Unusual functions of cheap parts

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.

GAASfets make good fast analog switches; they behave pretty much like jfets.

Wide-open LDO regulators make nice resettable fuses.

Ferrite beads do all sorts of interesting stuff.

Power mosfets make good heaters, and TO-220 bipolar transistors make nice temperature sensors.

LVDS line receivers are surprisingly good comparators, and *fast*

I could go on...

John

I know a guy who uses surface-mount resistors as explosive detonators.

John

Cool. 3T regulators, 317 and LM1117 types, can be neat power amps, for driving unipolar loads like motors and such. Sort of a follower with a largish offset.

Hmmm, an LM1117 followed by a monster darlington becomes a super-follower with roughly zero offset.

John

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

[snip]

That's an interesting use of the 1N4007. I've not tried that, what kind of off capacitance do you get?

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Google "Grekhov diode." A lot of the papers are for members only, but this one gives the general idea:

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...

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

I never tried it myself, but I heard that some people abused opened memory chips as cameras, back when CCD camera chips were too expensive for hobbyists.

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)

void _-void-_ in the obvious place

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

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

The LM317 as a radio transmitter

Tuner Switching Diodes like the european BA244 (NOT PIN-Diodes!) work well as medium fast Step Recovery Diodes.

Jorgen

Take apart a couple of D cell carbon-zinc batteries.

Wash off the carbon rods. Put each in a wooden clothes pin and connect the attached ends to the mains voltage (US customers only, please).

Tap the free ends of the rods together. Move them apart as necessary. Very bright! Much brighter than you are.

Jon

Henry Kiefer wrote: [...]

Take away the hat of a 2N3055 and use it as a light sensor (sensitive).

Robert

-- 'Vom Standpunkt eines Beamtenrechtlers aus betrachtet ist der Tod die schärfstwirkenste aller bekannten, langfristig wirkenden Formen der vollständigen Dienstunfähigkeit.' aus: Kommentar zum Beamtenrecht.

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 000µF 350V), charge them, and apply the voltage to the part with a very large relay. LOUD!

An LED as a shunt regulator. Also, as a varicap. Ed

One of the MIT EE course videos on the web shows a demonstration of AC across a pickle... it is an interesting effect. Not sure how the pickle tastes afterward. Cooking hotdogs with AC is similar, but the pickle gives off a much nicer translucent flickering glow. Very pretty.

--
Regards,
  Bob Monsen

The question of the ultimate foundations and the ultimate meaning of 
mathematics remains open; we do not know in what direction it will find its 
final solution or even whether a final objective answer can be expected at 
all. "Mathematizing" may well be a creative activity of man, like language 
or music, of primary originality, whose historical decisions defy complete 
objective rationalization.
- Hermann Weyl in 1944

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.

I like that trick. Esp the isolated tab type.

Graham