This circuit was found in a 1970s American documentation. It can be applied to almost any regulator. The transistor used admits equivalent, depending on the circuit current.
This circuit was obtained in a 1991 Electronics Handbook. The publication no longer exists, but...
This is another possible version of a negative voltage generator using a 555 integrated circuit. The...
This circuit is from a 1965 Electronic Design. The transistors may be general purpose and the...