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Power Filtering — Parallax Forums

Power Filtering

James LongJames Long Posts: 1,181
edited 2009-05-06 19:44 in General Discussion
Since I'm not the best designer in the world, I would like to ask a pretty simple question.

I'm trying to power a pcb from a 12 volt system with a permanent magnet alternator. I'm worried about noise from the alternator.

With using a switching regulator, what should I include to filter noise from the system.

James L

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James L
Partner/Designer

Lil Brother SMT Assembly Services

Comments

  • kwinnkwinn Posts: 8,697
    edited 2009-05-05 21:18
    A choke (inductor) between the alternator and the power supply input capacitor should be adequate. Auto supply stores used to carry them for radios but I am not sure if they still do.
  • PhilldapillPhilldapill Posts: 1,283
    edited 2009-05-05 22:20
    Also, it's a good idea to put a Low Drop-Out linear regulator after the switching regulator, to further reduce noise. And of course, over-kill bypassing with caps is great too.
  • James LongJames Long Posts: 1,181
    edited 2009-05-05 22:47
    kwinn said...
    A choke (inductor) between the alternator and the power supply input capacitor should be adequate. Auto supply stores used to carry them for radios but I am not sure if they still do.

    If I put one on the PCB, how would I size the inductor? Amperage??

    James L

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    James L
    Partner/Designer

    Lil Brother SMT Assembly Services
  • kwinnkwinn Posts: 8,697
    edited 2009-05-05 23:43
    Definitely amperage is the primary concern. As always it's a tradeoff between inductance and physical size. Get the highest inductance that will handle the current and fit in the space available.
  • James LongJames Long Posts: 1,181
    edited 2009-05-06 18:28
    I'm really having a hard time trying to reduce 13.9-14.1 volts down to 5 volts @750mA.

    Anyone have any great suggestions as to the best method to do so?

    I was looking at a buck regulator, but the parts are huge. I really wanted to keep the power supply part of the board small, if possible. It may not be so.......


    James L

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    James L
    Partner/Designer

    Lil Brother SMT Assembly Services
  • LeonLeon Posts: 7,620
    edited 2009-05-06 18:38
    Try the Nat Semi Simple Switcher chips, they don't need many components.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • James LongJames Long Posts: 1,181
    edited 2009-05-06 19:12
    Leon said...
    Try the Nat Semi Simple Switcher chips, they don't need many components.

    Leon

    I think I found a solution. Although maybe not the best, I'm going with an Artesyn Technologies LDO03C

    I can adjust it to 5 volts, and it is a buck dc to dc converter. It's a little pricey, but saves me the time to design the regulator into the board.

    James L

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    James L
    Partner/Designer

    Lil Brother SMT Assembly Services
  • LeonLeon Posts: 7,620
    edited 2009-05-06 19:44
    TI and someone else make a complete 5V output switcher in a 7805 package. They are a bit expensive. though.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
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