abusing transistors
John Larkin
collector and emitter, base open, putting a zenered e-b junction in
series with the forward-biased c-b junction, "reference zener" style.
BFT25 gives only 3.02 volts at 1 mA, with about 0.6 of that being c-b
drop.
BFS17 is 3.78, 0.53 of that c-b drop.
Those are RF transistors.
A more conventional BCX70 is 8.08 volts at 1 mA, 0.608 of that c-b,
and has a positive overall tc. The voltage is creeping up slowly,
which may be thermal. I'll watch it for a few days and see if there's
a longterm trend. Presumably I'm wrecking the beta, but I'm not
testing for that.
John
Jan Panteltje
<jjla...@highNOTlandTHIStechnologyPART.com> wrote in
<veu4k5liraigaepnd...@4ax.com>:
LM317 is very temperature satbel with no load.
:-)
Jim Thompson
Trying to fathom your inadequate description...
NPN transistor
Collector at ground
Base floating
Forcing a current _into_ the emitter
Is this correct?
You're measuring what would nominally be LVceo, except it's inverted,
so call it LVeco ?:-)
It's leakage dominated, so nothing is firm.
...Jim Thompson
--
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I love to cook with wine. Sometimes I even put it in the food.
Jon Kirwan
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
John Woodgate mentioned this in the LTSpice group, back on 30
Dec 2009:
"It's not like a zener diode; the breakdown voltage is
much larger than the maintained voltage - the voltage
across the device in the broken-down condition."
He wrote that in response to another saying this: "The base
emitter diode have a reverse breakdown at between 6-7 volts
in this mode. This is in series with the forward conducting
base collector diode which add about 0.6 volts to the B/E
zener diode."
Both were in a discussion about these pages:
http://www14.brinkster.com/aleatoriedad/DifNeg.htm
http://www.tompolk.com/inventions/455_KHz_Oscillator/455_KHz_Oscillator.html
Jon
John Larkin
At 1 mA, it's acting like a zener diode with about a 36 ohm dynamic
impedance... positive, not negative. Most of that is caused by the c-b
diode; the b-e zener is a lot stiffer, more like 10 ohms. That all
makes sense.
The voltage seems to be increasing by about 30 millivolts per hour or
so. I wonder if I'm migrating implants around. That might correspond
to the known beta damage effect of zenering the b-e junction.
Looks like a b-e junction isn't a very stable zener. So it may not be
a very stable noise diode.
John
RST Engineering
<To-Email-Use-Th...@My-Web-Site.com/Snicker> wrote:
The way I've always done it is tie base to collector and ground both
(NPN). Then feed a (+) current source into the emitter and use the
emitter voltage as a regulated voltage.
No?
Jim
Tim Wescott
Why aren't you shorting base and collector to ground, and putting current
into the emitter?
John Larkin
wrote:
Why should I?
This way, I get to measure both the zener voltage and the
forward-biased junction voltage.
Maybe I'll start with a fresh transistor tomorrow and measure both
versus time.
John
Bill Sloman
P.T. Rudge published a circuit for such a voltage reference in the
British Journal of Scientific Instuments in the 1968
"A plug-in transistorized shunt regulator"
P T Rudge 1968 J. Phys. E: Sci. Instrum. 1 493-494
According to page 198 of my Ph.D. thesis, he used a reverse-biased
2N3638A as his reference source.
IIRR the paper suggested tweaking the current through the forward-
biased collector-base diode and the reverse-biased emitter-base
junction for minimum voltage shift in response to a temperature shift
imposed on the device by prodding the package with a hot soldering
iron.
http://www.fairchildsemi.com/ds/PN/PN3638A.pdf
It is built with the National Semiconductor process 63 - PNP medium
poswer, non-overlay double-diffused - also used for the 2N2905 and
2N2907A.
--
Bill Sloman, Nijmegen
John Larkin
That happens around 6.2 volts.
