It is an improved version of the previous circuit with a voltage follower that reduces the load impedance. The circuit was found in American documentation from the 1980s.
The component used in this regulator is not common today. The switching circuit is from an 80's...
We found this circuit in a 1972 RCA technical documentation. The comparator can be any type and C1...
We found this circuit in the ON Semiconductor Thyristor Manual although similar configuration can be found...