schottky tempco

[gearhead]

Is it 2.2 mV/C?

 

[Richard Seriani]

"gearhead" <nospam@billburg.com> wrote in message
news:d6046b1f-8b28-4645-934f-9752ff5b10a1@j20g2000hsi.googlegroups.com...

Is it 2.2 mV/C?

Depends.

A 74S, 74LS or 74ALS series chips may be different from each other and
likely different from a Schottky diode. There are also differences between
SiC or GaAs or...Schottky diodes.

If for a specific component, look up the datasheet. If you want a general
range of temperature coefficients, look up representative components within
the families, create a table, and find the mean, median, or mode, as desired
(or see if Google really is your friend and if someone has already done
this).

Happy hunting.

Richard

 

[gearhead]

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

Is it 2.2 mV/C?

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop across the schottky
(which will have a constant current through it).
This way I can tune the circuit to give me the exact dV/C I need. It
will be for temperature compensation in a lead-acid battery charging
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C out of
nearly 2 volts (1.2 + Vf), giving me in the 1000 ppm range. So I need
to consider using a schottky.

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.

I'm going to set the current at 5 or 10 mA to make sure the 317 works
right.

 

[John Larkin]

On Wed, 12 Dec 2007 16:55:34 -0800 (PST), gearhead
<nospam@billburg.com> wrote:

On Dec 12, 1:23 pm, gearhead <nos...@billburg.com> wrote:
Is it 2.2 mV/C?

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop across the schottky
(which will have a constant current through it).
This way I can tune the circuit to give me the exact dV/C I need. It
will be for temperature compensation in a lead-acid battery charging
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C out of
nearly 2 volts (1.2 + Vf), giving me in the 1000 ppm range. So I need
to consider using a schottky.

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.

I'm going to set the current at 5 or 10 mA to make sure the 317 works
right.

Schottkies tend to run less, -1.5 maybe, except that the very small
signal-level diodes have decreasing tc's as the current increases.
Some go to zero tc at 10-20 mA. I think the exact tempco depends on
the metal used.

How about an LM35? It outputs 10 mV per degree C, so you could scale
that as needed. But it won't sink much current, so you'd have to
buffer it with an opamp or something.

Don't run an LM35 from over +5 volts! And don't pull the output below
ground!

John

 

[John Larkin]

On Wed, 12 Dec 2007 19:56:55 -0800 (PST), gearhead
<nospam@billburg.com> wrote:

On Dec 12, 7:34 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 12 Dec 2007 16:55:34 -0800 (PST), gearhead





nos...@billburg.com> wrote:
On Dec 12, 1:23 pm, gearhead <nos...@billburg.com> wrote:
Is it 2.2 mV/C?

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop across the schottky
(which will have a constant current through it).
This way I can tune the circuit to give me the exact dV/C I need. It
will be for temperature compensation in a lead-acid battery charging
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C out of
nearly 2 volts (1.2 + Vf), giving me in the 1000 ppm range. So I need
to consider using a schottky.

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.

I'm going to set the current at 5 or 10 mA to make sure the 317 works
right.

Schottkies tend to run less, -1.5 maybe, except that the very small
signal-level diodes have decreasing tc's as the current increases.
Some go to zero tc at 10-20 mA. I think the exact tempco depends on
the metal used.

How about an LM35? It outputs 10 mV per degree C, so you could scale
that as needed. But it won't sink much current, so you'd have to
buffer it with an opamp or something.

Don't run an LM35 from over +5 volts! And don't pull the output below
ground!

John- Hide quoted text -

- Show quoted text -

Whatever kind of temperature sensing element used, be it a diode, LM35
or whatever, needs to be screwed on to the battery terminal. The LM35
probably comes in some fragile package like a TO-92. On the other
hand, I can solder a ring terminal right onto the lead of a diode and
it will be rugged enough to screw to the battery terminal, and the
diode's lead will provide a good thermal path from the battery into
the diode.
Ambient temperature sensing really isn't feasible here. The battery
enclosure's temperature will undergo temperature variations to
extremes, from around freezing to at least 85 C (outdoor machinery).
The temp sensing must be through a direct connection to the battery
terminal. I think I'm kind of stuck with a diode just for physical
reasons.
Thanks for the advice, John.

Well, then use a diode, or maybe a TO-220 transistor, which would be
better thermally. The tempco of a silicon diode is around -2.5/650 =
-3800 PPM, so mix that with some constant voltage to get the result
you need.

