NPN protective zener

[John Larkin]

On 21 Jun 2019 18:00:58 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

George Herold wrote...

John Larkin wrote:

BFT25 is a phenomenal diode:
https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA
bias current opamp (difference measurement...

Lots of JFET gates can make it well below 1pA.
Our Table 5.3, Nine Low-input-current Op-amps,
on AoE III, page 303, lists three CMOS op-amps.
Try the LMP7721, rated 3fA typ, 20fA max. The
ADA4530-1 has guard pins, and claims < 1fA.

The PAD-1 picoamp diode was/is just a jfet with the source and drain
connected. It's expensive, and has a lot of capacitance and series
resistance. The BFT25 is a way superior diode. I recall that Ccb is a
few tenths of a pF.

The problem with fA current measurements is that it takes forever for
things to settle down, and any change in the electrostatic
environment, like walking or breathing in the same room, wrecks
things.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Steve Wilson]

John Larkin <jjlarkin@highlandtechnology.com> wrote:

The problem with fA current measurements is that it takes forever for
things to settle down, and any change in the electrostatic
environment, like walking or breathing in the same room, wrecks
things.

Put it in a shielded box. The cookie tin you use for phase noise measurements
should do fine.

 

[Steve Wilson]

John Larkin <jjlarkin@highlandtechnology.com> wrote:

On Sat, 22 Jun 2019 07:47:06 GMT, Steve Wilson <no@spam.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:

The problem with fA current measurements is that it takes forever for
things to settle down, and any change in the electrostatic
environment, like walking or breathing in the same room, wrecks
things.

Put it in a shielded box. The cookie tin you use for phase noise
measurements should do fine.

I do have a shield box to drop over my fA measurement thing. But it
still takes ages to settle down.

Is the box open at the bottom? I think it needs to be closed all around.

 

[John Larkin]

On Sat, 22 Jun 2019 07:47:06 GMT, Steve Wilson <no@spam.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:

The problem with fA current measurements is that it takes forever for
things to settle down, and any change in the electrostatic
environment, like walking or breathing in the same room, wrecks
things.

Put it in a shielded box. The cookie tin you use for phase noise measurements
should do fine.

I do have a shield box to drop over my fA measurement thing. But it
still takes ages to settle down.

Next time I do fAs, I'll use the capacitor charging idea. It will take
time too.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Winfield Hill]

Steve Wilson wrote...

John Larkin wrote:

I do have a shield box to drop over my fA measurement
thing. But it still takes ages to settle down.

Is the box open at the bottom? I think it needs to be
closed all around.

There's the matter of insulators with surface-charge
and dielectric-absorption issues.


--
Thanks,
- Win

 

[John Larkin]

On Sat, 22 Jun 2019 14:41:36 GMT, Steve Wilson <no@spam.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:

On Sat, 22 Jun 2019 07:47:06 GMT, Steve Wilson <no@spam.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:

The problem with fA current measurements is that it takes forever for
things to settle down, and any change in the electrostatic
environment, like walking or breathing in the same room, wrecks
things.

Put it in a shielded box. The cookie tin you use for phase noise
measurements should do fine.

I do have a shield box to drop over my fA measurement thing. But it
still takes ages to settle down.

Is the box open at the bottom?

Of course not. That wouldn't work.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[mixed nuts]

On 6/21/2019 1:21 PM, Winfield Hill wrote:

John Larkin wrote...

BFT25 is a phenomenal diode:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

600mV at 1uA. I'll keep it in mind next time I need a 100fA didoe.

Using b-e as a zener, there seems to be a small drift of
zener voltage vs total charge conducted, but that's
wouldn't effect its use as an ESD diode. Blow some up!

Yes.

What happens to collector current when you zener the
b-e junction? I've been meaning to investigate that
for some decades now.

Hmm, I coulda taken a look yesterday.

Low noise transistors become noisy transistors after the b-e junction
has been zenered a few times. I didn't have an opportunity to do a
rigorous before-after gain comparison but it didn't seem to change
dramatically.

--
Grizzly H.

 

[whit3rd]

On Saturday, June 22, 2019 at 7:20:20 AM UTC-7, John Larkin wrote:

I do have a shield box to drop over my fA measurement thing. But it
still takes ages to settle down.

Next time I do fAs, I'll use the capacitor charging idea. It will take
time too.

