| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply device which will not elongate a starting time at powering on, while keeping the rise in the temperature of a transformer to be within an allowance, when the output load is short-circuited. SOLUTION: At steady state, a PWM control circuit U1, which feeds an input DC current to a secondary winding S1 by converting it to a pulse current by an on/off-operation, obtains its starting voltage from a capacitor C1 charged with the input DC current flowing through a first starting resistor R1, by taking a prescribed time; whereas, when the output load Z of a secondary circuit is short-circuited and overcurrent flows to the transformer T1, short-circuiting of a second starting resistor R10 which is short-circuited at the stationary time is released, and the starting voltage of the PWM control circuit U1 is obtained by the currents flowing via a composite resistor formed of the first and the second resistors, by taking a time that is longer than a prescribed time at the stationary time. COPYRIGHT: (C)2008,JPO&INPIT
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