The circuit was designed to build a stable power supply the will provide a regulated voltage from 40 V to 70 V in a 3 A current. 2N3055 – a complementary Silicon Epitaxial-Base planar NPN transistor ...
The most common type of power supply today is the switching supply. These units use pulse-width modulation (PWM) to regulate output. Supplies today employ several different PWM circuit configurations.