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Max current from 8051 o/p pin

Discussion in '8051/8951' started by Deepjyoti Das, May 13, 2014.

  1. Deepjyoti Das

    Deepjyoti Das New Member

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    I wanted to know how i can glow multiple LEDs from a single 8051 MCU output pin (in my case i have to glow a max of 16 LEDs). Since the current that can be drawn from one such pin is very low. Can anyone suggest how i can fulfill my need? :banghead:
     
  2. Deepjyoti Das

    Deepjyoti Das New Member

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    Please help
     
  3. absf

    absf Active Member

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    Without reading the 8051 datasheet. I am sure the 8051 port pins will not be able to source or sink the amount of current needed to lite 16 LED. Why can you just use a BJT or a mosfet instead? The PIC is able to source/sink 25mA per output and total of 250mA per chip.
     
  4. dave

    Dave New Member

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  5. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Very small current indeed.... I have specified all this in the 8051 tutorials.... Lighting an LED

     
  6. Deepjyoti Das

    Deepjyoti Das New Member

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    Yes sir. BJT should work fine in this case. Thank you.
     
  7. Jon Wilder

    Jon Wilder Active Member

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    8051 I/O pins are not meant to drive external loads. They merely provide output signals to trigger external devices which can source/sink load current. They use a strong internal pull down but a weak internal pull up so their source current isn't very high at all (somewhere in the microamps range).

    The sink current of an 8051 I/O pin I believe is somewhere in the 15mA range, but you couldn't sink 15mA per pin simultaneously without exceeding the rated power dissipation of the chip.

    As mentioned previously, you would have to use a transistor of some sort to drive an external load with the 8051.
     
  8. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    There are 8051 micro's that can sink or source 300mA 6V PER PIN, silicon labs do them, I cant remember the 8051 part numbers but they also do 32 bit micro's with 300mA per pin (not sure of total port, but 300mA is for a single pin), the 32 micro's with this are the SIMul range. Look for high drive.
    The 8051 high power ones are under industrial and automotive range I think, not all micro's are small current. Pics and ATMEL are less capable in what they can sink and source but not all 8051 micro's are the same, also look at freescale I think they have a few capable of sinking/sourcing around 250mA per pin.
     
  9. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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  10. Jon Wilder

    Jon Wilder Active Member

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    Regardless, I like to treat a processor like a processor. Not a processor/driver. Let the external parts do all of the current handling work and leave the processor to being the main brains of the operation.
     

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