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Transistor question

D

Dave

Jan 1, 1970
0
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
[email protected]
 
D

Dave

Jan 1, 1970
0
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
[email protected]
 
D

Dave

Jan 1, 1970
0
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
[email protected]
 
N

Norm Dresner

Jan 1, 1970
0
Dave said:
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. :)

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

Jamie

Jan 1, 1970
0
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.
 
G

guy pastuzak

Jan 1, 1970
0
Dave said:
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

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.
 
F

Fred McKenzie

Jan 1, 1970
0
<< I am just trying to figure out why I got an hfe reading
of 1500 with the transistor basically reversed. Any ideas on that? >>

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
 
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