| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an AC/DC converter which has high efficiency and stably operates without causing low frequency oscillation, etc. due to duty variation by optimizing driving conditions of a switching element in accordance with a plurality of input AC voltages. Ž<P>SOLUTION: A comparator 22 compares a DC voltage obtained by rectifying, smoothing and dividing with resistance an AC voltage from an AC power source 10 with a reference voltage Vref3, and determines whether the input AC voltage is an AC100V system or an AC200V system to switchingly control a switch S1. When the determination shows the AC100V system, the switch S1 is turned ON, and an FET Q1 is driven from a control circuit 21 through a drive resistor circuit of a parallel composite resistor value between a resistor R1 and a resistor R20. On the contrary, when the determination shows the AC200V system, the switch S1 is turned OFF, a resistance value of the drive resistor circuit is defined only by the resistor R1, and the resistance value is larger than that of the AC100V system. In this way, excessive supply of charges to a gate of the FET Q1 at the time of input of AC voltage of the AC200V system is prevented. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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