HELP?? Convert to 12V DC

Discussion in 'General Electronics Chat' started by wcavanagh, Sep 18, 2007.

  1. wcavanagh

    Thread Starter New Member

    Aug 27, 2007
    Hi people.
    Got this circuit all working, but it runs off mains 240V AC. I would like to convert it to run of 12V DC.

    It has a 0 Crossing test, to check the 240V so need to fool this into thinking its all good, to run the program in the PIC.

    Any ideas? I can power up from 12V DC by supplying 12V to D1. But the self test fails.

    HELP please :)

  2. beenthere

    Retired Moderator

    Apr 20, 2004
    It is impossible to tell what is going on from your description. Can you post up a schematic?
  3. wcavanagh

    Thread Starter New Member

    Aug 27, 2007
    Doh I forgot to attach it, hehe.
  4. niftydog

    Active Member

    Jun 13, 2007
    Are you sure the zero crossing "test" isn't actually being used as the frequency reference for the clock?
  5. cumesoftware

    Senior Member

    Apr 27, 2007
    Why don't you use a transformer to lower the voltage first. It is bad practice to connect a LM78L05 regulator directly to the rectified mains voltage, even if you use a resistive association in series and a zenner to control voltage (that is C1, R1, R2 and R15). Don't forget that you have a variable load, and so, the current biasing the regulator will vary, and the regulator may deep the voltage from the zener. Also, your project without a transformer will drain much more current than with it. More current translates into more power, and since with that extra input power you will have the same output power, expect most of it to be converted to heat.

    In other words, you really should consider using a transformer.
  6. wcavanagh

    Thread Starter New Member

    Aug 27, 2007
    The kit is designed that way without tranny. I really want to run and control 12V DV lamps, as was hoping as they are converting 240V to 12V with that Zener, that I could fool it into thinking its running on 240 AC, and then it will pass the test.

    Info on the kit is here.

    Any help would be fab.