Help! Circuit output not right

Discussion in 'General Electronics Chat' started by peaac, Sep 25, 2011.

  1. peaac

    Thread Starter New Member

    Sep 17, 2011
    So I have this chip... SN74LS47N which I found the datasheet for and it is a TI BCD to 7-Segment driver.

    I have two of these and I have checked the circuit about 10 times and this is what I am getting:

    I have VCC = 5v
    and connected the H to the same VCC for high and to ground for L.

    What I see is that the chip "almost" works but the H and L outputs are at 0.11v and 0.07v!!! And I cannot figure out why!
  2. SgtWookie


    Jul 17, 2007
    Here is a link to the datasheet:

    Note that the very first thing on page 1 of the datasheet after the part numbers, description and revision date, is a bullet that says:

    "Open-Collector Outputs Drive Indicators Directly"

    Open collector means that the outputs can sink current, but cannot source current.
    If you wish to see if they are working as expected, use a ~270 Ohm resistor from +5v to the output; the resistor will source current so that you will then see the voltage on the output pin change.
  3. peaac

    Thread Starter New Member

    Sep 17, 2011
    Thanks! That was an aha moment!