[volt-nuts] Lm399 heater

[Andreas Jahn]

Hello Fred,

the heater is regulated to 90 degrees centigrade as is stated in the data 
sheet.
A current source for the heater would lead to a instable regulation.
Instead it is essential to supply the heater from a well regulated voltage 
source.
The output voltage of the zener changes with the heater voltage (or 
current?)
by up to 2ppm/Volt at low heater voltages (around 10V).
Higher heater voltages are more stable.

The LM399 is also sensitive to orientation.
The output voltage changes if you put the LM399 up side down to the sides or 
in normal orientation.
(needs 1-2 minutes for stabilization)

For the LTZ1000 try Arrow (USA) they usually have some from time to time. 
(today: 13 pieces if you are fast)
http://components.arrow.com/part/search/ltz1000

with best regards

Andreas


----- Original Message ----- 
From: "Fred Schneider" <pa4tim at gmail.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Saturday, September 15, 2012 2:04 AM
Subject: [volt-nuts] Lm399 heater


> Is the heater from a LM399 regulated, so it stayes at 85 degrees or is it 
> just drawing an vast amount of current like a lightbulb ? So if it gets 
> hotter around the LM the heater temp stays the same ?
>
> I just building a refrence with it and If it is not regulated i want to 
> feed it through a current source
> The Vref with a LTC1052 and OPA277 comes in a small closed aluminum box 
> shielded from the rest and mounted on rubber. Only feedthrough caps for in 
> and outputs. So it can get warmer in there, but this way i want to make it 
> more temp and mechanical stable ( the output will be the LM's native 
> voltage times Two so i minimise resistors ( use two 0.01% matched 
> resistors) then A Fluke 720 KV devider to make 10V out of it, then a 
> chopper buffer, ESI dekavider KV and another buffer to drive the cables 
> ( like the sub-ppm reference Jim Williams made, only he used a ( 
> handpicked ? ) LTZ1000 ( i hope to find one someday, tryed to order one 
> from LT but no luck as a private person) and managed to go sub-ppm, my 
> goal is more modest.
>
> Fred PA4TIM
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