Re: schottky tempco

On Dec 12, 1:23 pm, gearhead <nos...@xxxxxxxxxxxx> 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.
.

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