John

 

[gearhead]

On Dec 12, 7:34 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Dec 2007 16:55:34 -0800 (PST), gearhead





nos...@billburg.com> wrote:
On Dec 12, 1:23 pm, gearhead <nos...@billburg.com> wrote:
Is it 2.2 mV/C?

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop across the schottky
(which will have a constant current through it).
This way I can tune the circuit to give me the exact dV/C I need. It
will be for temperature compensation in a lead-acid battery charging
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C out of
nearly 2 volts (1.2 + Vf), giving me in the 1000 ppm range. So I need
to consider using a schottky.

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.

I'm going to set the current at 5 or 10 mA to make sure the 317 works
right.

Schottkies tend to run less, -1.5 maybe, except that the very small
signal-level diodes have decreasing tc's as the current increases.
Some go to zero tc at 10-20 mA. I think the exact tempco depends on
the metal used.

How about an LM35? It outputs 10 mV per degree C, so you could scale
that as needed. But it won't sink much current, so you'd have to
buffer it with an opamp or something.

Don't run an LM35 from over +5 volts! And don't pull the output below
ground!

John- Hide quoted text -

- Show quoted text -

Whatever kind of temperature sensing element used, be it a diode, LM35
or whatever, needs to be screwed on to the battery terminal. The LM35
probably comes in some fragile package like a TO-92. On the other
hand, I can solder a ring terminal right onto the lead of a diode and
it will be rugged enough to screw to the battery terminal, and the
diode's lead will provide a good thermal path from the battery into
the diode.
Ambient temperature sensing really isn't feasible here. The battery
enclosure's temperature will undergo temperature variations to
extremes, from around freezing to at least 85 C (outdoor machinery).
The temp sensing must be through a direct connection to the battery
terminal. I think I'm kind of stuck with a diode just for physical
reasons.
Thanks for the advice, John.

 

[John Larkin]

On Wed, 12 Dec 2007 20:23:43 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Dec 2007 19:56:55 -0800 (PST), gearhead
nospam@billburg.com> wrote:

On Dec 12, 7:34 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 12 Dec 2007 16:55:34 -0800 (PST), gearhead





nos...@billburg.com> wrote:
On Dec 12, 1:23 pm, gearhead <nos...@billburg.com> wrote:
Is it 2.2 mV/C?

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop across the schottky
(which will have a constant current through it).
This way I can tune the circuit to give me the exact dV/C I need. It
will be for temperature compensation in a lead-acid battery charging
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C out of
nearly 2 volts (1.2 + Vf), giving me in the 1000 ppm range. So I need
to consider using a schottky.

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.

I'm going to set the current at 5 or 10 mA to make sure the 317 works
right.

Schottkies tend to run less, -1.5 maybe, except that the very small
signal-level diodes have decreasing tc's as the current increases.
Some go to zero tc at 10-20 mA. I think the exact tempco depends on
the metal used.

How about an LM35? It outputs 10 mV per degree C, so you could scale
that as needed. But it won't sink much current, so you'd have to
buffer it with an opamp or something.

Don't run an LM35 from over +5 volts! And don't pull the output below
ground!

John- Hide quoted text -

- Show quoted text -

Whatever kind of temperature sensing element used, be it a diode, LM35
or whatever, needs to be screwed on to the battery terminal. The LM35
probably comes in some fragile package like a TO-92. On the other
hand, I can solder a ring terminal right onto the lead of a diode and
it will be rugged enough to screw to the battery terminal, and the
diode's lead will provide a good thermal path from the battery into
the diode.
Ambient temperature sensing really isn't feasible here. The battery
enclosure's temperature will undergo temperature variations to
extremes, from around freezing to at least 85 C (outdoor machinery).
The temp sensing must be through a direct connection to the battery
terminal. I think I'm kind of stuck with a diode just for physical
reasons.
Thanks for the advice, John.

Well, then use a diode, or maybe a TO-220 transistor, which would be
better thermally. The tempco of a silicon diode is around -2.5/650 =
-3800 PPM, so mix that with some constant voltage to get the result
you need.

John

Oh: National makes a TO-220 LM35!

John

 

[Jamie]

gearhead wrote:

On Dec 12, 7:34 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Dec 2007 16:55:34 -0800 (PST), gearhead





nos...@billburg.com> wrote:

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

Is it 2.2 mV/C?

