Power supply input 12vdc, output 0-12vdc?

Hey guys. I'm in a time crunch and need a power supply that takes in 12vdc and outputs anywhere from 0 to ~6vdc (up to 12 is preferable, but not necessary) at at least 4A. Voltage would have to be controlled with hardware, I think that that is standard. I've spent a lot of time on the net looking around, but I'm afraid that I don't know all the nooks and crannies. Right now my best option is:

http://www.current-logic.com/shop/index.php?main_page=product_info&cPath=22&products_id=217

But they're in china, so shipping will be time-consuming.

The most important part is that it can provide at least 4 amps continuously, 5 or 6 is preferable as it'll be going for hours at a time. I'd like it as efficient as possible as well, and quiet. I would sacrifice the last two for the voltage and amperage specs, though. Cheap would also be nice XD

Any links you can find are much appreciated!

Thanks a bunch!

That's a tall order. Variable output voltage supply with up to 6A of output.

How much money do you have?

I know, I know. I was hoping you guys knew a place :)

It's on a grant, so I guess a lot. Less than a hundred would be... much preferable, though.

Start designing.

There's no time, unfortunately. I could accomplish my goals with resistors, caps, etc, but it would be messy and inefficient. And, for the most part, uncertain in reliability. I got this dropped on me by a researcher that's going out in the field in a couple weeks, and I've already got a ton of stuff going on... yadda yadda yadda.

Time crush ?

hum… here I will do : Need a 6 A transformer ← expensive and hard to get… if possible, if not, I will use a PC power supply, rig it in a way, the 12 V side if it can provide 6 A, use a LM317, a bypass transistor - TO-3 type, a few resistors, a power resistor and a variable resistor , some big caps and a few heatsinks ( one for the LM317 and one big one for the TO-3.

The place to get a high current and the heatsinks, big caps is going to an electronics surplus store and look around.

http://www.mcmelectronics.com/product/TENMA-72-7295-/72-7295

http://www.mcmelectronics.com/browse/Single-Output/0000001256

Oh, 12V in
(Ooof.)
Power supply, yes; DC-DC converter, no.
Forget about it.
Regarding that unit linked from PLA, Inc. - “Note: this converter requires user to have basic knowledge of electronics, we cannot provide educational service. DO NOT adjust the output when the module is conneted to load, this may do harm to your load device or the module, please fixed the output before connect to load.”
Also, as they note, the output is always less than the input (12V in, < 12V out); it seems the 12V out will require 15V in.
Keep in spec’ing!

Wire up a switching controller in buck mode, with a programmable resistor for the reference voltage divider. You seldom get less than 1.25V out of the switching controllers, though, because that’s the common reference voltage.
Maxim has a nice I2C programmable resistor that would integrate well with an Arduino: http://search.digikey.com/us/en/products/MAX5387MAUD%2B/MAX5387MAUD%2B-ND/2242954
If you don’t need an arduino, just a knob, go for a regular potentiometer.

You’ll need a pretty big inductor to get one that can take > 6A current, plus a high-current schottky diode, and a low-ESR, high-ripple-current capacitor. However, you can make this work pretty quickly. Biggest problem is where you’ll get the PCB from, unless you have the gear to make it yourself, or hundreds of dollars to do a 24-hour quick-turn order.
There’s a zillion different switching controllers that could work. Getting to 6A is often a matter of applying your own power MOSFET instead of the built-in switching transistors, and scale up the external circuitry to match. You could do that with a good-old MC34063, even.

How fine grained control do you need? If you only need 4-5 different options, you could just wire up a number of separate regulators, and switch between them with relays.