Unusual functions of cheap parts
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From: Phil Hobbs on 24 Nov 2005 14:47 John Larkin wrote: > A 1N4007 can also be used as a drift step-recovery diode and as a > plasma avalanche diode. Together, two can generate a kilovolt edge > with a 100 ps risetime. Okay, so I'm intrigued already. I have all the hardware available--two 1N4007s and a 3 kV adjustable power supply! How do I build one? Cheers, Phil Hobbs
From: Boris Mohar on 24 Nov 2005 14:33 Cadmium sulphide ( CdS ) LDR as a Beta radiation detector. Not sensitive to Gamma radiation which can be an advantage because it will detect Beta in presence of Gamma. You have to paint it black. Horrible temperature sensitivity but you can use another CdS as reference. Regards, Boris Mohar Got Knock? - see: Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca void _-void-_ in the obvious place
From: John Larkin on 24 Nov 2005 15:27 On Thu, 24 Nov 2005 14:47:37 -0500, Phil Hobbs <pcdhSpamMeSenseless(a)us.ibm.com> wrote: >John Larkin wrote: > >> A 1N4007 can also be used as a drift step-recovery diode and as a >> plasma avalanche diode. Together, two can generate a kilovolt edge >> with a 100 ps risetime. > >Okay, so I'm intrigued already. I have all the hardware available--two >1N4007s and a 3 kV adjustable power supply! How do I build one? > >Cheers, > >Phil Hobbs Google "Grekhov diode." A lot of the papers are for members only, but this one gives the general idea: http://www.ece.jhu.edu/~pps/ECE777/ADMAT/CircDev/Pulse-GENERATORS-SHAPERS/sub-nano-pulse1.pdf Grekhov discovered both the DSRD and the plasma avalanche effects in cheap power diodes. The core of the DSRD effect is that, if a PIN diode is forward biased for not too many nanoseconds, the carriers don't have time to float all around the place so the charge profile is good for a nice reverse snap. HP did the same thing in their classic 1430 12-GHz sampling head, circa 1965 roughly. This box used the DSRD effect, in a semiconductor that one would not expect to be used in an application like this... http://www.highlandtechnology.com/DSS/T220DS.html We bias the snap diode +48 volts (yes, forward direction) for about 80 ns before we turn the drive around for the snap. It was originally designed for use in a LEAP atom probe. John
From: Robert Obermayer on 24 Nov 2005 16:02 Hi, 2N3055: one-time trigger diode with abt. 160v triggering voltage [had some ones of unknown state left from a PSU that blew one of 5 transistors, replaced them with MJ15003] various, sometimes expensive components: firecrackers, smoke bombs, lamps (most of the time unintended ;) ) old EPROMs: Lamp.Find some pins with low resistance and apply .5-2A. the IC/transistor that was broken and took you some hours to find the trouble: Get 1-5 large caps (like 12 000?F 350V), charge them, and apply the voltage to the part with a very large relay. LOUD!
From: Roy Lewallen on 24 Nov 2005 18:13
Zener diodes work fine as varicaps, at least at HF. The lower the zener voltage and higher the power dissipation rating, the higher the C. As someone else mentioned, transistor emitter-base junctions can be used as either zeners (typical zener voltage around 5 volts) or varicaps. A zener can be used as a broadband noise source. I've had the best luck with zeners of 10 - 15 volt breakdown, with around 100 uA current. Some are noisier than others, and they often have a critical current where the noise is the greatest. Tektronix used selected transistors to generate high voltage (~100 volts) fast steps (~100 ps rise time if I recall correctly) by avalanching the collector. Some fraction of some common transistor types worked satisfactorily in this application. 1N914 type diodes can be used as step recovery diodes to generate a step with about a ns risetime -- maybe faster with a chip component and some care. This could be the basis of a broadband harmonic generator. Roy Lewallen, W7EL |