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: 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.

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