NPN in unusual quadrant...

[whit3rd]

On Monday, September 11, 2023 at 5:33:14 AM UTC-7, John Larkin wrote:

On Mon, 11 Sep 2023 11:01:46 +0100, piglet <erichp...@hotmail.com
wrote:
On 11/09/2023 4:16 am, whit3rd wrote:

So, to expect this in future, should we assume the B-E breakdown creates light, and
the collector current is a photodiode detecting that light? That does explain the
effect, and predicts emitter current proportional to collector current..

Yes, I think you meant collector current proportional to emitter
current?

PV optocouplers are great for generating a quiet floating voltage,
but a transistor is cheaper.

Cheaper, yes, but not durable (the base breakdown makes
dirt move on the transistor surface, kills the base leakage). The passivation of
a transistor assumes B-E voltages an order of magnitude lower than breakdown,
and in the opposite direction.

You\'ll hate the current transfer ratio of that \'PV optocoupler\', but the light source has much
better aging characteristics than the transistor does.

 

[John Larkin]

On Mon, 11 Sep 2023 22:57:24 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Monday, September 11, 2023 at 5:33:14?AM UTC-7, John Larkin wrote:
On Mon, 11 Sep 2023 11:01:46 +0100, piglet <erichp...@hotmail.com
wrote:
On 11/09/2023 4:16 am, whit3rd wrote:

So, to expect this in future, should we assume the B-E breakdown creates light, and
the collector current is a photodiode detecting that light? That does explain the
effect, and predicts emitter current proportional to collector current.

Yes, I think you meant collector current proportional to emitter
current?


PV optocouplers are great for generating a quiet floating voltage,
but a transistor is cheaper.

Cheaper, yes, but not durable (the base breakdown makes
dirt move on the transistor surface, kills the base leakage). The passivation of
a transistor assumes B-E voltages an order of magnitude lower than breakdown,
and in the opposite direction.

You\'ll hate the current transfer ratio of that \'PV optocoupler\', but the light source has much
better aging characteristics than the transistor does.

A phototransistor doesn\'t damage itself. It biases its own b-e
junction forward about 0.6 volts.

The official PV couplers make, typically, 8 volts and 30 uA. They are
just a string of photodiodes in series. They usually make more volts
and uA than specified. Maybe that\'s to account for degrdation, but
more likely it\'s because LEDs have kept getting better.

 

[Piglet]

On 11/09/2023 15:16, John Larkin wrote:

On Mon, 11 Sep 2023 08:50:54 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-09-11 08:32, John Larkin wrote:
On Mon, 11 Sep 2023 11:01:46 +0100, piglet <erichpwagner@hotmail.com
wrote:

On 11/09/2023 4:16 am, whit3rd wrote:
On Sunday, September 10, 2023 at 12:55:12?PM UTC-7, John Smiht wrote:
On Sunday, September 10, 2023 at 7:57:03?AM UTC-5, Piglet wrote:
On 06/09/2023 03:38, John Larkin wrote:
On Wed, 6 Sep 2023 02:31:04 -0000 (UTC), Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:

Now pull the base negative, through a current-limiting resistor. What
happens?

Nothing until you exceed the emitter base reverse breakdown (or
collector base breakdown) voltage,

Not literally nothing, but not much interesting. It gets more
interesting when the base zeners.


Bitter-base is usually about 5V

Behaves kind of like a zener diode and damages the transistor.

Haven’t tried it, at least not on purpose, but I’d guess that when the
avalanche starts, most of the electrons will get sucked up by the
collector.

Since it’s the electrons and not the holes that do the avalanching in
silicon, that might partially suppress the avalanche. If that were true,
putting a positive voltage on the collector would make the base voltage
slightly more negative.

Cheers

Phil Hobbs

I\'d expect that zenering fills the b-e junction with lots of carriers,
and some find their way into the collector. I don\'t know how many.

Probably a lot less than foward base current.

I suppose I should try it.

Did you try it? I did today with a junk box NPN and results are kind of
as expected:

https://www.dropbox.com/scl/fi/rqr7n3uunosswqhx4e59h/NPNunusualQuadrant.pdf?rlkey=6kcqwz3soawgxws2ouhbdktq3&raw=1

Very good, Piglet. That is very linear which I did not expect. Your data results in
Ic(nA) = 9.2536Veb - 74.33

So, to expect this in future, should we assume the B-E breakdown creates light, and
the collector current is a photodiode detecting that light? That does explain the
effect, and predicts emitter current proportional to collector current.

