This simple three-LED sensor uses an NTC at the input. The circuit is based on an uncommon integrated component today. We found it in documentation from the 80s.
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...