Voltage to Current converter

Discussion in 'The Projects Forum' started by pratapkollu, Dec 13, 2006.

  1. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
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    0
    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
     
  2. Papabravo

    Expert

    Feb 24, 2006
    9,912
    1,724
    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.
     
  3. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    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
     
  4. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    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
     
  5. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    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
     
  6. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    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
     
  7. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    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.
     
  8. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    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
     
  9. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    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.
     
  10. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    Yes, you are right, I need some "X" amount of current, Can you comment on the 2 circuits I uploaded?

    Thanks and Regards
    Pratap
     
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,590
    777
    I took a look at the second one, and changed it into this. You just need to invert your input voltage.
     
  12. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    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
     
  13. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
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    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
     
  14. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    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
     
  15. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    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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