Switching Power Supply Glossary


A-B C D E F G-H  I  J-K-L M N O P Q-R S T U V W-Z




Ambient Temperature:


The temperature of the environment in which the power supply is operating, usually referred to "room temperature." For forced air-cooled units, the ambient temperature is measured at the air inlet.






When used in reference to a power supply, bandwidth means the difference between the lowest and highest frequency and is measured in hertz.




Battery Backup:


A power supply system where if the ac line fails, a battery will provide input energy to keep the dc outputs from failing.




Bleeder Resistor:


This type of resistor functions by reducing the charge of a capacitor. This is referred to as a small current drain.






A type of circuit, also called a rectifier that will use either four diodes or two diodes. A four diode circuit is referred to as a full bridge, while a two diode circuit is referred to as a half bridge




Burn In:


The process of operating a power supply (usually at full load), typically in an elevated ambient temperature, immediately after manufacture. This process is useful in eliminating early life failures.






A system of conductors that deliver power to the power supply load. Bus can also refer to the communications field, when a bus is used to control a sub-system, for example an IEEE-488 bus.




Class 2:


This is a UL definition for an output which is below 60Vdc (42.4Vpk) and 8A.




Class I


This is a 3 pin input type - tied to earth ground. Output may or may not be tied to earth ground.




Class II


A 2 pin input WITHOUT Ground present. To comply, a power supply design would include reinforced insulation as it could not rely on Ground for safety.




Common Mode Noise:


The component of noise voltage that appears equally and in phase on conductors relative to a common reference.




Constant Current Power Supply:


A power supply which is designed to regulate its output current within a specified range.




Constant Voltage Power Supply:


A power supply which is designed to regulate its output voltage within a specified range.




Control Section:


In a closed-loop system, the circuitry which maintains the control loop is referred to as the control section by incorporating an error amplifier in the feedback of the system.






I.A type of device that produces DC power when energized by another DC source.

II.Can also refer to a part of a switching power supply that converts power and produces final rectification.





When a power supply is heated through regulation, rectification or transformation, it is necessary to cool the device.





A core, in the field of electronics, is a device used in the construction of an inductor that can enhance its amount of inductance that will be produced.



Cross Regulation:


The effect of a load change to one output upon the other outputs in a system.







A method of over voltage protection which shorts the output to ground in the event an excessive voltage is detected. Usually done by a SCR (Silicone Controlled Rectifier)





CSA (Canadian Standards Association)


The CSA is an independent organization which performs public safety testing. This organization is similar in nature to the Underwriters’ Laboratories in the United States.




Current Limiting:


The limiting of the output current to prevent damage to the power supply and the system in which it is used.





A reduction in the power output capacity of a power supply due to its external environment such as altitude, airflow and ambient temperature.


Differential Mode Noise:


The conducted noise of an output as referenced to its return path. This is typically how "ripple and noise" specifications are defined.


Double Insulation:


ndependent insulation applied to basic insulation in order to reduce the risk of electric shock in the event of a failure of the basic insulation.




Dynamic Load:


This is a type of load that can quickly change levels. In order to state this type of load, you must calculate the total change and the rate of change.






The ratio total output power to total input power, expressed as a percentage, under specified conditions.




EMC(Electromagnetic Compatibility):


The requirement for electromagnetic emissions and susceptibility dictated by the physical environment and regulatory governing bodies in whose jurisdiction a piece of equipment is operated.




EMI (Electromagnetic Interference):


Signals emanating from internal or external sources that disrupt or prevent operation of electronic systems. This can also be called RFI or radio-frequency interference. In present practice, the term "EMI" (which refers to the emission of unwanted signals), has been replaced by "EMC" (which refers to both emissions and susceptibility).


ESR (equivalent series resistor):


ESR refers to the amount of resistance in series with an ideal capacitor. If the ESR level is low, the capacitor will operate more effectively. ESR is used to determine the cause of a ripple in switching power supplies.


External Power Supply:


A device that is designed to supply the DC power that is needed to operate electrical equipment and is located outside of the equipment which it powers.



Faraday Shield:


In order to reduce common or differential noise in a power supply’s output, a faraday shield is applied to reduce intertwining capacitance.


Federal Communications Commission (FCC):


A government agency in the United States. The FCC’s recent limitations on EMI have greatly affected digital electronic systems and power supplies in design and production.




A ferrite is a specific type of inductor that uses a core that is made of a certain type of ferromagnetic compound.




A filter is a frequency sensitive network that functions by removing unwanted noise and/or ripple components in rectified outputs.


Floating Ground:


A circuit whose electrical common point in not tied to earth ground. The common point potential can be different than that of earth ground.


Flyback Converter:


A type of power supply that uses a single transistor as well as a flyback diode, referred to as a flyback converter


Foldback Current Limiting:


The method of limiting the output current in which the current decreases as the voltage is decreased by the output overload.


Forward Converter:


A type of power supply that is configured using a single transistor.


Frequency Changer


This is a type of equipment that can convert AC electrical power to different frequencies without changing any other characteristics.


Full-Bridge Converter:


A power supply that uses four transistors to control high power levels.


