UDN2981A outputs stay high

Discussion in 'The Projects Forum' started by Jaden66, Jan 25, 2013.

  1. Jaden66

    Thread Starter New Member

    Jan 3, 2013
    7
    0
    Hi,
    As per the attached image I am having an issue with my output to the four seven segments.... Now, the four seven segments to the right are 4" segments and require 9V forward voltage so the MAX7219 cannot drive the segments. The SS's are common cathode. The Picaxe drives the display quite happily without the 2981 in circuit on my simulation program (VSM), Now when I place the 2981 in circuit, Vs = 12V I get a constant high output! I try a few pull down resistors and get rubbish on the SS's. I have the PCB built and get the same response as the simulator! I would like to use the common cathodes and the bits I already have. I think next time common anode would be a simpler path to go!
    Thanks

    :confused:
     
  2. Jaden66

    Thread Starter New Member

    Jan 3, 2013
    7
    0
    Ahhhh. I was toying with pull down resisitors, 1Meg on the lines going to the SS's and presto! All works. I was trying 10k and it was still not working! Will try a lower value.
     
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