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John Larkin
Guest

Sat Jan 19, 2019 1:45 am   



On Fri, 18 Jan 2019 17:47:04 +0000, Tom Gardner
<spamjunk_at_blueyonder.co.uk> wrote:

Quote:
On 18/01/19 16:57, Phil Hobbs wrote:
On 1/18/19 11:07 AM, John Larkin wrote:
On Fri, 18 Jan 2019 15:19:15 -0000 (UTC), Cursitor Doom
curd_at_notformail.com> wrote:

On Thu, 17 Jan 2019 23:03:46 -0500, Tom Biasi wrote:

Blackboard devices are perfect. If the battery was to have an internal
resistance it should have been drawn in.

If I'd been asked that question as a fresh graduate applying for his
first job, I've had assumed there *must* be a trap there somewhere; it's
an absurdly simple a question to ask someone who's just got his EE degree.
"A stiff 10V source" would have been unambiguous.

There was no trap. Most recent EE grads panic when asked that
question.

If they understand anything about how a transistor works, they get a
job offer. Most recent grads have had some sort of VLSI design course
but don't know how a mosfet works.




A lot of it is the fault of the high schools. Profs I know complain that
they've had to dumb down their courses because the kids can't handle the real
thing. And this is in good places such as MIT and CU Boulder.

I was taught semiconductor bandgap theory and simple
electronics in Physics at my state school (i.e. before
university).

The teacher did a pretty good job of it too, and noted that
although it was on the syllabus, there had never been a
question on it in the formal external "A-level" exam.

They also allowed us to play with scopes at lunch and
had a supply of transistors that we could pull of
surplus PCBs.

The downside was that thermodynamics wasn't taught.


I suffered through two semisters of thermo, and it was a waste of
time. Nobody in EE school mentioned useful stuff like heat conduction
or convection cooling. Thermo was a lot of junk about entropy and
enthalopy, great if you design steam engines.







--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

John Larkin
Guest

Sat Jan 19, 2019 1:45 am   



On Fri, 18 Jan 2019 14:01:45 -0500, Ralph Mowery
<rmowery28146_at_earthlink.net> wrote:

Quote:
In article <q1qe33$sii$1_at_dont-email.me>, curd_at_notformail.com says...

10 volt battery, 9K and 1K resistors in series. What's the voltage
across the 1K? I had one kid instantly reply "one volt" without
thinking, so I hired him as an intern. A month later, he was full-time.

Sorry, John, that's a fail. You didn't state the internal resistance of
the battery. ;-






With all that is given, any battery worth while will have an internal
resistance large enough to take it out of the equation. Also the
tollorence of the resitors are not stated, neither is how accurate is
the meter. Too much fly poop in the pepper.

Even if the battery resistance is 10 ohms the answer would have to be
moved out many decimal places. For most work who cares if it is .99
volts. For most repairs if you measure to 5 or maybe even 10 % that is
close enough.



Right. Another thing the question addresses is whether the kid can
answer a simple practical question or get paralyzed by complexities.

I have a transistor question for more experienced candidates. It's fun
to get the basic answers there but ask about nuances. If he says
"temperature will change Vbe" or "it might oscillate at 100 MHz" he's
a sure bet.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

Cursitor Doom
Guest

Sat Jan 19, 2019 2:45 am   



On Fri, 18 Jan 2019 19:03:29 -0500, Phil Hobbs wrote:

Quote:
Even with tightly-specced transistors, beta varies 2:1 at a given
current. Ebers-Moll is way, way tighter than that--two random BJTs at
the same temperature and collector current will have the same
transconductance to very high accuracy. There are offsets due to die
size and device details, but there's nothing comparable in any other
active device.


Yes, I fully agree with you, Phil. Yet if we were on SED right now with
this thread, you'd have had half a dozen people already sticking up for
Beta! Precisely why I cannot for the life of me understand.



