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'[EE] Datasheet question for LM317'
2007\12\21@083302 by Rikard Bosnjakovic

picon face
I'm having a couple of LM317:s which I'm about to use in a hockey
arena (with ambient temperature around -10 degrees Celcius). In the
datasheet - maximum ratings section - for the 317, I find "T_op
Operating junction temperature: 0-125".

I'm a bit confused by "junction" in this statement. Does this mean
that an ambient temperature of -10 will make the LM317 unable to work,
or does it mean that it will be fine as long as the junction is no
colder than 0 degrees?


--
- Rikard - http://bos.hack.org/cv/

2007\12\21@090700 by M. Adam Davis

face picon face
Yes, that's the temperature of the silicon itself, and unless you're
really pushing the chip hard you can pretend that the case temperature
and Tj are the same.

For simple applications you can run it slightly out of range, but if
you're really interested in making certain it is within its operating
range, put a 2W resistor nearby and insulate the resistor and
regulator.  Calculate the resistor to run of the unregulated voltage
with 1/4W heat output and you should be fine.

Also kee in mind that while the ice is at a nice cool -10C, it is very
unlikely that the air high off the ice is at that same temperature -
though it can get down there - especially when the rink (and therefore
your device) is in use.  Consider mounting the power supply outside
the rink.

Alternately, get the LM317A which has a much larger temperature range
and then don't worry about it.

-Adam

On 12/21/07, Rikard Bosnjakovic <spam_OUTrikard.bosnjakovicTakeThisOuTspamgmail.com> wrote:
{Quote hidden}

> -

2007\12\21@092909 by Alan B. Pearce

face picon face
> I'm a bit confused by "junction" in this statement. Does this mean
> that an ambient temperature of -10 will make the LM317 unable to work,
> or does it mean that it will be fine as long as the junction is no
> colder than 0 degrees?

The way these devices are specified that is the temperature of the chip
inside the package at which the specifications are guaranteed. In practice
even with a -10C rink temperature the temperature of the chi will most
likely be within its quoted operating range, because of temperature
dissipation in the chip.

2007\12\21@100755 by David VanHorn

picon face
On Dec 21, 2007 8:32 AM, Rikard Bosnjakovic
<.....rikard.bosnjakovicKILLspamspam@spam@gmail.com> wrote:
> I'm having a couple of LM317:s which I'm about to use in a hockey
> arena (with ambient temperature around -10 degrees Celcius). In the
> datasheet - maximum ratings section - for the 317, I find "T_op
> Operating junction temperature: 0-125".

In this case, they are meaning that the device is guaranteed to meet
the data sheet specs over that temperature range.  On the high end,
the chip will shut down, but on the low end, you're sort of "on your
own"   It may work ok, it may get itself into an odd state that it
can't recover from, who knows.

What I'd do, is test it.  Set up the circuit, put it in the coldest
environment that it could reasonably be asked to work in, let it sit
for hours, so that it's all "cold soaked", the apply power and see
what happens.

Normally, we try to use devices within the data sheet parameters, but
sometimes, we have to color outside the lines a bit.  :)  At the
moment, I'm trying to find a device to replace a microprocessor's
crystal, that won't be too much bothered by millisecond impacts of
2000Gs.  So far, i'm having no luck finding anything that specs that
high, and we may end up getting some pretty rugged devices, and
testing them ourselves.

Someone else suggested pre-heating the device, and that's not a bad
option. Once it's operating and within the 0-125C range, it should be
fine.

> I'm a bit confused by "junction" in this statement. Does this mean
> that an ambient temperature of -10 will make the LM317 unable to work,
> or does it mean that it will be fine as long as the junction is no
> colder than 0 degrees?

When they say "junction", they mean that the actual physical chip,
inside the plastic, is where the temperature matters, as opposed to
outside on the plastic or on the heatsink.

