[volt-nuts] Trimming the LTZ1000 tempco
willvolts at gmail.com
Thu Oct 6 15:52:04 UTC 2011
Datasheet page 6 shows a way to "null" the overall tempco. As far as I
understand (most likely I don't) adding the R1 doesn't much change the
zener current. But the op-amp output voltage goes higher to maintain
the balance which increases the transistor Ic which slightly changes
the VBE tempco. But could we get the same result by adjusting the 70k
I tried the influence of the 70k Resistor on tempco since I had to
build mine of a 50K + a 20K precision WW resistor and wanted to save
the 20K resistor. The change in tempco on my LTZ1000A #1 is from about
48ppm/K with 70kOhms to 52ppm/K with 50kOhms.
A rough estimation: Change in Ic when R1 is set from 0 to max value
200 ohms is equivalent to changing the 70k resistor to 60k. I haven't
prototyped or simulated, so there can be more complex interactions
that I haven't included.
It seems that the page 6 trick slightly reduces the tempco but it
still stays in the 50ppm/C area. Or I have forgot something in my
calculations. I don't have a spare LTZ1000 available at the moment to
run the tests but maybe Andreas has time in the future.
The original unheated tempco is surprisingly high when compared to
ordinary temperature stabilised zeners. Better stability at the
expense of tempco?
Another alternative is to adjust the 120 ohm resistor which changes
the zener current. It could be more effective way to alter the tempco
but there can be some side effercts?
2011/10/6, Bruce Griffiths <bruce.griffiths at xtra.co.nz>:
> Then you can easily trim the tempco as illustrated in the diagram taken
> from the bottom of page 6 of the current datasheet.
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