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop across the schottky
(which will have a constant current through it).
This way I can tune the circuit to give me the exact dV/C I need. It
will be for temperature compensation in a lead-acid battery charging
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C out of
nearly 2 volts (1.2 + Vf), giving me in the 1000 ppm range. So I need
to consider using a schottky.

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.

I'm going to set the current at 5 or 10 mA to make sure the 317 works
right.

Schottkies tend to run less, -1.5 maybe, except that the very small
signal-level diodes have decreasing tc's as the current increases.
Some go to zero tc at 10-20 mA. I think the exact tempco depends on
the metal used.

How about an LM35? It outputs 10 mV per degree C, so you could scale
that as needed. But it won't sink much current, so you'd have to
buffer it with an opamp or something.

Don't run an LM35 from over +5 volts! And don't pull the output below
ground!

John- Hide quoted text -

- Show quoted text -


Whatever kind of temperature sensing element used, be it a diode, LM35
or whatever, needs to be screwed on to the battery terminal. The LM35
probably comes in some fragile package like a TO-92. On the other
hand, I can solder a ring terminal right onto the lead of a diode and
it will be rugged enough to screw to the battery terminal, and the
diode's lead will provide a good thermal path from the battery into
the diode.
Ambient temperature sensing really isn't feasible here. The battery
enclosure's temperature will undergo temperature variations to
extremes, from around freezing to at least 85 C (outdoor machinery).
The temp sensing must be through a direct connection to the battery
terminal. I think I'm kind of stuck with a diode just for physical
reasons.
Thanks for the advice, John.
why not NTC or PTC resistors?

you can get those with face mountable tabs.


--
"I'd rather have a bottle in front of me than a frontal lobotomy"
http://webpages.charter.net/jamie_5

 

[John Larkin]

On Thu, 13 Dec 2007 21:59:12 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

gearhead wrote:

On Dec 12, 7:34 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Dec 2007 16:55:34 -0800 (PST), gearhead





nos...@billburg.com> wrote:

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

Is it 2.2 mV/C?

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop across the schottky
(which will have a constant current through it).
This way I can tune the circuit to give me the exact dV/C I need. It
will be for temperature compensation in a lead-acid battery charging
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C out of
nearly 2 volts (1.2 + Vf), giving me in the 1000 ppm range. So I need
to consider using a schottky.

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.

I'm going to set the current at 5 or 10 mA to make sure the 317 works
right.

Schottkies tend to run less, -1.5 maybe, except that the very small
signal-level diodes have decreasing tc's as the current increases.
Some go to zero tc at 10-20 mA. I think the exact tempco depends on
the metal used.

How about an LM35? It outputs 10 mV per degree C, so you could scale
that as needed. But it won't sink much current, so you'd have to
buffer it with an opamp or something.

Don't run an LM35 from over +5 volts! And don't pull the output below
ground!

John- Hide quoted text -

- Show quoted text -


Whatever kind of temperature sensing element used, be it a diode, LM35
or whatever, needs to be screwed on to the battery terminal. The LM35
probably comes in some fragile package like a TO-92. On the other
hand, I can solder a ring terminal right onto the lead of a diode and
it will be rugged enough to screw to the battery terminal, and the
diode's lead will provide a good thermal path from the battery into
the diode.
Ambient temperature sensing really isn't feasible here. The battery
enclosure's temperature will undergo temperature variations to
extremes, from around freezing to at least 85 C (outdoor machinery).
The temp sensing must be through a direct connection to the battery
terminal. I think I'm kind of stuck with a diode just for physical
reasons.
Thanks for the advice, John.
why not NTC or PTC resistors?
you can get those with face mountable tabs.

Sure. NTC's have a huge change with temperature, but are pretty
nonlinear. There are some simple ways to linearize them over a
reasonable temp range.

RTD type ptc's usually run around +4000 ppm. The ceramic ptc's are
pretty much too nonlinear to be useful for temp sensing... thy most;y
are used for current limiting.

John

 

[John Popelish]

John Larkin wrote:
(snip)

The ceramic ptc's are
pretty much too nonlinear to be useful for temp sensing... thy most;y
are used for current limiting.

....or temperature limiting.

--
Regards,

John Popelish

 

[whit3rd]

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

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop ...
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C

Any diode will have about .003 * Vf tempco; Shottky diodes
have lower Vf, so lower tempco. If you need something
higher than a silicon diode, use two silicon diodes in series, OR
make a difference with some fixed voltage, as

(A+ B*T ) - C = result

so as to subtract from the non-temp-dependent A term; B can be
any fraction of the result that you want, just chose C correctly...

