Re: [Electronics_101] Re: John's ULN2803 lesson.....
- Shawn Upton wrote:
> Quick question: on the 'LS series (on page 3), theYes, the squiggly bases and means that the base to collector
> 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.]
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.
- Hi, try this one.
>[Non-text portions of this message have been removed]
> 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]