A comparator U1 having inputs from the upper out
put terminal and source of voltage V’, as depicted, is
adapted to compare V01 with reference voltage Vr.
Comparator U1 is connected to pulse width modulating
(PWM) circuit 1 which is connected to the comparator
U1 as depicted, and is adapted to produce upon receipt
of the output from comparator U1, a pulse width signal
corresponding to the difference between output V01 and
reference voltage V,. The PWM circuit 1 is connected
to drive circuit 2 which is adapted to receive the ouput
from PWM circuit 1. A switching transistor Q1 is con
nected to drive circuit 2 at its base, and to input source
and primary m, at its emitter and collector. Transistor
Q] is turned ON and OFF by drive circuit 2 so as to turn
ON and OFF input DC voltage Vin supplied to the
primary coil ml of transformer T1.