Yes, I think you meant collector current proportional to emitter
current? We did discusss all this back in 2015 under the thread \"a very
silly circuit\". About 25 years ago I think Stephen Woodward posted a
design idea in ED magazine using the effect to create a tiny negative
bias for opamp offset nulling in a positive rail only environment.

piglet

PV optocouplers are great for genereating a quiet floating voltage,
but a transistor is cheaper.

I guess a regular, transistor type optocoupler, will generate a
floating voltage too. Something else to try.


It will, but you have to accept an efficiency on the order of CTR/beta,
i.e. something below 0.1%.

One could parallel the c-b and b-e junctions. Might help a little.


Cheers

Phil Hobbs

OK for some tiny bias thing, probably not for running motors.

This would be another curiosity measurement. You never know if such a
thing might be useful some day.

Here are some measurements I just made:

<https://www.dropbox.com/scl/fi/jp7r2vkrqo8npkf2kws0t/OptoCoupler_PV.pdf?rlkey=cg5o780xvyjdepe74k750799q&raw=1>

Seems bulk of the goodness comes from the C-B junction and paralleling
E+C makes hardly any difference.

piglet

 

[Piglet]

On 11/09/2023 13:50, Phil Hobbs wrote:

On 2023-09-11 08:32, John Larkin wrote:
On Mon, 11 Sep 2023 11:01:46 +0100, piglet <erichpwagner@hotmail.com
wrote:

On 11/09/2023 4:16 am, whit3rd wrote:
On Sunday, September 10, 2023 at 12:55:12?PM UTC-7, John Smiht wrote:
On Sunday, September 10, 2023 at 7:57:03?AM UTC-5, Piglet wrote:
On 06/09/2023 03:38, John Larkin wrote:
On Wed, 6 Sep 2023 02:31:04 -0000 (UTC), Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:

Now pull the base negative, through a current-limiting
resistor. What
happens?

Nothing until you exceed the emitter base reverse breakdown (or
collector base breakdown) voltage,

Not literally nothing, but not much interesting. It gets more
interesting when the base zeners.


Bitter-base is usually about 5V

Behaves kind of like a zener diode and damages the transistor.

Haven’t tried it, at least not on purpose, but I’d guess that
when the
avalanche starts, most of the electrons will get sucked up by the
collector.

Since it’s the electrons and not the holes that do the
avalanching in
silicon, that might partially suppress the avalanche. If that
were true,
putting a positive voltage on the collector would make the base
voltage
slightly more negative.

Cheers

Phil Hobbs

I\'d expect that zenering fills the b-e junction with lots of
carriers,
and some find their way into the collector. I don\'t know how many.

Probably a lot less than foward base current.

I suppose I should try it.

Did you try it? I did today with a junk box NPN and results are
kind of
as expected:

https://www.dropbox.com/scl/fi/rqr7n3uunosswqhx4e59h/NPNunusualQuadrant.pdf?rlkey=6kcqwz3soawgxws2ouhbdktq3&raw=1

Very good, Piglet. That is very linear which I did not expect. Your
data results in
Ic(nA) = 9.2536Veb - 74.33

So, to expect this in future, should we assume the B-E breakdown
creates light, and
the collector current is a photodiode  detecting that light?   That
does explain the
effect, and predicts emitter current proportional to collector current.

Yes, I think you meant collector current proportional to emitter
current? We did discusss all this back in 2015 under the thread \"a very
silly circuit\". About 25 years ago I think Stephen Woodward posted a
design idea in ED magazine using the effect to create a tiny negative
bias for opamp offset nulling in a positive rail only environment.

piglet

PV optocouplers are great for genereating a quiet floating voltage,
but a transistor is cheaper.

I guess a regular, transistor type optocoupler, will generate a
floating voltage too. Something else to try.


It will, but you have to accept an efficiency on the order of CTR/beta,
i.e. something below 0.1%.

Cheers

Phil Hobbs

I made some tests and I think you are correct, lower beta gives higher
output.

<https://www.dropbox.com/scl/fi/jp7r2vkrqo8npkf2kws0t/OptoCoupler_PV.pdf?rlkey=cg5o780xvyjdepe74k750799q&raw=1>

piglet

 

[John Larkin]

On Tue, 12 Sep 2023 16:02:19 +0100, Piglet <erichpwagner@hotmail.com>
wrote:

On 11/09/2023 15:16, John Larkin wrote:
On Mon, 11 Sep 2023 08:50:54 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-09-11 08:32, John Larkin wrote:
On Mon, 11 Sep 2023 11:01:46 +0100, piglet <erichpwagner@hotmail.com
wrote:

On 11/09/2023 4:16 am, whit3rd wrote:
On Sunday, September 10, 2023 at 12:55:12?PM UTC-7, John Smiht wrote:
On Sunday, September 10, 2023 at 7:57:03?AM UTC-5, Piglet wrote:
On 06/09/2023 03:38, John Larkin wrote:
On Wed, 6 Sep 2023 02:31:04 -0000 (UTC), Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:

Now pull the base negative, through a current-limiting resistor. What
happens?

