Patent ID: 8922182

Claim:
A DC converter circuit comprising: an inductor comprising a first terminal and a second terminal; a transistor electrically connected to the first terminal of the inductor, the transistor comprising: an oxide semiconductor layer including a channel formation region over a substrate, the oxide semiconductor layer including indium and zinc; and a gate insulating layer adjacent to the oxide semiconductor layer; a rectifier electrically connected to the first terminal of the inductor; and a control circuit electrically connected to the transistor, wherein the control circuit comprises a hysteresis comparator which outputs a pulse signal to a gate of the transistor, wherein a duty ratio of the pulse signal is set in accordance with a voltage of the second terminal of the inductor, and wherein the hysteresis comparator comprises: a first comparator to which a first reference voltage and the voltage of the second terminal of the inductor is applied; a second comparator to which the voltage of the second terminal of the inductor and a second reference voltage is applied; a first inverter to which a voltage of the first comparator is applied; a second inverter to which a voltage of the second comparator is applied; a first NOR gate to which a voltage of the first inverter is applied; and a second NOR gate to which a voltage of the second inverter is applied, wherein the first NOR gate outputs a voltage to the gate of the transistor, and wherein the second NOR gate outputs a voltage to the first NOR gate.