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Thread: What is the maximum current a digital output pin can pass through itself?

  1. #1
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    What is the maximum current a digital output pin can pass through itself?

    What is the maximum current a digital output pin can pass through itself?
    What is the maximum amperage of the load Teensy can drive at 3.3v?

    I see that it can drive an LED through some diode of unknown value. Maybe 50kOhm. Not sure. I cant find the Absolute Maximum specks for this wonderful hobby microcontroller product.

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    I think the maximum per pin is 10ma, when driving less make sure not to go over that. Usually LEDs are rated between 20-25ma depending on the color, so you will need a higher valued resistor than what you would normally use for that voltage.

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    See this answer by Paul for a more detailed explanation:
    http://forum.pjrc.com/threads/5455-T...aximum+current

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    usually differs in sourcing vs. sinking current.

  5. #5
    Senior Member PaulStoffregen's Avatar
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    To drive a LED with 25 mA, a transistor or buffer chip is best.

    However, you might try testing the LED you're using. Many LEDs have non-linear brightness vs current, where you get diminishing returns in brightness as you approach or exceed the rated max current. The human eye is also similarly non-linear. Most modern LEDs are pretty efficient, where 10 mA might be plenty to make it appear bright enough. With many LEDs, even 5 mA is plenty. But not all are so efficient. Sometimes 20 mA really is best. Just flowing a test current through the LED for a few seconds will give you a lot more insight than hours of studying specs.

    Often the required current depends on the surroundings. A LED poking through a hole in a dark colored material is a lot easier to see that one which has other bright stuff nearby.

    If you have a lab bench power supply with adjustable voltage, a 1K resistor in series with the LED is the easiest way to test. Put a voltmeter across the 1K resistor, where each 1V read is 1mA in the LED, and then play with the voltage knob to find brightness that works well.
    Last edited by PaulStoffregen; 10-29-2013 at 07:18 PM.

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    A closely related question - how much capacitance can one put directly on an output pin? Either teensy 3.2 or 4.0.

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