Nothing until you exceed the emitter base reverse breakdown (or
collector base breakdown) voltage,

Not literally nothing, but not much interesting. It gets more
interesting when the base zeners.


Bitter-base is usually about 5V

Behaves kind of like a zener diode and damages the transistor.

Haven’t tried it, at least not on purpose, but I’d guess that when the
avalanche starts, most of the electrons will get sucked up by the
collector.

Since it’s the electrons and not the holes that do the avalanching in
silicon, that might partially suppress the avalanche. If that were true,
putting a positive voltage on the collector would make the base voltage
slightly more negative.

Cheers

Phil Hobbs

I\'d expect that zenering fills the b-e junction with lots of carriers,
and some find their way into the collector. I don\'t know how many.

Probably a lot less than foward base current.

I suppose I should try it.

Did you try it? I did today with a junk box NPN and results are kind of
as expected:

https://www.dropbox.com/scl/fi/rqr7n3uunosswqhx4e59h/NPNunusualQuadrant.pdf?rlkey=6kcqwz3soawgxws2ouhbdktq3&raw=1

Very good, Piglet. That is very linear which I did not expect. Your data results in
Ic(nA) = 9.2536Veb - 74.33

So, to expect this in future, should we assume the B-E breakdown creates light, and
the collector current is a photodiode detecting that light? That does explain the
effect, and predicts emitter current proportional to collector current.

Yes, I think you meant collector current proportional to emitter
current? We did discusss all this back in 2015 under the thread \"a very
silly circuit\". About 25 years ago I think Stephen Woodward posted a
design idea in ED magazine using the effect to create a tiny negative
bias for opamp offset nulling in a positive rail only environment.

piglet

PV optocouplers are great for genereating a quiet floating voltage,
but a transistor is cheaper.

I guess a regular, transistor type optocoupler, will generate a
floating voltage too. Something else to try.


It will, but you have to accept an efficiency on the order of CTR/beta,
i.e. something below 0.1%.

One could parallel the c-b and b-e junctions. Might help a little.


Cheers

Phil Hobbs

OK for some tiny bias thing, probably not for running motors.

This would be another curiosity measurement. You never know if such a
thing might be useful some day.


Here are some measurements I just made:

https://www.dropbox.com/scl/fi/jp7r2vkrqo8npkf2kws0t/OptoCoupler_PV.pdf?rlkey=cg5o780xvyjdepe74k750799q&raw=1

Seems bulk of the goodness comes from the C-B junction and paralleling
E+C makes hardly any difference.

The photocurrent is driving the diode forward conduction curve, 60 mV
per decade of current. Solar cells short themselves out.

piglet

That\'s cool. I bet we\'d see more voltage without the 1 meg resistors.

One might pulse the LED hard at some low duty cycle and hang a cap on
the output, to get more voltage.

There must be a use for this! Opamp nulling has been suggested.

I might have to design a multi-channel super-precise DC power source.
This might fit in.

 

[whit3rd]

On Tuesday, September 12, 2023 at 8:02:28 AM UTC-7, Piglet wrote:

On 11/09/2023 15:16, John Larkin wrote:
On Mon, 11 Sep 2023 08:50:54 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 2023-09-11 08:32, John Larkin wrote:

I guess a regular, transistor type optocoupler, will generate a
floating voltage too. Something else to try.

It will, but you have to accept an efficiency on the order of CTR/beta,
i.e. something below 0.1%.

One could parallel the c-b and b-e junctions. Might help a little.

Here are some measurements I just made:

https://www.dropbox.com/scl/fi/jp7r2vkrqo8npkf2kws0t/OptoCoupler_PV.pdf?rlkey=cg5o780xvyjdepe74k750799q&raw=1

Seems bulk of the goodness comes from the C-B junction and paralleling
E+C makes hardly any difference.

That\'s expected; geometrically, the E is just a tiny dot, and an opaque one (heavy doping, nearly
a conductor) and the collector is virtually the entire volume of the semiconductor die.