| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply capable of preventing the excessive heating of a switching transistor even if an AC input voltage falls or rises. SOLUTION: A rectifier diode D101 and a smoothing capacitor C101 connected to the positive end of a secondary side LOW+B winding of a transformer T1 generate a positive side smooth voltage V1 while a rectifier diode D102 and a smoothing capacitor C102 generate negative side smooth voltages -V2. An intermediate voltage value Va is generated at a connection point A between a resistor R101 and a resistor R102, and supplied to the base of a switching transistor Q101 through a resistor R103. A Zener diode D105 is connected to the connection point A. If an AC input voltage falls or rises beyond a prescribed range, a PROTECT pin of a microcomputer 100 comes to be Low. COPYRIGHT: (C)2005,JPO&NCIPI
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