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Op amp supply

  1. Aug 8, 2009 #1
    I have a circuit with single supply lm324 and I need to replace them with precision opamps but I can only get dual supply ones. How would I connect the dual supply opamps in the circuit?
    (the circuit also has PNP and NPN transistors).
     
  2. jcsd
  3. Aug 8, 2009 #2
    Use a precision band gap reference to generate a virtual ground if feasible. They come in several flavors, 1.23V, 2.5V, 5.0V, etc.

    Exactly how you can impliment what you want depends on a lot of factors, like how much precision, what frequency range, where does the precision have to be, etc.
     
  4. Aug 8, 2009 #3

    berkeman

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    Staff: Mentor

    What power rails do you have available? Why can't you get single-supply CMOS opamps? Have you done much searching? What voltage range is your signal, and what kind of gain/functionality are you using the opamp for?
     
  5. Aug 9, 2009 #4
    For single supply operation, I usually make a "virtual ground." Make a resistor divider from Vcc to ground and bypass it with a cap to ground (2x100K resistors and a .1uF). Then, follow it with a unity gain op-amp buffer (use a cheap op amp).

    Put a 33 ohm resistor between the output of the op-amp and the "virtual ground," and bypass the virtual ground to real round with a 47 - 100uF cap.

    There are cheaper ways, and there are better ways, but you can usually depend on this method without taking more into consideration.

    - Mike
     
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