Found in American documentation from the 1980s, this circuit has a diode feedback. At the exit we have an indicator LED. The LM3900 is a transconductance operational amplifier.
Using the 723 integrated circuit, this power supply has the voltage determined by R2 and R3, which...
This circuit with two transistors was found in Radio Electronics magazine from February 1968. The...
This circuit was found in the 1987 Radio Electronics magazine. The components used are integrated...