Analog control of a 12v, 2A supply

Forum 2005-2010 (read only) Hardware Interfacing
1

I want to use an Arduino to control a 12v, 2A circuit and I need some advice on what components to use to make the interface.

My main concern is that I want the control to be fairly smooth. I don't want to use the raw PWM output because it can introduce a bunch of high frequency noise that I don't want. I can low-pass filter it with a simple RC circuit, but then I need to know what kind of components to use to have the resulting analog 0-5v output adjustably attenuate the power supply.

I think I need some kind of adjustable linear regulator, but I'm just not very familiar with these parts and so I don't know what one will handle the 2A currents that I'm using.

I hope this is an easy question. I also hope I'm not bringing an old question that has already been answered back up. I searched the forum before I posted and found some helpful ideas, but not all my questions were answered so I wanted to post.

Thanks.
James

2

Here's one good video tutorial about driving bigger loads: Transistor / MOSFET tutorial - YouTube

3

I like that video. Thanks for the tip.

But if I understand correctly, the current across the MOSFET increases exponentially with the gate voltage. So they're great for switching, but maybe not so great for analog control. Am I mistaken?

I don't need it to be perfectly linear, but I want it to be somewhat close.

4

Maybe a BJT is what I should use?

5

Check this
http://www.arduino.cc/playground/Main/RegulatedPositiveVoltageBooster

6

What range of output voltage to you require? Do you need to go to zero?
How much current are you going to draw at the low voltages?

If you adjust a linear supply from 12V to 2V and draw 2A you
are dissipating well over 20W in the regulator
[I originally had 200W which is what you get when you mutliply 10*2 before a Cappuccino :wink: Ran Talbott is correct with the 20W value. Sorry about that.] The good news is that
the dissipated power quickly drops to 0 after the fire :wink:

You really want a DC-DC converter. A lot of converters can trimmed
with a DAC.

(* jcl *)

www: http://www.wiblocks.com
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blog: http://luciani.org

7

If you adjust a linear supply from 12V to 2V and draw 2A you
are dissipating well over 200W in the regulator.

If you feed the regulator an unregulated 15V or so, you can bring that down to 20-30W. Which is still a lot, but more manageable.

This surplus L165 is cheap, and rated to handle the load. It would need some major heatsinking, though. Probably including a fan.

At that price, I'd recommend buying a few, 'cuz you may well smoke one or two getting the setup right.

8

My 200W value is wrong. 10V * 2A only equals 200W before a Cappuccino :wink:

Ran Talbott is correct with the 20-30W value. Thanks Ran.

A thermal solution in the 3-4degC/W could be difficult.

(* jcl *)