Full-Wave Rectifier:


A diode network that transforms an AC source into a full-wave DC source.



Ground Loop:


Undesirable voltages caused by ground currents of several circuits flowing in a common ground circuit or ground plane.


Half-Bridge Converters:


A type of power supply that uses two transistors. Commonly used for medium-power equipment or applications.


Half-Wave Rectifier:


This is a single diode rectifier circuit that will only rectify half of an AC wave’s input.


Heat Sink:


A device that conducts and disperses heat commonly produced by electronic equipment and components.


Hold-Up Time:


The period of time during which the output voltage will stay within its specified regulation in the event of the loss of the input power.







A passive electrical component that is designed to have a specific value of inductance. Inductors are important in the design of electronic equipment such as power supplies for functions such as voltage transformation, filtering and energy storage. Among the types of electrical components that use the property of inductance are chokes, coils, toroids, relays, transformers and motors.


Input Voltage Range:


The specification for power supplies under different ranges of line voltage.


Inrush Current:


The ac input current as measured during the initial turn-on of the power supply.


International Commission on Rules for the Approval of Electrical Equipment (CEE):


A European safety agency that is mainly regional. The United States participates in the CEE in the observer capacity only.


International Electrotechnical Commission (IEC):


A safety agency located in Geneva, Switzerland.




I.A section referred to as a “chopper section” in a switching power supply.

II.kind of device that will deliver AC power when provided with DC power.






The degree of the electrical separation between 2 points of a power supply, usually between input and output.




Isolation Transformer:


A transformer in which one or more output windings is electrically separated from the input winding and all other output windings by insulation at least equivalent to double insulation or reinforced insulation.




Isolation Voltage:


The level of ac or dc potential which can be applied to the various portions of a power supply, e.g., input-to-output, output-to-ground, primary-to-secondary, etc.



Leakage Current:


Leakage current occurs when there are flaws in certain electrical components, or in the design of the components themselves. The result is current that flows between the current ground and output buses.


Line Regulation:


The percentage change in output voltage due to a change in input voltage level. This is usually a measurement of the output deviation as the input voltage is varied from low line to high line.






Defined as the output current in voltage regulated power supplies.


Load Regulation:


The percentage change in output voltage due to a change in output loading. This is usually a measurement of the output deviation as the loading is changed from no load to full load.


Logic Enable:


Logic enable refers to the ability to use logic circuits like Transistor-Transistor Logic (TTL) signal to turn a power supply off or on.



Minimum Load:


The minimum amount of current which must be drawn from an output to maintain output regulation.



Modular power supply:


A power supply that consists of numerous subsections, for example, an input module, filter module or power module.


MTBF (Mean Time Between Failures):


This is an indicator of reliability, and may be calculated or demonstrated, using the procedures set down by MIL-HDBK 217.




Multiple Output Supply:


When a power supply has two or more different output voltages, it is referred to as a multiple output supply.





A component, normally random, of deviations in output voltage. Noise is undesirable, and normally will be specified in conjunction with ripples.


Nominal Output Voltage:


The model voltage of an output.



Open Frame Power Supply (Open-Frame Construction):


A power supply that does not have an enclosure. Commonly seen with OEM power supply manufacturing techniques. An open-frame construction may consist of a circuit board that is mounted on a chassis that does not have a cover or a stand-alone printed circuit board.


Operating Temperature:


A specified limit wherein a power supply can perform at optimal levels.




An opto-isolator consists of a light emitting diode that is located next to or close by a phototransistor. Commonly used within a feedback loop in order for a power supply to achieve electrical isolation between input and output. An opto-isolator functions by using a signal path from an electrical to optical to electrical signal transformation.


Output Impedance:


The value of an ideal voltage source in conjunction with a fictional resistor that would supply the same amount of AC voltage across a power supply’s terminal that the magnitude and frequency of alternating current would supply.


Output Noise:


The differential-mode output ripple and noise as measured with a 20 MHz bandwidth.


Output Power:


The specified level of power of which a power supply is capable.




Over-Voltage Protection (OVP):


The use of circuitry which will protect the user's system in the event of a failure in the power supply. This circuit will limit the output voltage to a predetermined limit which, if exceeded, will cause the power supply to shut down.



Parallel Operation:


When two or more power supplies are connected, it is referred to as parallel operation. This allows supplies to combine current into a single load.


Peak Current:


The maximum amount of current which an output is capable of sourcing for brief periods of time.





Peak Transient Output Current:


During transient loading conditions, peak transient output current refers to the utmost amount of peak current that can be delivered to a load.



Phase-Controlled Modulation:


A type of circuit that is commonly employed in switching regulators. It is used when an operating frequency is kept at a constant level, usually 60-Hz. It can control line and load changes simultaneously without causing much dissipation.


Power Conversion:


A type of processing for medium-quality electrical power that is delivered by utilities. This conversion makes this power acceptable for electronic circuits that are sensitive.


Power Factor:


The ratio of true ac input power to the apparent ac input power. If both voltage and current are sinusoidal, power factor is the cosine of the phase angle between them.