>
>http://www.fairchildsemi.com/ds/PN/PN3638A.pdf
>
>It is built with the National Semiconductor process 63 - PNP medium
>poswer, non-overlay double-diffused - also used for the 2N2905 and
>2N2907A.
Reference diodes, like the 1N827, are a zener in series with a regular
PN diode, and the tc can be tweaked to zero by varying the current. GE
used to make "reference transistors" which was an NPN transistor with
a zener in the emitter, also tweakable to zero TC. The classic
solid-state Fluke differential voltmeters mostly used reference
transistors as their main voltage reference.
Maybe older diffused transistors didn't change voltage much as a
function of integrated b-e zener current. The BCX70 sure seems to.
John
Gerhard Hoffmann
>Thought I'd zener some NPN b-e junctions. The mode is to use the
We had this topic here only 11 years ago. Maybe it should go into the FAQ.
From the test frequencies, you can tell I'm a ham.
But I have upgraded to an Agilent 346C in the meantime. :-)
regards, Gerhard, dk4xp
Bill Sloman
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Mon, 4 Jan 2010 20:22:09 -0800 (PST), Bill Sloman
>
The paper seems to suggest that the combined voltage drop is at around
7.0V at the zero temperature coefficient, which is what Rudge claimed
to be able to set up at a current of around a few mA - less than the
7.5mA you needed for a 1N823/5/7/9 or the like (which was what you
would have bought to to the job at the time).
> >http://www.fairchildsemi.com/ds/PN/PN3638A.pdf
>
> >It is built with the National Semiconductor process 63 - PNP medium
> >poswer, non-overlay double-diffused - also used for the 2N2905 and
> >2N2907A.
>
> Reference diodes, like the 1N827, are a zener in series with a regular
> PN diode, and the tc can be tweaked to zero by varying the current. GE
> used to make "reference transistors" which was an NPN transistor with
> a zener in the emitter, also tweakable to zero TC. The classic
> solid-state Fluke differential voltmeters mostly used reference
> transistors as their main voltage reference.
>
> Maybe older diffused transistors didn't change voltage much as a
> function of integrated b-e zener current. The BCX70 sure seems to.
You might take a look at the 1997 thread "ZENER DIODE OSCILLATION",
where on the 5th August Winfield Hill eventually dug out the
physicists papers on how avalanche discharges in higher voltage (over
about 6V) "zener" diodes actually work, with most of the action
happening in localised microplasmas (which get warm. as well as
emitting light). He also posted a follow-up on the 6th August which
clarified a few points.
A micro-plasma in a very thin base diffusion might make it a little
less thin. A zener discharge at 3.25V ought to be occurring by the
Zener mechanism
http://en.wikipedia.org/wiki/Zener_diode
which ought to be better behaved, but it does have a negative
temperature coefficient, which could cause the reverse current to
concentrate into narrow channels which could then warm up enough to
anneal the original doping profile into something a little less sharp-
edged.
--
Bill Sloman, Nijmegen
Wimpie
>
> >Jon
>
> At 1 mA, it's acting like a zener diode with about a 36 ohm dynamic
> impedance... positive, not negative. Most of that is caused by the c-b
> diode; the b-e zener is a lot stiffer, more like 10 ohms. That all
> makes sense.
>
> The voltage seems to be increasing by about 30 millivolts per hour or
> so. I wonder if I'm migrating implants around. That might correspond
> to the known beta damage effect of zenering the b-e junction.
>
> Looks like a b-e junction isn't a very stable zener. So it may not be
> a very stable noise diode.
>
> John
Hello John,
You probably read the noise source thread also:
http://groups.google.es/group/sci.electronics.design/browse_thread/thread/b7bb3ce8f4c62fde?hl=es
I did some reverse measurements on a 1n4448 (and mentioned them in the
noise thread). Though the average current can be very low (for example
100uA), the peak current was in the 40mA range with ns rise time, so
not good for a Gaussian noise source. Heating the diode does stabilize
the breakdown process. I know from experience that reverse biasing BE
junctions, destroys low current HFE completely (BC84x series).
