Eqn. for current

Discussion in 'The Projects Forum' started by pratapkollu, Jan 9, 2007.

  1. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    Some please tell me the equation for CURRENT OUT in the circuit that is given in attachment. And please tell me how to calculate the transfer function( equation for current)

    Thanks and regards
    Pratap
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    655
    If you understand the following three things, you can understand the analysis in the attached schematic.
    1. Ohm's law.
    2. Operational amplifiers (and feedback theory).
    3. MOSFETs.
    If there is something you don't understand, post it here.
     
  3. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    HI, Thanx for your explanation, can u please give the eqn for current as function of resistors and input voltage? for ex: I = [r2/ (r1.r3)]. Vi
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    655
    Why don't you provide a schematic with reference designators (r1, r2, etc.), figure out what you think the transfer function is, and we will tell you if it's correct or not.
     
  5. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    I dont know the exact eqn for current , I just gave u that eqn to let u know that I need the eqn for current as function of resisor newtwork and input voltage

    Thanks and regards
    Pratap
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    What resistor network? The output depends on the gate voltage of the second FET. That comes from the output of the second op amp, which is being driven by the first op amp. The limit is 100 milliamps into a 50 ohm load.

    If you can get a transfer curve for the FET, find the voltage on the gate that corresponds to the D-S resistance necessary to allow 100 milliamps into your chosen load. Hint: the circuit is dynamic, so no calculation will be valid except as it applies current into some load. As there is no load in the schematic, output current is zero. Put some resistance between the terminals and see what happens. One suspects further that the 5 volt control level may correspond to 100 ma into 50 ohms.
     
  7. pratapkollu

    Thread Starter Active Member

    Dec 13, 2006
    42
    0
    Thank you very much for the replies.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    655
    I didn't even look at your equation. I just suggested that
    You should be able to do that from the output current equation that I put on the schematic. Just substitute R1 for 499, etc.
     
  9. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I think what Ronh is asking of you is that you examine the annotations from his attachment and use your schematic containing the reference designators (R1, R2, R3, etc.) to produce the circuit's transfer function.

    Ronh's has done a stellar job of annotating the schematic. He has even left the values of all of the resistors and the power supply voltage in the final expression.

    hgmjr
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    655
    Yes, that's what I am asking.
    Thanks for the compliment. I should point out that the power supply voltage does not appear in the final expression. Perhaps you meant "control voltage".
     
  11. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Oooooppppssss!!!!!! You're correct. I did have the control voltage in mind when I typed power supply voltage.....

    hgmjr
     
Loading...