--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

Cursitor Doom
Guest

Sat Jan 19, 2019 2:45 am   



On Fri, 18 Jan 2019 16:29:15 -0800, John Larkin wrote:

Quote:
Right. Another thing the question addresses is whether the kid can
answer a simple practical question or get paralyzed by complexities.


Good point.

Quote:
I have a transistor question for more experienced candidates. It's fun
to get the basic answers there but ask about nuances. If he says
"temperature will change Vbe" or "it might oscillate at 100 MHz" he's a
sure bet.


A sure bet for what?





--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

Phil Hobbs
Guest

Sat Jan 19, 2019 6:04 am   



On 1/18/19 8:01 PM, Cursitor Doom wrote:
Quote:
On Fri, 18 Jan 2019 19:03:29 -0500, Phil Hobbs wrote:

Even with tightly-specced transistors, beta varies 2:1 at a given
current. Ebers-Moll is way, way tighter than that--two random BJTs at
the same temperature and collector current will have the same
transconductance to very high accuracy. There are offsets due to die
size and device details, but there's nothing comparable in any other
active device.

Yes, I fully agree with you, Phil. Yet if we were on SED right now with
this thread, you'd have had half a dozen people already sticking up for
Beta! Precisely why I cannot for the life of me understand.


You can do a lot of useful stuff with a 2:1 beta spread--it's
dramatically better than the old-timey parts such as the 2N2222, which
had beta specs like min 35, max 300.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Cursitor Doom
Guest

Sat Jan 19, 2019 9:45 pm   



On Fri, 18 Jan 2019 23:04:45 -0500, Phil Hobbs wrote:


Quote:
You can do a lot of useful stuff with a 2:1 beta spread--it's
dramatically better than the old-timey parts such as the 2N2222, which
had beta specs like min 35, max 300.


Yes, there were some shocking spreads with some devices. But that was
just a run-of-the-mill consideration for designers using those parts; as
you well know yourself you had to take such spreads into account when
setting up the bias networks and whatnot - and it was just one of those
things that had to be factored in and no big deal.





--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.


Guest

Sun Jan 20, 2019 8:45 am   



If we all, umm, shit I forgot.

Later.

George Herold
Guest

Mon Jan 21, 2019 4:45 pm   



On Friday, January 18, 2019 at 7:23:55 PM UTC-5, John Larkin wrote:
Quote:
On Fri, 18 Jan 2019 17:47:04 +0000, Tom Gardner
spamjunk_at_blueyonder.co.uk> wrote:

On 18/01/19 16:57, Phil Hobbs wrote:
On 1/18/19 11:07 AM, John Larkin wrote:
On Fri, 18 Jan 2019 15:19:15 -0000 (UTC), Cursitor Doom
curd_at_notformail.com> wrote:

On Thu, 17 Jan 2019 23:03:46 -0500, Tom Biasi wrote:

Blackboard devices are perfect. If the battery was to have an internal
resistance it should have been drawn in.

If I'd been asked that question as a fresh graduate applying for his
first job, I've had assumed there *must* be a trap there somewhere; it's
an absurdly simple a question to ask someone who's just got his EE degree.
"A stiff 10V source" would have been unambiguous.

There was no trap. Most recent EE grads panic when asked that
question.

If they understand anything about how a transistor works, they get a
job offer. Most recent grads have had some sort of VLSI design course
but don't know how a mosfet works.




A lot of it is the fault of the high schools.  Profs I know complain that
they've had to dumb down their courses because the kids can't handle the real
thing.  And this is in good places such as MIT and CU Boulder.

I was taught semiconductor bandgap theory and simple
electronics in Physics at my state school (i.e. before
university).

The teacher did a pretty good job of it too, and noted that
although it was on the syllabus, there had never been a
question on it in the formal external "A-level" exam.

They also allowed us to play with scopes at lunch and
had a supply of transistors that we could pull of
surplus PCBs.

