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#11
December 1st 05, 12:53 AM
posted to de.sci.electronics,rec.radio.amateur.homebrew,sci.electronics.components,sci.electronics.design
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Unusual functions of cheap parts
John Larkin wrote: On 30 Nov 2005 14:32:29 -0800, wrote: Jim Thompson wrote: snip quote A 2N2369 is a gold-doped NPN, gold-doped to kill storage time and improve recovery from saturation. I don't recall any PNP device with gold-doping... or the equivalent. ...Jim Thompson National Semi's (now Fairchild) 2n5771 was a gold-doped PNP. ft=850MHz. For avalanche mode one might try the lower-Vce-rated PN3640 (12v), or PN3639 (6v). I might even have notes on this. I tested/compared various BJTs in avalanche mode some years ago, trying to find the "best." ISTR picking the 2n2369, both because it was fast, and because it avalanched reliably where other types wouldn't. James Arthur Hi, James, Interestingly, the best avalanchers aren't usually super-fast transistors, but old klunky things. The Zetex avalanche transistors have lowish Ft's and are made in Russia, maybe on an old process. John Howdy John, I was unclear: by "...it was fast..." I meant the 2n2369 was one of the devices with the fastest avalanche edges. Digging through some of my notes, I don't see the BJT comparison, but a 2n2222 biased to +100Vce, banged / triggered by a 74HC-series gate, gave synchronous 750pS risetime pulses. Not very impressive, really, though good for higher-power stuff than I needed. Interestingly, I found a 74AC00 driving an MPS2369 was faster & less trouble: 360pS fall (turn on) time, & 570pS rise (turn off) time, and no nasty high voltage supplies. It was possibly even a little faster than measured--at 360pS I was pushing my poor little 7S14 1-GHz sampling plug-in pretty hard. Best, James |
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