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Need help finding resistance for 12V to get 300 mA.

Discussion in 'Electronic Basics' started by Ricky Spartacus, Dec 3, 2003.

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  1. Assuming an ignition control module's trigger input can't exceed 300 mA,
    what should resistor value to trigger this device with 12V. I've triggered
    this device with 1.5V cell and works fine but not sure how to do the math
    regarding the question above. I lost the website that has a current
  2. Brian

    Brian Guest

    Why not have your own program that can do that (plus a lot more), for less
    than the price of a good technical book. See what I mean at

    It has a demo that you can download.

    R = E / I
    P = E * I

    R = resistor value
    E = volts
    I = current
    P = Power rating needed for resistor

    12 / .3 = 40 ohms
    12 * .3 = 3.6 watts

    Hope this helps,
  3. Rich Grise

    Rich Grise Guest

    Can you post the specs on that module? I can't imagine something
    designed for a car that would be damaged with up to 12 volts at
    the input. The spec _might_ be saying that the input won't load
    your driver circuit more than 300 mA. I don't know if anybody's
    ever seen a spec for an input where the drive to that input has
    to be current-limited.

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