2007\12\21@111120 by Spehro Pefhany

picon face
Quoting Rikard Bosnjakovic <rikard.bosnjakovicspamKILLspamgmail.com>:

> I'm having a couple of LM317:s which I'm about to use in a hockey
> arena (with ambient temperature around -10 degrees Celcius). In the
> datasheet - maximum ratings section - for the 317, I find "T_op
> Operating junction temperature: 0-125".
>
> I'm a bit confused by "junction" in this statement. Does this mean
> that an ambient temperature of -10 will make the LM317 unable to work,
> or does it mean that it will be fine as long as the junction is no
> colder than 0 degrees?

It means they don't guarantee it to work (for example, it might not
start), and if it does work, it may not be within specifications (for
example, the output voltage might be high or low or it could conceivably
oscillate or do other bad things). As others have said, Tj will be
pretty close to Tc, and especially initially after an overnight cold soak
with power off, that will likely be just about the same as Ta.

In this case, it's dead easy to buy automotive rated parts such as the
LM317BT which is guaranteed to work from -40°C to +125°C, or even
military rated parts (-55°C to +150°C).

I would buy parts rated for the actual temperature range, but more importantly
perhaps make sure that your capacitors have acceptable values at those
temperatures (esp. electrolytics), and generally be careful of anything
analog-ish such as clock oscillators and so on. Given typical hockey arena
environments and times when they are used (eg. 5:30am on a snowy winter
weekend), I'm sure you'd like it to be robust and not require fixing. That
said,  I'd lay odds that the stock 'commercial' temperature range  
LM317 will work just fine-- you're not close to the lower limit for  
the automotive/mil parts, and it's really just the same chip inside  
for all the types with different test parameters.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
.....s...KILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2007\12\21@111713 by Rikard Bosnjakovic

picon face
On 21/12/2007, M. Adam Davis <EraseMEstienmanspam_OUTspamTakeThisOuTgmail.com> wrote:

> Also kee in mind that while the ice is at a nice cool -10C, it is very
> unlikely that the air high off the ice is at that same temperature -
> though it can get down there - especially when the rink (and therefore
> your device) is in use.  Consider mounting the power supply outside
> the rink.

This device is going to reside within a box outside the rink, in the
"speaker's corner". It's a control device for a beacon project I'm
working on.

While it's not in direct contact (or near) the ice, the air
temperature is pretty cold in the arena. Atleast in the place where
the spectators are, but I'm not yet sure about the "speaker's corner".
I have sent an inquiry to the club to measure it for me, but I find it
difficult to believe it is above 0 degrees.

The higher the input voltage the quicker the LM317 will dissipate
heat, kind of heating itself up. But what David VanHorn suggested,
building the circuit and put it in the freezer (or something) and then
powering it up to see what happens, is not a bad idea at all.


--
- Rikard - http://bos.hack.org/cv/

2007\12\21@114222 by John Coppens

flavicon
face
On Fri, 21 Dec 2007 14:32:36 +0100
"Rikard Bosnjakovic" <rikard.bosnjakovicspamspam_OUTgmail.com> wrote:

> I'm having a couple of LM317:s which I'm about to use in a hockey
> arena (with ambient temperature around -10 degrees Celcius). In the
> datasheet - maximum ratings section - for the 317, I find "T_op
> Operating junction temperature: 0-125".

It'll most probably work well. Manufacturers test their products and if
they are within specs -55 - 125, or so they're put in the mil-spec box,
etc. What's left, if they still work, is sold as commercial range. So,
taking into account probability, your ICs are likely to work till -20C,
could work till -40, but unlikely below that, 'cause they be sold as
automotive (more expensive) parts. Even then, it's highly unlikely they'd
present some irreversible damage - they'd probably just be outside the
specs.

Of course probability is just that.

John

2007\12\21@115839 by Enki

picon face
On 21 Dec 2007 at 17:16, Rikard Bosnjakovic wrote:

> The higher the input voltage the quicker the LM317 will dissipate
> heat, kind of heating itself up. But what David VanHorn suggested,
> building the circuit and put it in the freezer (or something) and then
> powering it up to see what happens, is not a bad idea at all.
> --
> - Rikard - http://bos.hack.org/cv/
> --


       Just put a fixed load (resistor) at the LM317 output and it will
heat enough. Couple the resistor to the LM317 body for more heat.

