Diodes [was: The 2N2/256-BSCP [was: Homebrew Drum Computer]]

[Allison]

>
>Subject: Diodes [was: The 2N2/256-BSCP [was: Homebrew Drum Computer]]
>   From: Tom Watson <tsw-cc at johana.com>
>   Date: Sun, 23 Dec 2007 15:02:01 -0800 (PST)
>     To: cctech at classiccmp.org
>
>In a previous message, Allison <ajp166 at bellatlantic.net> said:
>
>
>> Shotkey diodes are common.  Aka 1n5711.  Widely used in Rf and microwave.
>> They are low capacitance fast switching with low threshold.
>> 
>> Allison
>
>A couple of things here.  There are TWO different things:
>1)  Yes, there are Schottky diodes as you have mentioned.  They have very low
>forward voltage drop and are the basis for a faster TTL series (74Sxxx/74LSxxx,
>and probably others).  Another attribute is that they switch fast.  These are
>very available.
>2)  The other type of diode is a Shockley (like the "co-inventor of
>transistor").  These are 4 layer devices and behave similar to a neon bulb only
>at a lower voltage, and without the glow.  They have a high "trigger" voltage,
>and a lower "sustaining" voltage that keeps the current flowing (look at how a
>neon bulb "NE-2" works).  I don't remember much more than that, but my high
>school science teacher wanted to make up a storage array using them.  This was
>in the 60's, and we didn't have DRAM them, so it looked "interesting".  I
>suppose you could simulate them with a connected PNP/NPN transistor pair (as
>mentioned here), or use a higher voltage to trigger and use an SCR (another 4
>layer device) and not connect the trigger lead.  These went out of style long
>ago I understand.  In looking things up, I ran across this:
>http://www.allaboutcircuits.com/vol_3/chpt_7/3.html
>which explains things in great detail.

Mixed them up.  You can simulate that using two transistors.  I've done 
that mant times as it's easier to have a few 2n3904/06s handy rahter than 
some part thats not unobtainium.  The transistor equivilent is more 
flexible.


Allison

>
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