schottky tempco

[kell]

Do schottkys have the same temperature coefficient as other silicon
diodes? Many thanks.

 

[Tim Williams]

Not really. In fact I seem to remember discussion about the tempco
reversing at certain (usefully low) current levels. This would happen by an
effective positive tempco in series with a negative semiconductor tempco,
combined with the nonlinear behavior of that semiconductor.

Lemme see here...
Popular, relatively small schottky 1N5817L
http://boss.iele.polsl.gliwice.pl/pdf/Vishay/1n5817.pdf
(Middle left page 2.) The graph shows two curves, the hotter curve
consistently less than the cooler curve. Nope, that's no good... how about
something with a little more juice?
http://boss.iele.polsl.gliwice.pl/pdf/Vishay/sbl3030p.pdf
(Same place.) Hmm nope, still negative tempco...

Might Google for the discussion. It was last yearish...

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"kell" <kellrobinson@billburg.com> wrote in message
news:1148908508.542829.155820@g10g2000cwb.googlegroups.com...

Do schottkys have the same temperature coefficient as other silicon
diodes? Many thanks.

 

[kell]

Tim Williams wrote:

Not really. In fact I seem to remember discussion about the tempco
reversing at certain (usefully low) current levels. This would happen by an
effective positive tempco in series with a negative semiconductor tempco,
combined with the nonlinear behavior of that semiconductor.

Lemme see here...
Popular, relatively small schottky 1N5817L
http://boss.iele.polsl.gliwice.pl/pdf/Vishay/1n5817.pdf
(Middle left page 2.) The graph shows two curves, the hotter curve
consistently less than the cooler curve. Nope, that's no good... how about
something with a little more juice?
http://boss.iele.polsl.gliwice.pl/pdf/Vishay/sbl3030p.pdf
(Same place.) Hmm nope, still negative tempco...

Looking at the second of the datasheets you linked to, it looks like
the schottky tempco starts around -1.6mV/C and gets to around -1mV/C at
higher currents.

Here's a datasheet I pulled up more or less at random that shows a
rectifier with a tempco that eventually goes positive as the forward
current increases past a certain point
http://www.irf.com/product-info/datasheets/data/10ets.pdf
(see diagram 8), but it's not a schottky. Maybe the discussion you
remembered wasn't about schottkys... I did a desultory search but
didn't come up with anything.

 

[Phil Allison]

"kell"

Here's a datasheet I pulled up more or less at random that shows a
rectifier with a tempco that eventually goes positive as the forward
current increases past a certain point
http://www.irf.com/product-info/datasheets/data/10ets.pdf
(see diagram 8), but it's not a schottky.

** You should not use the term " tempco " loosely and wrongly like this.

Diode "tempco" of a diode is simply the incremental change in conduction
voltage per degree C of ambient temp change.

What YOU are looking for is called the "Forward Voltage Drop
Characteristic" as seen on the data sheet YOU quoted.





....... Phil

 

[kell]

** You should not use the term " tempco " loosely and wrongly like this.

Diode "tempco" of a diode is simply the incremental change in conduction
voltage per degree C of ambient temp change.
Well yes, if you want to be exceedingly stringent about it.

For example, in citing Vf at 3 amps in Figure 3 of
http://boss.iele.polsl.gliwice.pl/pdf/Vishay/sbl3030p.pdf
I use deltaVf/deltaT over an interval of 100 degrees C as a stand-in
for dVf/dT. And even according to elementary calculus, there has to
exist some temperature between 25 degrees and 100 degrees where dVf/dT
equals deltaV/deltaT over the interval of 25 to 100 degrees, assuming
Vf as a function of C (and the first derivative) exhibit(s) no
discontinuity, you know the drill.

 

[Phil Allison]

"kell"

** You should not use the term " tempco " loosely and wrongly like this.

Diode "tempco" is simply the incremental change in conduction voltage
per degree C of ambient temp change.

What YOU are looking for is called the "Forward Voltage Drop
Characteristic" as seen on the data sheet YOU quoted.

Well yes, if you want to be exceedingly stringent about it.

** No, my smartarse over snipping, context shifting friend, YOU are plain
wrong.

You simply asked: " Do schottkys have the same temperature coefficient as
other silicon
diodes? "

It was the wrong question.




......... Phil

 

[John Larkin]

On Mon, 29 May 2006 10:34:23 -0500, "Tim Williams"
<tmoranwms@charter.net> wrote:

Not really. In fact I seem to remember discussion about the tempco
reversing at certain (usefully low) current levels. This would happen by an
effective positive tempco in series with a negative semiconductor tempco,
combined with the nonlinear behavior of that semiconductor.

Schottkies tend to have somewhat lower junction tc's than pn diodes.
There are a lot of schottky chemistries around, so they vary.

Any semiconductor diode acts like an ideal semiconductor in series
with some bulk resistance, and that bulk r tends to have a positive
tempco. So most real diodes have negative tc's at low currents and
positive tc's at very high currents, with a zero tc point somewhere
between, sometimes but not always at sane currents. I posted a graph
of a small-signal schottky to a.b.s.e., and it has a zero tc point
around 15 mA.