       Mark Jordan

2007\12\21@120312 by David VanHorn

picon face
>
> Of course probability is just that.


In theory, there is no difference between theory and practice.

2007\12\21@143455 by David VanHorn

picon face
>        Just put a fixed load (resistor) at the LM317 output and it will
> heat enough. Couple the resistor to the LM317 body for more heat.

That brings it's own problems of additional heat and power, and
dosen't address starting the thing up when it's already cold.

Note that these motor-driven revolving lights do not require regulated voltage.
That's why I suggested batteries to drive them. They aren't on all
that long when in use anyway.

2007\12\21@155206 by Jinx

face picon face
> In theory, there is no difference between theory and practice.

Isn't there a Line2 to that ?

"In practice, there is"

In theory that is, practically speaking

As for the LM317, I'd agree with John Coppens. Yours will fall
outside of Milspec, but could possibly be close to it. The same
way that PICs are sorted. You might find a -04 that works up to
almost, or even at, 20MHz - although "works" is a word to be
careful with

Regardless, easy enough to heat the 317. As in other threads
about low-temperature circuits or those prone to condensation,
a warming resistor would do it

2007\12\21@160531 by Jinx

face picon face
> it's highly unlikely they'd present some irreversible damage....they'd
> probably just be outside the specs

I've done that with commercial-grade PICs. Frozen them to -20C and
dunked them in boiling water. Meh, it's a hobby. They stop working
but come back to life within the graded temperature range. That's with
simple timing test s/w running. You'd want to be careful with current
ratings and capabilities at the extremes and not have something super-
critical relying on the PIC or, in Rikard's case, the LM317

2007\12\21@200146 by Steven Howes

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face
> I've done that with commercial-grade PICs. Frozen them to -20C and
> dunked them in boiling water. Meh, it's a hobby.

Cooled a device using one to -40 and up to +85, they are resilient  
little bastards aren't they!

2007\12\21@214609 by Herbert Graf

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face

On Sat, 2007-12-22 at 01:01 +0000, Steven Howes wrote:
> > I've done that with commercial-grade PICs. Frozen them to -20C and
> > dunked them in boiling water. Meh, it's a hobby.
>
> Cooled a device using one to -40 and up to +85, they are resilient  
> little bastards aren't they!

Agreed. I've got about 14 12F675s running some LEDs outside, I've never
seen any of them go down, no matter how cold it's gotten, it went to
around -30C last year and all of them kept running.

TTYL

2007\12\23@092506 by Vasile Surducan

face picon face
On 12/21/07, Herbert Graf <@spam@mailinglist3KILLspamspamfarcite.net> wrote:
>
> On Sat, 2007-12-22 at 01:01 +0000, Steven Howes wrote:
> > > I've done that with commercial-grade PICs. Frozen them to -20C and
> > > dunked them in boiling water. Meh, it's a hobby.
> >
> > Cooled a device using one to -40 and up to +85, they are resilient
> > little bastards aren't they!
>
> Agreed. I've got about 14 12F675s running some LEDs outside, I've never
> seen any of them go down, no matter how cold it's gotten, it went to
> around -30C last year and all of them kept running.

Try an experiment variation:
- warm at +85
- cool slowly only to +5...+8C and stay there half hour

It still works ?

"In theory, there is no difference between theory and practice."
In practice there is.

2007\12\23@105809 by hgraf

picon face

On Sun, 2007-12-23 at 06:24 -0800, Vasile Surducan wrote:
> > Agreed. I've got about 14 12F675s running some LEDs outside, I've never
> > seen any of them go down, no matter how cold it's gotten, it went to
> > around -30C last year and all of them kept running.
>
> Try an experiment variation:
> - warm at +85
> - cool slowly only to +5...+8C and stay there half hour
>
> It still works ?

FWIW they are all permanently mounted outdoors, I don't think I've see a
day hit 85C here, yet... :)

My point was PICs seem to be pretty robust, I wouldn't trust a
commercial design to these results, but for hobby stuff I've never seen
a problem.

