Can't be...Originally Posted by DeltaFX
I seem to recall from my basic physics that a current (AC or DC) through a coil on an iron core generated an electromagnetic inductance. However ONLY if the magnetic inductance came from AC, could that be collected into another coil as current.
If the power supply in your home PC simply took 240V AC and rectified it to 240V DC and then used a DC power convertor to drop the voltage down to 12, 5, 3.3 then there would be no need for the big coil of wire or the heat it generates!
What will be happening is there is a big coil and a small coil on the same ferrite core. The big coil carries the 240V and the small coil the output voltage. Lets assume that the Small coil is a 10th of the size of the big coil - it would output 24V which would still be AC (this assumes a lot of things like no loss of energy etc etc. ) That would then be rectified through a group of diodes to give a DC voltage - which would basically be about 24V... ...this would then be converted down to the correct voltage. This is of course an over simplification:
1. Most AC computer power supplys have a 110V and 220V switch - this probably halfs the length of the AC input when 220V is selected.
2. Most AC-DC transformers will often have more than one voltage output - for the example I gave (which is theoretical - I have no idea what outputs a real PC transformer has)... might be 1/10th length (i.e. 24V) 1/20th length (i.e 12V) 1/40th length (i.e. 6V) 1/100th length (i.e 2.4V) each of which would then be voltage corrected through seperate circuits.
IF you knew what the DC voltage coming out of the regulator was then you SHOULD be able to feed a simillar DC voltage in at that point... If you were happy to play with casing off (not recommended) you could measure the voltage(s) and see what they need as inputs... ...but you'd almost certainly end up having to build a circuit to covert (some of) your 12v DC from the car battery to use on these inputs... ...and THAT defeats the point...
If anyone wants to prove me wrong and refer me to a web page that says you can use inductance coils to transform DC to DC then I'd be delighted to be proven wrong...