Powering Op Amps

Discussion in 'The Projects Forum' started by magikal, Dec 26, 2008.

  1. magikal

    magikal Thread Starter Active Member

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    How do I generate the negative voltage reference required to power an op amp? I want to use the non-inverted op amp configuration to multiply. BTW I have the LM3900 quad amp chip and the LM1458 dual amp. Is there a simple circuit to generate the negative voltage source?

    Thanks for the help.
  2. beenthere

    beenthere Retired Moderator

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    You will need to make a power supply to do that correctly. Use a center tapped transformer and bridge rectifier to make the positive and negative voltages - http://www.allaboutcircuits.com/vol_3/chpt_3/4.html. A pair of three terminal regulators will complete the power supply.
  3. Audioguru

    Audioguru New Member

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    Opamps do not need a negative supply if their inputs are biased at half the supply voltage. Then the input, output and feedback-common might need coupling capacitors.

    An LM3900 is obsolete and had very unusual inputs.
    The MC1458 is a dual lousy old 741 type. It has poor performance today.

    Attached Files:

  4. magikal

    magikal Thread Starter Active Member

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    what op amps are good and cheap?
  5. Audioguru

    Audioguru New Member

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    I use TL071 single, TL072 dual and TL074 quad low noise, low distortion and fairly wideband opamps. They cost $.53US for one TL071, $.50US for one TL072 and $.48US for one TL074 at Digikey today. They have thousands in stock in many different packages.
  6. gee_emm

    gee_emm Active Member

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  7. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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  8. John Luciani

    John Luciani Active Member

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    For low currents look at the ICL7660. One IC (8 pin dip) + 2 caps to generate a negative supply (similar idea to the 555 schematic that was posted).

    It is low current and unregulated but for a bias supply you may be OK. Some
    versions of the chip add regulators. Intersil, Maxim, TI, Linear Technology and Analog
    Devices all make various versions of these devices.

    (* jcl *)
  9. magikal

    magikal Thread Starter Active Member

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    Thanks for the help, I figure it out. Does anybody know a good analog cheap squaring chip? The input range only has to be -1V to 1V or so.

    I've looked at the AD532, but its a bit too expensive for me.
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