Maybe you can add a small resistor in series with your transistor
zener, so you can observe the current with an oscilloscope. Make sure
you have good (RF) decoupling from emitter to ground, so current peaks
are not limited by stray inductance.
Best regards,
Wim
PA3DJS
www.tetech.nl
please remove abc in case of PM
pawihte
>
> I know from experience that reverse biasing BE
> junctions, destroys low current HFE completely (BC84x series).
>
If you'll forgive me for inserting a beginner's question here:
Destruction of HFE by reverse biasing the b-e junction has been
mentioned more than once in this thread. I never knew about this.
My usual method of quickly testing a BJT for shorts, open
circuits and excessive leakages is to use an analog MM in the
ohmmeter range - low range for forward bias and high range for
reverse and Iceo. For identifying c and e of an unknown
transistor, I set the meter to the high resistance range - driven
by a 9V battery. This causes the e-b junction to break down while
c-b doesn't, thus identifying which is e and which is c. The
reverse emitter current is of the order of tens of microamps.
Have I been damaging transistors this way all these years?
Tim Williams
Curious, does that method work on high voltage power transistors? I've seen
a lot rated for Veb = 10V or so. Not that it's a big deal, power
transistors are all BCE (or GCE or GDS) anyway.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"pawihte" <paw...@fake.invalid> wrote in message
news:hhvqrs$dcc$1...@news.eternal-september.org...
Jim Thompson
wrote:
A simple one-time ID test with low current doesn't do enough damage to
discern.
However, continuous breakdown currents above ~5mA will cause gradual
electromigration and beta degradation. This effect is accelerated by
high temperatures... as I found out the hard way under the hood of a
car :-(
Wimpie
Hello,
As what Tim and Jim says: only little. The reason is that testing the
transistor takes just a few seconds and you are using tens of uA as
emtiter current. As a transistor has HFE in reverse direction also,
the base current will be far below tens of uA. The time*current
product is of importance, not the reverse voltage itself.
When you want to do some experiment, just take a fresh general purpose
small signal transistor, measure the HFE at low collector current (for
example 10uA). Then do your CE determination test and measure HFE
again (at same current and same transistor temperature). When you
would do your determination test all day long, you will probably
notice a reduction in HFE.
Best regards,
Wim
PA3DJS
www.tetech.nl
without abc, the address is valid
Tim Wescott
Well, for starters because the base-emitter junction is going to act
differently if you're draining carriers out of the base, and that's going
to change the 'zener' voltage -- possibly a lot, and possibly in a way
that has a significant effect on the temperature coefficient and aging
properties.
>
> This way, I get to measure both the zener voltage and the forward-biased
> junction voltage.
Or something like those, yes.
pawihte
> Yes, but only very slightly. I wouldn't worry about it.
>
> Curious, does that method work on high voltage power
> transistors? I've seen a lot rated for Veb = 10V or so. Not
> that it's a big deal,
> power transistors are all BCE (or GCE or GDS) anyway.
>
internal Rbe. However, since most power transistors in the same
standard package have the same lead-outs, ID-ing the leads is
usually not necessary. And for repairing and reverse engineering
work, it's usually easy to identify the leads from their
associated parts on the PCB.
It's with low-power transistors that it's sometimes necessary to
employ something like my method to identify the leads, especially
in the absence of a datasheet. TO-92s in particular come with all
possible orientations of the leads. I even had a stock of
different batches of PN2222As with different lead-outs. I thought
one batch was defective until I discovered that they had the
collector and emitter leads swapped.
pawihte
Ah. Thanks to you, Tim and Jim for the clarification. I'm not
exactly a raw newcomer to electronics, but being self-taught, I
obviously neglected to delve deeply enough into semiconductor
physics.