Tempco EN article

[gstopp at fibermux.com]

     Yikes good catch Tim, forgot about that! There's another article in 
     Electronotes somewhere about self-heating of tempco's and how that may 
     affect their operation, but I'm not sure which issue... I'll keep my 
     eyes peeled next time I browse...
     
     Sorry!
     
     - Gene


______________________________ Reply Separator _________________________________
Subject: Re: Tempco EN article 
Author:  Tim Cockram <tim at redragon.demon.co.uk> at ccrelayout
Date:    2/6/97 2:10 PM


Hi
     
Using such a low impeadance scheme could cause a problem with drift due to self 
heating of 
the tempco resistor:  eg 15V across a 1K resistor  produces a power disipation 
of 0.225 
Watts.  I don't have too much experience with tempco resistors, however I am 
inclinded to 
believe that this will cause the temperature of the resistor to rise 
significantly and hence 
change the resistance.
     
There is a solution though:- maintaining the exponential transistors at a fixed 
temperature 
in an "oven"(as per Rick Jansens schematic).  This technique was used for years 
to produce 
accurate crystal oscillators.  Has any one tried this? and if so with what 
results?
     
Regards
     
Tim
     
     
------------------------------------- 
Tim Cockram
E-mail: tim at redragon.demon.co.uk 
     
Phone:-UK-1222-384041
Fax:-    UK-1222-390326
     
"Sociology is the study of those who don't need studtying by those who do." 
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