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Home > Archive > Electrical Engineering > January 2007 > current amplifier question (with a little LabVIEW)
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current amplifier question (with a little LabVIEW)
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| panfilero 2007-01-25, 5:25 pm |
| 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:
> 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.
>
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 ;-)
--
Regards, Joerg
http://www.analogconsultants.com
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| panfilero 2007-01-25, 5:25 pm |
| 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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| Genome 2007-01-25, 5:25 pm |
|
"panfilero" <panfilero@gmail.com> wrote in message
news:1169761279.767237.167960@v45g2000cwv.googlegroups.com...
> Hello, I need to design a current amplifier. I'm trying to design a
> virtual instrument in LabVIEW
>
> appreciate any help i could get with this
> thanks
> joshua
>
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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| Matthew Beasley 2007-01-25, 5:25 pm |
| 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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| Klaus Kragelund 2007-01-25, 5:25 pm |
|
On 25 Jan., 23:31, "Genome" <mrspamizg...@yahoo.co.uk> wrote:
> "panfilero" <panfil...@gmail.com> wrote in messagenews:1169761279.767237.167960@v45g2000cwv.googlegroups.com...
>
>
>
> 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 $84121.54 for the rest of the stuff.......
>
> Bummer
Yep, I use LabWindows at work. Actually a great piece of software even
if you only need to do some windows programming without driving
instruments.
But, NI have insane prices manyu places. For example a GPIB board or
USB GPIB costs 800$. 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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| panfilero 2007-01-25, 5:25 pm |
| 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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| John Popelish 2007-01-25, 8:25 pm |
| panfilero wrote:
> 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.
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?
| |
|
| panfilero wrote:
> 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
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.
--
ciao Ban
Apricale, Italy
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| panfilero 2007-01-26, 5:25 pm |
| 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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