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Re: [Electronics_101] Re: John's ULN2803 lesson.....

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  • John Popelish
    ... Yes, the squiggly bases and means that the base to collector diode junction is paralleled with a Schottky diode that becomes forward biased when the
    Message 1 of 48 , Dec 31, 2006
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      Shawn Upton wrote:
      > Quick question: on the 'LS series (on page 3), the
      > pulldown NPN with the vertical line a bit squiggly:
      > that's just shorthand for the Shotkey diode from base
      > to collector, right? IIRC, that's what helped the LS
      > series retain speed while running at lower currents.
      > [The diode prevents saturation of the pulldown
      > transistor, thus helping it turn off faster.]

      Yes, the squiggly bases and means that the base to collector
      diode junction is paralleled with a Schottky diode that
      becomes forward biased when the transistor approaches
      saturation. The schematic would look a lot more confused if
      they drew those diodes as separate components. I think they
      also make those diodes by just overlapping the first
      metalization layer across the junction. Schottky diodes
      are, after all just the right kind of metal and
      P-semiconductor, in contact.

      Transistor saturation really slows down the turn off process
      if the collector to base junction becomes forward biased
      enough to flood the the normally reverse biased (and
      therefore depleted) junction with charge carriers. Since
      the conduction voltage for a Schottky half junction is about
      half of that for a full PN junction. The current through
      the diode robs the base current to go out through the
      collector, so the transistor is prevented from saturating
      further, preventing full saturation (full forward bias of
      the collector to base junction) of the transistor.

      The diodes with the squiggly cathodes are other Schottky
      diodes that perform other normal diode functions, while
      having the inherently fast reverse recovery time and low
      forward drop that Schottkys have, compared to PN junctions.
    • Bilal Najjar
      Hi, try this one. www.datasheetcatalog.net ... [Non-text portions of this message have been removed]
      Message 48 of 48 , Feb 9, 2007
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        Hi, try this one.

        www.datasheetcatalog.net

        JanRwl@... wrote:
        >
        > Can anyone tell me how to get a PIN-OUT diagram of the ULN 2803 off the
        > Internet? I can't find it ANYwhere! AND, correction for whoever: I
        > read one of
        > the letters about this ULN 2803 thread recently which said it was a
        > DIP with
        > SEVEN Darlingtons in it. NOT! It is EIGHT Darlingtons! The ULN2003 has
        > only seven. Thanks! Jan Rowland
        >
        > [Non-text portions of this message have been removed]
        >
        >



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