Getting a dual supply for opamps from a single ended AC supply

Discussion in 'The Projects Forum' started by Circuitfreak101, May 2, 2016.

  1. Circuitfreak101

    Thread Starter New Member

    Apr 13, 2016
    11
    0
    Hi guys.
    I've experimenting with obtaining a dual + - 15V supply from a single 17V AC in by using 2 diodes as half wave recitifiers and then feeding their output into 78 and 79 regulators. It works but I'm thinking there must be a better more refined circuit that does the job. The resulting power supply is being used to power some high gain mic pre amps so I need a nice stable low noise output from it.

    Any ideas ?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    For low current, two half wave rectifiers are fine.
    I don't know what "more refined" would be.
    Add some extra filtering at the rectifier and regulator outputs if power supply noise is a problem.
    You can also add a small resistor in series with the power to the preamp power pins, with a capacitor to ground at that point to further suppress any supply noise. The resistor should be sized so as to drop no more than a fraction of a volt at the preamp operating current.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    78 and 79 regulators have relatively high analog noise on their outputs. Consider the LM317 and LM337 regulators as alternatives.

    ak
     
  4. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    The 2 rectifier method is the only cheap, reasonable way to do a low current dual supply off a single winding. The next step up would be a charge pump or an inverting switching supply. Way too much complication for a job that can be done with a couple of capacitors and a couple of regulator chips. You're barking at a non-problem. Yeah, it looks simple to the point of looking crude, but that's all you need for a mic pre-amp.
     
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