Ampere or Amp

Reply:Unit of measure of current flow. At a given point in a circuit, an Amp (1A) equals 1 coulomb of electrons passing in 1 second.

Back plane

Reply:A circuit board that can combine two or more redundant power module.

Ball-bearing Fan

Reply:A cooling fan with a center hub that glides on precision steel balls. Though more expensive, ball bearing fans typically last longer than fans made with bushings.

Breakdown Voltage

Reply:The maximum AC or DC voltage that may be applied from input to output and/or chassis of a power supply.


Reply:A complete path for electrical flow from one terminal to the other of a power source such as a power supply or battery.


Reply:A device used to transform one DC voltage to another.


Reply:The ratio of total power output to input power. Efficiency is typically measured at full load and nominal input voltage.

Electromagnetic Interference (EMI)

Reply:An effect of undesirable energy. EMI is typically emitted by switching power supplies, and may be conducted or radiated.

European Communities (CE)

Reply:Products sold in most parts of Europe must be tested and certified to comply with CE standards. These standards include limits on how much electromagnetic interference (EMI) a device may emit, and its susceptibility to EMI induced problems.

Hold-up Time

Reply:The period during which a power supply's output voltage remains within specifications following a loss of input power.


Reply:To remove and replace a system component while power is on and the system is functional (without first shutting the system down).

Inrush current

Reply:The peak instantaneous input current drawn by a power supply when it is powered on.


Reply:International Standardization Organization

Mean Time Between Failure (MTBF)

Reply:The average failure rate of power supply, expressed in hours, established by the actual operation or calculation.

Output Voltage

Reply:The nominal value of the DC voltage at the output terminals of a power supply

Over-voltage Protection

Reply:A power supply feature that shuts down the supply, or crowbars or clamps the output, when its voltage exceeds a preset level.

Rack Mount

Reply:Variety of device whose special design enables it to be mounted in a standard cabinet, often in a 19" wide opening.

Redundant Array of Inexpensive Disks (RAID)

Reply:A technique for storing data on multiple hard disk drives, to provide higher reliability and faster data access.

Redundant Power Supply

Reply:A power supply made by duplicating identical components to provide greater reliability. In the event the primary supply should fail, a secondary supply is activated (or it assumes the entire load instead of merely half the load).

Remote Sensing

Reply:Technique of regulating the output voltage of a power supply at the load by means of sensing leads which extend from the load to the regulator. This method compensates for voltage drops in the load leads.

Uaderwriters Laboratories (UL)

Reply:A independent, U.S.-based non-profit organization that tests and certifies components and products for safety.

Verband Deutscher Electrotechniler (VDE)

Reply:German national standards and test agency.