Voltage to Current converter

Thread Starter

pratapkollu

Joined Dec 13, 2006
42
Respected Members
I am developing a GMI sensor, in the negative feedback loop I wish to include a Voltage to Current converter. The input for the V/I converter is 5V dc. I wish to have 100mA output. I developed one converter by op-amp and other is current source using transistors. Can any one please give me a better design either by using op-amp or transistors ?
If possible plz email me the circuit diagram.
Thanks and Regards
Pratap

---------------------
PRATAP.KOLLU, Ph.D. Scholar
Division of Materials Science and Engineering,
Engineering building # 1
Chungnam National University(CNU),
220 Gung-dong, Yuseong-gu, Daejeon 305-764,South Korea.
Phone :+82-42-8216227, pratapkollu@yahoo.com
 

Papabravo

Joined Feb 24, 2006
14,700
If we knew what a GMI sensor was and could see your two designs we would be in a better position to help you. In Southeast Michigan, GMI used to stand for General Motors Institute, although I believe they changed their name at some point in the last decade or so.
 

Dave

Joined Nov 17, 2003
6,970
If we knew what a GMI sensor was...
Its a Giant Magneto-Impedance Sensor. Seems its a fairly new wireless technology from the papers over at IEEExplore and at the Cat.Institute. I'm working from home at the moment so can't bring up the papers till I get back to work.

Perhaps for the purposes of those of us who don't know how a GMI sensor works it would be better to upload the circuit designs the OP is working with and we can look through the design, hopefully we can assume the GMI sensor is a black box with defined chaarcteristics.

Dave
 

Thread Starter

pratapkollu

Joined Dec 13, 2006
42
Hello All
GMI stands for Giant Magneto Impedance, leave abt the sensor design and just tell me abt the Voltage to current converter for 5 V dc input signal.
First design was a simple op-amp(TL-082) V-to-I converter, second one I havnt tried yet. Its current source using 2 transistors.
If you want them in detail, I can send you the circuit diagram
Thanks and Regards
Pratap
 

Dave

Joined Nov 17, 2003
6,970
...
If you want them in detail, I can send you the circuit diagram
...
You can upload the circuit diagrams to the forums. Below the Post Reply dialog box you will see a button called Manage Attachments. Clicking this will open a new window from which you can upload diagrams from your computer. In the interests of those on dial-up, try to use JPGs.

Dave
 

Thread Starter

pratapkollu

Joined Dec 13, 2006
42
Hello

Input voltage is 5 V (d.c.)
Please suggest best condition for 100 mA current output.
In the second circuit( V-to-I converter-2), R1 = 1K, R2= 100 Ohm, R = 100 Ohm, Coil resistance ,Rc= 50 Ohm, Vcc= 15 V. I just used 50 Ohm resistance inplace of feedback coil.

Thanks and regards
Pratap
 

Attachments

Distort10n

Joined Dec 25, 2006
429
Are you limited by the op-amp itself? You may want to look at the OPA561, a power amplifier from Texas Instruments...about 1.2A. Could be a contender in your transconductance application.
 

Thread Starter

pratapkollu

Joined Dec 13, 2006
42
Are you limited by the op-amp itself? You may want to look at the OPA561, a power amplifier from Texas Instruments...about 1.2A. Could be a contender in your transconductance application.
If you have any alternative design for 100mA output voltage to current converter, please share it. I would like to test its performance
Thanks and regards
Pratap
 

Distort10n

Joined Dec 25, 2006
429
It is not really an out of the box transconductance solution with the OPA561. I was wondering if you simply need 'x' amount of current then just use a high current amplifier.
 

Thread Starter

pratapkollu

Joined Dec 13, 2006
42
It is not really an out of the box transconductance solution with the OPA561. I was wondering if you simply need 'x' amount of current then just use a high current amplifier.
Yes, you are right, I need some "X" amount of current, Can you comment on the 2 circuits I uploaded?

Thanks and Regards
Pratap
 

hgmjr

Joined Jan 28, 2005
9,029
pratapkollu,

If you choose to use a dual PNP solution, I would recommend that you use a dual PNP array. In this way, you will obtain better thermal tracking between the two transistors.

hgmjr
 

Thread Starter

pratapkollu

Joined Dec 13, 2006
42
pratapkollu,

If you choose to use a dual PNP solution, I would recommend that you use a dual PNP array. In this way, you will obtain better thermal tracking between the two transistors.

hgmjr
Do you mean like darlington amplifier, please let me clearly know whats u dual PNP array. If you can give me the design or please explain it
Waiting for your reply
Thanks and regards
Pratap
 

hgmjr

Joined Jan 28, 2005
9,029
Do you mean like darlington amplifier, please let me clearly know whats u dual PNP array. If you can give me the design or please explain it
Waiting for your reply
Thanks and regards
Pratap
I was not thinking of a darlington pair. What I was referring to is a package containing two individual PNP transistors such as the example device in the link below.

Dual PNP example

In a two transistor current mirror such as the one kubeek suggested, it is important that temperature of the two transistors track even as the ambient temperature varies. By using transistors contained in the same package, the thermal tracking is maintained. Another benefit is that transistors in the same package are more likely to exhibit matched electrical characteristics such as beta, and Vbe. The closer the transistors are matched, the better the current mirror will perform over varying temperatures and the intended input signal range.

hgmjr
 

Thread Starter

pratapkollu

Joined Dec 13, 2006
42
I took a look at the second one, and changed it into this. You just need to invert your input voltage.
Thank you for sugggestion. I will try it . If you can check, please comment on the first design also.
One more thing is , have u removed the op-amp from my second circuit? are we supposed to take the current output at Q1(as per your design)?, I am providing +15 V as Vcc, have u changed it? Please clarify.
Thanks and regards
Pratap
 
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