Semiconductor device and power supply device

Abstract

A power supply topology is used in which a transistor is provided on the side of an output node of a rectifying circuit. An inductor is provided on the side of a reference node, a resistor is inserted between the transistor and the inductor, and one end of the resistor is coupled to a ground power supply voltage of a PFC circuit. The PFC circuit includes a square circuit which squares a result of multiplication of an input voltage detection signal and feedback information (output voltage of an error amplifier circuit). The PFC circuit drives on the transistor when a detection voltage developed at the resistor reaches zero, and drives off the transistor when the detection signal reaches an output signal of the square circuit.

What is claimed is: 
     
         1 . An LED illuminating device comprising:
 a first output node and a second output node coupled with a light emitting diode;   a rectifying circuit which rectifies ac power and supplies power to a rectified output node;   an N-channel type MOSFET having a gate terminal, a drain terminal and a source terminal, the drain terminal being coupled with the rectified output node;   a current detection resistor coupled with the source terminal and a ground node, the ground node being coupled with a ground voltage;   an inductor coupled with the ground node and the first output node;   a diode whose anode and cathode are coupled with the second output node and the source terminal of the N-channel type MOSFET, respectively;   an output capacitor coupled with the first output node and the second output node; and   a control circuit coupled with the gate terminal and the source terminal of the N-channel type MOSFET, a detection voltage of the source terminal being inputted into the control circuit,   the control circuit providing a PWM signal to the gate terminal to control the N-channel type MOSFET.