please help with battery/voltage regulator

[phatdats]

ok, i am not an EE, but a friend refered me to this page, telling me if anyone can help, you guys could....

i have some audio gear that runs off of SLA (lead acid) batteries. one unit needs 6 volts, and draws .62amps and turns off at 5.25v
the other piece needs 12V and draws 1.2amps and shuts down at 10.4volts

carrying around a 6v and a 12v sla is beginning to hurt my back. there is a company called eco-charge (

http://www.ecocharge.com)

that has introduced an SLA (the EC90) that gives off 12volts and 6volts on different connectors.
I know that this is done with a voltage regulator circut. and i want to try and build my own (i am sure at a fraction of what they charge)

here are my requirements:
1. i have either 7.2ah or 10ah 12v cells. i need to run both peices for 3.5 hours (with a total draw of 1.8ah, the 7.2 battery will just work, but will a volatge regulating circut either draw some power or make this system run in-efficiently?)

2. i also need to be concerned about heat. is this gonna reduce my runtime?

i am pretty good with simple circuts, and can assemble radio shack boards and parts all day long. can someone help me with the specifics??

thanks a bunch!
steve

 

[AliPentland]

Basically there are 2 types of regulator, linear (sometimes called analogue) and switching.

A linear regulator will simply 'drop' the extra voltage across it, so you put in 12V get out 6V and the extra
6V voltage you do not need is 'dropped' across the regulator IC. The problem with this as you mentioned
is that the excess power must be dissipated as heat. You will need a heat sink as you will have 620mA
and 6V. Power = Current * Voltage ie 3.7Watts.

The alternative is a switching regulator, in your case step down. It will involve a diode, capacitor and inductor,
and is a bit more complex than the linear regulator. A simple way to think of it that your 12V is switched on
half the time and smoothed out to give an average level of 6V. The advantages of this are that it will generate
little heat and be almost twice as efficient, making your battery last longer. However, because it switches
it will generate 'noise' which could affect sensitive circuits.

Maxim and National Semiconductor both do good regulators (Maxim are good at supplying free samples
too!), but there are many other manufacturers as well. Most have good application notes, find the nearest to
what you want. If you decide on a switcher make sure you use the right type of diode, it makes a difference!

Good Luck, Ali