The downside was that thermodynamics wasn't taught.

I suffered through two semisters of thermo, and it was a waste of
time. Nobody in EE school mentioned useful stuff like heat conduction
or convection cooling. Thermo was a lot of junk about entropy and
enthalopy, great if you design steam engines.


Engineering thermo was the pits. Turbines/ steam tables/ and confusion.

You needed to take Physics Thermo. "Little Reif"* is a fun Thermo book

It's really a beautiful subject in some ways.
George H.
*https://www.amazon.com/Statistical-Physics-Berkeley-Course-Vol/dp/0070048622
Quote:







--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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


John Larkin
Guest

Mon Jan 21, 2019 5:45 pm   



On Mon, 21 Jan 2019 07:07:17 -0800 (PST), George Herold
<gherold_at_teachspin.com> wrote:

Quote:
On Friday, January 18, 2019 at 7:23:55 PM UTC-5, John Larkin wrote:
On Fri, 18 Jan 2019 17:47:04 +0000, Tom Gardner
spamjunk_at_blueyonder.co.uk> wrote:

On 18/01/19 16:57, Phil Hobbs wrote:
On 1/18/19 11:07 AM, John Larkin wrote:
On Fri, 18 Jan 2019 15:19:15 -0000 (UTC), Cursitor Doom
curd_at_notformail.com> wrote:

On Thu, 17 Jan 2019 23:03:46 -0500, Tom Biasi wrote:

Blackboard devices are perfect. If the battery was to have an internal
resistance it should have been drawn in.

If I'd been asked that question as a fresh graduate applying for his
first job, I've had assumed there *must* be a trap there somewhere; it's
an absurdly simple a question to ask someone who's just got his EE degree.
"A stiff 10V source" would have been unambiguous.

There was no trap. Most recent EE grads panic when asked that
question.

If they understand anything about how a transistor works, they get a
job offer. Most recent grads have had some sort of VLSI design course
but don't know how a mosfet works.




A lot of it is the fault of the high schools. Profs I know complain that
they've had to dumb down their courses because the kids can't handle the real
thing. And this is in good places such as MIT and CU Boulder.

I was taught semiconductor bandgap theory and simple
electronics in Physics at my state school (i.e. before
university).

The teacher did a pretty good job of it too, and noted that
although it was on the syllabus, there had never been a
question on it in the formal external "A-level" exam.

They also allowed us to play with scopes at lunch and
had a supply of transistors that we could pull of
surplus PCBs.

The downside was that thermodynamics wasn't taught.

I suffered through two semisters of thermo, and it was a waste of
time. Nobody in EE school mentioned useful stuff like heat conduction
or convection cooling. Thermo was a lot of junk about entropy and
enthalopy, great if you design steam engines.

Engineering thermo was the pits. Turbines/ steam tables/ and confusion.

You needed to take Physics Thermo. "Little Reif"* is a fun Thermo book

It's really a beautiful subject in some ways.
George H.
*https://www.amazon.com/Statistical-Physics-Berkeley-Course-Vol/dp/0070048622


It would be great to have a course that talks about thermal
conduction, cooling semiconductors, Johnson noise, radiation, temp
effects on components, convection, heat sinks, liquid cooling,
Peltiers, thermal system simulation, thermal measurements, useful
stuff like that. Steam engines are pretty rare these days; factories
use electricity and ships/trains are mostly diesels.