Schottky diodes aren't specified for their operating conditions under
modest currents, so you'll get nothing from their data sheets. Use
a transistor instead as a planar diode (connect B and C together)
for temperature sensing.

I think if you make the LM317 current source with a fixed resistor,
and
feed the output current into an R + diode series pair, you'll find
the tempco you want is achievable that way.

 

[gearhead]

On Dec 16, 1:23 pm, whit3rd <whit...@gmail.com> wrote:

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

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop ...
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C

Any diode will have about .003 * Vf tempco; Shottky diodes
have lower Vf, so lower tempco. If you need something
higher than a silicon diode, use two silicon diodes in series, OR
make a difference with some fixed voltage, as

(A+ B*T ) - C = result

so as to subtract from the non-temp-dependent A term; B can be
any fraction of the result that you want, just chose C correctly...

Schottky diodes aren't specified for their operating conditions under
modest currents, so you'll get nothing from their data sheets. Use
a transistor instead as a planar diode (connect B and C together)
for temperature sensing.

I think if you make the LM317 current source with a fixed resistor,
and
feed the output current into an R + diode series pair, you'll find
the tempco you want is achievable that way.

Yes, that's the way to do it of course.

 

[John Popelish]

gearhead wrote:

On Dec 16, 1:23 pm, whit3rd <whit...@gmail.com> wrote:
On Dec 12, 4:55 pm, gearhead <nos...@billburg.com> wrote:

I need a diode with a low voltage drop and a known temperature
coefficient.
I'm going to put it in series with the adjust terminal of a lm317 in
constant-current
configuration, so the voltage with respect to ground at the output pin
of the 317 will be 1.2 volts plus the voltage drop ...
circuit. Since I need about 2000 ppm/C, or maybe a little more, a
"regular" silicon diode won't work. It would have 2.2 mV/C
Any diode will have about .003 * Vf tempco; Shottky diodes
have lower Vf, so lower tempco. If you need something
higher than a silicon diode, use two silicon diodes in series, OR
make a difference with some fixed voltage, as

(A+ B*T ) - C = result

so as to subtract from the non-temp-dependent A term; B can be
any fraction of the result that you want, just chose C correctly...

Schottky diodes aren't specified for their operating conditions under
modest currents, so you'll get nothing from their data sheets. Use
a transistor instead as a planar diode (connect B and C together)
for temperature sensing.

I think if you make the LM317 current source with a fixed resistor,
and
feed the output current into an R + diode series pair, you'll find
the tempco you want is achievable that way.

Yes, that's the way to do it of course.

I have been simulating simple transistor circuits in an
attempt to make a lead acid battery float voltage reference
that has the proper temperature coefficient.

One way, using a 1 mA current source looks very good. It
uses a low current transistor, like a 2N5089, with a
resistor divider collector to negative rail, base to the
divider node, and a small emitter resistor to provide the
negative feedback needed to reduce the tempco by the right
amount. Values that simulate a good result are:
emitter resistor 508 ohms
Base to negative rail resistor 1.3k
Collector to base resistor 2.28k

Another version, fed from a +12 volt regulated supply
through a 10k resistor (instead of a regulated 1mA source)
simulated well with the following values:
emitter resistor 411 ohms
Base to negative rail resistor 1.3k
Collector to base resistor 2.45k

I was trying to match a reference curve of
2.374 - (3.447E-3 * Temp), with Temp in degrees C.

--
Regards,

John Popelish

 

[Ecnerwal]

In article <5-GdnSmpFbQOK_vanZ2dnUVZ_rGrnZ2d@comcast.com>,
John Popelish <jpopelish@rica.net> wrote:

I have been simulating simple transistor circuits in an
attempt to make a lead acid battery float voltage reference
that has the proper temperature coefficient.

Brute force, nothing fiddly:

A sensor (either analog out such as LM34/LM35 or digital out) tosses a
fairly reliable temperature to a microprocessor, and the microprocessor
tosses a fairly reliable reference out a DAC (perhaps needing to be
multiplied up, depending on the DAC's abilities). Given all the other
stuff that a good battery charger should be doing (switching modes and
voltages depending on time of charging, etc), and the present price of
microprocessors, it does not appear to be overkill to use one - the job
gets done, and variations in batches of parts are expected to be well
controlled in dedicated temperature sensing parts.

--
Cats, coffee, chocolate...vices to live by