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Transistor question

Was trying to test a 2N3906 (PNP 2N2222 substitute) and found something strange. My DMM has a transistor built into it with a socket marked EBCE and I wasn't sure which configuration the transistor had. When plugging what should be the emitter/base/collector into the appropriate slots, it came up with an hfe reading of 150, which is a little low but in the ballpark. But if I move it down one slot and plug what should be the collector into the bottom emitter slot/base into the collector slot/emitter into the base slot, the hfe reads 1500! Anybody have any idea what gives with this? Is it possible that the transistor has two operable configurations? Or do I have a faulty tester built into my DMM?

Crossposted to sci.electronics.equipment, just in case

Thanks much,

Dave snipped-for-privacy@hotmail.com

Reply to
Dave
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Oh yeah, no doubt. I am just trying to figure out why I got an hfe reading of 1500 with the transistor basically reversed. Any ideas on that?

Thanks,

Dave snipped-for-privacy@hotmail.com

EBCE

slot/emitter

gives

Reply to
Dave
150 is more like it.

Dave wrote:

Reply to
Jamie

Hmm. Okay. Makes more sense than anything I can think of. My wife says that 20 years ago I told her about this effect and explained it. Only, that was 20 years ago. :)

Thanks for the feedback. It is appreciated.

Dave snipped-for-privacy@hotmail.com

reading

plugging

it

Reply to
Dave

that

She remembered and you didn't. What does that tell you about memory and aging and gender?

Reply to
Norm Dresner

short effects due to improper polarity throwing off your meter. if you put the vcc in the Base the emitter will sure get a lot for output with no current on the base leg. this will give the illusion of high gain.

Dave wrote:

Reply to
Jamie

says

YEAH! And testosterone and Estrogen. It's not fair...

(But what is?)

Dave snipped-for-privacy@hotmail.com

Reply to
Dave

"Dave" a écrit dans le message news: cje99p$ snipped-for-privacy@library2.airnews.net...

Hi Dave The transistor tester is made of a known current generator, connected to the base. Emitter is grounded. Collector has a voltage generator, probably a resistor to limit the current, and a current measure.

If you shift the plugs, you connect E to the base generator, B to collector, and C to ground. So, the current generator is ignored because reverse biased. The collector/base junction of the tested transistor has, in serie, the voltage generator, the milliameter and the protective resistor, direct biased. The current is MAXIMUM limited by R. Usually, the indication is overflow (no value), but on your DMM it is the same as the current for hfe 1500.

-- Guy Pastuzak

Adresse ANTISPAM ANTISPAM address

Reply to
guy pastuzak

Dave-

As others have pointed out, you may not have it exactly reversed. Finite output divided by zero input equals infinite apparent gain!

If you did have the transistor connected with collector and emitter reversed, it should still function as a transistor, but most likely would have much lower gain. You would also expect it to have a lower breakdown voltage.

At one time in the development of computer circuits, a transistor was designed and produced that was somewhat symmetrical. According to its specifications, it worked equally well connected either way. I do not recall a specific part number or the circuit in which it was used. This was probably around 40 years ago.

Fred

Reply to
Fred McKenzie

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