limits for 28Vdc powered circuits
used in military vehicles.
- Humidity, Vibration.
- Minimum Load:
- The minimum amount of output
current required by a SMPS in order to maintain all
- Metal Oxide Silicon Field Effect
- Mean Time Between Failure. The
failure rate of a SMPS expressed in hours, usually calculated
using the MIL-HDBK-217F, at 25°C and a Ground Benign environment.
- National Electrical Code (USA).
- Norsk Electroteknisk Komite
- National Fire Safety Code (USA).
- Norges Elektriske Materiell
- Noise, Common Mode:
- The component of noise which is
common to both lines of input (or output) of a SMPS with respect
- Noise, Differential Mode:
- The component of the noise
measured between the two input or two output wires).
- Off-Line SMPS:
- A SMPS which operates off the AC
line directly, without using a transformer prior to rectification
- Output Impedance:
- The ratio of the change in output
voltage to change in load current.
- Over Voltage Protection. A feature
or circuit of a SMPS for protecting the SMPS and the load if an
abnormal high voltage occurs to the output.
- Safety agency, Austria.
- Periodic and Random Deviation. A
term used for the sum of all ripple and noise components measured
over a specified frequency band, and stated either as Peak-to Peak
or RMS values.
- Power Factor Correction.
- Power Supply:
- Usually a DC power source derived
from an AC input voltage.
- Power Supply, Programmable:
- A Power Supply with the output
(Voltage and/or current) controlled by an external analog signal
(resistance, voltage, current) or digital code.
- The term was originally applied to
the first unit of a production run, which was used as the final
check of a design before full production started.
- Prototype, Engineering:
- A prototype that is hand built
outside the production line, but with the circuit, physical
construction and PCBs close to the final product.
- Pulse Width Modulation. A method
of voltage regulation used in SMPS where the output is controlled
by varying only the width of a train of pulses.
- Push-Pull Converter:
- A SMPS topology which is using
usually a center-tap transformer and two switches that are driven
ON and OFF alternately.
- Radiation, Heat Transfer:
- A heat transfer that is due to
electromagnetic (infrared) emission which is inherent with any
physical object with a temperature above 0 K.
- Rated Output Current:
- The maximum load current a SMPS
was designed to provide under specified conditions.
- Recovery Time, Power Supply:
- The time it takes for the output
voltage of a Power Supply to settle within a tolerance band
following a change in a resistive load.
- The ability of a system of
multiple Power Supplies to continue to provide power to a common
load if one or more Power Supplies of the system fail. The SMPS
should be designed from start to be compatible with a redundant
system design. The system designer should specify the level of
redundancy for the system ("M" Power Supplies in a system of "N"
may fail and the system will still provide adequate power to the
load. Of course, M<N).
- The ability of a SMPS to maintain
an output voltage within specified limits under varying of input
voltage and output load.
- The ability of a SMPS to maintain
its functionality and the specifications under stated conditions
for a stated period of time.
- Resolution, Output Voltage
- The smallest change in the output
voltage that can be realized by the adjustment.
- Resonant Converter:
- A SMPS topology in which a
resonant tank circuit is used to transfer energy from input to the
- The name for the Common terminal.
- Reverse Voltage Protection:
- A feature which protects a SMPS
against a reverse voltage applied at the input or output
- Radio Frequency Interference.
- Ripple and Noise, Output:
- The magnitude of the AC voltage on
the output of a SMPS expressed usually in milivolts peak-to-peak
or RMS, within a specified bandwidth.
- Ripple Current, Reflected:
- The AC current generated at the
input of a SMPS generated by the switching operation, stated as
peak-to-peak or RMS.
- Royer Converter:
- A self-oscillating push-pull
converter used in low cost, low power designs.
- Secondary Side:
- Output side of an isolated SMPS.
- Svenska Elektriska Kommissionen
- Sensing, Remote:
- A technique of regulating the
output voltage of a SMPS at the load, by using a separate pair of
leads for voltage sensing.
- Electrical Inspectorate Finland
- Schweizerischer Elektrotechnischer
- Short Circuit Protection:
- A feature which limits the output
current of a SMPS to a safe value under a short circuit condition,
so that the SMPS will not be damaged.
