Technical Power Supply Glossary
The A-Z guide on technical terms: topologies, protections, efficiency, and regulations.
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A
Capacitive Coupling: Unwanted transfer of signal or interference between circuits through parasitic capacitance or capacitive components. Constant Voltage Power Supply: A power supply designed to keep the output voltage stable despite variations in input, load, temperature, and time. This is the classic logic of AC/DC and DC/DC power supplies. Cased/Enclosed Power Supply: A power supply enclosed in a metal or plastic casing, often safer to touch compared to an open frame. Wall Mount Power Supply: An external power supply that plugs directly into the wall socket. Green Mode Power Supply: A power supply designed to reduce no-load consumption and improve efficiency even at partial loads. At very low loads, it may use burst mode and sometimes produce slight acoustic noise. Modular Power Supply: A power supply configurable with multiple output modules, useful when different voltages or customized configurations are needed. Altitude: Maximum operating altitude without power reduction. At altitude, air cools less, and derating may be necessary. Ground Loop: An unwanted current path caused by multiple ground/earth connections. It often generates disturbances that are difficult to diagnose. Distributed Power Architecture: A system in which a bus voltage is distributed and then converted locally near the loads, often with isolated DC/DC converters and point-of-load. ATEX: Directive/certification for equipment intended for potentially explosive atmospheres. An "robust" power supply is not enough; specific suitability is required.
B
Balun: A transformer or magnetic component that presents high impedance to common mode disturbances and low impedance to differential signals. Useful in EMI filters. Bandwidth: The range of frequencies considered in a measurement or performance, such as ripple and noise measured within a certain band. Brownout: Temporary drop in mains voltage below the nominal value. It can cause shutdowns or malfunctions if the power supply cannot withstand the range. Voltage Dips and Interruptions: Tests or conditions where the input voltage drops or briefly interrupts. They serve to verify robustness concerning the quality of the network. Burn-in: Load test performed on products to intercept early failures before shipping.
C
CAN Bus: A two-wire communication bus, robust and suitable for electrically noisy environments. Widely used in automation, automotive, and industrial systems. Load: Circuit or powered device that draws current from the output. Peak Load: Ability to provide current higher than the nominal for short periods, useful with motors or impulsive loads. Dynamic Load: Load that changes rapidly, testing the transient response of the power supply. Maximum Load: Maximum continuous load deliverable under specified conditions. Minimum Load: Minimum load necessary to maintain regulation specifications in some power supplies. CB Report: Test report used to facilitate the recognition of safety certifications across different countries. CCC: China Compulsory Certification: Chinese certification for product safety and EMC. CEC: California Energy Commission: historical reference for efficiency requirements of external power supplies. CENELEC: European Committee for Electrotechnical Standardization. CISPR: International committee that defines references for radio and electromagnetic interference. Class II (Safety Class II): Double insulated equipment that does not require a protective earth connection. Temperature Coefficient: Average variation of the output voltage with changes in ambient temperature. Electromagnetic Compatibility (EMC): Ability of the device to not disturb and not be disturbed beyond regulatory limits. Common: Return conductor shared by one or more circuits. Should not be automatically confused with ground. Current Sharing: Function that allows multiple power supplies in parallel to distribute the load. Droop Sharing: Passive method of load distribution in parallel based on controlled voltage drop. Blind Mate Connection: Mechanical connection that automatically engages when the module is inserted, typical of redundant or hot-swap systems. Remote Control: Logical command to turn on or off the power supply output. Boost/Step-Up Converter: DC/DC converter that generates an output voltage higher than the input voltage. DC/DC Converter: Device that receives DC voltage and provides a different DC voltage, isolated or non-isolated. Flyback Converter: Economical and widely used switching topology, often used in low and medium power supplies. Forward Converter: Switching topology where energy is transferred to the secondary while the switch is on. LLC Resonant Converter: High-efficiency switching topology, generally used between 100 and 500 W, often paired with active PFC. Natural Convection: Condition where air can circulate freely without fans or significant obstacles. Constant Current: Mode where the power supply regulates the output current. Typical in LED drivers and battery chargers. Leakage Current: Current that flows between input, output, chassis, or ground in an isolated power supply. Earth Leakage Current: Current that flows in the protective conductor under normal conditions. It is limited by standards and becomes critical in medical environments or systems with many power supplies. Input Current: Current drawn by the device based on input voltage and load. AC Input Current: Current drawn by the power supply from the grid under high load conditions. Used to size fuses, switches, and upstream wiring. AC Inrush Current: Instantaneous peak current at power-on, mainly due to the charging of internal capacitors. Not to be ignored: it is what trips poorly chosen circuit breakers. Standby Current: Current drawn when the power supply is logically off or without load. Nominal Current: Maximum continuous current deliverable under declared conditions. CSA: Canadian organization for electrical certification and safety.
