and gate and uln2803

Discussion in 'The Projects Forum' started by bluedevil, Jan 20, 2011.

  1. bluedevil

    Thread Starter New Member

    Jan 20, 2011
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    0
    can a ANDgate ic 7403 can able to switch the uln2803 input to produce output to actuate a 12v relay?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What 74xx series are you talking about?
    74HC03, 7403 (actual), 74S03, 74LS03?

    What is the current requirement of the relay, or the coil resistance?

    ULN2803's should be able to be driven directly by TTL.
    However, the maximum practical sink current is about 350mA; above that, Vce gets to be rather high, and the IC will heat up.
     
    Last edited: Jan 20, 2011
  3. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    The 7403 is an open collector chip, so a ~1K pull-up is all you should need.
     
  4. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Come to think of it, if it satisfies your logic state, and if it's a low current relay, the 7403 can drive (Current Sink) a relay directly when the output is in the logic Lo state.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Sometimes I get the feeling that AAC gets stuck somewhere in the 'Space/Time Continuum'. I really don't like parroting other members as done here, but when I posted 'both' of my posts no one had replied as yet. Now my posts are last in the list. :confused:
     
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