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.

Transistor Tester (CB4370E)
This circuit was found in an English magazine from 1979. The magazine no longer exists, but the...
VCO- Voltage Controlled Oscillator (CB12170E)
We found this circuit in a PopularElectronics of 1993. The circuit generates signals whose...
Two Phase Voltage Controlled Oscillator (CB13741E)
This circuit was found in an English technical documentation from 1973. The circuit generates...