Consider a UV LED inside the shield box; nothing discharges (leaks) better
than a photoconductor (and almost all insulators ARE at least a little
photoconductive).

A few milliseconds after the LED is turned off, the insulators will insulate
again.

 

[Winfield Hill]

mixed nuts wrote...

Low noise transistors become noisy transistors
after the b-e junction has been zenered a few
times. I didn't have an opportunity to do a
rigorous before-after gain comparison but it
didn't seem to change dramatically.

Others have observed a serious loss in beta.
There are rumors of ways to resurrect the
poor beast, but if its role in life is as
a low-capacitance zener clamp, who cares?
When it's wired up on a PCB, with the base
and collector shorted, there's little else
that it could ever do!


--
Thanks,
- Win

 

[Jan Panteltje]

On a sunny day (22 Jun 2019 10:58:12 -0700) it happened Winfield Hill
<winfieldhill@yahoo.com> wrote in <qelq7k021kq@drn.newsguy.com>:

mixed nuts wrote...

Low noise transistors become noisy transistors
after the b-e junction has been zenered a few
times. I didn't have an opportunity to do a
rigorous before-after gain comparison but it
didn't seem to change dramatically.

Others have observed a serious loss in beta.
There are rumors of ways to resurrect the
poor beast, but if its role in life is as
a low-capacitance zener clamp, who cares?
When it's wired up on a PCB, with the base
and collector shorted, there's little else
that it could ever do!

Sure,. but I was thinking the same thing
did you try a zillion pulses and see if the curves are still the same after that?
I mean something must physically change in those transistors,
especially at high current?

 

[George Herold]

On Friday, June 21, 2019 at 8:48:47 PM UTC-4, John Larkin wrote:

On Fri, 21 Jun 2019 17:09:45 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:
On 21 Jun 2019 03:05:47 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

This is the paragraph I'm adding, as a
footnote to the graph in the x-Chapter
section on protection devices:

"The reverse avalanche breakdown of the 2N3904
is very sharp, with no current conducted at all
below 7 volts. Once it starts conducting, it
has a low dynamic resistance, with the breakdown
voltage increasing only 5mV / decade up to 1mA,
where its resistance is about 5 ohms. The
voltage increases by a volt at 100mA, and its
still about 5 ohms. We get only one more volt
by 0.5A, where the resistance is even lower.
Above 50mA the breakdown voltage will be a
little higher if you leave the collector pin
open, you need it connected to benefit from
its assistance with inverted-mode gain. The
2N3904 is fine carrying very high currents,
protecting your fragile devices, if the time
is short enough. It's worth noting that the
r_bb' base-resistance we measured and reported
in Table 8.1a, which was 110 ohms for the
2N3904, is not relevant to the breakdown."

I'm hoping that by the time the book goes to
print, I'll have replaced the graph with one
that goes to 10A. I'm confidant the 2N3904,
as with most other zener (actually avalanche)
devices, can handle full 10A peak currents in
the 8-20us surge tests, and pass. So it's a
totally viable low-capacitance protection device.

If one gets it in the SC-70 SOT-323 package
(at least four manufacturers*), it's not even
that large (I still prefer diode-package parts).
Fairchild offers a dual 2N3904 in an SC-70-6
package, FFB3904.** Huge stocking levels and
low prices, too, for all of these.
Lots of interest. Amazing, who knew?

* ON Semi MMBT3904WT1G, Diodes MMST3904-7-F,
Nexperia PMSS3904, MCC MMST3904-TP.

** and the FMB3946, get one each 2n3904 and
2n3906 in SC-70-6, and other manuf as well.


BFT25 is a phenomenal diode:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.
Huh, can you say anything about the measurement rig.
(610 electrometer?)

I built a thing:

https://www.dropbox.com/s/zmilmhn1tg4ts4q/99A260A1.JPG?raw=1

https://www.dropbox.com/s/j57mqvywvytrtwh/99A260A3.JPG?raw=1
Is that a plastic 8-pin dip socket?.. those can leak too.

https://www.dropbox.com/s/6ia0wgo88jnbwbq/99S260A.JPG?raw=1

Huh.. that's simple.. I think I did the somewhat the same thing,
different opamp and the resistor on the bottom, to gnd.

After it was all built, I discovered that the crummy nylon banana
terminals were leaky as heck, so I had to mill out the holes and add
the polycarb insulator. That was a major nuisance.

