4017 Outputs

Discussion in 'Electronics Resources' started by edwardholmes91, May 10, 2013.

  1. edwardholmes91

    Thread Starter Member

    Feb 25, 2013
    181
    18
    Hello,

    Just a really quick question really, can I connect LEDs straight to the outputs of this without a resistor or will it damage the LEDs?

    I am trying to simulate this on a software package and even with no current limiting resistor the LEDs light very dimly.

    The circuit that I am adapting is this: Electronic Die I know I could use transistors is needed but I am trying to keep it as simple as possible. I read elsewhere on his website that with the 4000 series you can get about 10mA on the outputs when powering the chip with 9V. The specifcation on my LEDs say they have a max of 30mA so surely no resistor is needed?

    Looking forward to hearing from someone. Sorry if it sounds like a really noobish question! :rolleyes:
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,431
    3,360
    CMOS outputs are generally current limited. You can connect the LEDs directly.

    One problem is you cannot use the same output to drive another logic input because a logic high will not be guaranteed.
     
  3. edwardholmes91

    Thread Starter Member

    Feb 25, 2013
    181
    18
    Thanks for the fast response. I will have a go at breadboarding what I have got both with and without the resistors. As one of the outputs is going to be 1 LED and the other three outputs will be 2 LEDs I may use a resistor on the single LED so they appear to light the same brightness.
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,995
    3,229
    The current limit of the CMOS devices may vary from unit to unit in which case you could add resistors so that all LEDs are the same brightness.
     
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