| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent an output transistor in a high side output form from being unnecessarily turned on due to decrease in a power voltage to a transistor driving circuit. <P>SOLUTION: A device 41 comprises: an N channel MOSFET 11 (Metal Oxide Semiconductor Field Effect Transistor) feeding a current to an electrical load 1 by being turned on; a capacitor 15 charged by the output voltage of a step-up circuit 13 having a voltage higher than the voltage VB of a load power supply; and a transistor driving circuit 17 for protecting the FET 11 operated by a power voltage VD different from that of the load power supply to turn on the FET 11 by supplying the charging voltage VC of the capacitor 15 to the gate of the FET 11 in accordance with a signal Sc from a personal computer 3, and forcibly suspending the supply of the charging voltage VC to the gate when detection is made that an excess current is allowed to flow to the FET 11. Where, means 45, 47 are provided to forcibly discharge the electric charge of the capacitor 15 at the time of decreasing the power voltage VD. Thus, the unnecessary turn-on of the FET 11 caused by the decrease in the power voltage VD is prevented. <P>COPYRIGHT: (C)2004,JPO |
