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Author Topic: 12v DC PC PSU to 9V DV  (Read 2562 times)
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Hi , i have a couple of projects that im working on low power , and want to use a PC ATX psu to drive them.
Using the 12v rail from one of the molex connectors i get 12v , but i need to drive the arduino board 9v from it any help?
Whats the best way of doing this?

Similarly , 12v from a car cigarette lighter to power 12v and a 9v arduino supply?

Any Advise?

Cheers
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The arduino will run quite happily from a 12 volt supply, so why do you want 9 volts.   If you really do want 9 then use a simple voltage regulator such as an LM7809
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i have a Arudino Mega ,thought the socket was 9v , my mistake.

It was not just for the arduino i was looking for some other stuff that using 9v psu's to save having several , just run them off one big psu etc

Cheers
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Get a switching power supply from places like pololu.com to efficiently convert your 12 to 14v+ input down to 5V or 9V ...
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Get a switching power supply from places like pololu.com to efficiently convert your 12 to 14v+ input down to 5V or 9V ...

Well, he's already using a PC ATX power supply - it has a regulated 5VDC output (or it should) - so...

Also - the LM7805 needs about 7 volts (7.2 volts based on this datasheet: http://www.national.com/ds/LM/LM341.pdf) to maintain regulation; maybe you could use the 5V rail as "ground" and the 12V rail as the positive rail - leaving you with 7 volts...

Not sure how well this would play with other items - but I know that is one way to get 7 volts from a PC supply...

Personally, I think bypassing the regulator and using the 5V rail from the power supply is the best bet.

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That's good for 5V, still need a regulator for 9V for the other circuit mentioned.
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12 volt DC Input PC ATX-12 Style Power Supplies. DC Input ATX style power supply, 24 volts input, DC Input ATX-12 Style power supplies ...
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Quote
maybe you could use the 5V rail as "ground" and the 12V rail as the positive rail - leaving you with 7 volts...

No, that's not going to work, voltage regulators only source current on their outputs, they can't sink it.
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It actually works quite well, lots of computer enthusiasts do just that with fans to run them at a slower (and quieter) speed.
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It only works if something is there to sink the current - for a SMPS that means it uses active commutation rather than schottky diodes - you may be lucky, but it's not something the PSU was spec'd for.
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