Found in Maxim's documentation from the 90's, this circuit uses a component from the time and has its performance curve shown next to the diagram.
This circuit is from the 1977 GE semiconductor manual. The components used are uncommon today....
This circuit has 4 operating modes and was found in the 1995 Encyclopedia of Electronic Circuits...
The voltage of 30 V indicated in this project, shown in the figure, depends on the diac used. It...