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Temperature compensating diode drops

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Joerg
Guest

Mon Jan 09, 2017 7:35 am   



On 2017-01-08 16:15, pcdhobbs_at_gmail.com wrote:
Quote:
Problem is, there's a cable in between, so if there's a short to
ground it has a 50:50 chance of being on the wrong side of the
current limiter if there's only one.


I thought you only needed to protect the TEC, not the driver.

Right. But the driver is a bridge, and a short to ground on the wrong
side will do b ad things if the protection is asymmetric.


Maybe I am understanding it wrong but if the current limiters are
directly in line with and physically at the Peltier it shouldn't matter.
You could have one current limit for cool and another for heat. Of
course, if there is a chance that a wrench falls directly onto the
Peltier contacts that's bad.


Quote:
Thus I'd need one set on each side, which is more complicated
than what I'm doing already.


Can't the driver be beefed up a bit and adequately fused by
electronics means so it won't smoke?

'Tain't the driver I'm worried about, it's the TEC. Symmetric drive
over a cable requires symmetric protection. If the current limits
were the same for positive and negative drive, it would be easy, but
they aren't.


Just select different resistor values. One LM317 is for heat, the other
for cool, regardless of whether the TEC is driven ground based or from
an H-bridge. As long as that limiter is right at the Peltier. Else you'd
need four LM317 or similar and four resistors. They are cheap but that
adds voltage drop.

--
Regards, Joerg

http://www.analogconsultants.com/

John Larkin
Guest

Mon Jan 09, 2017 8:22 am   



On Sun, 08 Jan 2017 16:25:27 -0800, Joerg <news_at_analogconsultants.com>
wrote:

Quote:
On 2017-01-08 15:59, John Larkin wrote:
On Sun, 08 Jan 2017 15:50:08 -0800, Joerg <news_at_analogconsultants.com
wrote:

On 2017-01-08 15:28, John Larkin wrote:
On Sun, 08 Jan 2017 14:24:50 -0800, Joerg <news_at_analogconsultants.com
wrote:

On 2017-01-08 12:50, John Larkin wrote:
On Sun, 8 Jan 2017 15:31:58 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:

On 01/08/2017 03:02 PM, Jim Thompson wrote:
On Sun, 8 Jan 2017 13:39:00 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:


[snip]

so once I get back on my feet I'll do
some measurements and see if I can afford an extra volt-and-a-bit for
the TLV431/LM4041-ADJ version.

[snip]

Have you suffered an injury, or a surgery?

I'm considering having the joint in my right big toe replaced. I'm a
"walker" and the arthritis is impending my speed ;-)

Nah, nothing so dramatic--just a bad cold that turned into a nasty sinus
infection. I'll be back in the lab some time this week.
Cheers

Phil Hobbs

I have about a hundred Cipros on hand, in case of emergency. You can
buy them from fish-supply sites.


None here, the world is using too much antibiotics as it is.

Sometimes an antibiotic will save your life. Cipro has saved mine.
Lots of people used to die from initially minor scrapes or sore
throats that turned into deadly infections.


I know. One of my relatives died from a simple infection because
antibiotics were not released to German patients right after the war.

But 100 pills? That's a lot. I only take antibiotics when there really
is no other choice.

I haven't taken any of the fish meds yet. But we could have an
earthquake or something.


The last one east of here a couple weeks ago was felt my most neighbors.
I didn't wake up.


We felt that one in Truckee, vaguely around midlight.

There is a fault almost directly below our cabin, but those dinky
faults don't do much damage.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

George Herold
Guest

Mon Jan 09, 2017 6:27 pm   



On Monday, January 9, 2017 at 10:35:31 AM UTC-5, Joerg wrote:
Quote:
On 2017-01-08 16:46, pcdhobbs_at_gmail.com wrote:
Maybe I am understanding it wrong but if the current limiters are
directly in line with and physically at the Peltier it shouldn't
matter.

Right, except that they aren't. The current limiters are on the
board, and the laser/TEC is at the other end of a cable. Otherwise I
wouldn't be worried about shorts.