TTYL

2007\12\23@114435 by Vasile Surducan

face picon face
On 12/23/07, hgraf <KILLspamhgrafKILLspamspamemail.com> wrote:
>
> On Sun, 2007-12-23 at 06:24 -0800, Vasile Surducan wrote:
> > > Agreed. I've got about 14 12F675s running some LEDs outside, I've never
> > > seen any of them go down, no matter how cold it's gotten, it went to
> > > around -30C last year and all of them kept running.
> >
> > Try an experiment variation:
> > - warm at +85
> > - cool slowly only to +5...+8C and stay there half hour
> >
> > It still works ?
>
> FWIW they are all permanently mounted outdoors, I don't think I've see a
> day hit 85C here, yet... :)
>
> My point was PICs seem to be pretty robust, I wouldn't trust a
> commercial design to these results, but for hobby stuff I've never seen
> a problem.

The ideea was not the temperature but the moisture. If you keep it at
say -10C for one hour an then increase the temperature fast to +8C the
water could make it inoperable.
The same can be seen if warm at 85C and 90% humidity followed by a
fast decreasing temperature down to 8C.


best,
Vasile

2007\12\23@115151 by Carl Denk

flavicon
face
As long as the moisture is isolated hermetically  (I think thats the
correct term - impervious) so that the water cannot condense or freeze
on the electrical conducting (pins and traces, etc.), I don't think
moisture is an issue. This could be done with a conformal coating. It is
not unusual to see in equipment instructions - must be in a
non-condensing atmosphere.

Vasile Surducan wrote:
{Quote hidden}

2007\12\23@133228 by Steven Howes

flavicon
face
>>
> The ideea was not the temperature but the moisture. If you keep it at
> say -10C for one hour an then increase the temperature fast to +8C the
> water could make it inoperable.
> The same can be seen if warm at 85C and 90% humidity followed by a
> fast decreasing temperature down to 8C.

Epoxy.

2007\12\23@224036 by Apptech

face
flavicon
face
>> The ideea was not the temperature but the moisture. If
>> you keep it at
>> say -10C for one hour an then increase the temperature
>> fast to +8C the
>> water could make it inoperable.
>> The same can be seen if warm at 85C and 90% humidity
>> followed by a
>> fast decreasing temperature down to 8C.

> Epoxy.

Silicone :-)

       http://www.robertmckeown.com/Doc_Folder/10899A01ConformalFamilyds.pdf

       http://www.syscoindia.com/pdf/1-2577.pdf


I'm looking at using 1-2577 for an application at present.
Horrendous price, but applies very thinly if desired.

Transparent (which is a necessity for my task).
Silicones have a significantly higher bond energy than
epoxies (or other organics) so are much more UV resistant.
(This is the reason that silicone window sealers can have
lifetimes of around 20 years) whereas epoxies degrade far
sooner under UV. Whether that matters depends on your
application.



       Russell


1-2577

" ... One-part, transparent, medium viscosity; ozone-safe
(VOC exempt)
solvent-borne, elastoplastic silicone resin; excellent
abrasion resistance; RTV or heat-accelerable cure."

2007\12\23@224133 by Herbert Graf

flavicon
face

On Sun, 2007-12-23 at 08:44 -0800, Vasile Surducan wrote:
> > FWIW they are all permanently mounted outdoors, I don't think I've see a
> > day hit 85C here, yet... :)
> >
> > My point was PICs seem to be pretty robust, I wouldn't trust a
> > commercial design to these results, but for hobby stuff I've never seen
> > a problem.
>
> The ideea was not the temperature but the moisture. If you keep it at
> say -10C for one hour an then increase the temperature fast to +8C the
> water could make it inoperable.
> The same can be seen if warm at 85C and 90% humidity followed by a
> fast decreasing temperature down to 8C.

Perhaps, that said, due to some damage from a tree limb, one of the
circuits has been fully exposed to the elements for a few weeks. It's
been rained on, snowed on, frozen, thawed, a bunch of times, and at this
very moment is still going! (just went from 7C today with rain to -5C at
the moment, supposed to go down to -7C tonight).

TTYL

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