The operation of this can be judged by varying the duty cycle, i.e. by changing the duration for which GTO is switched ON.
Hence, by making Pulse Width of the Pulse Gen. 10%.
O/P Vol. = (.1) * (I/P Vol.)
Similarly for Pulse Width 20%
O/P Vol. = (.2) * (I/P Vol.)
& so on the Output Voltage can be Stepped Down.