The power supply of a Desktop PC, sometimes also referred to as a Silverbox (figure 1), supplies all the power needed in a Desktop PC. During normal operation a number of DC power supply voltages have to be provided: a 12V, 5V and 3.3V supply voltage, a 5V standby supply and a low current, less accurate "12V supply. The 12V, 5V and 3.3V supplies must each be capable of supplying 20A or more with a voltage accuracy of ±5%. The average efficiency per today at maximum load is about 70%, so when 300W is delivered to the load about 100W of power is wasted and thus converted into heat. This heat subsequently has to be removed using heat sinks and fans.
Figure 1: PC Desktop Power Supply or "Silverbox"
The 5V standby supply must be active in both the normal mode and in standby mode. In both modes it must be ±5% accurate and capable to supply a current of 4A or even more.
During standby mode all supplies must be switched off except for the 5V standby supply. New energy requirements like Energy Star (EPA) and 80PLUS (Ecos consulting) demand a standby power of less then 2W for a PC Desktop power supply. When the standby supply has to comply with the 'Blue Angel' specification, it must even have an efficiency of at least 50% at a load of 0.5 W.
Recently a trend towards higher power densities and to more silent power supplies can be observed. This requires efficiency improvements, because there is a limit in the number of fans that can be applied. Besides that, also a tendency towards more silent power supplies can be observed, asking for lowering the fan speed or removing the fan completely. This leaves the question whether this can be achieved with the standard topology or if a more intelligent way to reach this, without significant cost increase, can be found.