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Mystery Component

This is a fairly common term for a composite device... it's packaged like an ordinary transistor (SMT or TO-92), but includes a current-limiting resistor in the base lead (and often a base-to- emitter pulldown).

It's used as a power-switching device, driven directly from a logic signal (often a microcontroller pin).

Think of it as "just about the simplest sort of 'integrated circuit' you can imagine". It's even simpler than the tiny little "simple glue logic" chips you can buy these days (e.g. a NOT gate in a four-pin SMT package, or a NAND in a 5-pin).

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Reply to
Dave Platt
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Ian Field Inscribed thus:

In that case watch the exchange rate for your credit card ! Mine is 1.602 to the £ today.

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Best Regards: 
                        Baron.
Reply to
Baron

On a sunny day (Fri, 1 Feb 2013 11:13:45 -0800) it happened snipped-for-privacy@radagast.org (Dave Platt) wrote in :

For a very short moment I did think 'unijunction transistor', at least those are either on or off, but then I dismiossed that on context. I bought a bunch of 2n4246 UJTs last year from ebay. Make nice oscillators.

Reply to
Jan Panteltje

The Nixie drivers in the calculators might have been 8T series - but its a long time to remember obscure details like that!

Reply to
Ian Field

Also called "pre-biased transistors" or "resistor-equipped transistors" (RETs).

Reply to
krw

7441
Reply to
Michael A. Terrell

does B-E look like a diode or a diode plus some resistors.

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Reply to
Jasen Betts

have a look at some datasheets, they'e just odinary transistors with a resistor network on base and emitter (or a single resistor on the base)

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?? 100% natural
Reply to
Jasen Betts

7490.. one of the TTL chips with power pins not in the corners.
7441 or 74141

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

When I was a kid RTL became very available in surplus surface-mount packages (called "flat pack"). Probably some big military change-over. DTL didn't seem to last long.

Spacing was tight for attaching fly wires.. looks like it was relatively coarse by today's standards- maybe 1.27mm pitch like today's SOICs.

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

On a sunny day (Sat, 02 Feb 2013 05:25:57 -0500) it happened Spehro Pefhany wrote in :

You could get cheap DTLand TTL chips here sold as 'bipack'. Those were for example 7474 D flip flops with one defective flip flop in the package, or a 7400 with one or more gates defective. Once bought some of those, tested them, and marked the defective pins with red marker. Great for hobby projects :-) Not so good if you made a PCB I guess :-)

mm I have wire wrapped several designs with TTL.

Reply to
Jan Panteltje

package,

Hey I remember those, in UK you could get bags (literally) of 7400 and

4000 series stuff, all of them test rejects. Many of them unmarked or with some house code I think. As a kid I built a succession of "IC Testers" , fixtures with LEDs and push buttons on each pin. Never actually *did* much with them, it was more fun testing them. The CMOS gates were cool, you could make a the outputs go on and off by waving your hand near them. 
--

John Devereux
Reply to
John Devereux

Mmmm, I'd have to call a locum.

Reply to
Dennis

I remember that one - when I worked at the calculator repair firm, the chip they used became temporarily unavailable.

After canibalising all the scrap boards we were pretty much scuppered - for some reason it wasn't practical to patch the 74141 in.

Reply to
Ian Field

The (old) Peak Atlas reports 2 diodes if it can't find any gain.

Reply to
Ian Field

Poly-Paks was THE place in the US to buy them. I bent the pins for any bad section, and used lots of them to either build or repair equipment that didn't need that section.

Poly-Paks also sold some parts by the pound. It was a good way for a kid to get an assortment of resistors, caps sockets & such cheap enough to learn electronics. Do you have any idea how many resistors were in a five pound box? :)

Reply to
Michael A. Terrell

Unless, of course, you count DTL redux (LSTTL). ;-)

Reply to
krw

their

PC (I

Wonderful example of something inexpensive now that would be difficult and expensive 25 years ago.

?-)

Reply to
josephkk

There was a hobby magazine project published somewhere at least 2 decades ago, similar type of thing as the DCA55 - it was pretty much someone thinking up something impressive to do with a HD44780 LCD module.

IIRC it was mostly SSI/MSI - unfortunately I can't remember what magazine it was, or whether a PIC based version was ever released into the public domain.

Reply to
Ian Field

On Wednesday, January 30, 2013 8:16:28 PM UTC-8, Paul Hovnanian P.E. wrote: [about a large quantity of as-found TO92 items labeled]

Three branches: (1) paper search in NTE (and if you have an old stack of books, ECG and SK) cross-references. "650" crosses to NTE109 - but that's a two-terminal diode

(2) start diode-testing the leads, one pair at a time; a Huntron tracker, or (better) a curve tracer with three-terminal socket is also useful. It's easy to tell a NPN or PNP or even a dual diode, but SCR, unijunction, MOSFET, jFET and other components are trickier. Three-terminal ICs are harder still. You can connect a three-terminal regulator output to its reference/gnd through a resistor, and the two-terminal test (input to reference) shows constant current at voltages high enough to bias the regulator.

(3) Pull it apart. Microscopic examination will show you the die size, layout, and maybe you'll get lucky and find a databook that has the die pattern documented (National Semiconductor's old diode /transistor databook did).

Reply to
whit3rd

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