This filter, found in an old manual, has characteristics of reduced overvoltage given by the graph next to the diagram. Formulas for component calculations are given next to the diagram.
This circuit is from a Radio Electronics from May 1994. In it we have the way to connect three 4017...
In the figure we present an extremely simple circuit of a voltage source regulated by a zener...
We found this circuit in a 1987 documentation. It is a multi-tester with neon lamp and LEDs...