- Single Fault Condition (IEC
- Condition in which one means for
protection against hazard is defective. Note: If a Single Fault
Condition results unavoidably in another Single Fault Condition,
the two failures are considered as one Single Fault Condition.
- Surface Mount Technology.
- A component or a circuit, active
or passive, dissipative or regenerative used in a SMPS to reduce
components stress by limiting peak voltage or current, dV/dt,
- Soft Start:
- A feature of a SMPS which, which,
at start-up, gradually rise the output voltage of a SMPS to its
final value, therefore protecting both the power supply and the
- Stability, Long Term:
- The output voltage change of a
SMPS, in percentage, usually due only to time, with all other
factors held constant. Some time other factors are also included.
- Temperature, Ambient:
- The temperature of the objects
(not necessary the temperature of the intake air), surrounding the
- Temperature Coefficient:
- The average percentage variation
in the output voltage of a SMPS due to temperature variation
(specified as parts per million per degree Centigrade, over a
specified temperature range).
- Temperature, Intake Air:
- The temperature of the intake air
used to cool a SMPS. Usually the main task for the intake air
would be to cool the heatsink(s), and the magnetics. A secondary
task would be to cool other components such as ICs, resistors,
- Temperature, Operating Ambient:
- The temperature interval within
which a SMPS would operate with reasonable electrical
specifications and reliability. It should not be considered,
unless specified such, that a SMPS will be able to deliver the
full output power over the entire operating temperature range, or
that the SMPS will maintain the same electrical specifications
over the entire operating temperature range.
- Transfer Function:
- A mathematical expression that
shows how two entities or events occurring in different places or
at different times are related.
- Transient Recovery Time:
- Time required for a converter
output to return to within specified limits, following a step
change in output load current.
- Technisher Uberwachungs-Verein
(Germany). A testing agency only, authorized to approve products
to VDE standards.
- Underwriters Laboratories, Inc..
An independent, non-profit US organization that tests products for
- UL standard, Flammability of
- UL standard, Power Supplies.
- UL 1262:
- UL standard, Laboratory Equipment.
- Safety of Information Technology
- Uninterruptible Power Supply. A
Power Supply which continues to supply power during a loss of the
AC input voltage.
- Verband Deutscher Elektrotechniker
(Association of German Electrical Engineers). A private German
organization that sets standards for product safety and noise
emissions and also tests and certifies equipment to those
- Warm-up Drift:
- The initial change in output
voltage of a SMPS from turn-on until it reaches thermal
equilibrium at nominal line, full load and 25C ambient
- Warm-up Time:
- The time needed, after turn-on,
for a SMPS to reach thermal equilibrium at nominal line, full load
and 25C ambient temperature. Usually estimated to be about 30
- Winding, Split Bobbin:
- A method of winding a transformer
whereby the primary and secondary are wound side-by-side on a
bobbin with an insulation barrier between the two windings.
- X Capacitors:
- RFI Capacitor used in positions
where if failed would not be hazardous to anyone who touches the
case of the equipment. The X capacitors are connected across the
line conductors. There are three sub-classes of X capacitors: X1,
X2 and X3. The most common is X2 sub-class, used for IEC-664
Installation Category II. The X2 capacitors are rated for peak
pulse voltage in service of less or equal to 2.5KV.
- Y Capacitors:
- RFI Capacitor used in positions
where if failed could be hazardous to somebody who touches the
case of the equipment. The Y capacitors are connected between
power lines and chassis/earth. There are four sub-classes of Y
capacitors: Y1, Y2, Y3 and Y4. The most common is Y2 sub-class,
used across a Basic or Supplementary insulation. The Y2 capacitors
are rated for nominal working voltages less or equal to 250Vac and
for peak impulse voltage before endurance test of less or equal to
5KV. Because Safety Standards stipulate maximum current towards
earth for different applications, the capacitance of Y capacitors
must be limited to a certain value depending on the type of
equipment in which the capacitor is used.
- Zero Voltage Switching:
- Technique in which the power
switch(es) in a SMPS turns on when there is zero voltage across
it, in order to minimizes switching transient noise and switching
- First Revision: 17 Apr 1987
- Web first published: 11 Jul 2001
- Last Revision: 26 Oct 2003