Help choosing transistors for current control

[GooeyGus]

Hi guys,
I'm starting a new project, building myself a good variable power supply for driving diodes, or whatever else I feel like powering. I've obtained a non-adjustable 24V 37.5A power supply and am going to be using that as the 'meat' of my power supply.

Now, being that this is not adjustable, I need to build a means to adjust the current and voltage. I figured the best way would to be to use some MOSFET's, but I could be very wrong.

This will be my first circuit that I'll be building that utilizes transistors for current control. In the past I've built all sorts of circuits using voltage regulators and that sort of thing, but nothing that can really deliver a lot of current like I need.

I'm having trouble picking out specific components, because I don't really know exactly what I need. I know I'm going to have some analog gauges for both voltage and current, and I know I'm going to need to build a circuit to control the transistors but again I've never done this before so I'm just looking for some pointers.

I want it to be adjustable via potentiometer on the front panel of the box, and have as much 'fine tuning' resolution as possible.

Thanks in advance for the help!!

[FourDee]

How much current exactly do you want? Do you want modulation?

[lasersbee]

Hey GG..
I would start with a Google search for some 40Amp (minimum) variable PS circuits...
and for fine tuning control... look into multiturn pots... like my 40 Amp commercial
LD Driver uses...


Jerry

[-bart-]

for driving diodes, or whatever else I feel like powering

You really have to be a lot more specific than that.

A schematic that turns a generic 24v supply into a universal anything-you-feel-like-powering driver, will be hard to find.

Keep in mind that if you 'll build a supply using a 'simple schematic' that does 0-24v 0-30A, that if you try to drive 30A at 2.5 V, you'll have to dump 645 Watts of heat.

[GooeyGus]

I knew heat dissipation was going to be an issue... In a perfect world I would love to be able to do 0-24V 0-30A, but I think it would be a pain. The problem is that I'm going to be doing mostly low voltage high amperage stuff. I can't imagine ever needing more than 9VDC.

[mixedgas]

10 or 20 250 watt NPNs with a beta of at least 60.

or a array of fets. These are good:

http://www.goldmine-elec-products.co...?number=G16711


place 20 or 30 of them a in array, on a heatsink, with the packages nearly touching so their gain vs temperature tracks. Use a .45 ohm resistor in each source for stabilty by degeneration. sum the voltages across all the source resistors with 1 Kohm resistors as the current sense.

Steve

[RedlumX]

Going from 24V to 3V at 30Amps with a linear regulator is definitely not what you ever want do to, unless you want to use a huge fan cooled tunnel acting as a room heater (or use water cooling). The only good way is to use a switchmode regulator, but that's not exactly an easy task for this current. Don't waste your time and $ on this!

[Hemlock Mike]

Old thread -- new idea.
Has anyone tried using a large IGBT transistor for current regulation?

Mike

[mixedgas]

Old thread -- new idea.
Has anyone tried using a large IGBT transistor for current regulation?

Mike

They like to be on or off, some do linear but most dont.

steve

[laserbiker]

I suggest you look into mean-well DC to DC converters. You may find one on ebay. I am using a 300 volt to 5 volt converter it can supply 40A and the output voltage is easily adjusted. Visit their web site..
For the 300V supply I use a simple voltage doubler circuit using parts from an old computer power supply.
Good Luck