Bad batch of 2N2222 transistors?

[rhb]

I can still feel my elation at acquiring that tiny bit of knowledge.  I find it very sad that it is not well known.

[bd139]

It’s actually taught in the art of electronics supplementary lab manual right back from the first edition in about 1980. Very very useful bit of knowledge.

[rhb]

I didn't get AoE until ed 2 at which time I already knew about it.  And I never did anything with the lab manual even though I have it.

[T3sl4co1l]

SPICE uses Gummel-Poon model, standard.  It's a more general model, and yes, includes inverted operation!  You're effectively measuring the BF and BR parameters of the model.

However, as is the case with any model -- the parameters fitted may not be most representative for your situation.  Example: low-Vce(sat) transistor models typically have BR ~ 5, but real devices are closer to 100-150.

Tim

[David Hess]

Testing it as a zener would be more reliable, since that gets you breakdown directly.  Beware of symmetrical junctions, though... then again... nevermind, because if it's symmetrical, who cares, right?   (Rarely found among silicon parts, but some exist; mainly, old Ge transistors were made with symmetrical or near-symmetrical junctions.)

Back before JFETs became available, they made "chopper" bipolar transistors with symmetrical or at least more symmetrical junctions.  Like JFETs, they are useful for wide differential input voltage differential pairs, audio muting and switching, and synchronous modulation and demodulation applications like chopper amplifiers.

They are still manufactured and can be found if you know what to look for:

https://www.mouser.com/ProductDetail/Toshiba/2SC3326-ALF?qs=%2fha2pyFaduiyTvpx89IGbfH1eNAndtaXwZN3qxNTDg4%3d
https://www.mouser.com/ProductDetail/Central-Semiconductor/CMPT404A-TR?qs=sGAEpiMZZMshyDBzk1%2fWiw99kSkYzPxmA%252bTeVhEzuE0%3d

[Simon]

I have found various pinouts for these transistors. Always check a datasheet from the actual manufacturer.

[splin]

BJT pinouts are a total disaster for a hobbyist. If you have parts that you are not 100% sure about, the only way is to test the pinout, e.g. using a multimeter with a transistor tester capability (very handy for finding the pinout). It shows about the "expected" Hfe when it's correctly connected - otherwise it shows way too little or [bold]way too much[/bold].

Interesting, does this mean there are some transistors with higher current gains when reverse connected or is it an artifact of the measuring technique?
EDIT: Fixed quoting error.

[T3sl4co1l]

Meters measure collector current for some collector voltage and base current.  If there's an erroneous sink of "collector" current at that voltage, it'll look like hFE is huge.  Which, isn't wrong...

I don't know of any that have higher inverted hFE, but some do have very useful hFE: purpose-made "muting" transistors (higher Vebo, inverted hFE over 100 usually, and specified in terms of Rce(on) -- used much like JFETs for analog switching, but with base current rather than gate voltage), and low-Vce(sat) [power] switching transistors, which are not specified for inverted operation (and have ordinary Vebo), but are often rated in terms of Rce(on), and typically have quite high inverted hFE (presumably, a consequence of their low Vce(sat), because saturation isn't a one-sided thing, it's symmetrical around zero and to do well in one direction, it should do ~equally well the other way too).

Tim

[splin]

Meters measure collector current for some collector voltage and base current.  If there's an erroneous sink of "collector" current at that voltage, it'll look like hFE is huge.  Which, isn't wrong...

Tim

But how could you get an erroneous collector current (unless the junction had broken down due to excessive voltage - very unlikely)? Surely hFE measurement is about as simple as it gets in most meters - a fixed base and collector resistor to VCR and measure the collector voltage? A more sophisticated meter might use a true constant current source for Ib but I still can't see how it could cause an erroneous reading.

[T3sl4co1l]

Certainly:
- Shorted or leaky transistor
- Reversed, breakdown (at DMM test voltages, would probably be a superbeta or RF type with Veb <= 3V say)
- Actually a FET (probably JFET or depletion MOS)
- Actually an SCR
etc.

Tim