I've done a bit more work on my voltage divider TC compensation from last week. This time setting for 2mA. Compensation performance seems similar to before. There are clearly fixed end-stops to the compensation range (see attached diagram):
Alex's Zener-only @ Iz=1.45mA: R1=[edit]0R, R2=0R (Zener only TC turnover point)
Last week, Zener+Diode @ Iz=5mA R1=765R, R2=1k3
Today, Zener+Diode @ Iz=2mA R1=1k6, R2=460R
Zener+Diode @ Iz=20mA approx. R1=0R, R2=infinite (Zener+Diode TC turnover point)
These set the bounds of passive voltage divider compensation, with a (possibly linear) ratio range for different operating currents. One thing that isn't clear to me... Can some (small) amount of divider compensation improve on the TC of Zener alone?
EDIT: The Diode isn't Present in Alex's Zener only configuration. In the voltage divider configurations, regardless of the divider ratio, the entire Diode forward voltage is in series with the Zener supply. This will change the Zener current with temperature and is another factor that the divider needs to compensate (so maybe not linear).