Ok, didn't know that, then you need four LM317.


You could have one current limit for cool and another for heat. Of

That's the point of the exercise, right.

course, if there is a chance that a wrench falls directly onto the
Peltier contacts that's bad.

If the laser assembly could be mounted on the board, I wouldn't be
worried, but it can't. The application is an industrial tester for
manufacturing other things, so reliability is key because down time
is expensive.

Not all of the users are in the first world, so "expensive" has to
take account of the BOM cost as well. If it were like Ford and GM,
I'd throw a couple of bucks' BOM cost at it and move on.


However, power consumption probably isn't much of a concern and even if
you'd need four LM317 they are around 50 cents. Depending on curent
they'll need heatsinking.

Probably the best is to revise the driver ciruitry so that it contains
intelligent current limiting. You might get away with just sensing and
shutdown (OR-ing the comparators) because if a short occurred it's a
service call anyhow where at least a factory technician has to come over.

Yeah I've been a bit confused by Phil's problem. If he runs the TEC feedback
loop by controlling/sensing the current, then a current limit seems easy.
(But I'm probably missing something obvious. For one I don't understand
the four quadrant thing... why does the current matter if it's being
sourced by the TEC temperature difference?)

George H.
Quote:


Joerg
Guest

Mon Jan 09, 2017 10:35 pm   



On 2017-01-08 16:46, pcdhobbs_at_gmail.com wrote:
Quote:
Maybe I am understanding it wrong but if the current limiters are
directly in line with and physically at the Peltier it shouldn't
matter.

Right, except that they aren't. The current limiters are on the
board, and the laser/TEC is at the other end of a cable. Otherwise I
wouldn't be worried about shorts.


Ok, didn't know that, then you need four LM317.


Quote:
You could have one current limit for cool and another for heat. Of

That's the point of the exercise, right.

course, if there is a chance that a wrench falls directly onto the
Peltier contacts that's bad.

If the laser assembly could be mounted on the board, I wouldn't be
worried, but it can't. The application is an industrial tester for
manufacturing other things, so reliability is key because down time
is expensive.

Not all of the users are in the first world, so "expensive" has to
take account of the BOM cost as well. If it were like Ford and GM,
I'd throw a couple of bucks' BOM cost at it and move on.


However, power consumption probably isn't much of a concern and even if
you'd need four LM317 they are around 50 cents. Depending on curent
they'll need heatsinking.

Probably the best is to revise the driver ciruitry so that it contains
intelligent current limiting. You might get away with just sensing and
shutdown (OR-ing the comparators) because if a short occurred it's a
service call anyhow where at least a factory technician has to come over.

--
Regards, Joerg

http://www.analogconsultants.com/

Phil Hobbs
Guest

Mon Jan 09, 2017 11:25 pm   



On 01/09/2017 10:35 AM, Joerg wrote:
Quote:
On 2017-01-08 16:46, pcdhobbs_at_gmail.com wrote:
Maybe I am understanding it wrong but if the current limiters are
directly in line with and physically at the Peltier it shouldn't
matter.

Right, except that they aren't. The current limiters are on the
board, and the laser/TEC is at the other end of a cable. Otherwise I
wouldn't be worried about shorts.


Ok, didn't know that, then you need four LM317.


You could have one current limit for cool and another for heat. Of

That's the point of the exercise, right.

course, if there is a chance that a wrench falls directly onto the
Peltier contacts that's bad.

If the laser assembly could be mounted on the board, I wouldn't be
worried, but it can't. The application is an industrial tester for
manufacturing other things, so reliability is key because down time
is expensive.

Not all of the users are in the first world, so "expensive" has to
take account of the BOM cost as well. If it were like Ford and GM,
I'd throw a couple of bucks' BOM cost at it and move on.


However, power consumption probably isn't much of a concern and even if
you'd need four LM317 they are around 50 cents. Depending on curent
they'll need heatsinking.

Probably the best is to revise the driver ciruitry so that it contains
intelligent current limiting. You might get away with just sensing and
shutdown (OR-ing the comparators) because if a short occurred it's a
service call anyhow where at least a factory technician has to come over.


