Undervoltage detector with the LM3900 (CB25172E)

The figure shows how to implement an undervoltage detector using a Norton amplifier and a zener diode as the main elements.

FET Input Operational (CB13628E)
This configuration was obtained in a 1977 FET Databook. The circuit can be practically any JFET...
Negative Voltage Regulator 723 (CB5460E)
The integrated circuit used in this regulator is not very common today. The circuit is from old...
Constant Current Source II (CB19950E)
The operational used is uncommon today, but equivalents can be used. Unlike the previous one, this...