Autotransformer vs. conventional

Discussion in 'The Projects Forum' started by raisintoe, Mar 24, 2012.

  1. raisintoe

    Thread Starter Active Member

    Mar 24, 2012
    I have a project which requires some strange voltages. It is an LCD screen, and requires -22VDC, +5VDC and then 100VAC at 500Hz for the back light.

    For this project, I decided I ought to make my own transformer. But I am not sure what type of transformer to build.

    My power source being 120VAC (60Hz), I figured that the best way would be to use an auto-transformer set-up for the 100V, and use an isolated transformer (coupled with it) for the -22, and +5 VDC.

    My question is whether or not I could use an auto-transformer set-up for the whole thing. I have been taught that an auto-transformer should only be used in slight step-up/step-down configurations.

    could I use an auto-transformer for all the different voltages? Is there anything wrong with doing that?
  2. jimkeith

    Well-Known Member

    Oct 26, 2011
    Avoid using an autotransformer because it does not provide the required isolation.

    My suggestion is that you make a low voltage power supply using a conventional step-down transformer to provides ±22VDC. Then put in something like a National simple switcher IC to get +5V. Since your 100VAC @ 500hZ is low power, it may be generated by a small inverter and 500hZ transformer that runs on 22VDC.
  3. panic mode

    Senior Member

    Oct 10, 2011
    do you have datasheet for the unit?

    AAC Fanatic!

    Jul 1, 2008
    Not true. Ignition Coils, Flybacks and Variacs are all forms of autotransformers.

    EDIT: I appear to be in error. Ignition coils have isolated primaries and secondaries.
    Last edited: Mar 26, 2012
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
    Please explain how an ignition coil is an autotransformer?

    Oh I get it..... its a transformer in an AUTOmobile;):D:):p:rolleyes:

    AAC Fanatic!

    Jul 1, 2008
    Uh, it's either what you said or a brain fart. I'll correct that. How come we don't have embarrassment smilies?
    shortbus likes this.