A DC-DC converter prevents through current from flowing in an output
transistor. A first transistor receives an input voltage. A second
transistor is connected to the first transistor. A comparator is
connected to the second transistor. The comparator detects current
flowing through a choke coil based on the potential difference between
two terminals of the second transistor to generate a switching control
signal for turning the second transistor on and off. The second
transistor and the comparator form an ideal diode. A control circuit of
the DC-DC converter generates an activation signal for turning the first
transistor on and off based on a pulse signal to keep an output voltage
constant. A through current prevention pulse generation circuit generates
a pulse signal for turning off the second transistor from before the
first transistor is turned on to after the first transistor is turned on.