| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a switching power supply unit having a simple circuit configuration, which can prevent an erroneous operation of a main oscillation circuit due to ringing generated in a driving transformer without causing a large loss. Ž<P>SOLUTION: The switching power supply unit has main oscillation elements Q1, Q1 for turning on/off an input voltage to generate a DC voltage; and a control pulse generating section 16 for generating a control pulse subjected to a predetermined pulsewidth modulation. The unit is provided with a driving circuit 18 for outputting a driving pulse having the same phase as that of the control pulse to drive the main oscillation circuits Q1, Q2. The driving circuit 18 has a main switch element Q3 for generating an AC voltage on a primary winding of a driving transformer T2. The driving circuit 18 has a main oscillation element driving sections 26a, 26b connected to a secondary winding of the driving transformer T2 and for outputting a driving pulse for driving the main oscillation elements Q1, Q2 by turning on/off the main switch element Q3. The driving circuit 18 is provided with a winding wire clamping section 24 for suppressing the generation of a voltage of positive direction in the primary winding wire of the driving transformer T2 during the main switch element Q3 is in an off-state. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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