# How to get 9 volt from a computer power supply?

To save some energy i thought it would make sense to remove all those small powersupplys. They all transform pricey power (24 eurocents per kw/h here) into heat. However, in my computer is a powersupply that actually is very efficient, also, if i take more energy from it, it wouldn't have much more loss. Right now my computer uses about 54 watts if idle (i selected the components to be as efficient as possible). My DSL-Router uses 14 watts, but i guess most of it goes away as heat in it's own little PSU. The DSL-Router needs 12 volt and my computers PSU can deliver that, and since the DSL-Router is only needed when the computer is switched on i plan to use the computers PSU to power it. I have a pair of speakers with an internal PSU and AMP. After opening them i saw that both are on separated boards. The PSU gives 9 volt to the AMP and gets quite hot while doing it. The problem: as far as i know there is no 9 volt power connection in the computers PSU :(.

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8 years ago
i would hookup a 9 volt power step-down regulator circuit. unfortunately, those extra 3 volts will go to waste as heat. there should be circuits for this on instructables and on google.
8 years ago
As zero says - either a 7809 regulator which will burn off the excess as heat, or a step-down transformer (buck puck) to relatively efficiently (at a cost of more money) give you lower voltage. The step-down version is commonly used for LED headlights, among other things. They operate on the same switch-mode theory as your computer psu does.
dgraham-25 years ago
@dtwai:
12 V as positive and 3.3V as negative would give 8.7 volts that is correct. Superposition theorem of voltage states that a voltage will shift up or down according to the reference point that the circuit sees as "ground." So if you reference all ground points to 3 volts all 12 volt points will be "seen" by the other circuit as 9 volts. Now whether the computer PSU is fused to handle this type of action is a form of black magic I haven't dabbled in. Good luck!
gaudat7 years ago
12V as Positive and 3.3V as Negative = 8.7V Maybe?
tecneeq (author)  gaudat7 years ago
I'm not really sure i understand where you are going. Would you mind explaining a bit more?