I'm not an electronics person but I need to power up a device that requires 12v using 9volt battery or even two 9v batteries to start with 18v. I need to put together something very small and was looking at lm317


12v-----[lm317]---|
| | 1.6 2w Resistor
| |_____|
|


Does that sound about right?

 

Do you HAVE to use 9 volt batteries?

They have extremely poor current output. Draw more than 20-30 mA and the voltage will fall to 6 volts or lower.

 

If the 9 volt batteries are the only way, then a 7812 regulator at least saves parts. It will only need a 1 uF capacitor on the input and a .1 on the output.

 

if you want to use two 9 volts then connect it in series and take the output through 7812.

Or connect two 1.5 volts cell in series with a 9v to get 12

 

or you could build a boost regulator. Linear tech has some good solution try them out at:

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1042,P1313