D
Power density: The ratio between the delivered power and the volume of the power supply. The higher it is, the more compact the product is for the same wattage. Derating: Reduction of the deliverable power or current under unfavorable conditions, especially high temperature or poor cooling. Thermal derating: Reduction of output power with increasing temperature to maintain reliability and safety. Drift: Slow variation of the output voltage over time, under constant line, load, and temperature conditions. Warm-up Drift: Initial variation of the output voltage during the warm-up period after power-on. Bode Diagram: Gain/frequency graph used to evaluate the stability of a power supply's control loop. OR-ing diodes: Diodes used to isolate parallel/redundant power supplies, preventing current feedback between modules. ErP Directive: European regulation on efficiency and no-load consumption of external power supplies. Heat Sink: Metallic element that increases the thermal exchange surface and lowers the temperature of components. Internal Dissipation: Power lost as heat inside the power supply. It mainly depends on efficiency. Clearance: Minimum direct distance through the air between conductive parts. It serves to prevent electrical arcs. Creepage: Distance along the surface of an insulator between two conductors. Important in the presence of dirt, humidity, and high voltages. Harmonic distortion: Presence of harmonics in the absorbed AC current. PFC also serves to reduce it. Network disturbance: Anomaly on the AC network, such as surges, voltage dips, harmonics, or transients. Not all power supplies react the same way: the datasheet is not decoration. Double insulation: Second level of insulation to increase protection against dangerous contacts.
E
Efficiency: Ratio between delivered power and absorbed power. The higher it is, the less energy is dissipated as heat. Load-dependent efficiency: Curve showing how efficiency varies with load changes. Many power supplies do not perform best at very low loads. EFT/burst: Fast electrical transients used in conducted immunity tests, typical of switching contactors, relays, or inductive loads. Eighth brick: Standard industrial size for DC/DC converters, smaller than quarter brick and full brick. Conducted EMI: High-frequency disturbance traveling on input or output cables. Radiated EMI: Electromagnetic disturbance emitted in the space around the power supply. Enable: Logical input that enables the power-on of the power supply or a specific output. ESD electrostatic discharge: Discharge generated by the accumulation of static charge. It can damage sensitive electronic components. ESR: Equivalent series resistance of a capacitor. Low values help reduce ripple and losses. ETSI: European Institute for Telecommunications Standards. EU Code of Conduct: Voluntary European standard related to the energy efficiency of external power supplies and adapters.
F
Power factor: Measure of how much current absorption follows the waveform of the AC voltage. FCC: U.S. entity that defines limits and tests on electromagnetic emissions. Filter: Input or output circuit used to attenuate ripple and disturbances. EMI Filter: Filter used to reduce conducted emissions and improve electromagnetic compatibility. Pi Filter: Filter with two capacitors and an inductor, used to reduce ripple and disturbances. AC Input Frequency: Frequency of the network accepted by the power supply, normally 50/60 Hz. Many switching power supplies operate approximately between 47 and 63 Hz. Switching Frequency: Fundamental switching frequency of the switching stage. AC/DC Front-end: AC/DC power supply, often high-power, used as the first stage in distributed architectures or redundant systems. Full brick: Standard size for high-power DC/DC converters, typically mountable on a board with mounting holes and a heat sink. Parallel Operation: Connecting multiple identical outputs to increase current or redundancy. It should only be done with suitable products. Series Operation: Connecting outputs in series to achieve higher voltage. The current remains limited to the most restrictive module. Redundant Operation: The use of multiple power supplies to ensure continuity even in case of failure of a module.
G
Abnormal Failure: Failure artificially induced during safety or compliance tests. It serves to verify that the product fails in a controlled manner, without creating hazards.
H
Half brickStandard intermediate format for DC/DC converters, between full brick and quarter brick.
I
IECInternational Electrotechnical Commission, a reference for many global technical standards. ImmunityThe power supply's ability to withstand electromagnetic disturbances or ESD without malfunctioning. Conducted immunityThe product's ability to resist electrical disturbances conducted through cables, such as bursts, fast transients, or disturbances generated by inductive loads. Radiated immunityThe ability to function correctly in the presence of radiated electromagnetic fields. EncapsulatedModule sealed in resin or similar material, often for robustness, insulation, and thermal conduction. Autoranging inputCircuit that automatically recognizes the input range, for example, 90-132 Vac or 180-264 Vac, without a manual selector. Universal inputWide-range AC input, typically 90-264 Vac, usable in many countries without selectors. Electromagnetic interference (EMI)Electrical or radiated disturbance that can compromise the operation of other devices. Intermediate Bus Architecture (IBA)Architecture with an intermediate bus: one stage generates a bus voltage, then local converters produce the final voltages near the load. InverterDevice that generates alternating voltage from a direct source. Basic insulationFirst level of insulation required to protect against the risk of electric shock. Safety insulationElectrical separation between primary and secondary required by safety standards. Galvanic isolationElectrical separation without ohmic connection between input and output, achieved with a transformer or optocoupler. Reinforced insulationAdditional insulation compared to basic, used for more stringent safety requirements.
