Electronics Simple voltage converter, how?

I need a simple voltage converter circuit

I need 1,2V out and I wan't to be able to hook it up to various batteries, 7,2 9 or 12 volts or the likes

I'm not quite sure as to how much current I need out of this thing, but no more then 1 amp

It will drive the glow plug on a Nitro RC car

In short:

2-20 Volts in

1,2-1,3 volt out max 1000mA

edit:

I guess this could be used at Farnell #9493301

 

Just get any fixed 1.2V voltage regulator, or use one like the one at farnell. Basically, any electronic company will sell something suitable, best if you can get a fixed 1.2V one. (Less parts)

 

You can use a linear regulator like the LM317T (see digikey)
The only trick is that if you pull 1 Amp from the output,
that means 1 Amp is pulled from the input power source.
That's all fine, but 1 Amp at 1.2V is only 1.2 Watts,
what happens to the (20v - 1.2V) * 1Amp = 18.8W ?
It gets turned into heat in the regulator. So you're going to need a
BIG heatsink if you run this for more than a minute or two.
Even if you only run it for a few seconds, you still need a heatsink,
that TO-220 package will burn out with 18W.

Your other option is a switching power supply. These are more expensive,
but far more efficient. The problem is, finding one that fits your
requirements of 3-20V in and 1.2V @1A out. Not a big problem if
you can design your own. Look up National Semiconductor's Simple Switch
line, they have a web-based circuit designer. They also sell SimpleSwitch
kits, not cheap, but they do what you want.

 

The lm317 only goes down to 1.5 v

 

Nominally 1.25V (+/-0.05V) which shouldn't hurt, and you could treat it as a fixed voltage regulator, no need for any resistors. Just connect the adjust pin straight to negative. Presumably this is only on for a short time, so whilst you need a decent heatsink it doesn't need to be enormous.