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.
This circuit provides a symmetrical voltage of 15 V output from the 6.3 V secondary of a small...
We found this circuit in an American 1980s documentation. The operational ones used are not common...
This transistor source can supply currents up to 2 A and the voltage determined by the zener...