| 摘要 |
PROBLEM TO BE SOLVED: To inhibit an operation at a high frequency during at light loading, reduce a switching loss, improve the efficiency of a power supply, and reduce power consumption. SOLUTION: This power supply device is provided with an external signal input terminal 42 connected to an external resistor. An input voltage VIN is divided by resistors 120, 121, and inputted to a variable signal generating circuit 43. An upper limit of a reference voltage is varied. The reference voltage is compared with an output voltage from a drain current detecting circuit 32 in an over current protection reference voltage source 31 for receiving a first variable signal 45 outputted from the variable signal generating circuit 43. A delay circuit 27 receives a second variable signal 44 outputted from the variable signal generating circuit 43, and varies a delay time. The switching loss of a switching element 1 is reduced, and the efficiency of the power supply is improved by implementing intermittent control at light loading. The delay circuit 27 provides a drain current detecting signal with the fixed delay time. Switching-on control based on a signal from a tertiary winding 103c in a transformer 103 is limited. An operation of the switching element 1 is stopped, and its timing is delayed. Cost performence is improved by controlling the operation light loading. COPYRIGHT: (C)2007,JPO&INPIT
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