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convert voltage to current

Discussion in 'Electronic Design' started by alireza_s85, Jun 1, 2007.

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  1. alireza_s85

    alireza_s85 Guest

    i need a ic that covert the voltage to current , capable to be sink
    and source
     
  2. Donald

    Donald Guest

    This does not make sense !!

    Please explain what you really need.

    thanks

    donald
     
  3. BobG

    BobG Guest

    =======================
    Resistor in feedback loop of an opamp voltage follower?
     
  4. He's talking about a transconductance amplifier, which has
    a voltage input and current output. You can make discrete
    circuits that do this, as Tony Williams and I have written
    about here on s.e.d., but an transconductance IC would be
    much easier. Burr-Brown offers OTA ICs, or operational
    transconductance amplifiers. The opa660 was a favorite
    of mine, because of its current programmability, but TI
    has just replaced it with the opa860 and opa861 parts.
    http://focus.ti.com/docs/prod/folders/print/opa860.html
    http://focus.ti.com/docs/prod/folders/print/opa861.html

    They have a raft of application notes, which are most
    easily found by searching on opa660. I find that OPA
    ICs can be very useful in making precision integrators,
    ramps, log converters, gyrators, etc., but Burr-Brown's
    app notes concentrate on making amplifiers, etc., which
    to my mind is better done with ordinary opamps.
     
  5. D from BC

    D from BC Guest

    An op amp with feedback off a current sensing resistor.
    D from BC
     
  6. whit3rd

    whit3rd Guest

    In addition to OTA, one can use a pair of current mirrors, op amp,
    and sense resistor.

    Feed program voltage to (+) input of op amp; connect (-) input
    to output, and run a resistor R from output to ground. Input of
    current
    mirror (two matched transistors, or three if you want to be fancy)
    connects to each of the power leads to the op amp. Connect both the
    current mirror outputs to the load, and of course feed the
    current mirrors from appropriate +/- power supplies.

    Compliance should be within a volt of power supply, bipolar.

    The idea is that the imbalance in the current from the op amp power
    pins is due to the output current (in that sense resistor R). The sum
    of the current mirrors is equal to the difference of those two
    currents,
    thus equal to the current in the sense resistor, which has GND at
    one end and your signal (program voltage) at the other (because the op
    amp is configured as a voltage follower of the input signal).

    Alas, it isn't just 'an IC'; it takes at least two chips.
     
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