| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply unit which has a simple circuit structure, is low in cost and prevents an insecure state in the event that a half short-circuit occurs in a main switching element. SOLUTION: In this switching power supply unit, a series circuit composed of the main switching element Q1, a switching element SW1 and a transformer 8 connects power supply lines A and B. A ripple voltage detection circuit 15 is provided so as to detect that the ripple voltage of the power supply line A is a predetermined value or more in the event that a half short-circuit occurs in the main switching element. When the ripple voltage detection circuit 15 detects that the ripple voltage is the predetermined value or more, current supply (voltage supply) to the main switching element Q1 is interrupted by opening the switching element SW1. COPYRIGHT: (C)2008,JPO&INPIT
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