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Variable Bipolar Power Supply

Discussion in 'Electronic Projects' started by Hero999, Sep 27, 2006.

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  1. jfice13

    jfice13 New Member

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    As a followup, I do realize that the op-amp does not have a resistor on it's positive leg to counteract the input bias current as it should for a precision integrator. Obviously you'd want to use something like a JFET input op-amp with low input bias current and a resistor that on the positive leg that is equal to the equivalent resistance seen from the negative leg to mitigate integrator error.

    Like I said previously, however, this is just a quick schematic for a proof of concept and the values don't really matter nor does it have all the trappings of something you'd want to build.
     
  2. Roff

    Roff Well-Known Member

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    Jfice13, much of this thread is about stability and transient response. Read my post #11. It suggests adding the cap to make an integrator of the op amp.
     
  3. mneary

    mneary New Member

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    Not obvious to me. The worst bipolar op amp I could find has a worst case bias current of 1.5µA. Even if you fail to put a resistor in the (+) input, the 6k ohm equivalent resistance could cause an offset error of only 9 millivolts. I would select an op amp based on input offset voltage, which rules out most JFET input op amps.
     
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