Semiconductor device for controlling power source

A semiconductor device for power supply control, that generates and outputs a driving pulse to turn on or off a switching element which intermittently supplies current to a primary-side winding wire of a transformer for voltage conversion, by inputting voltage in proportion to current flowing in the primary-side winding wire of the transformer and an output voltage detection signal from a secondary side of the transformer, the semiconductor device comprising:

• an on/off control signal generation circuit which generates a control signal to turn on or off the switching element;
• a high-voltage input start terminal to which alternating-current voltage of AC input or voltage rectified in a diode bridge is input;
• a high-voltage input monitoring circuit which is connected to the high-voltage input start terminal and monitors voltage of the high-voltage input start terminal;
• and
• a discharging unit which is connected between the high-voltage input start terminal and a ground point, wherein
• when the high-voltage input monitoring circuit has detected that a time for which the voltage of the high-voltage input start terminal is not lower than a predetermined voltage value for a predetermined period, the discharging unit is turned on.