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.

Power supply using a Transistor as Rectifier (CB12851E)
This power source, obtained in a 1973 publication, suggests the use of partially burned germanium...
560 kHz to 1 MHz VCO (CB21499E)
This circuit was obtained from an Electronic Design from 1964. Transistors admit modern...
Operational Fast Wave Rectifier (CB14421E)
The circuit is from the 1994 National Semiconductor Linear Applications Handbook but can be...