Posted: Wed Jul 02, 2008 4:58 am
Hi again Craig,Craig wrote:This sound like a good idea, however, I have looked and looked for a 20-24 volt, 3 amp+ voltage regulator but have been unable to find one. Do you know the part number for one, or point me in the right direction?The best choice is a switching regulator, built from a Simple Switcher
IC chip available from National Semiconductor, or another type
of switcher chip.
Just to recap, i was recommending a switcher to reduce power dissipation
in the heat sink and of course to waste less power.
Since the current is relatively low (3amps) there are switching regulator
IC's available that are pretty easy to use. National Semiconductor makes
several IC's called "Simple Switchers" that are basically an IC plus
a few other parts. They even have a web page that allows you to design
the circuit right in the web page (they call it Web Bench) so you can do
a design without even having to calculate anything (much).
All you have to know are things like Min supply voltage, Max supply
voltage, load current, and output voltage.
The LM2670 handles up to 3 amps, and the LM2677 goes up to 5 amps.
Note that these devices do not require any external pass elements such
as transistors (MOSFETs, Bipolars). They do require an inductor of
suitable size, and at least two capacitors of suitable size and a couple
resistors (a pot for variable output) and a high current Schottky diode,
all which are available on the web for prices that are not too bad.
Just to note, these are not power supply 'controllers', they are complete
regulators similar to LM317 but they are switchers instead. The other
type of IC's out there would be classified as 'controllers' only, in that
they need external pass transistors (at least one) and these days
you really only need that if you have to handle large currents like
20 amps or 50 amps where you may not be able to find a chip that
does it with all the active elements on the chip itself.
Here is a comparison of the circuits for linear and switchers: