9v DC inside the case?

[O1dieburg]

Hello,
Since my DC circuit building skills have waned since college, I was wondering if someone knows of what I would need to do to get a 9vdc current off a standard PC power supply. I know I can get 12v and 5v, obviously, so I figure I would need to step down the 12v supply somehow. The less work the better, as I can probably snake a 120vac/9vdc adapter cord into the case, but was looking for a more "elegant" solution.

Thanks!

 

[CTho9305]

I think ATX provides 3.3V... hook the positive from your load to 12 and the negative to the 3.3, but I don't think you can draw much current. Why do you need 9V?

 

[Mark R]

What do you need the 9V for? How much current will you be taking? Are you sure your device will be damaged by 12V?

If you only need less than 1 A, you could connect positive of your device to +12, and negative to +3.3 to get 8.7V (risk of PSU and mobo damage if your device uses a lot of current, and your system switches into standby mode; not suitable if your peripheral is cased in metal).

If you need less than 3A, then you can buy a chip called a 7809, which is a 9V voltage regulator - connect 12V, and get 9V out. It will need a heatsink if you need more than 0.5 A. These chips cost from around $.50 - higher power ones are more expensive.

 

[O1dieburg]

I think I'll try the 7809 route as the device uses .1A. I would rather not feed off the 3.3v connector, just for the potential risk.

Thanks!

 

[Bowfinger]

You might also look for a 9 volt car adapter, e.g., used to plug a Walkman or radio into a cigarette lighter. That would give you all the electronics you need preassembled.

 

[Lynx516]

Make a potential divider it is pretty easy and should work