Turns out I do have enough headroom to do the TLV431/LM4041-ADJ thing,
which costs about 14 cents per corner (Micrel/Microchip LM4041DYM3-ADJ
and Diodes TLV431AFTA) and saves four transistors and four diodes.

Interesting discussion, though!


Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Phil Hobbs
Guest

Mon Jan 09, 2017 11:42 pm   



On 01/09/2017 11:27 AM, George Herold wrote:
Quote:
On Monday, January 9, 2017 at 10:35:31 AM UTC-5, Joerg wrote:
On 2017-01-08 16:46, pcdhobbs_at_gmail.com wrote:
Maybe I am understanding it wrong but if the current limiters are
directly in line with and physically at the Peltier it shouldn't
matter.

Right, except that they aren't. The current limiters are on the
board, and the laser/TEC is at the other end of a cable. Otherwise I
wouldn't be worried about shorts.


Ok, didn't know that, then you need four LM317.


You could have one current limit for cool and another for heat. Of

That's the point of the exercise, right.

course, if there is a chance that a wrench falls directly onto the
Peltier contacts that's bad.

If the laser assembly could be mounted on the board, I wouldn't be
worried, but it can't. The application is an industrial tester for
manufacturing other things, so reliability is key because down time
is expensive.

Not all of the users are in the first world, so "expensive" has to
take account of the BOM cost as well. If it were like Ford and GM,
I'd throw a couple of bucks' BOM cost at it and move on.


However, power consumption probably isn't much of a concern and even if
you'd need four LM317 they are around 50 cents. Depending on curent
they'll need heatsinking.

Probably the best is to revise the driver ciruitry so that it contains
intelligent current limiting. You might get away with just sensing and
shutdown (OR-ing the comparators) because if a short occurred it's a
service call anyhow where at least a factory technician has to come over.
Yeah I've been a bit confused by Phil's problem. If he runs the TEC feedback
loop by controlling/sensing the current, then a current limit seems easy.


It isn't difficult, but I was sick in bed and therefore bored stiff, so
I wanted to talk about electronics. Kicking around this sort of stuff
is always good for keeping the mental joints from seizing up, and not
every design has enough headroom to waste an extra volt-and-a-half for
the TLV431/LM4041 approach or three volts or more for the symmetrical
LM317 approach.

The last one I did ran off +8 and ground, so I did two current sources
fighting each other, and put voltage feedback around one of them to keep
the bridge centred. Not that it would have mattered if I hadn't, but I
had a spare op amp section and it's tidier that way--spreads out the
power dissipation.

Quote:
(But I'm probably missing something obvious. For one I don't understand
the four quadrant thing... why does the current matter if it's being
sourced by the TEC temperature difference?)


It needs two different current limits, not four, that's right.

The four-quadrant thing is why you need to drive the TEC with a current
rather than a voltage. It has a large and poorly-controlled offset
voltage due to being a big thermopile with a potentially large
temperature drop.

Cheers

Phil Hobbs

"back in the saddle again"


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Dave Platt
Guest

Tue Jan 10, 2017 2:30 am   



In article <kki57ch9es8tffjgiqn7okktrrite0gs3j_at_4ax.com>,
John Larkin <jjlarkin_at_highlandtechnology.com> wrote:
Quote:
None here, the world is using too much antibiotics as it is.

Sometimes an antibiotic will save your life. Cipro has saved mine.
Lots of people used to die from initially minor scrapes or sore
throats that turned into deadly infections.


_Appropriate_ use is highly beneficial. _Inappropriate_ use is a huge
problem, as it tends to promote the development of antibiotic-
resistant strains and thus limits further appropriate use of those
same antibiotics. Using massive quantities of antibiotics as "growth
promoters" in animal feed is one of the greater insanities of the last
few decades.