Plastics should be mostly suspect in terms of leakage,
I've had some issues with 8-pin dip plastic sockets.
When there's no spec from the manufacturer. Then you learn
to test every new order... some sales /rep guy said
they will change the plastic mix for the same part.
You end up ordering a bunch at one time.

I have a set of Pomona dual bannana plugs with various resistors from
1M to 1T ohms to use with that.
My biggest R is a 1G.

George H.

I'm thinking that instead I could get a really good film cap and
charge it with a device's leakage current. Let that sit for some hours
or days and then measure the cap voltage. That would easily get below
1 fA. Some good film caps have self-discharge time constants of
decades.

1 nF would charge 1 uV per second at 1 fA. That gives 86 mV/day per
fA.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[mixed nuts]

On 6/22/2019 1:58 PM, Winfield Hill wrote:

mixed nuts wrote...

Low noise transistors become noisy transistors
after the b-e junction has been zenered a few
times. I didn't have an opportunity to do a
rigorous before-after gain comparison but it
didn't seem to change dramatically.

Others have observed a serious loss in beta.
There are rumors of ways to resurrect the
poor beast, but if its role in life is as
a low-capacitance zener clamp, who cares?
When it's wired up on a PCB, with the base
and collector shorted, there's little else
that it could ever do!

Just don't put them back in the drawer after you finish playing.


--
Grizzly H.

 

[Mikko OH2HVJ]

whit3rd <whit3rd@gmail.com> writes:

Consider a UV LED inside the shield box; nothing discharges (leaks) better
than a photoconductor (and almost all insulators ARE at least a little
photoconductive).

A few milliseconds after the LED is turned off, the insulators will insulate
again.

Any experience on what is short enough wavelength for this ? I happen to
have a rather large stash of 280nm LEDs..

--
mikko

 

[Jan Panteltje]

On a sunny day (Sun, 23 Jun 2019 11:43:10 -0400) it happened mixed nuts
<melopsitticus@undulatus.budgie> wrote in <qeo6md$p0r$1@gioia.aioe.org>:

On 6/22/2019 1:58 PM, Winfield Hill wrote:
mixed nuts wrote...

Low noise transistors become noisy transistors
after the b-e junction has been zenered a few
times. I didn't have an opportunity to do a
rigorous before-after gain comparison but it
didn't seem to change dramatically.

Others have observed a serious loss in beta.
There are rumors of ways to resurrect the
poor beast, but if its role in life is as
a low-capacitance zener clamp, who cares?
When it's wired up on a PCB, with the base
and collector shorted, there's little else
that it could ever do!

Just don't put them back in the drawer after you finish playing.

Winfield makes an assumption,
only testing can confirm it stays working as a zener in the long run.
If anything physically changes in that transistor
why should it not affect the Vbe zener.
Not testing is bad practice.

 

[Winfield Hill]

mixed nuts wrote...

On 6/22/2019 1:58 PM, Winfield Hill wrote:
mixed nuts wrote...

Low noise transistors become noisy transistors
after the b-e junction has been zenered a few
times. I didn't have an opportunity to do a
rigorous before-after gain comparison but it
didn't seem to change dramatically.

Others have observed a serious loss in beta.
There are rumors of ways to resurrect the
poor beast, but if its role in life is as
a low-capacitance zener clamp, who cares?
When it's wired up on a PCB, with the base
and collector shorted, there's little else
that it could ever do!

Just don't put them back in the drawer
after you finish playing.

One of them went into the trash can! The rest
are taped to the page of data, as evidence.


--
Thanks,
- Win

 

[John Larkin]

On Sat, 22 Jun 2019 11:25:57 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Saturday, June 22, 2019 at 7:20:20 AM UTC-7, John Larkin wrote:

I do have a shield box to drop over my fA measurement thing. But it
still takes ages to settle down.

Next time I do fAs, I'll use the capacitor charging idea. It will take
time too.

Consider a UV LED inside the shield box; nothing discharges (leaks) better
than a photoconductor (and almost all insulators ARE at least a little
photoconductive).

A few milliseconds after the LED is turned off, the insulators will insulate
again.

Have you tried that? Got any numbers?


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Winfield Hill]

Jan Panteltje wrote...

Winfield makes an assumption,
only testing can confirm it stays working
as a zener in the long run.
If anything physically changes in that transistor
why should it not affect the Vbe zener.
Not testing is bad practice.

