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Power Supply from Automotive System

Discussion in 'Electronic Design' started by Chris Maryan, Sep 13, 2003.

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  1. Chris Maryan

    Chris Maryan Guest

    Can anyone point me to how one would go about designing a power supply for a
    small microcontroller (5V) from a very poorly regulated automotive 12V
    supply? My main concern is feedback from the ignintion system which I
    understand causes significant voltage spikes. Is there a one chip solution?

    Thanks,

    Chris Maryan
     
  2. Chris Quayle

    Chris Quayle Guest

    You need an LC low pass filter on the input and a transient limiting
    diode (transorb ?) at the other side of it, then you can go straight
    into a 7805 style regulator, assuming you don't need too much current.

    Have built quite a few of the above for projects and one thing to note
    is the avoidance of ground loops inside the box, which is ideally metal
    throughout. The incoming filter and power ground should be as close as
    possible to the input wires and all the circuitry from then on floats. I
    use small diecast boxes as they are cheap, easily machined and fully
    screened.

    Chris
     
  3. Ian Stirling

    Ian Stirling Guest

    Probably.
    The right way is to as the other poster suggested use an LC filter.
    However, if you don't need lots of power, a simple and reliable option is
    something like a resistor dropping a couple of volts at the maximum current
    drawn by the micro circuit, a 1N4007 diode in series and a big capacitor
    (time-constant of a second or so) and a 7805 on the end of it is the easy
    solution.

    For minimum parts count, you might even get away with the resistor and a
    zener with a capacitor across it.
     
  4. Jeff

    Jeff Guest

    LT3010-5 seems interesting for low current apps.
    and has a very wide DC input range.
    Jeff
     
  5. ST Microelectronics have some application notes which may help.

    http://us.st.com/stonline/books/pdf/docs/3583.pdf

    describes the automotive electrical environment, and

    http://us.st.com/stonline/books/pdf/docs/3584.pdf

    discusses applying their devices, plus the data sheets are available.

    Regards
    Malcolm.
     
  6. Jim Thompson

    Jim Thompson Guest

    [snip]

    Back EMF "from the coil" doesn't appear at the battery, and full load
    dump doesn't either anymore. Look at the wiring differences between a
    '60's car and a modern one.

    ...Jim Thompson
     
  7. Jim Thompson

    Jim Thompson Guest

    I think 42V systems will still have load dump issues, perhaps not
    quite as high a voltage pulse since the currents will be lower.

    ...Jim Thompson
     
  8. David Lesher

    David Lesher Guest

    Err, I seem to recall 15KW continuous/30 peak being mentioned....
     
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