| 摘要 |
PROBLEM TO BE SOLVED: To provide a constant voltage power supply circuit capable of highly accurately performing regulating and overcurrent protecting operation even when input voltage has large variations.SOLUTION: A constant voltage power supply circuit 1 includes a first output transistor M1 and a second output transistor Q2 which is controlled by drain current of the first output transistor M1. Overcurrent is detected based on difference between power supply voltage Vin, which is voltage across a current detection resistor R3, and short-circuit voltage Vshort. An overcurrent control signal Vcont is generated based on a result of comparison between first sum voltage, obtained by adding feedback voltage Vfb and second reference voltage Vref2, and second sum voltage obtained by adding overcurrent detection voltage Vsub and third reference voltage Vref3. An overcurrent control transistor M3 provided between the source of the first output transistor M1 and the ground G2 is turned off when the second sum voltage is equal to or greater than the first sum voltage. |