John

 

[John Larkin]

On 29 May 2006 12:57:37 -0700, "kell" <kellrobinson@billburg.com>
wrote:

Here's a datasheet I pulled up more or less at random that shows a
rectifier with a tempco that eventually goes positive as the forward
current increases past a certain point
http://www.irf.com/product-info/datasheets/data/10ets.pdf

Yup, zero tempco at about 15 amps. Nice.

Ignore Phil; he has a disorder.

John

 

[Phil Allison]

"Don Klipstein"

I am rather sensitive

** ROTFL !!!!

Klipstein is a completely pompous ass !

And I note in addition a bit of characteristic
spelling issues that appear to me more specific to a somewhat famous
sub-troll than to a nationality.

** Take that up with Microsoft.

I use the MS Word "spellchecker" like most OE users.





........ Phil

 

[Don Klipstein]

In article <4e1lncF1chkm7U1@individual.net>, Phil Allison wrote:

"kell"

** You should not use the term " tempco " loosely and wrongly like this.

Diode "tempco" is simply the incremental change in conduction voltage
per degree C of ambient temp change.

What YOU are looking for is called the "Forward Voltage Drop
Characteristic" as seen on the data sheet YOU quoted.

Well yes, if you want to be exceedingly stringent about it.

** No, my smartarse over snipping, context shifting friend, YOU are plain
wrong.

You simply asked: " Do schottkys have the same temperature coefficient as
other silicon diodes? "

It was the wrong question.

I am rather sensitive and on the lookout for anyone with any headers
from Australia claiming so severely that someone is "plain wrong" by
arguing on finer points. And I note in addition a bit of characteristic
spelling issues that appear to me more specific to a somewhat famous
sub-troll than to a nationality.
This makes me wonder if you are the major Australian sub-troll that got
his own FAQ!

- Don Klipstein (don@misty.com)

 

[Don Klipstein]

In art. <4e23viF1c5l2lU1@individual.net>, supposedly Phil Allison wrote:

"Don Klipstein"

I am rather sensitive

** ROTFL !!!!

Klipstein is a completely pompous ass !

And I note in addition a bit of characteristic spelling issues that
appear to me more specific to a somewhat famous sub-troll than to a
nationality.

** Take that up with Microsoft.

I use the MS Word "spellchecker" like most OE users.

And I know how spellcheckers allow misspellings and less-common
spellings that are outside their dictionaries and/or are deliberate.

I hope you can quickly better distinguish yourself from the bigtime
famous/infamous Australian sub-troll better than implementing a few words
with low usage count in the megareams of garbage already spewed by that
sub-troll but sounding slightly more-often-used by oldtimers and Britons
in the sci.electronics newsgroups!

Are you currently capable of denying that you are the famous/infamous
sub-troll widely mentioned to be from Australia and so bad a sub-troll as
to get his own FAQ?
If you can, can you also deny being among the probably
part-per-billion-range fraction of this planet's population that is insane
enough to be in any way a fan of that major offender?

- Don Klipstein (don@misty.com)

 

[Phil Allison]

"Don Klipstein" <

( snip reams of TRIPE )


** Piss off - you ASD fucked half wit.





......... Phil

 

[kell]

John Larkin wrote:
I posted a graph

of a small-signal schottky to a.b.s.e., and it has a zero tc point
around 15 mA.

Thanks. Unfortunately, I'm a Google groupie. No a.b.s.e. for me!

 

[John Larkin]

On 1 Jun 2006 15:48:18 -0700, "kell" <kellrobinson@billburg.com>
wrote:

John Larkin wrote:
I posted a graph
of a small-signal schottky to a.b.s.e., and it has a zero tc point
around 15 mA.

Thanks. Unfortunately, I'm a Google groupie. No a.b.s.e. for me!

It was an HSMS2810, originally an HP part. Most small-signal
schottkies look similar.

John

 

[gearhead]

On Dec 12, 4:55 pm, gearhead <nos...@billburg.com> wrote:

On Dec 12, 1:23 pm, gearhead <nos...@billburg.com> wrote:


Apparently temperature coefficient varies with the log of the current
according to the shockley equation. If I can determine the parameters
(like the ideality factor) for a particular schottky I can get the
math worked out and fiddle with the current setting to get the
temperature characteristic of the circuit right.

After manipulating the Shockley equation algebraically, I came up with

an interesting result. Assuming that a diode actually obeys the
Shockley equation, then you can take some measurements of the diode at
room temperature and calculate the temperature coefficient from those
results.

Assuming you only need to deal with currents well above the saturation
current, which of course is the case in the vast majority of practical
circuits, you can characterize the diode's behavior with an equation
of the form
ln I = a Vf + b
where I is the diode current and Vf is the voltage across the diode
Let T' represent the temperature in Kelvins at which you determine the
parameters a and b.
Then the diode's temperature coefficient = (ln I - b) / (T' x a)
(b is a negative number)
I did this for a 1N4003, 1N4148, 1N5818 schottky and MBR3035PT
schottky, also a pink led.
the schottkys have a lower tempco than the standard silicon diodes.
Also, schottkys have an emission coefficient near unity.
I thought this was pretty slick. As expected, there's a wide current
range for which standard silicon diodes have a temperature coefficient
near 2.2 mV/K.
But having this formula makes life easier. Takes some of the
guesswork out.