This circuit was obtained from the September 1977 issue of Radio Electronics magazine. The circuit is based entirely on transistors and two SCRs. The power supply with the inclusion of a battery is given.
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...