The object of the present invention is to improve the power factor and at the
same time to obtain a high efficient operation. It is constituted such that one
terminal of a DC power supply 12 from which a pulsating flow is obtained
is connected to a connection mid point of one terminal of a primary winding 15a
and the other terminal of an auxiliary winding 15c wound in phase
on a converter transformer 15 by means of a series circuit of a choke coil
13 and a first diode 14; one terminal of the auxiliary winding 15c
of the converter transformer 15 is connected to the other terminal of
the DC power supply 12 through a first capacitor 16 and at the same
time the other terminal of the primary winding 15a is connected to
the other terminal of the DC power supply 12 through a switching device
17; a secondary winding 15b wound in counter phase with the
primary winding 15a for the converter transformer 15 is connected
to a DC voltage output terminal 19a, 19b through a
rectifying circuit 18; the DC voltage output terminal 19a is
connected to an input side of a pulse width modulation control circuit 20;
and an output terminal of the pulse width modulation circuit 20 is connected
to a control electrode of the switching device 17.
