current amplifier question (with a little LabVIEW)

Hello, I need to design a current amplifier. I'm trying to design a virtual instrument in LabVIEW to which I can type in a current (for
example 1.5 Amps) and then have that current realized at the output of a current amplifier. I believe LabVIEW will provide a small voltage which I can feed into the current amplifier and then use the output of that.
I'm going to be using this to drive a real small load of only 15 Ohms. and would like to be able to push 2 Amps through it (this would be my maximum current). I think I will be driving the amplifier wtih millivolts from that DAQ. So I guess this would be the same as having a 30 Volt output?
This is the first time I've ever attempted to design an amlifier and was wondering if anyone could give me a little guidance or point me in the right direction. I think what I'm trying to make is a: voltage controlled current amplifier. I was wondering
1) Where should I be looking for something like this, at Op-Amps, FETs, BJTs? 2) Whats the difference between a current amplifier and a voltage amplifier, in this case it seems like you could describe this as either.
appreciate any help i could get with this thanks joshua
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panfilero wrote:

That's a lot of current. Opamps don't do that much. You didn't mention the max frequency. If audio or at least under 50kHz you could look at larger audio amps. National, TI etc. Else you'd have to follow the opamp with some beefy transistors. Driver chips such as the LH0063 and LH0033 have unfortunately become almost extinct. I kept a few just in case but I wouldn't design a new circuit with these. Also, don't forget a rather large heat sink if this needs to operate more than a few seconds ;-)
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Regards, Joerg

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Hmmmm.... it's not for any audio purposes, i just need a steady current at the output. When you mention larger audio amps, are you talking about Op-amps ot transistors made by National, TI...etc? Would you say this may be a little difficult to make? If it ends up too much work to build a good realiable current amplifier, I would just go purchase one instead.
thanks joshua
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End of story then.
You have to buy the appropriate hardware modules from National Instruments.
So, not only do you get a shitty visual programming language you also have to shell out $84121.54 for the rest of the stuff.......
Bummer
DNA
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message

Yep, I use LabWindows at work. Actually a great piece of software even if you only need to do some windows programming without driving instruments.
But, NI have insane prices manyu places. For example a GPIB board or USB GPIB costs 800$. But looking at the board it looks like an ethernet board that costs 10$ with very low part counts. I guess the NI profit comes from selling these converters......
So when I wanted a system at home, I bought cheap USB to serial converters and used the serial inputs for the instruments. That worked, but cost me many hours of programming using the SCPI command language. But otherwise the GPIB cables and the GPIB card would have cost me half all my instruments.....
Also, I like the CompactDAQ system, but also rediculous prices here.
Regards
Klaus
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I have LabVIEW 8.0 and an NI DAQ already, i just want to be able to ampify the output signal from the DAQ, I'd like to build my own current amplifier for it, but I've never built an amplifier before. I need to get the current up to a maximum of 2 Amps.
thanks joshua
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If you're after low development cost and time, check out http://www.apexmicrotech.com
They make real big opamps, but be prepared to pay through the nose for them.
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panfilero wrote:

We are not there, yet.
Will the signal in and out unidirectional or bidirectional?
What will be the maximum frequency or time rate of change of the output current?
Must one end of the 15 ohm load be grounded or connected to some other voltage, or is it a two terminal device that you can connect to your driver as needed?
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panfilero wrote:

Me thinks it will be better for you to buy some prefabricated modules, because a current amp with that power is not an easy project. If you need only an unipolar and slowly changing signal, a programmable power supply would probably be the easiest. It could be set in current limiting mode and can be adressed via RS232 (or USB). If the output shall be bipolar and of higher frequency content, you can easily modify an DC-coupled audio amp like those vintage Crown DC350A, if there is the possibility of putting a small sense resistor in the gnd-leg of your load. I don't see how LabView can provide "some small voltage" without extra hardware. Everything else (fix gnded, floating) is also possible but requires some additional circuitry. At the end, why don't you descibe your load a bit better, or what you want to achieve? I'm sure you'll get much more useful responses.
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ciao Ban
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my load is a Shape Memory Alloy wire.... its basically a wire that will contract when he heated, so I need to put current through it in a range from 0-2 Amps. I'm going to be using a few millivolts at the input of my "current amplifier" to drive it. I need to keep a steady (DC) current through the wire... I'm having a hard time finding anything online about building a current amplifier, most everything always seems to be related to audio amplifiers.
thanks joshua
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