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Topic: 12v DC PC PSU to 9V DV (Read 3039 times) previous topic - next topic

Stuart Faust

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

jackrae

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

Stuart Faust

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

CrossRoads

Get a switching power supply from places like pololu.com to efficiently convert your 12 to 14v+ input down to 5V or 9V ...
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

cr0sh


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.

:)
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

CrossRoads

That's good for 5V, still need a regulator for 9V for the other circuit mentioned.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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 ...

MarkT

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.
[ I won't respond to messages, use the forum please ]

Bobnova

It actually works quite well, lots of computer enthusiasts do just that with fans to run them at a slower (and quieter) speed.

MarkT

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.
[ I won't respond to messages, use the forum please ]

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