i would like to know how to build a 9V to 12V dc to dc converter. I want to use a 9Volt battery as the voltage source(input).

 

What is the power consumed by the 12V load?

hgmjr

 

http://www.national.com/appinfo/power/

Plug in the values and it will spit out the part you need. I came up with the LM25575 but I can't find the specs on the power output of a 9v battery so don't know how much power it can produce.

 

9v PP3 "transistor" batteries are pretty low-power devices, perhaps 150mAh

If the load was more than a few mA, the battery would get sucked flat pretty quick.

 

how do i calculate the power load for a circuit?

 

A X Hours = AH

What you need is a measurement of current your circuit requires from the 12V source, and we'll work from there.

 

my circuit is using a 12 Volt input and the amp is below then 500mA

 

If you make a voltage converter circuit that is 85% efficient and need 400mA at 12V then then 9V battery must supply 640mA.

A 9V alkaline battery's voltage drops quickly with such a heavy load. I have graphs from energizer.com and the highest current calculated is "only" 400mA.