This work from last year did not get entered into the blog, but it represents an important building block: a temperature stable voltage reference comprised of very inexpensive commodity components.
When working with BJTs (including those on an integrated circuit) you get quite used to "sniffing around" for temperature effects on any given circuit design. One of things that become noticeable is when temperature compensating designs work -- you can tell immediately. Whether looking at the DC voltages on an oscilloscope, or probing more deeply with a high-resolution DMM, you can sense immediately when a thermal feedback loop is closed with relatively temperature stable results.
The circuit design below balances the negative temperature coefficient of the Vbe at the LM3900 -input with the matching temperature positive coefficient of a 5.6 Zener diode. The result is a temperature stable output of 6V ±5%, which is based on the tolerance of the Zener diode. However, the temperature coefficients of the Zener diode and the LM3900 match substantially well, result in ≈0 change.
A very useful building block for constructing unipolar signal processing circuits with the LM3900.
UPDATE
Instead of the older 1N752A as used originally here, there are newer B-series Zener diodes available like the 1N5232B which have ±2% tolerance, but matching temperature coefficient. This enables a tighter spec reference voltage output in this circuit design.
Below are the engineering notes for testing this voltage reference design.
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