Transformers producing +/- voltages

Discussion in 'General Electronics Chat' started by Federov, Dec 6, 2010.

  1. Federov

    Thread Starter New Member

    Sep 14, 2010
    So I recently bought this transformer from radio shack:

    When I was buying it I thought it would fit my needs but from what I can tell it wont =(. Here are the requirements I need to power my circuit:

    +/- 20 Volts for the Op-amps.

    + 5 Volts for Micro-controller.

    I was hoping to achieve this by using fixed voltage regulators, but the thing I forgot about was the -20V's. I know you can ground the center tap on the transformer and get +/-12.6V, but does anyone have some technique of getting +/- the 25.2V its rated for? From what I can tell/know its not possible, but I figured I would ask.
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    You could use a voltage doubler arrangement as shown ...
  3. SgtWookie


    Jul 17, 2007
    Just an expansion on t_n_k's circuit - how you can get the regulator source for the 5v output, and what the waveforms look like with no load on the outputs.

    1mF = 1,000uF.
  4. Federov

    Thread Starter New Member

    Sep 14, 2010
    Thanks for the responses, its much appreciated. My only question about the Greinacher circuit is how do I know the maximum current output? It will be supplying a current source, and I need to supply up to 750mA. Can this circuit do it? And is there a way to really know?