Patent ID: 7609039

Claim:
A DC-DC converter comprising: a first transistor receiving input voltage; a second transistor coupled in series to the first transistor; and a controller controlling the first transistor and the second transistor to select either one of a first mode in which the DC-DC converter operates as a switching regulator and a second mode in which the DC-DC converter operates as a linear regulator, wherein output voltage and output current changing in accordance with the output voltage are generated through a node between the first transistor and the second transistor, and wherein the controller includes a mode control circuit which monitors the input voltage, the output voltage, and the output current, the mode control circuit including: a multiplier which determines a load current in which efficiency of the switching regulator and efficiency of the linear regulator are substantially the same based on a consumption current consumed in the controller, a monitored input voltage and a monitored output voltage, and a comparator which compares the load current with a monitored output current, and generates a mode control signal for selecting the one of the first mode and the second mode based on a comparing result.