Don't worry, my setup is test-ready. I'm
using a $10k SMU that I got on eBay for $5k,
and it has scripts for doing extended tests,
measuring as you go. But I would also add a
comment, this isn't my scheme, many have been
using it for decades, and I suppose some did
thorough tests. Also, events this is meant
to protect against don't happen very often.
For now, the 10A projection is a dotted line
in the book, but it'll be tested before going
to publication.


--
Thanks,
- Win

 

[Jan Panteltje]

On a sunny day (23 Jun 2019 10:14:04 -0700) it happened Winfield Hill
<winfieldhill@yahoo.com> wrote in <qeoc0s02rrd@drn.newsguy.com>:

Jan Panteltje wrote...

Winfield makes an assumption,
only testing can confirm it stays working
as a zener in the long run.
If anything physically changes in that transistor
why should it not affect the Vbe zener.
Not testing is bad practice.

Don't worry, my setup is test-ready. I'm
using a $10k SMU that I got on eBay for $5k,
and it has scripts for doing extended tests,
measuring as you go. But I would also add a
comment, this isn't my scheme, many have been
using it for decades, and I suppose some did
thorough tests. Also, events this is meant
to protect against don't happen very often.
For now, the 10A projection is a dotted line
in the book, but it'll be tested before going
to publication.

OK, well I am curious as to what you will find,.
5 k$ is a lot of money, something that generates 10A
pulses should not be that expensive?
Very long time ago boss asked me if I could design a transistor curve tracer.
Took a day or 2, used relays too, and a scope.

I am at a loss here:
https://www.acronymattic.com/SMU.html

 

[Lasse Langwadt Christense]

søndag den 23. juni 2019 kl. 19.26.24 UTC+2 skrev Jan Panteltje:

On a sunny day (23 Jun 2019 10:14:04 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qeoc0s02rrd@drn.newsguy.com>:

Jan Panteltje wrote...

Winfield makes an assumption,
only testing can confirm it stays working
as a zener in the long run.
If anything physically changes in that transistor
why should it not affect the Vbe zener.
Not testing is bad practice.

Don't worry, my setup is test-ready. I'm
using a $10k SMU that I got on eBay for $5k,
and it has scripts for doing extended tests,
measuring as you go. But I would also add a
comment, this isn't my scheme, many have been
using it for decades, and I suppose some did
thorough tests. Also, events this is meant
to protect against don't happen very often.
For now, the 10A projection is a dotted line
in the book, but it'll be tested before going
to publication.

OK, well I am curious as to what you will find,.
5 k$ is a lot of money, something that generates 10A
pulses should not be that expensive?
Very long time ago boss asked me if I could design a transistor curve tracer.
Took a day or 2, used relays too, and a scope.

I am at a loss here:
https://www.acronymattic.com/SMU.html

Source Measure Unit, ~ a fancy powersupply

 

[Rick C]

On Sunday, June 23, 2019 at 2:22:00 PM UTC-4, Lasse Langwadt Christensen wrote:

søndag den 23. juni 2019 kl. 19.26.24 UTC+2 skrev Jan Panteltje:
On a sunny day (23 Jun 2019 10:14:04 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qeoc0s02rrd@drn.newsguy.com>:

Jan Panteltje wrote...

Winfield makes an assumption,
only testing can confirm it stays working
as a zener in the long run.
If anything physically changes in that transistor
why should it not affect the Vbe zener.
Not testing is bad practice.

Don't worry, my setup is test-ready. I'm
using a $10k SMU that I got on eBay for $5k,
and it has scripts for doing extended tests,
measuring as you go. But I would also add a
comment, this isn't my scheme, many have been
using it for decades, and I suppose some did
thorough tests. Also, events this is meant
to protect against don't happen very often.
For now, the 10A projection is a dotted line
in the book, but it'll be tested before going
to publication.

OK, well I am curious as to what you will find,.
5 k$ is a lot of money, something that generates 10A
pulses should not be that expensive?
Very long time ago boss asked me if I could design a transistor curve tracer.
Took a day or 2, used relays too, and a scope.

I am at a loss here:
https://www.acronymattic.com/SMU.html

Source Measure Unit, ~ a fancy powersupply

Seems like an odd name for that. I assume it has some special properties beyond a power supply which the name refers to?

I knew part of the name without looking it up, "unit"... lol

--

Rick C.

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