| 摘要 |
A temperature sensor ( 33 ) detects the temperature of a MOS transistor ( 7 ), and a current detecting circuit ( 35 ) detects current flowing in the MOS transistor ( 7 ). When the voltage corresponding to the detected temperature or the voltage corresponding to the detected current is increased to a threshold value or more, an overheat state detecting signal and further switching signal is set to a high level. As a result, a switch circuit in a driving circuit ( 17 ) is turned on, and the gate resistance value becomes the parallel value of a resistor ( 25 ), and the PWM frequency in the PWM control circuit is lowered, whereby the switching loss of the MOS transistor ( 7 ) can be reduced under the state that the motor ( 2 ) is rotated.
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