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Phil Hobbs
Guest

Mon Jan 09, 2017 3:30 am   



On 01/08/2017 02:59 PM, Jim Thompson wrote:
Quote:
On Sun, 8 Jan 2017 13:55:32 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:

On 01/08/2017 10:57 AM, Jim Thompson wrote:
On Fri, 6 Jan 2017 16:23:04 -0800 (PST), pcdhobbs_at_gmail.com wrote:

I'm not totally following your scheme, but wouldn't you want to
_replace_Q2_ with the TLV431 (using drawing _above_)? Then your
current limit is 1.2V/R2 with a _very_low_ TC. A TLV431 is
transistor-sized... TO-92 pack, unless you're in love with SOT's.

Yup. The LM385-ADJ is the same sort of thing except that it holds
the 1.2V between ADJ and K, so it works with PNPs. (To make a 1.2V
reference with a TLV431 you short ADJ to K, whereas with an LM385 it's
ADJ to A.)

Still costs an extra volt-and-a-bit of headroom, and another buck or
so on the BOM. Might be worth it.

My previous followup seems to have gone off into the Howling Ether.

I didn't have your @gmail address white-listed Sad It is now.

(I have various @gmail/@google posters whitelisted followed by a
blanket kill of all the rest :-)


I didn't have in mind tying ADJ to K, etc, I had in mind some
variation of this...

http://www.analog-innovations.com/SED/PCDH_CL_2017-01-08.png

Yes, exactly--it's an IC-ified version of the normal 2-terminal limiter.
The 431-style refs only work with NPNs and NFETs, though, because they
hold Vref between ADJ and A. For PNPs you need something upside-down
such as the LM385 or LM4041-ADJ, which hold Vref between K and ADJ.

I can envision various switching schemes where this structure becomes
part of the H-bridge.

Yup, that's the idea, except that mine is linear. The maximum current
is +-250 mA, so the dissipation is modest, and this avoids problems
with switching crap getting into the laser.

Cheers

Phil Hobbs

If it's linear, wouldn't it be easier to merge limits into the
"conveyor"?


There are 4 current limiters, because I need it to have asymmetric
limits and also survive having one side shorted to ground. Because the
laser is on a cable, the short would have a 50-50 chance of being on the
wrong side of the current sense resistor. I could put a bipolar current
limiter in series with each lead, something like this:


Q1
0-*--------- -----*---->|---R2R2---*------0
| \ A | |
| ------ ------- |
| | / V Q2 |
*--R1R1-------*---- -------------*
| |
| Q3 |
*--------- -----*----|<---R2R2---*
| \ V | |
| ------ ------- |
| | / A Q4 |
*--R1R1-------*---- -------------*

but that's no simpler and runs the risk of avalanching the emitters of
Q2 and Q4.

Another approach would be to put a low-sat PNP in series with the whole
shebang and diode-OR the outputs of a quad op amp to throttle it if any
of the currents go out of spec. That's probably the leading candidate
if I can't stand the extra volt-and-a-bit for the references.

I sort of like the diode/transistor version because it's super fast by
comparison, but realistically a fault current of an amp for a few
microseconds won't blow up any of these TECs, and, on reflection,
relying on the matching of a transistor V_BE and a diode in production
is just _asking_ for midnight phone calls.

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 3:31 am   



On 01/08/2017 03:02 PM, Jim Thompson wrote:
Quote:
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 Wink


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

--
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

John Larkin
Guest

Mon Jan 09, 2017 3:50 am   



On Sun, 8 Jan 2017 15:31:58 -0500, Phil Hobbs
<pcdhSpamMeSenseless_at_electrooptical.net> wrote:

Quote:
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.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Jim Thompson
Guest

Mon Jan 09, 2017 3:51 am   



On Sun, 8 Jan 2017 15:31:58 -0500, Phil Hobbs
<pcdhSpamMeSenseless_at_electrooptical.net> wrote:

Quote:
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 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 |

Joerg
Guest

Mon Jan 09, 2017 5:19 am   



On 2017-01-08 10:39, Phil Hobbs wrote:
Quote:
On 01/08/2017 01:11 PM, Joerg wrote:
On 2017-01-06 00:42, Phil Hobbs wrote:
Hi, all,

I'm designing a diode laser controller board for a customer in
Scandinavia. It has a sub-Poissonian adjustable current supply, a
resistor-linearized thermistor temperature sensor, and of course a
thermoelectric cooler driver.

The TEC requires different current limits in different quadrants.
(A TEC is actually a four-quadrant device since it generates
electrical power from the temperature difference as well as the
other way round.)

With a bridged current driver, that can run into quite a few
parts--you need one current limiter per polarity, or if you want
any short circuit protection, one per leg (4 in all). So
simplicity is at a bit of a premium.

The usual two-terminal, two-BJT current limiter suffers from a
fairly gross temperature coefficient, like 3000 ppm/K. Protecting
a TEC isn't a super high precision application, but something a bit
better than that would be good.

I've sometimes got round that by putting a Schottky diode in series
with the sense resistor, like this. (The base current for Q1
actually comes from a RRO op amp via R1--it's a class B
complementary bridge.)

Q1 0-*--------- -----*---->|---R2R2---*------0 | \
A | | | ------ ------- | |
| / V Q2 | *--R1R1-------*----
-------------*

Trouble is, Schottkies don't have the same dV/dT as BJTs--it's more
like 1 mV/K at high current, vs. 2 mV/K at low current, so you
don't gain that much--about 1500 ppm/K.

A PN diode connected as above plus something like a TLV431 in
series with Q2's emitter will do a good job, probably 300-500
ppm/V, which would be fine. However, that costs four more ICs and
another 2.4V of headroom (1.2V per side in each polarity).

Seems like an arbitrage opportunity. ;)

My current thinking is to put the diode in series with the base of
Q2 and use Q1's V_BE to provide a reasonably stable bias current,
like this:

Q1 1ohm 0-*---------
--------*-------R2R2-----*------0 | \ A |
| | ------ A Schottky | | |
| | *---R1R1------*--R3R3----* | |
| | | ------ | | / V Q2
| *------- --------------*

The diode runs at much lower current, and so has a higher dV/dT,
and by choosing R2 correctly, I can adjust it to match Q2's a bit
better.

One wouldn't want to bet one's firstborn child on the unit-to-unit
consistency being too wonderful, but ISTM that I ought to be able
to get a factor of maybe 6 this way.

Anybody else done this sort of thing? Better suggestions welcome!


Why not use linear regulators as current sources? If the total drop
is too high you could look for an LDO that can be pressed into such
service. This can reduce the BOM to two parts per leg.

That runs into money, though. Negative LDOs especially.


Why negative LDOs? You'll have to look for the LM317-kind of
three-legged regulators. Resistor in series, ADJ terminal to other side,
done. Since you need it to work in both directions you'll have to hang a
Schottky across and then another such (positive) regulator in series,
also with a Schottky. Except that one is reversed. Not much money.
Sometimes diodes are already included, to prevent regulator damage if a
large electrolytic wants to dump its charge back after turn-off.


Quote:
... I have samples
of the laser/TEC combinations, 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.


Alternatively build the limiter into your driver and use a
comparators as quadrant detectors to switch gears on the limiter.

That might be interesting. The issue is that neither side of the TEC is
grounded, and it's on the other end of a cable, which makes it somewhat
vulnerable to having one side shorted to ground. That makes any
asymmetrical on-board solution a bit problematic--the TEC can melt
before the thermistor notices anything wrong.


TECs are fickle, they can die fast. Non-grounded is fine as long as you
can guarantee that things remain within the common mode range of the
comparators.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg
Guest

Mon Jan 09, 2017 5:24 am   



On 2017-01-08 12:50, John Larkin 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

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.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg
Guest

Mon Jan 09, 2017 6:17 am   



On 2017-01-08 14:34, pcdhobbs_at_gmail.com wrote:
Quote:
That runs into money, though. Negative LDOs especially.


Why negative LDOs? You'll have to look for the LM317-kind of
three-legged regulators. Resistor in series, ADJ terminal to other
side, done. Since you need it to work in both directions you'll
have to hang a Schottky across and then another such (positive)
regulator in series, also with a Schottky. Except that one is
reversed. Not much money.

Thanks.

I misunderstood--you're talking about putting them in series with the
TEC rather than using them directly as the pass elements in the
bridge.

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.


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?

--
Regards, Joerg

http://www.analogconsultants.com/

Jim Thompson
Guest

Mon Jan 09, 2017 6:20 am   



On Sun, 08 Jan 2017 15:17:45 -0800, Joerg <news_at_analogconsultants.com>
wrote:

Quote:
On 2017-01-08 14:34, pcdhobbs_at_gmail.com wrote:
That runs into money, though. Negative LDOs especially.


Why negative LDOs? You'll have to look for the LM317-kind of
three-legged regulators. Resistor in series, ADJ terminal to other
side, done. Since you need it to work in both directions you'll
have to hang a Schottky across and then another such (positive)
regulator in series, also with a Schottky. Except that one is
reversed. Not much money.

Thanks.

I misunderstood--you're talking about putting them in series with the
TEC rather than using them directly as the pass elements in the
bridge.

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.


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?


Apply the Mad Man Muntz rule... does it have too many parts? Seems
the whole deal should be safe if the drive is truly a "current
conveyor" (I hate buzz-word-named circuits... just say what function
it performs, properly 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 |

John Larkin
Guest

Mon Jan 09, 2017 6:28 am   



On Sun, 08 Jan 2017 14:24:50 -0800, Joerg <news_at_analogconsultants.com>
wrote:

Quote:
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.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Joerg
Guest

Mon Jan 09, 2017 6:47 am   



On 2017-01-08 15:20, Jim Thompson wrote:
Quote:
On Sun, 08 Jan 2017 15:17:45 -0800, Joerg <news_at_analogconsultants.com
wrote:

On 2017-01-08 14:34, pcdhobbs_at_gmail.com wrote:
That runs into money, though. Negative LDOs especially.


