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Multiple Regulators Question.

Discussion in 'Electronic Basics' started by Mike C., Oct 19, 2003.

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  1. Mike C.

    Mike C. Guest

    What kind of problems am I asking for by this setup?

    I have regulated input power of 24VDC at 1amp.

    The 24VDC is dropped down to 12VDC using a linear (7812) to run one
    device (200mA). The Linear has a large Heatsink.

    The 12VDC gets dropped again using a switch (LM2674) to 5VDC to run
    another device (100mA).

    The 5VDC gets dropped again with another Linear to 3.3VDC to run an
    MPU (75mA). This Linear has no Heatsink.


    Am I asking for trouble doing this?
    If so, what can happen?

    Mike C.
     
  2. Baphomet

    Baphomet Guest

    From a quickie look at some of the specs., it looks like everything is well
    within dissipative limits. If so, the question then becomes one of
    reliability. If the first regulator fails in the open mode, you will lose
    all of your voltages but then again, maybe that is precisely what you want.
    It's hard to tell from the way you posted the question.
     
  3. SHAUN

    SHAUN Guest

    Mike what devices are these source voltages running and how many amps are
    they pulling?
     
  4. SHAUN

    SHAUN Guest

     
  5. Mike C.

    Mike C. Guest

    Thanks for answering..

    As far as losing the 1st regulator open, I would want all other power
    lost.

    The 5VDC circuit has a crowbar circuit set at 5.6VDC. In a disaster
    when the 1st regulator shorts and 24VDC is passed through, the crowbar
    *should* protect the components on the 5VDC side. If the 5VDC to
    3.3VDC circuit fails shorted, the MPU circuit also has over-volt
    protection.

    Mike C.
     
  6. CFoley1064

    CFoley1064 Guest

    What kind of problems am I asking for by this setup?
    Perfectly acceptable, but make sure you have a good output cap (low ESR at
    higher frequencies) for the 7812, and use a low dropout regulator for pulling
    the 5V dowm to 3.3V -- you'll have bad regulation if you use an LM317, not
    enough headroom.

    Good luck.
    Chris
     
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