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sinking and sourcing current

Discussion in 'Electronic Basics' started by Wong, May 25, 2004.

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  1. Wong

    Wong Guest

    If I use a GPIO pin on a IC to drive LED, which configuration is the
    best ?
    1.) LED's negative pin to GPIO, positive pin to other power source.
    2.) LED's negative pin to Ground, and positive pin to GPIO. Of
    course both with current limiting resistor.

    Is this related to the current sinking and sourcing ?
    Thanks in advance.
  2. In most cases, 1) ist better, because many IO-Pins can sink more current
    than source, but newer Microcontrollers/Processors often have equal
    sink/source capabilites.
    Consult your data sheet, section "DC characteristics".
    Yes, 1) GPIO sinks current, 2) sources current.

  3. Wong wrote:

    Additionally, don't forget: If you use the "sink design", your software
    has to invert the outputs (because of writing "1" means H voltage level
    and led OFF, "0" means low voltage level and therefore led ON").

  4. Sinking is better (the first one).
    Look at the voltage drop curves for why it is better. The maximum
    current rating may well be the same in either direction, however the
    sinking (n-channel) transistor will typically have less voltage drop
    at the same current.

    Best regards,
    Spehro Pefhany
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