Why negative LDOs? You'll have to look for the LM317-kind of
three-legged regulators. Resistor in series, ADJ terminal to other
side, done. Since you need it to work in both directions you'll
have to hang a Schottky across and then another such (positive)
regulator in series, also with a Schottky. Except that one is
reversed. Not much money.

Thanks.

I misunderstood--you're talking about putting them in series with the
TEC rather than using them directly as the pass elements in the
bridge.

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.


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?

Apply the Mad Man Muntz rule... does it have too many parts?


Snip .. snip .... snip .. *POOF* ... "Oh, better put that last one back in".


Quote:
... Seems
the whole deal should be safe if the drive is truly a "current
conveyor" (I hate buzz-word-named circuits... just say what function
it performs, properly Wink


AFAIU Phil needs different current limits for each quadrant. I think it
could be done either in the driver or via external limiters.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg
Guest

Mon Jan 09, 2017 6:50 am   



On 2017-01-08 15:28, John Larkin wrote:
Quote:
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.

--
Regards, Joerg

http://www.analogconsultants.com/

Jim Thompson
Guest

Mon Jan 09, 2017 6:56 am   



On Sun, 08 Jan 2017 15:47:38 -0800, Joerg <news_at_analogconsultants.com>
wrote:

Quote:
On 2017-01-08 15:20, Jim Thompson wrote:
On Sun, 08 Jan 2017 15:17:45 -0800, Joerg <news_at_analogconsultants.com
wrote:

On 2017-01-08 14:34, pcdhobbs_at_gmail.com wrote:
That runs into money, though. Negative LDOs especially.


Why negative LDOs? You'll have to look for the LM317-kind of
three-legged regulators. Resistor in series, ADJ terminal to other
side, done. Since you need it to work in both directions you'll
have to hang a Schottky across and then another such (positive)
regulator in series, also with a Schottky. Except that one is
reversed. Not much money.

Thanks.

I misunderstood--you're talking about putting them in series with the
TEC rather than using them directly as the pass elements in the
bridge.

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.


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?

Apply the Mad Man Muntz rule... does it have too many parts?


Snip .. snip .... snip .. *POOF* ... "Oh, better put that last one back in".


... Seems
the whole deal should be safe if the drive is truly a "current
conveyor" (I hate buzz-word-named circuits... just say what function
it performs, properly Wink


AFAIU Phil needs different current limits for each quadrant. I think it
could be done either in the driver or via external limiters.


Should be easy enough to convey to the "conveyor" what quadrant it's
in... n'est-ce pas ?Smile

...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 |

John Larkin
Guest

Mon Jan 09, 2017 6:59 am   



On Sun, 08 Jan 2017 15:50:08 -0800, Joerg <news_at_analogconsultants.com>
wrote:

Quote:
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.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Joerg
Guest

Mon Jan 09, 2017 7:25 am   



On 2017-01-08 15:59, John Larkin wrote:
Quote:
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.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg
Guest

Mon Jan 09, 2017 7:27 am   



On 2017-01-08 15:56, Jim Thompson wrote:
Quote:
On Sun, 08 Jan 2017 15:47:38 -0800, Joerg <news_at_analogconsultants.com
wrote:

On 2017-01-08 15:20, Jim Thompson wrote:
On Sun, 08 Jan 2017 15:17:45 -0800, Joerg <news_at_analogconsultants.com
wrote:

On 2017-01-08 14:34, pcdhobbs_at_gmail.com wrote:
That runs into money, though. Negative LDOs especially.


Why negative LDOs? You'll have to look for the LM317-kind of
three-legged regulators. Resistor in series, ADJ terminal to other
side, done. Since you need it to work in both directions you'll
have to hang a Schottky across and then another such (positive)
regulator in series, also with a Schottky. Except that one is
reversed. Not much money.

Thanks.

I misunderstood--you're talking about putting them in series with the
TEC rather than using them directly as the pass elements in the
bridge.

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.


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?

Apply the Mad Man Muntz rule... does it have too many parts?


Snip .. snip .... snip .. *POOF* ... "Oh, better put that last one back in".


... Seems
the whole deal should be safe if the drive is truly a "current
conveyor" (I hate buzz-word-named circuits... just say what function
it performs, properly Wink


AFAIU Phil needs different current limits for each quadrant. I think it
could be done either in the driver or via external limiters.

Should be easy enough to convey to the "conveyor" what quadrant it's
in... n'est-ce pas ?Smile


That is what I meant with the comparators. Commutate them so the current
limit shifts gears with each quadrant change. Costwise it's all probably
a wash and not expensive but doing it at the driver saves energy.

--
Regards, Joerg

http://www.analogconsultants.com/

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