Patent ID: 7994737

Claim:
A drive circuit for controlling on/off state of a switching transistor of a DC/DC converter, comprising: a first resistor provided on a path of current flowing through a primary coil of a transformer connected to the switching transistor and of which one end is grounded; a first voltage comparator configured to compare a first detection voltage appearing at the other end of the first resistor with a predetermined first threshold voltage; a second resistor provided on a path of current flowing through a secondary coil of the transformer and of which one end is grounded; a level shifter configured to shift a second detection voltage appearing at a connection node between the second resistor and the secondary coil of the transformer in the positive direction; a second voltage comparator configured to compare the level-shifted second detection voltage shifted by the level shifter with a predetermined second threshold voltage; and a switching controller configured to turn off the switching transistor according to an output of the first voltage comparator and to turn on the switching transistor according to an output of the second voltage comparator; wherein the switching controller turns off the switching transistor when the first detection voltage exceeds the first threshold voltage and, turns on the switching transistor after lapse of predetermined delay time since the output voltage of the level shifter exceeds the second threshold voltage.