Image Number 4 for United States Patent #8116052.
A protection ability of a power supply control circuit is improved so as to protect an output transistor against a back electromotive voltage from a load, a dump surge voltage, and a positive spike surge voltage which has a smaller energy but is higher than the dump surge voltage. The power supply control circuit includes: an output MOS transistor (power semiconductor device) connected between a first power supply terminal and an output terminal; a load connected to the output terminal; a first dynamic clamping circuit for controlling a voltage difference between a first power supply line and the output terminal; and a first switch connected between the first dynamic clamping circuit and the output MOS transistor, in which a conductive state is determined according to a result of comparison between a reference voltage and a voltage at the output terminal. The power supply control circuit further includes a second dynamic clamping circuit for controlling a voltage difference between the first power supply terminal and the output terminal to protect the output MOS transistor. The second dynamic clamping circuit operates in response to application of a positive spike surge voltage which is higher than the dump surge voltage.