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seek automobile 5.5V power

Discussion in 'Electronic Design' started by 2007 May, Jun 6, 2007.

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  1. 2007 May

    2007 May Guest

    Seek automobile 5.5V switching power supply circuit.
    Require over voltage (when car is jump start), over current, surge and
    transient protection circuits.
    What IC would you choose? Is ON SemiconductorNCP1200 a good choice? Thank
    you for you advice.
  2. martin

    martin Guest

    5.5v at what current?
  3. 2007 May

    2007 May Guest

    around 800mA.
  4. mpm

    mpm Guest

    The National Semiconductor LM2575T-ADJ will handle that.
    They make a high-voltage input variety, but even the normal one
    handles 40-volts in, or something like that. 1.5A out. It's a
    switcher, so you'll need a Shottkey diode, an inductor, and input &
    output caps. Switching frequency is 52kHz, so parts size /
    availability / cost / real estate are all within reason.

    For protection, you could design circuits ahead of this (don't forget
    the fuse too).
    Also, the LM2575T has a shutdown pin if that helps?
    And because it's a switcher, it'll produce less heat compared to a
    linear regulator, and you might not need a heat sink.

    ON Semiconductor 2nd sources the LM2575T-ADJ, so look there too.

    Note: Take this for what's its worth. There may be better options
    out there for you...
  5. 2007 May

    2007 May Guest

    Thank you mpm. Can you tell me where to look for over voltage (when car is
    jump start), over current, surge and transient protection circuits. Also, I
    was told to use a PTC (Positive Temperature Coefficient) device. Can you
    tell me where to find this kind of devices & circuit?

    So far, I found Vishay 2381 PTC Thermistors seems to be applicable to over
    temperature. Zener Diode with SCR thyristor seems to protect on
    over-voltage. But how about protection of over-current, surge and transient?
  6. w_tom

    w_tom Guest

    Restart you quest for information by learning about 'load dump'.
    Both ISO and SAE have standards for this automotive problem that must
    be addressed in the design of that power supply.

    For example, a 40 volt regulator is not sufficient. Load dump on 12
    volts is defined as up to 260 volts - but designs should make at least
    60 volt electronics protection sufficient.
    SGS Thompson put this in a 1996 application note of numbers your
    design must address:
    "The overvoltage is named the load dump and can be defined by the
    following figures:
    - Peak voltage 80 to 100 volts
    - Duration 300 to 400 milliseconds
    - Series resistance 0.2 to 1 ohms"
  7. 2007 May

    2007 May Guest

    Thank you Tom. Can you tell me what kind of device or circuit I should look
    at for 'load dump' protection? I understand to simulate "load dump", you
    charge capacitors in test fixture, and then discharge into Device under

    Can you give me the link to this SGS Thompson 1996 app note?
    Are you talking about STMicro's RBO40-40 type of devices?
  8. mpm

    mpm Guest

    I'm curious now.
    Can you tell me exactly what you are building?
    Or at least enough go get the drift...

  9. 2007 May

    2007 May Guest

    Similar to auto cigarette plug to power wireless prototype boards.
  10. w_tom

    w_tom Guest

    The SGS Thompson part is installed in auto electronics by the
    manufacturers. But as the app notes says, that still is not
    sufficient protection. As noted earlier, your designs must be
    undamaged by 60 volts on the 12 volt circuit. That is why some
    semiconductor manufacturers make a different line of regulators for
    automotive service. How reliable must your electronics be. Then the
    power supply must withstand even high voltages without damage.
  11. There was a thread discussing some of these issues few months ago:

  12. D from BC

    D from BC Guest

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