BACKFLOW PREVENTION CIRCUIT, STEP-DOWN DC/DC CONVERTER USING THE SAME, CONTROL CIRCUIT FOR THE SAME, CHARGING CIRCUIT, AND ELECTRONIC APPARATUS

PROBLEM TO BE SOLVED: To prevent a backflow of current from a source to a drain while keeping characteristics of an N channel MOSFET intact.SOLUTION: A backflow prevention circuit 30 prevents a backflow current from a source to a drain of a switching transistor M1 comprising an N channel MOSFET. A first switch SW21 is disposed between a back gate of the switching transistor M1 and a ground terminal. A second switch SW22 is disposed between the back gate of the switching transistor M1 and the source thereof. A back gate controller 32 compares an input voltage Vand an output voltage Vof a DC/DC converter, and (1) turns off the first switch SW21 and turns on the second switch SW22 when the input voltage Vis the higher and (2) turns on the first switch SW21 and turns off the second switch SW22 when the input voltage Vis the lower.