| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent a semiconductor switching element from being overheated or recover it from overheated state without exerting influence on the rotational speed of a motor. <P>SOLUTION: A temperature sensor 33 detects the temperature of a MOS transistor 7, and a current detection circuit 35 detects the current passing through the MOS transistor 7. When a voltage Va corresponding to the detected temperature or a voltage Vc corresponding to the detected current rises and exceeds a threshold value, an overheated state detection signal Sb and further switching signals Sd and Se are brought to the H level. As a result, in a drive circuit 15, a switch circuit 26 is turned on and the gate resistance value becomes equal to the parallel value of resistors 24 and 25, and in a PWM control circuit 14, the PWM frequency is lowered. Thus, while the motor 2 is rotationally driven, the switching loss in the MOS transistor 7 can be reduced. <P>COPYRIGHT: (C)2004,JPO&NCIPI |
