Power supply
Power supplies for desktop PCs have rated efficiencies of 65-75%. For special (expensive), 'silent' PCs efficiencies are in 80-90% range. The function of the power supply is to transform the 115 or 230 V AC power into 3,3 V, 5 V and 12 V DC power for peripheral busses and the motherboard. Lower voltages than 3,3 V , e.g. for the most modern CPUs, come from a Voltage Regulator Module on the motherboard. Modern power supplies are of the switching type (SMPS) and are sold as a complete unit, including SMPS, power switch, logic for voltage regulators, (surge, overheating) protection and a 3-4 W fan. The fan speed is controlled on the basis of internal temperature feedback or through logic that sits in the Southbridge chip on the motherboard.
In notebooks, the power supply is almost always external and is probably the only feature where energy efficiency is not an issue, because it doesn't influence battery life. Efficiencies of external power supplies are in the range of 65-75%.
Since June 2000 there is a Code of Conduct between external power supply manufacturers at the initiative of the European Commission which should improve things, at least as far as no-load power consumption is concerned (see table and http://energyefficiency.jrc.cec.eu.int/html/standby_initiative.htm)
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No-load power consumption |
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Rated Input Power |
Phase 1 |
Phase 2 |
Phase 3 |
1.1.2001 |
1.1.2003 |
1.1.2005 |
> 0.3 W and < 15 W |
1.0 W |
0.75 W |
0.30 W |
> 15 W and < 50 W |
1.0 W |
0.75 W |
0.50 W |
> 50 W and < 75 W |
1.0 W |
0.75 W |
0.75 W |
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Targets CoC external power supplies
Although standby loss is important, Chris Calwell argues that 73% of energy is lost when the equipment is in active use and that actual part-load efficiency is far less than the rated efficiency (read article Power Supplies Ecos.pdf)
Courtesy of the French Energy Agency ADEME, Future Electronics project.
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