Electronics > Metrology

LM399 based 10 V reference

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imo:

--- Quote from: Kleinstein on September 30, 2021, 12:51:36 pm ---..
If it is about a more pulsed operation (e.g. 99 ms zener and 1 ms temperature measurement) the more suitable way would be a switch to turn off the connection when in temperature mode.

--- End quote ---
You can even use the substrate diode as a "heater", imho. Say 20mA*0.65V=130mW. TO18 thermal resistance is something like 300C/Watt, 0.13*300 = 39C, with Tamb=25 you'll get Tpackage=25+39=64C.
With 50mA diode current you may anneal all defects off the silicon  :-DD

Kleinstein:
Current through the substrate diode can interact with the rest of the circuit. Usually this is not in a good way. So once there is substarte current all bets are off.



For filtering I would not consider electrolytic caps practical, because of the temperature effect and leakage that can change with time and temperature. The DA will also requite extremely long settling - maybe not as long as the LM399, but it would start all over after power off.
The question is more if polyester caps are sufficient or if it needs polyporpylene.

Filtering is mainly an option if the instruments to measure or use the reference are especially sensitive to a certain not too low frequency band. The main slow part would be someting like the DMM auto zero cycle with maybe 2-4 readings of 200 ms each. So this would be frequencies of some 1-4 Hz.
Instead of the effort for filtering a lower noise reference could be the easier way.

guenthert:

--- Quote from: Kleinstein on September 30, 2021, 03:31:57 pm ---[..]
For filtering I would not consider electrolytic caps practical, because of the temperature effect and leakage that can change with time and temperature. The DA will also requite extremely long settling - maybe not as long as the LM399, but it would start all over after power off.
[..]

--- End quote ---
      Is DA really an issue, if one uses two capacitors in series and charges the mid point from the output of the zener using a 2nd resistor (as described in AoE3)?

Cerebus:
That little trick is designed to deal with leakage currents, not dielectric adsorption.

guenthert:

--- Quote from: Cerebus on September 30, 2021, 05:05:14 pm ---That little trick is designed to deal with leakage currents, not dielectric adsorption.

--- End quote ---
      Well, yes, but what is the ill-effect of DA, if not voltage drop over the resistor due to the charging current?

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