| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply apparatus which does not need a complicated circuit configuration and completely and certainly protects a load from excess voltage. SOLUTION: A dc voltage power from a primary side rectifying/smoothing circuit 300 that rectifies and smoothes an ac voltage Vin from an ac power supply 2 is transmitted through a transformer 5 to a secondary side rectifying/smoothing circuit 400. In a case where an excess voltage develops in an output voltage to a load 1 when power is supplied from the secondary rectifying/smoothing circuit to the load 1, this excess voltage develops on a primary auxiliary coil 502 and on a secondary auxiliary coil 503 that make up a switching transformer for detecting the development of excess voltages at different voltage levels in correspondence to the number of coil turns N502 and N503. When the voltage level of the primary auxiliary coil rises due to the development of the excess voltage, an operating voltage from the secondary auxiliary coil for detecting the excess voltage at a voltage level lower than the voltage level of the primary auxiliary coil is supplied as power to a power terminal P320c of a control IC320. As a result, switching of the transistor 301 is controlled by latching to be brought to a stop. COPYRIGHT: (C)2009,JPO&INPIT
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