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problem using 7404-hex inverter

Discussion in 'General Electronics' started by Ankur, Feb 23, 2004.

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  1. Ankur

    Ankur Guest

    I m getting the H output as 3.3V and L output as .94V ... can't i get
    the outputs to more accurate limits ? I need '1' to be above 4.5V and
    '0' to be below .3Vs.

    Pin connection :

    1 - GND ( input = 'o')
    2 - 3.6V ( observed value when open .. and the value falls to 2.6V
    when a load of 1K was used)
    7 - GND
    14 - 5V
    rest pins open !!

    pls help
  2. Robert Baer

    Robert Baer Guest

    Check the loading and the datasheet specs.
    If you want a high near 3 or 4V, then you must add a pull-up.
    But the more current that you make the output sink, the higher the low
    is going to be.
    Now, if you absolutely want both, then replace it with a 74HC04 and
    the high will be close to the supply and the low will be close to ground
    - as long as the output is not sourcing or sinkking too much current
    (again, check the datasheet).
  3. Something is wrong if you're getting .94 volts as a low level.
    Should be under .4 volts.

    But as Robert points out, TTL was never designed to drive
    the outputs rail to rail. Think CMOS and low output currents.

    Dave Kinsell
  4. Robert Baer

    Robert Baer Guest

    The HC series is better on drive, and one can always use a hex
    inverter and parallel all six for even more drive...
  5. Welll, yes, HC is indeed one of the CMOS families, but the output voltage
    could be real marginal in this application. Depending on what current
    he really needs to deliver, a common emitter NPN transistor stage could
    be a good choice. First he needs to figure out why he's getting an illegal
    low logic level out of his current circuit. Maybe there's some load he's not
    telling us about, or maybe there's a wiring problem.
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