See below for the special Power Glossary, listing providing a concise description of all the unusual jargon and acronyms used in the power industry.

ronment measured a minimum of 100mm from the power supply

DC: Direct Current or undirectional voltage or current

Derating: The specified reduction in an operating parameter to improve reliability. Compensates for a change in one or more other parameters. In power supplies, the output power rating is generally reduced at elevated temperatures.

Differential mode noise: That component of noise measured between the DC and output return. It does not include common-mode noise.

DPA (Distributed Power Architecture): A system where the supply power is fed to each electronic unit on a busbar and then locally converted at rack or PCB level to such voltages as the electronic circuits require.

Drift: See: Stability.

Dynamic load: A load that rapidly changes from one level to another. To be properly specified both the total change and the rate of change must be stated.

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

EMC (Electromagnetic compatibility): Any electromagnetic effect: Emissions from elements within apparatus (motors, converters, choppers), disturbance of elements and measures for improving the functionality.

EMI (electromagnetic interference): Also called radio-frequency interference (RFI), EMI is unwanted high frequency energy caused by the switching transistors, output rectifiers, and zener diodes in switching power supplies. EMI can be conducted through the input or output lines or radiated through space.

ESR (Equivalent Series Resistance): The amount of resistance in series with an ideal (lossless) capacitor, which duplicates the performance of a real capacitor. In general, the lower the ESR, the higher the quality of the capacitor and the more effective it is as a filtering device. ESR is a prime determinant of ripple in switching power supplies.

ETSI (European Telecommunications Standards Institute): Non-profit making organisation whose mission is to determine and produce the telecommunications standards that will be used for decades to come.

Faraday shield: An electrostatic shield wound on a transformer, designed to reduce interwinding capacitance. The result is less common- and differential-mode noise at the output of the power supply.

FCC (Federal Communications Commission): United States federal regulating body whose new EMI limitations are affecting the design and production of digital electronics systems and their related subassemblies, such as power supplies.

Ferroresonance: The principle used open-loop (non-feedback) voltage stabilizing power supply.

Filter: A frequency-sensitive network that attenuates unwanted noise and ripple components of a rectified output.

Flyback converter: Switching power supply configuration using a single transistor and a flyback diode.

Foldback current limiting circuit: Current-limiting circuit that gradually decreases the output current under overload conditions until some minimum current level is reached under a direct short circuit.

Forward converter: Switching power supply configuration using a single transistor.

Frequency changer: Power-conversion equipment that transforms AC electric power from one frequency to another without affecting its other characteristics.

Full Brick: An industry standard size and pin-out for DC-DC Converters. The package size is 2.50? x 4.8? with the pins on a 4.47? spacing. The height is usually 0.50? without heatsink.

Full-bridge converter: Four-transistor switching power supply configuration used to handle high power levels.

Full-wave rectifier: Rectifier circuit that rectifies both halves of an AC wave.