plz help to design the adjustable 12VAC circuit

Discussion in 'The Projects Forum' started by elektroman, Mar 11, 2009.

  1. elektroman

    Thread Starter New Member

    Mar 11, 2009
    Hello dear all

    I'm Irfan and I have searched alot to find the the circuit that can adjust stepdownd 12V AC with 1Amp or 0.5Amp current like variac device(vary the AC voltages by using winding tapings),but i havnt found yet.Let me tel u all, mostly every where I have DC adjustable circuit with LM317 etc., 1 thing more I dont wana use transformer secondry tapings to vary the AC voltages on diffrent secondry positions I just want 12vac from 240 v main, using step down transformer and wanna make it vary...plz plz help me........

    Thanking u all in anticipation....
    Last edited: Mar 12, 2009
  2. SgtWookie


    Jul 17, 2007
    1 milliamp or less? What are you going to do with so little current?

    If you don't want to use a transformer, then you'll need to use batteries, and build an oscillator circuit.

    It is very dangerous to attempt to power circuits directly from the mains without a transformer.
  3. thingmaker3

    Retired Moderator

    May 16, 2005
  4. elektroman

    Thread Starter New Member

    Mar 11, 2009
    sorry dear I did spell mistake its ampere(amp) and let me tll u I used the word stepdownd its mean im using 240vac to 12 vac stepdown trasformer....thanks for reply

    Last edited: Mar 11, 2009
  5. bertus


    Apr 5, 2008
  6. DickCappels


    Aug 21, 2008

    What you probably need is an buck converter. As far as I know, this forum will not give you assistance for a circuit that connects directly to the power line without a transformer of some kind for isolation. I think this is a safety concern. Circuits that connect directly to the power lines should only be designed and tested by people with a lot of experience in the design of this kind of circuit, a thorough understanding of the dangers and safety practices, and only when properly trained medical help is available (never work on line powered equipment when alone.)

    You can step down and regulate AC. I once hired a consulting company to do that. It was complicated and it was very difficult to make it reliable. If you really need to do that (simulate a Variac with AC in and AC out), I suggest you hire a consultant who has experience in this). Even better would be to use a transformer or a Variac.
    Last edited: Mar 11, 2009
  7. thatoneguy


    Feb 19, 2009
    Choice A) Variac.

    Choice B) Non Sinusoidal adjustable RMS AC. A Triac with some support components could accomplish the task. If a closer representation to a sinewave is required, adding a multiple pole low pass filter could help, though unsure about the current levels.

    Choice C) Sinewave generator IC feeding a variable gain power amplifier having a stout DC Power supply. This option keeps you away from line voltages completely, outside of the power supply for the amplifier.