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SX Protoboard Supply Voltage — Parallax Forums

SX Protoboard Supply Voltage

VonSzarvasVonSzarvas Posts: 3,527
edited 2007-10-02 14:43 in General Discussion
Perhaps an insanely silly question, but I am really curious...

The proto boards are marked 6-9v supply voltage. The datasheet for the LM2940 states up to 26v is ok!

Would I be safe to use an 11-13v supply?

Perhaps just the 47uf cap on the 5v side should be lowered to a 10uf? That is what I have seen on other example circuits...

I am really tempted to try, but don't wish to smoke a protoboard unnecessarily!

Thank you for any advice.

Comments

  • BeanBean Posts: 8,129
    edited 2007-10-02 11:59
    As long as you are not trying to using alot of current from the 5 volt supply, you should be fine.
    100mA or so should be okay.

    Don't bother changing the cap, that won't make any difference.

    Bean.

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  • VonSzarvasVonSzarvas Posts: 3,527
    edited 2007-10-02 12:52
    I see.

    So that would mean the issue is the heat created by the voltage difference and power consumption? I can appreciate some projects using juicy servos etc.. may rely on more power, so the 6-9v plays it safe.

    100mA would keep the power consumption (5v x 0.1a = 1/2 watt) manageable up to about 85 degrees (according to the datasheet).
    -- But the important factor is the PD (Power Dissipation) calculated as voltage dropped across the regulator multipled by current consumed.
    -- Ie. (Vin - Vout) * Io = (13 - 5) * 100 mA = 0.8watts.


    so it seems I can do this well within spec, as I am pulling about max 60ma at the moment !

    Thank you Bean. smile.gif

    A few more years I may develop the confidence to trust what I read and know without careful scrutiny!!



    Edited: To include Beans correction below, so as not to mislead future readers.

    Post Edited (Maxwin) : 10/2/2007 4:15:23 PM GMT
  • BeanBean Posts: 8,129
    edited 2007-10-02 14:43
    The power disapation with 13V input and drawing 100mA = (13-5) *0.1 = 0.8 Watts of heat.
    The power disapation with 26V input and drawing 100mA = (26-5) *0.1 = 2.1 Watts of heat.

    I'd stay below 1 watt of heat to be safe.

    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    I know what I know, don't confuse me with the facts...
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    www.hittconsulting.com
    ·
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