L
Inrush current limitingCircuit that limits the initial current peak at power-on. Current limitingProtection that limits the current to a safe value in case of overload. Foldback limitingProtection where the current decreases as the overload increases, reducing internal dissipation. Sense linesA pair of wires used to relay the voltage measured directly on the load back to the power supply.
M
CE MarkingDeclaration of conformity to applicable European directives. It is not a quality mark: it is a compliance requirement. Chassis groundingConnecting the chassis to ground, used as a reference and for electrical safety. Hiccup modeProtection where the power supply attempts cyclic restarts during a short or overload, limiting heat. DIN rail mountingMounting system on a DIN rail, standard in industrial installations and electrical panels. PCB mountingPower supply designed to be soldered or mounted directly on a printed circuit board. MOSFETTransistor widely used as the main switch in switching power supplies. MTBFMean time between failures. Useful for comparisons, but should not be read as a guarantee of the single piece's lifespan. MTTRMean time to repair of a faulty unit.
O
Open framePower supply made on a PCB without a closed enclosure. Requires attention to protections, installation, and safety. OTP - thermal protectionProtection that shuts down or limits the power supply when the temperature exceeds the limit. OvershootTemporary peak of the output voltage, often during rapid load changes. OVP - overvoltage protectionProtection that intervenes when the output voltage exceeds a safe limit.
P
PARDSum of the periodic and random components of ripple and noise, measured over a specific bandwidth. Active PFCElectronic circuit that corrects the power factor, reducing harmonics and impulsive absorption from the network. Passive PFCPower factor correction with inductors and capacitors, less sophisticated than active PFC. Base plateMetal surface used to transfer heat to the chassis or heatsink. Full loadMaximum continuous load allowed under nominal conditions. PMBusDigital power management bus that allows monitoring, configuration, and diagnostics of compatible power supplies and converters. Non-isolated Point of Load (POL)Local, non-isolated DC/DC converter placed near the load to generate low voltages with high current and better regulation. Bridge rectifierCircuit that converts an AC voltage into DC using diodes or equivalent components. Apparent powerIn alternating current, it is the product of RMS voltage and RMS current, without considering the power factor. Measured in VA, not in watts: confusing them is the classic elegant way to undersize everything. Peak powerPower higher than continuous, deliverable only for short periods and under specified conditions. Useful for motors, actuators, and impulsive loads. Output voltage accuracyAllowed tolerance of the output voltage set at the factory. Center tapConnection to the center of a transformer or inductor winding, used to obtain two equivalent sections. Designed to meetIndicates that the product is designed to comply with a standard, but it may not have formal certification. To verify: marketing here loves to play dirty. Short circuit protectionProtection that limits or interrupts the output in case of a short, restoring automatically or manually. Crowbar protectionOvervoltage protection that creates a low-resistance path to trigger upstream protection. Reverse polarity protectionProtection against the application of reverse polarity on input or output. Overload protectionFunction that limits current or power to prevent damage in case of excessive load. Thermal protectionCircuit that intervenes if the internal temperature exceeds a preset limit. PWMPower control through variation of pulse width at a constant frequency.
Q
Quarter brickStandard industrial format for DC/DC converters, often used in telecom, networking, and distributed architectures.
