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SMPS Terminology
Brought to you by SMPS Power Supplies
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, Component:
Specifications which, if exceeded, could cause permanent damage to the component. These are not continuous ratings, and proper operation is not implied.
Ae, Effective Area:
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.
 
ATP:
Acceptance Test Procedure.
BABT:
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 hierarchy.
BJT:
Bipolar Junction Transistor.
BOM:
Bill of Material.
Boost:
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.
Breadboard:
The first physical implementation of a circuit. It may be incomplete and may have no resemblance to the final product.
BS:
British Standard.
BSI:
British Standards Institution (United Kingdom). A institution that develops standards and tests products for compliance.
Buck:
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.
Buck-Boost:
See Flyback.
Burn-In:
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.
CENELEC:
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 Directive.
CE Mark:
Indicating compliance with all relevant European Union directives.
CFM:
Cubic Feet per Minute.
CISPR:
Committee International Special des Perturbations Radioelectriques.
Common:
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.
Convection:
A heat transfer mode that occurs at the interface between a solid surface and surrounding still air.
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.
Crowbar:
An overvoltage protection circuit which places an almost short circuit is placed across the points where the overvoltage was detected.
CSA:
Canadian Standards Association. A independent organization that set standards and conducts safety testing for Canadian market.
CSA 22.2 No. 950:
See UL1950.
Cuk:
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.
DEMKO:
Dansk Electroteknisk Komite. (Denmark).
Derating:
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, etc.
DF:
Dissipation Factor.
DHHS:
Department of Health and Human Services (USA).
Drift:
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.
ECO:
Engineering Change Order.
Efficiency:
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 ambient temperature.
EMC, Electromagnetic Compatibility:
The ability of a device to function satisfactorily in its electromagnetic environment without introducing intolerable disturbances to that environment or to other devices therein.
EMI:
Electromagnetic Interference. Unwanted energy, generated from the SMPS which may be conducted or radiated.
EN:
Euro Norme.
ESL:
Equivalent Series Inductance. The value of a inductance in series with an ideal capacitor , which duplicates the performance of a real capacitor.
ESR:
Equivalent Series Resistance. The value of a resistance in series with an ideal capacitor, which duplicates the performance of a real capacitor.
EUT:
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.
FCC:
Federal Communications Commission (USA).
Feed Forward:
A control technique whereby the line regulation of a SMPS is improved by directly sensing the input voltage.
FET:
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 terms.
Full Bridge Converter:
A SMPS topology in which four transistors are connected in a bridge configuration to drive the primary of a transformer.
GaAs:
Gallium Arsenide.
Ground Benign:
Ideal laboratory environment.. Applies to test and medical equipment, laboratory instruments, etc.
Ground Fixed:
Less than ideal environment. Applies to rack mount equipment, or used in a unheated building, etc.
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.
H.A.L.T.:
Highly Accelerated Life Testing.
H.A.S.S.:
Highly Accelerated Stress Sampling.
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 OFF.
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) without damages.
IEC:
The International Electrotechnical Commission. An organization that sets standards for electronic products and components. Does not conduct any testing.
IMQ:
Safety agency, Italy.
Inrush Current:
The peak instantaneous input current drawn by a SMPS at turn-on.
Insulation, Basic (IEC Definition):
Insulation, the failure of which could cause a risk of electric shock.
Insulation, Double (IEC Definition):
Insulation comprising both Basic Insulation and Supplementary Insulation.
Insulation, Reinforced (IEC Definition):
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 Definition):
Independent insulation applied in addition to Basic Insulation in order to provide protection against electrical shock in the event of a failure of Basic Insulation.
Inverter:
A power source with DC input and AC output.
ISO:
International Standards Organization.
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.
le, Effective Length:
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.
LISN:
Line Impedance Stabilization Network.
Load Regulation:
The change in output voltage, in percentage, as the load is varied from minimum to maximum, all other parameters held constant.
MIL-STD:
US military standards.
MIL-STD-202F:
Describes the test methods for determining a component 's resistance to the effects of natural elements and conditions. Typically used for small components such as resistors.
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.
MIL-STD-461C:
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.
MIL-STD-462C:
Describes test methods used to verify the compliance with EMC limits set by MIL-STD-461C.
MIL-STD-704D:
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.
MIL-STD-810E:
Environmental Test Methods and Engineering Guidelines.
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.
MIL-STD-1275A:
Describes the transient voltage characteristics and steady state limits for 28Vdc powered circuits used in military vehicles.
MIL-T-28800E:
Humidity, Vibration.
Minimum Load:
The minimum amount of output current required by a SMPS in order to maintain all specifications.
MOSFET:
Metal Oxide Silicon Field Effect Transistor.
MTBF:
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.
NEC:
National Electrical Code (USA).
NEMCO:
Norsk Electroteknisk Komite (Norway).
NFC:
National Fire Safety Code (USA).
NEMKO:
Norges Elektriske Materiell Kontroll (Norway).
Noise, Common Mode:
The component of noise which is common to both lines of input (or output) of a SMPS with respect to chassis.
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 and filtering.
Output Impedance:
The ratio of the change in output voltage to change in load current.
OVP:
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.
OVE:
Safety agency, Austria.
PARD:
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.
PFC:
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.
Prototype:
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.
PWM:
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.
Redundancy:
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).
Regulation:
The ability of a SMPS to maintain an output voltage within specified limits under varying of input voltage and output load.
Reliability:
The ability of a SMPS to maintain its functionality and the specifications under stated conditions for a stated period of time.
Resolution, Output Voltage Adjustment:
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 output.
Return:
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 terminals.
RFI:
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.
SEMKO:
Svenska Elektriska Kommissionen (Sweeden).
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.
SETI:
Electrical Inspectorate Finland (Finland).
SEV:
Schweizerischer Elektrotechnischer Verein (Switzerland).
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 Definition):
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.
SMT:
Surface Mount Technology.
Snubber:
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, dI/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 load.
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 SMPS.
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, capacitors.
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.
TUV:
Technisher Uberwachungs-Verein (Germany). A testing agency only, authorized to approve products to VDE standards.
UL:
Underwriters Laboratories, Inc.. An independent, non-profit US organization that tests products for safety (USA).
UL94:
UL standard, Flammability of Plastic Materials.
UL1012:
UL standard, Power Supplies.
UL 1262:
UL standard, Laboratory Equipment.
UL1950:
Safety of Information Technology Equipment.
UPS:
Uninterruptible Power Supply. A Power Supply which continues to supply power during a loss of the AC input voltage.
VDE:
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 standards.
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 temperature.
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 minutes.
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 losses.

 

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