Power Supply Glossary

PcPowerZone Power Supply Terminology Glossary

PFC: Geeky definitions aside, a given power supply utilizing PFC is better able to convert incoming power current into power than power supplies which do not utilize PFC. The resulting effect is lower peak and harmonic current which reduces stress on many critical components which can result in longer component life

NOISE: measured in dB(A) or decibel. For every 3dB decrease, the noise level will be reduced by half. dB levels may be affected by fan speed, size, pitch of fan blades, fan bearing as well as the layout of power supply components. Typically smaller fans spin faster which create more noise levels making power supplies with larger fans a better option to keep noise levels down. A db rating under 36 is a pretty decent rating.

Examples to help put the Decibel rating in perspective:

Total Silence: 0dB

Lawn Mower: 90dB

Car Horn: 110dB

Firecracker: 140dB

Normal Talking: about 60dB

FAN RATING: Rated in CFM which stands for cubic feet per minute. The higher the CFM rating, the more air flow a fan produces. The higher ratings equal significant decrease in system temperatures resulting in longer component life. (you may see higher noise levels if a high speed fan is used for increased CFM ratings)

MTBF: (mean time between failure) The Higher the MTBF rating the better, about half of the given power supplies will die before the given rating, and about half sometime after the rating.

OPERATING RANGE: It is recommended to choose a power supply listing a wider input range for applications in which line voltage is commonly subjected to power fluctuations.

EFFICIENCY: the effieciency of a PC power supply is calculated by dividing the output power by the input AC power giving you the perecentage of effieciency. The higher the effieceincy of a given power supply the lower the operating costs due to power consumption. Cheapo budget power supplies will struggle to see efficiency ratings of 75%, some of which are as low as 64%.

EMI: (electromagnetic interference), noise generated from the switching action of a given power supply. There are two types of Emi, Conducted EMI and radiated EMI. As the name implies, Conducted EMI effects the power line which can be addressed via a line filter. Radiated EMI is broadcast into free space and is addressed by encasing the power supply circuitry in a metal case (note, this is one reason not to purchase a power supply utilizing clear plastic casing).

OUTPUT CURRENT: This is simply the maximum power current which can be drawn from any given power connector for said power supply.

TRANSIENT RESPONSE: This is the time required for output voltage in a given power supply to make the return trip within the regulation envelop following a 50% load change. A quick transient response time will help prevent the risk of read/write errors during drive access.

RIPPLE: Choosing a power supply with a clean DC output with the lowest possible ripple is critical for today's high-speed CPU and memory components. Ripple is simply AC voltage compositing on the DC output normally expressed as a percent of the nominal output voltage for a given power supply.

HOLD-UP TIME: The measure of time after loss of input power that a power supply output will remain within specified limits.

OVERVOLTAGE PROTECTION: This circuit will shut down a given power supply where present, if the output voltage exceeds the given specified limits.

OVERCURRENT PROTECTION: This circuit protects a given power supply where present from excessive current as well as short-circuits

OPERATING TEMPERATURE: This is the range of ambient temperatures that a given power supply can be operated within.