Power Factor Correction (PFC):


Technique of increasing the power factor of a power supply. Switching power supplies without power factor correction draw current in short, high-magnitude pulses. These pulses can be smoothed out by using active or passive techniques. This reduces the input RMS current and apparent input power, thereby increasing the power factor.




Power Fail Detect:


A logical signal which indicates that the input power has failed. This signal gives the user a chance to store information or switch over to backup power before the system goes down.




Power Limiting:


The limiting of the total output power of a power supply.




Pulse-Width Modulation (PWM):


A type of circuit that is used in switching regulated power supplies. This type of circuit holds the frequency constant while the width of power pulse is varied, and controls both line and load changes without major dissipation.


Push-Pull Converter:


A type of converter that in the central switching circuit utilizes two transistors that operate in a push-pull. This type of converter is very simple in design.



Recovery Time:


The amount of time that is necessary for a transient undershoot or overshoot in a stabilized output quantity to decay, usually within a precise limit.




By connecting more than one power supply, or using parallel power supplies, a redundancy is created. This means that should one power supply fail, the others can continue to provide power to the load. Redundancy is commonly employed when power supply failure is not an option.




A known amount of stable voltage that is used to compare output voltage in order to stabilize the amount of voltage in a power supply.




A component of a power supply that controls output voltage. Also acts as a stabilizer to maintain output voltage at a present level.


Reinforced Insulation:


An improved basic insulation with such mechanical and electrical properties that, in itself, the insulation provides the same degree of protection against electrical shock as double insulation. It may consist of one or more layers of insulation material.





Remote Sensing:


The monitoring of the output voltage directly at the load rather than at the power supply output terminals; this improves regulation. Useful when using long load cables.


Response Time:


The reaction time for an output to react to a dynamic load change. Response time also includes the time that it takes for the load to settle within the tolerance band after a load change.




The often used term that refers to the common terminal for all of the outputs on a power supply. It also carries the return current for all of the outputs on the device.


Reverse Voltage Protection:


A power supply’s capacity to withstand reverse voltage in output terminals when it is hooked up in reverse polarity.






A power supply output voltage AC noise component that is periodic. Usually measured over a 20 MHz bandwidth.



Secondary Circuits:


Secondary circuits are those circuits supplied from transformer output windings that are electrically separated from the input windings.



Semiregulated Output:


A multiple outlet power supply has secondary outputs that are referred to as semiregulated outputs. These outputs simply receive line regulation.






Sequencing controls the order and time delay for output voltage appearance as well as dropout when power supplies are turned on and/or off.




Schottky Diode: 


A type of diode that is featured with fast recovery time and a low forward voltage drop (0.6V). If a diode is needed for a high current, low voltage supply (5v DC) and when low losses and high speed are important, a schottky diode can be used with great success.




Short Circuit Protection:


In the event that the output is shorted, this circuit will protect the power supply by limiting the amount of current flowing through the short circuit.







A network comprised of a capacitor, resistor and diode that is used in switching power supplies. This network works by trapping high-energy transients as well as for the protection of sensitive components.




Soft Start:


A type of input surge-current limiting that is used in a switching power supply, where the supply drive is gradually ramped on.






Refers to the ability of a power supply's control circuit to maintain control and produce a constant output voltage as load and environmental conditions fluctuate.




Standby Current:


The amount of input current that is drawn in by a power supply during minimum load conditions.




Static Load:


A type of load that does not change over a specified amount of time. This can also be referred to as a percentage of a full load.






A process that forces burn-in failures by exposing a power supply to several different stressors.




Switching Frequency:


The frequency at which the pulse-width modulator switches the dc voltage in a switching power supply.




Switching Regulator: 


A type of DC-to-DC converter that is comprised of inductors and capacitors that sort energy and switch elements, which then open or close, as needed to regulate the voltage across a load. This is normally controlled by a feedback loop in order to even out output voltage.




Temperature Coefficient: 


The effect of ambient temperature changes upon output voltage regulation, expressed as a percentage change per degree of temperature. 




Temperature Range:


The specified ambient temperature over which it is safe to Operate or Store the power supply.




Thermal Protection:


A type of device that provides protection through a thermally actuated switch that will stop the operation of a power supply once the temperature inside the supply reaches a specified level.






A type of magnetic device that will convert one level of AC voltages to other level of AC voltages.




Transient Response:


The response of a circuit to a sudden change in an input or output quantity. In power supplies, this is the excursion of the output voltage and the time it takes to recover from a step change in the output load or the input voltage.




UL (Underwriters’ Laboratories):


A public safety testing company located in the United States that is an independent, not-for-profit agency. A UL recognition may be mandatory for equipment that is used in certain applications.






Undershoot is the amount that an output falls under its final value after a sudden change in load.




UPS (Uninterruptible Power Supply):


A device that can operate either with a DC battery back-up or an AC input line. Commonly used to provide power for equipment during temporary or permanent loss of power.




VDE (leVerband Deutscher Ektrotechniker):


A public safety testing company located in Germany. Similar in operation to its United States counterpart, UL.




Warm-Up Time: 


The amount of time that the internal components of a power supply need to reach thermal equilibrium.


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