I'm personally grateful for the availability of good antibiotics. My
wife developed a nasty bacterial infection while we were traveling
overseas last year. The proper antibiotics (which included Cipro),
administered by some very savvy doctors at a small Greek hospital,
saved her life. My biggest fear at the time was that she might have
contracted something which was so antibiotic-resistant that it would
be untreatable... in which case I would probably have ended up
bringing her ashes home in an urn Sad

Joerg
Guest

Tue Jan 10, 2017 5:20 am   



On 2017-01-09 08:42, Phil Hobbs wrote:
Quote:
On 01/09/2017 11:27 AM, George Herold wrote:
On Monday, January 9, 2017 at 10:35:31 AM UTC-5, Joerg wrote:
On 2017-01-08 16:46, pcdhobbs_at_gmail.com wrote:
Maybe I am understanding it wrong but if the current limiters are
directly in line with and physically at the Peltier it shouldn't
matter.

Right, except that they aren't. The current limiters are on the
board, and the laser/TEC is at the other end of a cable. Otherwise I
wouldn't be worried about shorts.


Ok, didn't know that, then you need four LM317.


You could have one current limit for cool and another for heat. Of

That's the point of the exercise, right.

course, if there is a chance that a wrench falls directly onto the
Peltier contacts that's bad.

If the laser assembly could be mounted on the board, I wouldn't be
worried, but it can't. The application is an industrial tester for
manufacturing other things, so reliability is key because down time
is expensive.

Not all of the users are in the first world, so "expensive" has to
take account of the BOM cost as well. If it were like Ford and GM,
I'd throw a couple of bucks' BOM cost at it and move on.


However, power consumption probably isn't much of a concern and even if
you'd need four LM317 they are around 50 cents. Depending on curent
they'll need heatsinking.

Probably the best is to revise the driver ciruitry so that it contains
intelligent current limiting. You might get away with just sensing and
shutdown (OR-ing the comparators) because if a short occurred it's a
service call anyhow where at least a factory technician has to come over.
Yeah I've been a bit confused by Phil's problem. If he runs the TEC feedback
loop by controlling/sensing the current, then a current limit seems easy.

It isn't difficult, but I was sick in bed and therefore bored stiff, so
I wanted to talk about electronics.


Now that you are well again don't stop the orange juice. My wife thought
she was over it and three days later ... bam ... it was back. Worse than
before.

In order to ward off any flu bug I just got a shipment of nine more
brewing ingredient kits, including another Belgian Tripel, a Superior
Strong Ale and a Sabotage Saison. Just for medicinal purposes, of course ...

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

John Larkin
Guest

Tue Jan 10, 2017 6:31 am   



On Mon, 9 Jan 2017 11:30:44 -0800, dplatt_at_coop.radagast.org (Dave
Platt) wrote:

Quote:
In article <kki57ch9es8tffjgiqn7okktrrite0gs3j_at_4ax.com>,
John Larkin <jjlarkin_at_highlandtechnology.com> wrote:
None here, the world is using too much antibiotics as it is.

Sometimes an antibiotic will save your life. Cipro has saved mine.
Lots of people used to die from initially minor scrapes or sore
throats that turned into deadly infections.

_Appropriate_ use is highly beneficial. _Inappropriate_ use is a huge
problem, as it tends to promote the development of antibiotic-
resistant strains and thus limits further appropriate use of those
same antibiotics. Using massive quantities of antibiotics as "growth
promoters" in animal feed is one of the greater insanities of the last
few decades.

I'm personally grateful for the availability of good antibiotics. My
wife developed a nasty bacterial infection while we were traveling
overseas last year. The proper antibiotics (which included Cipro),
administered by some very savvy doctors at a small Greek hospital,
saved her life. My biggest fear at the time was that she might have
contracted something which was so antibiotic-resistant that it would
be untreatable... in which case I would probably have ended up
bringing her ashes home in an urn :-(




My wife had a problem in a small town in Ireland so we walked into a
local clinic. The doc saw us right away, did his thing, and wrote a
prescription for antibiotics and said "oh, just give me ten pounds"
which I suspect was beer money. The drugs, at a pharmacy, were
expensive, $75 or so.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

Clifford Heath
Guest

Tue Jan 10, 2017 8:05 am   



On 09/01/17 07:51, Jim Thompson wrote:
Quote:
On Sun, 8 Jan 2017 15:31:58 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:
On 01/08/2017 03:02 PM, Jim Thompson wrote:
On Sun, 8 Jan 2017 13:39:00 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:
[snip]
so once I get back on my feet I'll do
some measurements and see if I can afford an extra volt-and-a-bit for
the TLV431/LM4041-ADJ version.
[snip]
Have you suffered an injury, or a surgery?

