| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a power supply circuit capable of preventing fluctuation in output voltage when supplying the output of a step-up converter to a linear regulator, because of the voltage drop of a power supply input in the linear regulator, even if no capacitor is provided to the input side of the linear regulator. <P>SOLUTION: When a voltage of a battery 91 drops down to a drop detection level, an output of an input voltage drop detection circuit 14 changes from a high level to a low level. When the output of the input voltage drop detection circuit 14 comes to be low level, field-effect transistors Tr4 and Tr5 come into a shielded state. When the field-effect transistor Tr5 comes into the shielded state, the electric charge of a capacitor C4 is supplied to a current source I1. As the gate voltage of a field-effect transistor Tr2 drops at a constant rate. the current that flows from the source of the field-effect transistor Tr2 to the drain gradually increases, with a switch output side voltage VSW rising at a predetermined rate as well. <P>COPYRIGHT: (C)2011,JPO&INPIT |
