# 2N3904 in zener mode

F

#### Frederic

Jan 1, 1970
0
Hi everyone,

I was checking a dozen of 2N3904 I got in stock in the zener mode (with 15V
and 10K limiting resistor) and they all give the same voltage, about 8.2V.
And quite a sharp knee.

Anyone can confirm if this voltage is always the same from batch to batch?

Frederic

J

#### Jim Thompson

Jan 1, 1970
0
Hi everyone,

I was checking a dozen of 2N3904 I got in stock in the zener mode (with 15V
and 10K limiting resistor) and they all give the same voltage, about 8.2V.
And quite a sharp knee.

Anyone can confirm if this voltage is always the same from batch to batch?

Frederic

In a given process run ("batch") they'll be the same. Next "batch",
probably could differ by as much as a volt.

...Jim Thompson

E

#### Eeyore

Jan 1, 1970
0
Frederic said:
Hi everyone,

I was checking a dozen of 2N3904 I got in stock in the zener mode (with 15V
and 10K limiting resistor) and they all give the same voltage, about 8.2V.
And quite a sharp knee.

It's avalanche breakdown btw.

Graham

F

#### Frederic

Jan 1, 1970
0
Jim Thompson said:
In a given process run ("batch") they'll be the same. Next "batch",
probably could differ by as much as a volt.

Mmmh... not too bad after all.
Thanks!

E

#### Eeyore

Jan 1, 1970
0
Frederic said:
Hi everyone,

I was checking a dozen of 2N3904 I got in stock in the zener mode (with 15V
and 10K limiting resistor) and they all give the same voltage, about 8.2V.
And quite a sharp knee.

Anyone can confirm if this voltage is always the same from batch to batch?

FWIW when I tried this I got ~ 7V.

Nat Semi also couldn't or wouldn't guarantee the long term viability of the
device in this mode, although if you don't exceed Ib(max) I imagine you'd be OK.

Graham

J

#### John Popelish

Jan 1, 1970
0
Eeyore said:
FWIW when I tried this I got ~ 7V.

Nat Semi also couldn't or wouldn't guarantee the long term viability of the
device in this mode, although if you don't exceed Ib(max) I imagine you'd be OK.

I think the zener (or avalanche, if you prefer) is pretty
stable, but using the transistor in this mode will

D

#### Didi

Jan 1, 1970
0
In a given process run ("batch") they'll be the same. Next "batch",
probably could differ by as much as a volt.

This reminds me an old (12 years or so) design of mine, where I
needed variable gain cells, DC to say 10 MHz, 12 bit, 1:50 factor or
so.
I used paired 2N4391-s; one for compensation feedback, the other
as a variable resistor (having the gates shorted was handy as
it allowed me to solder the cans together for temperature coupling).
all of them from the same wafer and I could find decent pairs
easily enough.
Now obviously I did not get 12-bit temperature stability, but I had
sensor next to them . I had an MCU and it did turn the fine gain
to compensate; this gave me a 10x+ advantage over competitors
(who were _awarded_ all major deals in spite of that, but that's
another story).
Now the rest of the story is that I got no 12-bit integral non-
linearity,
either. Obviously even the 4391, in the reasonable low-voltage
range where I used it, was about 0.5 to may be 1% non-linear,
which was not acceptable. Fortunately I had enough processing
power (on a 16.67 MHz 68340 to acquire the non-linear
data into a somewhat longer spectrum (8192 was the norm;
I did something like 8500 or so) and continuously (IIRC 10 times
a second) converted it down to a linearized version.... Worked
wonderfully, some are still in use.
Got carried away by just a phrase, I guess, but I see this
as a "heroic" design of mine (there are more reasons except
the above for me to think so and I felt like telling about it
although being only very remotely related to the context...

Dimiter

R

#### Robert Baer

Jan 1, 1970
0
Frederic said:
Hi everyone,

I was checking a dozen of 2N3904 I got in stock in the zener mode (with 15V
and 10K limiting resistor) and they all give the same voltage, about 8.2V.
And quite a sharp knee.

Anyone can confirm if this voltage is always the same from batch to batch?

Frederic
The zener voltage for a given transistor type does not seem to change
from batch to batch; sometimes one can even change vendors.
Changes seen seem to be less than 1%.
In the case cited, i believe you will not see oscillation or negative
resistance effects.
Run the current down toward zero to see some spetacular "bazz-fazz".

R

#### Robert Baer

Jan 1, 1970
0
Eeyore said:
Frederic wrote:

FWIW when I tried this I got ~ 7V.

Nat Semi also couldn't or wouldn't guarantee the long term viability of the
device in this mode, although if you don't exceed Ib(max) I imagine you'd be OK.

Graham
Zener operation of the E-V junction "injects" lattice defects and
thus reduces beta (at minimum). Baking in an oven (300-350F) for a few
hours will anneal out the damage.

R

#### Robert Baer

Jan 1, 1970
0
John said:
I think the zener (or avalanche, if you prefer) is pretty stable, but
using the transistor in this mode will cumulatively ddegrade the beta.
Yup!
That is why the uA709s used in Apollo had problems; seems that the
"testing" lab for NASA did not know what an op-amp was or how to test them.
Did not follow the datasheet for temp/stress testing: used voltage
follower configuration and a 5V pulse on input (good old slew rate
caused brakedown on inputs).
Hell, they even tried to measure gain and offset !open loop!.

K

#### Ken Smith

Jan 1, 1970
0
Hi everyone,

I was checking a dozen of 2N3904 I got in stock in the zener mode (with 15V
and 10K limiting resistor) and they all give the same voltage, about 8.2V.
And quite a sharp knee.

Anyone can confirm if this voltage is always the same from batch to batch?

I'll say it isn't the same batch to batch and maker to maker. Some
Darlingtons have a very cute EB breakdown. They oscillate.

K

#### Ken Smith

Jan 1, 1970
0
Eeyore said:
Nat Semi also couldn't or wouldn't guarantee the long term viability of the
device in this mode, although if you don't exceed Ib(max) I imagine you'd be OK.

No, you need to stay way below Ib(Max). There is a lot more heating.

R

#### RST Engineering $$jw$$

Jan 1, 1970
0
What the hell is bazz-fazz??

Jim

A

#### Ancient_Hacker

Jan 1, 1970
0
Anyone can confirm if this voltage is always the same from batch to batch?

No, there's no guarantee of this between batches. It's only
guaranteed to be above a certain minimum- that's what's on the spec
sheet.

But if they decide to cook the next batch a little longer, or change
the device geometry to improve some other spec, the zener voltage
could really change a lot. As long as it remains above the spec, you
have nothing to legitimately complain about if the zener voltage zooms
up to 15 volts in the next batch.

As an example, I have a batch of MPSA42's, spec says 300 volts
maximum, but a half-dozen I tested work fine up to about 830 volts
plus or minus about 10 volts. Does this mean I can depend on this?
No.

Better to not go into production if you're depending on this!

J

#### John Larkin

Jan 1, 1970
0
The zener voltage for a given transistor type does not seem to change
from batch to batch; sometimes one can even change vendors.
Changes seen seem to be less than 1%.
In the case cited, i believe you will not see oscillation or negative
resistance effects.
Run the current down toward zero to see some spetacular "bazz-fazz".

Some NPN transistors seem to be very consistant at about 5.5 volts Vbe
breakdown. If you then use them in collector-emitter zener mode, you
get a nearly zero TC 6.2 volt "reference zener."

John

F

Jan 1, 1970
0
F

#### Frederic

Jan 1, 1970
0
Robert Baer said:
The zener voltage for a given transistor type does not seem to change
from batch to batch; sometimes one can even change vendors.
Changes seen seem to be less than 1%.
In the case cited, i believe you will not see oscillation or negative
resistance effects.
Run the current down toward zero to see some spetacular "bazz-fazz".

bazz-fazz????

E

#### Eeyore

Jan 1, 1970
0
Ancient_Hacker said:
No, there's no guarantee of this between batches. It's only
guaranteed to be above a certain minimum- that's what's on the spec
sheet.

But if they decide to cook the next batch a little longer, or change
the device geometry to improve some other spec, the zener voltage
could really change a lot. As long as it remains above the spec, you
have nothing to legitimately complain about if the zener voltage zooms
up to 15 volts in the next batch.

As an example, I have a batch of MPSA42's, spec says 300 volts
maximum, but a half-dozen I tested work fine up to about 830 volts
plus or minus about 10 volts. Does this mean I can depend on this?
No.

Better to not go into production if you're depending on this!

If you need a higher voltage MPSA42/43 check out the little known MPSA44/45.

Graham

M

#### [email protected]

Jan 1, 1970
0
Hi everyone,

I was checking a dozen of 2N3904 I got in stock in the zener mode (with 15V
and 10K limiting resistor) and they all give the same voltage, about 8.2V.
And quite a sharp knee.

Anyone can confirm if this voltage is always the same from batch to batch?

Frederic

I remember doing that as an experiment in college. My recollection was
you only need 100uA or so. Maybe up the resistor a bit, say 47k to be
safe that it breaks down. [Of course, you need to do the
experiment. ;-) ]

R

#### Robert Baer

Jan 1, 1970
0
Ken said:
I'll say it isn't the same batch to batch and maker to maker. Some
Darlingtons have a very cute EB breakdown. They oscillate.
I strongly do not recommend darlingtons for that; too variable and a
high zener due to two E-B junctions to break down.
I have tested a number of transistors, and for a given brand and
type, the berakdown voltage (in the *stable* region for the part) is
remarkably "constant" between devices and between batches (even when a
year or so seperated).
All transistor E-B junctions have a range of currents where they
exhibit negative resistance as well as oscillate; some are really nasty.
It seems that a majority *start* with a large negative resistance
characteristic (even in the nanoamp region), and slowly go towards zero
then finally positive.
Then again, most zeners that are made also have similar problems.