| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a power supply circuit suppressing troubles when a soft-start circuit is provided while maintaining a function of the soft-start circuit. <P>SOLUTION: The soft-start circuit includes: a resistor R1 connected between a source S and a gate G of a P-channel FET 42; a transistor T1 with an emitter grounded; a resistor R2 connected to a collector of the transistor T1 and a gate G of the FET 42, and a capacitor C1 between the gate G and the drain D of the FET 42. A capacitor C1 is connected in series with a resistor R3, and the resistor R3 is connected in parallel with a diode D1. When an AC adapter 12 is connected, a current is significantly suppressed in charging the capacitor C1 by the resistor R3 to suppress the gate G from opening. When a power supply switch is turned on, the capacitor C1 is discharged not through the resistor R3 but through the diode D1 and the resistor R2, to achieve a function of the soft-start circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT |
