An inverting amplifier creates a voltage C using a reference voltage (voltage B) as a reference point. An adder composed of two input inverting amplifier circuits ultimately creates a voltage D by carrying out weighted addition of the voltage A and the voltage C. By using the voltage D created by an input front-end circuit, the internal functions of the control IC can prevent the operating points and control amounts for each function from being different relative to the input voltage and make it possible to distinguish voltage within the control IC from zero voltage when the lowest input voltage is received.