--

John Larkin Highland Technology, Inc trk

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

George Herold
Guest

Mon Jan 21, 2019 7:45 pm   



On Monday, January 21, 2019 at 11:10:37 AM UTC-5, John Larkin wrote:
Quote:
On Mon, 21 Jan 2019 07:07:17 -0800 (PST), George Herold
gherold_at_teachspin.com> wrote:

On Friday, January 18, 2019 at 7:23:55 PM UTC-5, John Larkin wrote:
On Fri, 18 Jan 2019 17:47:04 +0000, Tom Gardner
spamjunk_at_blueyonder.co.uk> wrote:

On 18/01/19 16:57, Phil Hobbs wrote:
On 1/18/19 11:07 AM, John Larkin wrote:
On Fri, 18 Jan 2019 15:19:15 -0000 (UTC), Cursitor Doom
curd_at_notformail.com> wrote:

On Thu, 17 Jan 2019 23:03:46 -0500, Tom Biasi wrote:

Blackboard devices are perfect. If the battery was to have an internal
resistance it should have been drawn in.

If I'd been asked that question as a fresh graduate applying for his
first job, I've had assumed there *must* be a trap there somewhere; it's
an absurdly simple a question to ask someone who's just got his EE degree.
"A stiff 10V source" would have been unambiguous.

There was no trap. Most recent EE grads panic when asked that
question.

If they understand anything about how a transistor works, they get a
job offer. Most recent grads have had some sort of VLSI design course
but don't know how a mosfet works.




A lot of it is the fault of the high schools.  Profs I know complain that
they've had to dumb down their courses because the kids can't handle the real
thing.  And this is in good places such as MIT and CU Boulder.

I was taught semiconductor bandgap theory and simple
electronics in Physics at my state school (i.e. before
university).

The teacher did a pretty good job of it too, and noted that
although it was on the syllabus, there had never been a
question on it in the formal external "A-level" exam.

They also allowed us to play with scopes at lunch and
had a supply of transistors that we could pull of
surplus PCBs.

The downside was that thermodynamics wasn't taught.

I suffered through two semisters of thermo, and it was a waste of
time. Nobody in EE school mentioned useful stuff like heat conduction
or convection cooling. Thermo was a lot of junk about entropy and
enthalopy, great if you design steam engines.

Engineering thermo was the pits. Turbines/ steam tables/ and confusion.

You needed to take Physics Thermo. "Little Reif"* is a fun Thermo book

It's really a beautiful subject in some ways.
George H.
*https://www.amazon.com/Statistical-Physics-Berkeley-Course-Vol/dp/0070048622

It would be great to have a course that talks about thermal
conduction, cooling semiconductors, Johnson noise, radiation, temp
effects on components, convection, heat sinks, liquid cooling,
Peltiers, thermal system simulation, thermal measurements, useful
stuff like that. Steam engines are pretty rare these days; factories
use electricity and ships/trains are mostly diesels.


Well you won't find much of that in a physics thermo book.
Do you have "building scientific apparatus"?
https://www.amazon.com/Building-Scientific-Apparatus-John-Moore/dp/0521878586

By some chemists, still good.
(I need to order another copy... mine grew legs.)

George H.
Quote:

--

John Larkin Highland Technology, Inc trk

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


John Larkin
Guest

Thu Jan 24, 2019 1:45 am   



On Sat, 19 Jan 2019 01:01:00 -0000 (UTC), Cursitor Doom
<curd_at_notformail.com> wrote:

Quote:
On Fri, 18 Jan 2019 19:03:29 -0500, Phil Hobbs wrote:

Even with tightly-specced transistors, beta varies 2:1 at a given
current. Ebers-Moll is way, way tighter than that--two random BJTs at
the same temperature and collector current will have the same
transconductance to very high accuracy. There are offsets due to die
size and device details, but there's nothing comparable in any other
active device.

Yes, I fully agree with you, Phil. Yet if we were on SED right now with
this thread, you'd have had half a dozen people already sticking up for
Beta! Precisely why I cannot for the life of me understand.


Beta is very useful. If I have a 3.3v logic swing and I want to
operate a 24V relay coil, I need to know what value of base resistor
to use.

