Unusual functions of cheap parts
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From: John Devereux on 25 Nov 2005 05:08 ehsjr <ehsjr(a)bellatlantic.net> writes: > Henry Kiefer wrote: > > Do you know of other interesting devices or circuits good for misuse? > > Best regards - > > Henry > > An LED as a shunt regulator. Also, as a varicap. > Ed Also a photodetector that is insensitive to long wavelengths (because of the high bandgap). -- John Devereux
From: Ban on 25 Nov 2005 04:46 Roy Lewallen wrote: > 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 At a leading Ultrasonic flaw detector company we used simple low frequency Motorola sot23 transistors in avalance mode for making a nice pulse generator for 100MHz probes. These were better than the Zetex avalance specified transistors. -- ciao Ban Apricale, Italy
From: Jorgen Lund-Nielsen on 25 Nov 2005 06:46 John Larkin wrote: > On Thu, 24 Nov 2005 18:30:06 +0100, Jorgen Lund-Nielsen > <jorgen.lund-nielsen(a)xxxxxxxxxxxxdesy.de> wrote: > > >>Henry Kiefer wrote: >> >>>Hi all - >>> >>>After my first thread going from "standard" cheap parts for up to vhf >>>frequency to a discussion about the usefulness of Spice simulator...... I >>>try it another time hopefully get attention of frustrated co-readers: >>> >>>For example the rechtifier diode 1N4007 can be used as a rf switching diode, >>>for example as rx/tx-switch. This is because it is a pin structure diode. >>>This type is cheap and you can get it almost everywhere. It shows good >>>performance for the price. Surely for high-end you should do it with another >>>type tuned to the application it is made for. But anyway it works in some >>>circuits. >>> >>>Do you know of other interesting devices or circuits good for misuse? >>> >>>Best regards - >>>Henry >> >>Tuner Switching Diodes like the european BA244 (NOT PIN-Diodes!) work >>well as medium fast Step Recovery Diodes. >> > > > Tell me about it. I tried some pins to see if they would snap, and > they turn out to have incredibly mushy reverse recovery, Slop Recovery > Diodes. > > I'll have to try the varicaps. > > John Hello John, I wrote: NOT PIN - Diodes - as they wouldn't snap. i mean Band Switching diodes for TV-Tuners like the BA244 and the BA682. BA682 Datasheet: http://www.vishay.com/docs/85530/85530.pdf - and they snap! Try it! Jorgen dj0ud
From: Jorgen Lund-Nielsen on 25 Nov 2005 08:23 Ban wrote: > Roy Lewallen wrote: > >>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 > > > At a leading Ultrasonic flaw detector company we used simple low frequency > Motorola sot23 transistors in avalance mode for making a nice pulse > generator for 100MHz probes. These were better than the Zetex avalance > specified transistors. 2N2369 for fast pulses. 2N2222 and even 2N2219 works, but a bit slower and they requiring more voltage to avalance, but still < 1nS rt The Zetex are slower but can deliver much more current (up to 60A, ZTX 415 family). Jorgen
From: skavanagh72nospam on 25 Nov 2005 09:28
As an addition to the various mentions of common diodes as varactors there is a well publicized British design for a frequency tripler that will put out 2 watts at 1.3 GHz and uses five 1N914's in parallel. I once built an HF transceiver that used CMOS logic chips for all functions except an audio low noise amp and a voltage regulator...with further thought those two could likely be done with CMOS logic too. |