This circuit was found in December 1983 Radio Electronics magazine. The maximum output current is 1 A and the supply voltage ranges from 4 to 28 V.
This circuit appears elsewhere on this site, but from different sources. Using the LM3900, we find this...
This interesting source or isolation transformer also allows to vary the output voltage by...
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...