[Gllug] Power supply problems - question...

[Chris Bell]

On Fri 10 Oct, Darren wrote:
> 
> First post, so hello folks! :-)
> 
> 
> Regarding power supplies...I'm wanting to build a low-power-consumption 
> mini-itx box, just running Debian base.
> 
> Standard power supplies are a lot cheaper than the specialised 65 or 100 watt 
> ones and I just want to confirm what I think I remember from GCSE Physics ;-) 
> "Conservation of Energy" - If I use a 350w power supply to power this setup, 
> it'll only consume whatever power the connected equipment draws (excluding 
> losses through heat generated etc).
> 
> Does this sound reasonable?

   Most linear power supplies rely on capacitor storage capable of holding
enough charge to supply the load current through a linear power stage, which
must be capable of dissipating a lot of heat. Power output components
normally have less gain than smaller components, so the driver stage must
also be fairly powerful. This means that a linear power supply is usually
physically large, expensive, and expensive on power, but the power used is
more or less proportional to the load. If properly designed it can have a
very long life.
   Switch mode power supplies tend to be much more power efficient,
physically small, and cheaper to manufacture, but require specially designed
very high grade components to work at all, some of which have a relatively
short life expectancy. There is often a specified minimum load about 10
percent of maximum, and an optimum load around 75 percent. Any single
component failure is likely to cause many other components to fail
immediately. They are usually designed so that they will fail safe and blow
a fuse rather than supply overvoltage, often by putting a dead short
("crowbar") across the output.
   Small switch mode power supplies are available, although the price may be
high compared with ones that are mass-produced in huge quantities.
   Have a look at

http://www.cjcomputers.co.uk

-- 
Chris Bell


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