I'm considering having the joint in my right big toe replaced. I'm a
"walker" and the arthritis is impending my speed ;-)

Nah, nothing so dramatic--just a bad cold that turned into a nasty sinus
infection. I'll be back in the lab some time this week.
Cheers

Phil Hobbs

That's my usual Winter malady... sinus infection(s)... since it's so
dry here in Winter... but it's rained a lot this year (giving you East
coast types lots of snow Smile, so none so far, knock on wood.


Jim, you might get some relief using a saline nasal spray, like the one
which is called Fess over here. Many of this kind of infection
associated with hot dry conditions follow on inflammation (rather than
causing it). The saline increases the osmotic gradient, which keeps the
nasal trachea moister, thus avoiding the inflammatory trigger. If you
still get trouble originating in the upper sinuses (as opposed to
migrating there after you start sneezing) then you might consider a neti
pot (widely used in India for the same reasons) or some other more
thorough saline wash.

In any case, it can't hurt to try it for a while.

Clifford Heath

Jim Thompson
Guest

Tue Jan 10, 2017 8:30 am   



On Tue, 10 Jan 2017 12:05:28 +1100, Clifford Heath
<no.spam_at_please.net> wrote:

Quote:
On 09/01/17 07:51, Jim Thompson wrote:
On Sun, 8 Jan 2017 15:31:58 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:
On 01/08/2017 03:02 PM, Jim Thompson wrote:
On Sun, 8 Jan 2017 13:39:00 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:
[snip]
so once I get back on my feet I'll do
some measurements and see if I can afford an extra volt-and-a-bit for
the TLV431/LM4041-ADJ version.
[snip]
Have you suffered an injury, or a surgery?

I'm considering having the joint in my right big toe replaced. I'm a
"walker" and the arthritis is impending my speed ;-)

Nah, nothing so dramatic--just a bad cold that turned into a nasty sinus
infection. I'll be back in the lab some time this week.
Cheers

Phil Hobbs

That's my usual Winter malady... sinus infection(s)... since it's so
dry here in Winter... but it's rained a lot this year (giving you East
coast types lots of snow Smile, so none so far, knock on wood.

Jim, you might get some relief using a saline nasal spray, like the one
which is called Fess over here. Many of this kind of infection
associated with hot dry conditions follow on inflammation (rather than
causing it). The saline increases the osmotic gradient, which keeps the
nasal trachea moister, thus avoiding the inflammatory trigger. If you
still get trouble originating in the upper sinuses (as opposed to
migrating there after you start sneezing) then you might consider a neti
pot (widely used in India for the same reasons) or some other more
thorough saline wash.

In any case, it can't hurt to try it for a while.

Clifford Heath


I'm good, so far, this year. The mini-ice-age will be beneficial to
us "desert rats" Wink

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

M Philbrook
Guest

Wed Jan 11, 2017 5:39 am   



In article <edfshjFk40jU1_at_mid.individual.net>,
news_at_analogconsultants.com says...
Quote:
Have you suffered an injury, or a surgery?

I'm considering having the joint in my right big toe replaced. I'm a
"walker" and the arthritis is impending my speed ;-)

Nah, nothing so dramatic--just a bad cold that turned into a nasty sinus
infection. I'll be back in the lab some time this week.
Cheers

Phil Hobbs

I have about a hundred Cipros on hand, in case of emergency. You can
buy them from fish-supply sites.


None here, the world is using too much antibiotics as it is. On a long
flight to a client I must have contracted a bug and it hit me hard two
days later. Their VC of Quality Control recommended a "guaranteed fix":
A bottle of Southern Comfort. It worked. I didn't drink the whole bottle
though.




Not that you could remember.

Jamie

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