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Current sources 101

Discussion in 'Electronic Design' started by martin griffith, Apr 1, 2007.

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  1. Hi John, think that comes out next month

  2. I must admit I use the simple R and LED, and hadn't thought about it
    that much. But I've never seen the emiitter to ground R before (I'm
    assuming a pnp).

    and, yes, maybe a part 2....

  3. John  Larkin

    John Larkin Guest

    For the simple LED or 2-diode type sources, a major error is the
    voltage divider formed by the bias resistor and the dynamic impedance
    of the led or diodes. A resistor from the transistor emitter to ground
    can cancel this error. Or drive the led/diodes with a very simple,
    ground-referenced current source. Or bypass the hell out of them.

    He doesn't show using an opamp to close the loop around a transistor
    or fet, which gives better dynamic and temperature performance; maybe
    in part 2?

  4. John  Larkin

    John Larkin Guest

    Well, I just invented it!

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