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Current sources

Discussion in 'Electronic Design' started by john, Jan 13, 2006.

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  1. john

    john Guest

    Please look at the following data sheet of an instrumentation amplifier


    I am using it as a constant current source ( figure 16, page 13 ). I
    made the following changes in the circuit

    1. I put a capcitor in series with the load for AC coupling reason.
    2. The power supply of the circuit is +/- 15 volts.

    I have a following questions about the circuit.

    1. For example, if the circuit is producing 100microA and the load
    resistance is 1mega ohm then the complaince voltage will be +/- 10
    volts or the voltage across the load will be +/- 10 volts. How can I
    keep the complaince voltage or voltage across the load equal to +/-
    0.7 volts with the current of 100microA without changing the power
    supply which is +/-15 volts?

    Please advice!
  2. Rich Grise

    Rich Grise Guest

    Well, what load resistance would develop 0.7V with 100 uA through it?

    What's the reactance of the cap at the frequency in question?

    Good Luck!
  3. john

    john Guest


    I am using a iridium oxide material as a load. when voltage exceeds the
    +/- o.7voltage limit, the material breaks down. I need to protect the

  4. john

    john Guest


    +/- 0.5 will be ok too! please advice

  5. How close to 0.7V do you have to go? Would (say) 0.5V compliance be
    enough, or do you need 0.699V?

    Best regards,
    Spehro Pefhany
  6. Rich Grise

    Rich Grise Guest

    What, exactly, is the specification of the load? Are you sure that
    what you want to use on it is a "current source", when the load is
    so touchy about voltage?

    What is it you're trying to accomplish? Please give an overall overview,
    like, "I'm trying to do so-and-so with such-and-such a thing, and the
    thing looks like this..." that sort of thing. (redundancy unintended,
    apologies to the pedant contingent ;-).)

  7. Ian Stirling

    Ian Stirling Guest

    If 0.6V (about) would do, then a couple of standard diodes across it
    will work.
    For 0.7V, two shocketty(sp?) diodes in series may work.
    If the sole aim is protecting the device.
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