Abstract: A switching power supply unit for providing an output voltage that is controlled such that a first detection voltage detected on the basis of the output voltage becomes equal to a first reference voltage. The peak voltage at the node of a serially connected coil and a switch of the switching power supply unit is detected and used as a second detection voltage for over-voltage protection. Thus, over-voltage protection of the switching power supply unit is secured with no additional terminal on the switching control IC for over-voltage protection even if such components as a feedback circuit and a rectifying diode of the power supply unit become open.

Abstract: A switching power supply unit for providing an output voltage that is controlled such that a first detection voltage detected on the basis of the output voltage becomes equal to a first reference voltage. The peak voltage at the node of a serially connected coil and a switch of the switching power supply unit is detected and used as a second detection voltage for over-voltage protection. Thus, over-voltage protection of the switching power supply unit is secured with no additional terminal on the switching control IC for over-voltage protection even if such components as a feedback circuit and a rectifying diode of the power supply unit become open.

Abstract: A main driver, in which NPN and PNP bipolar transistors are connected in series, is driven by an output of a pre-driver having a first CMOS circuit driven by an input signal. An assist circuit having a second CMOS circuit driven by the input signal and also having a current limit resistor is provided, and an output of the main driver is assisted by an output of the assist circuit. Therefore, it is possible to reduce a short circuit current in a transistor output circuit, to increase and decrease an output signal to an power-supply potential (upper limit) and a ground potential (lower limit), and to smoothly change the output signal near the power-supply potential and the ground potential. Further, an intensity of electromagnetic noise is reduced and a switching output having a sufficiently large amplitude is supplied.

Abstract: A main driver, in which NPN and PNP bipolar transistors are connected in series, is driven by an output of a pre-driver having a first CMOS circuit driven by an input signal. An assist circuit having a second CMOS circuit driven by the input signal and also having a current limit resistor is provided, and an output of the main driver is assisted by an output of the assist circuit. Therefore, it is possible to reduce a short circuit current in a transistor output circuit, to increase and decrease an output signal to an power-supply potential (upper limit) and a ground potential (lower limit), and to smoothly change the output signal near the power-supply potential and the ground potential. Further, an intensity of electromagnetic noise is reduced and a switching output having a sufficiently large amplitude is supplied.