R
Synchronous RectificationReplacement of output diodes with controlled MOSFETs to reduce losses and increase efficiency, especially at low voltages and high currents. Convection CoolingCooling through natural air circulation, without a fan. Forced CoolingCooling achieved with a fan or imposed airflow. Conduction CoolingHeat removal through contact with a metal base, heat sink, or chassis. Input RangeMinimum and maximum input voltage values within which the product operates correctly. Voltage RangeInput voltage range within which the power supply operates within specification. Linear RegulatorA regulator that dissipates excess energy as heat. Simple and clean, but less efficient than switching. Switching RegulatorHigh-efficiency converter that uses switching, inductors, and capacitors to regulate voltage. Load RegulationVariation in output voltage when the load changes, with constant input. Line RegulationVariation in output voltage with changes in input voltage, with constant load. Fine Output AdjustmentAdjustment of the nominal voltage through a trimmer, resistor, or external control. Cross RegulationIn multi-output power supplies, variation of one output caused by the load applied to another output. Voltage AdjustmentRange within which it is possible to modify the output voltage. Total RegulationOverall deviation of the output voltage due to variations in input, load, and temperature. Input Ripple RejectionThe power supply's ability to attenuate a disturbance present at the input. Remote SenseRemote measurement of voltage directly on the load to compensate for cable drop. Insulation ResistanceResistance offered by the insulator to the passage of current. RFIRadio frequency interference generated or experienced by electronic equipment. N+1 RedundancySystem with N power supplies necessary for the load plus one spare. If one fails, the system continues to operate. RippleResidual alternating component superimposed on the DC output voltage. Low ripple is important for sensitive electronics. Reflected RippleSwitching noise that returns towards the input source, typical in DC/DC. ResolutionMinimum variation obtainable in an adjustable parameter, such as output voltage or current. Transient ResponseBehavior of the output when the load changes rapidly: includes deviation and recovery time. RoHSEuropean directive that limits the use of hazardous substances in electrical and electronic products. NoiseHigh-frequency disturbance superimposed on the DC output, generally measured in mV peak-to-peak. Common Mode NoiseDisturbance present similarly on both lines relative to ground or chassis. Differential Mode NoiseDisturbance measured between output and return, distinct from common mode noise.
S
Faraday ShieldShielding between transformer windings to reduce capacitive coupling and common mode noise. SecondaryOutput section of an isolated power supply, separated from the AC network for safety and functionality. Power Good SignalLogical signal indicating that the outputs are present and in regulation. SELVExtra-low voltage for safety, defined by standards to reduce the risk of electric shock. SequencingControlled order of turning on outputs in multi-output power supplies or complex systems. Medical SafetySet of stricter requirements for power supplies intended for medical equipment, with specific limits on insulation, leakage, and patient/operator protection. Soft StartGradual startup that limits inrush current and initial overshoots. Hot-SwapAbility to replace a module without shutting down the system. Logical ShutdownRemote input that enables or disables the output via a logical signal. Thermal ShutdownAutomatic shutdown for overheating until safe conditions are restored. SurgeImpulse overvoltage used in EMC tests, designed to simulate events like nearby lightning or network maneuvers.
T
Ambient temperature: The temperature of the air surrounding the power supply. It is one of the most important parameters for duration and deliverable power. Allowed case temperature: The temperature range measured on the casing within which the product meets specifications. Storage temperature: The temperature range allowed for storing the product without degrading its performance. Operating temperature: The temperature range within which the product can operate according to specifications. Turn-on time: The time required to reach the specified output voltage after the application of input. Hold-Up time: The time the output remains within specifications after the loss of input voltage. Warm-up time: The time after turning on required to operate within specifications, especially at low temperatures. Rise time: The time required to move from 10% to 90% of the final voltage value during switching or turning on. Compliance voltage: The voltage available at the output of a constant current power supply to keep the current regulated within the expected range. AC input voltage: The range of alternating voltage accepted at input. A 100-240 Vac product is often usable on a universal grid. Isolation voltage: The voltage that the isolation barrier can withstand for a specified time. Working voltage: The maximum continuous voltage that can be sustained on the isolation barrier without stressing it. Breakdown voltage: The minimum voltage at which an insulator fails and becomes conductive. A critical parameter for safety and isolation. DC output voltage: The nominal continuous voltage provided by the power supply. Ground: Electrical connection to the physical earth. The common output is not ground unless connected to the earth. Safety ground: A conductive path to earth designed to protect people from dangerous currents in the event of a fault. HiPot test: High voltage test between input, output, and ground to verify isolation. Circuit topology: The conversion principle used by the power supply: flyback, forward, half bridge, full bridge, buck, boost, etc. Input transient: A peak or rapid change in input voltage. Requires adequate protection. TUV: German independent organization for product safety testing and certification.
U
Uframe -/ U-channel: Power supply mounted on a U bracket, useful for fixing to a chassis or plate. UL Listed: Product approved by UL as a complete device according to applicable US standards. UL Recognized: UL recognized component for integration into a system that requires final evaluation. Undershoot: Momentary drop in output voltage during a rapid load increase. UPS / uninterruptible power supply: System that keeps the load powered in the absence of mains supply, using batteries and DC/AC or DC/DC conversion. Floating output: Output not referenced to ground or another output. It can be connected by the user as positive or negative within the specified limits. UVLO - undervoltage lockout: Protection that prevents starting or turns off the converter if the input voltage drops below a threshold. Very useful with batteries.
V
VDE: German organization related to electrical safety testing and emissions. Expected life: The average expected duration of the product, often related to temperature, capacitors, and load profile.
W
Warm swap: Replacement of a module in a redundant system with the module's input turned off, while the rest remains operational.