Ebers-Moll isn't very useful for a transistor that is either off or
saturated.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Phil Hobbs
Guest

Thu Jan 24, 2019 5:45 am   



On 1/23/19 7:05 PM, John Larkin wrote:
Quote:
On Sat, 19 Jan 2019 01:01:00 -0000 (UTC), Cursitor Doom
curd_at_notformail.com> wrote:

On Fri, 18 Jan 2019 19:03:29 -0500, Phil Hobbs wrote:

Even with tightly-specced transistors, beta varies 2:1 at a given
current. Ebers-Moll is way, way tighter than that--two random BJTs at
the same temperature and collector current will have the same
transconductance to very high accuracy. There are offsets due to die
size and device details, but there's nothing comparable in any other
active device.

Yes, I fully agree with you, Phil. Yet if we were on SED right now with
this thread, you'd have had half a dozen people already sticking up for
Beta! Precisely why I cannot for the life of me understand.

Beta is very useful. If I have a 3.3v logic swing and I want to
operate a 24V relay coil, I need to know what value of base resistor
to use.


Sure, you have to know what the beta range is in order to use BJTs
effectively. It's just far sloppier than transconductance.
Quote:

Ebers-Moll isn't very useful for a transistor that is either off or
saturated.


Of course, neither is beta. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

John Larkin
Guest

Thu Jan 24, 2019 9:45 pm   



On Wed, 23 Jan 2019 22:51:35 -0500, Phil Hobbs
<pcdhSpamMeSenseless_at_electrooptical.net> wrote:

Quote:
On 1/23/19 7:05 PM, John Larkin wrote:
On Sat, 19 Jan 2019 01:01:00 -0000 (UTC), Cursitor Doom
curd_at_notformail.com> wrote:

On Fri, 18 Jan 2019 19:03:29 -0500, Phil Hobbs wrote:

Even with tightly-specced transistors, beta varies 2:1 at a given
current. Ebers-Moll is way, way tighter than that--two random BJTs at
the same temperature and collector current will have the same
transconductance to very high accuracy. There are offsets due to die
size and device details, but there's nothing comparable in any other
active device.

Yes, I fully agree with you, Phil. Yet if we were on SED right now with
this thread, you'd have had half a dozen people already sticking up for
Beta! Precisely why I cannot for the life of me understand.

Beta is very useful. If I have a 3.3v logic swing and I want to
operate a 24V relay coil, I need to know what value of base resistor
to use.

Sure, you have to know what the beta range is in order to use BJTs
effectively. It's just far sloppier than transconductance.

Ebers-Moll isn't very useful for a transistor that is either off or
saturated.

Of course, neither is beta. ;)

Cheers

Phil Hobbs


Given a preference to fry neither gates nor transistors, a beta spec
is very useful.

Another deplorable number is "forced beta."


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

Cursitor Doom
Guest

Sat Jan 26, 2019 1:45 am   



On Thu, 24 Jan 2019 12:26:38 -0800, John Larkin wrote:

Quote:
Given a preference to fry neither gates nor transistors, a beta spec is
very useful.


So say the beta range is 120 - 300 (just figures I've pulled out of my
arse for the sake of argument) You just design on the basis that all the
devices will be the worst case 120?

> Another deplorable number is "forced beta."

Wot's that?



--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

John Larkin
Guest

Sat Jan 26, 2019 2:45 am   



On Sat, 26 Jan 2019 00:13:57 -0000 (UTC), Cursitor Doom
<curd_at_notformail.com> wrote:

Quote:
On Thu, 24 Jan 2019 12:26:38 -0800, John Larkin wrote:

Given a preference to fry neither gates nor transistors, a beta spec is
very useful.

So say the beta range is 120 - 300 (just figures I've pulled out of my
arse for the sake of argument) You just design on the basis that all the
devices will be the worst case 120?

Another deplorable number is "forced beta."

Wot's that?


It's the actual ratio of Ic/Ib that the circuit runs at.

I might run a saturating relay driver at a forced beta of 20. Jam 1 mA
into the base for an expected coil current of 20 mA.

Or, nowadays, use a mosfet.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

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