DC converter circuit and power supply circuit

1. 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.

2. The DC converter circuit according to claim 1 ,

wherein the inductor is configured to generate electromotive force in accordance with a change in flowing current,

wherein the transistor is configured to control generation of the electromotive force in the inductor by being on or off,

wherein the rectifier is in a conducting state when the transistor is off, and

wherein the control circuit is configured to control on and off of the transistor.

3. The DC converter circuit according to claim 1 , wherein the rectifier comprises an oxide semiconductor with a hydrogen concentration of less than or equal to 5×10 19 atoms/cm 3 .

4. The DC converter circuit according to claim 1 , wherein the control circuit comprises an oxide semiconductor with a hydrogen concentration of less than or equal to 5×10 19 atoms/cm 3 .

5. The DC converter circuit according to claim 1 , further comprising a capacitor comprising:

a first electrode to which the voltage of the second terminal of the inductor is applied; and

a second electrode to which a low power supply voltage is applied.

6. The DC converter circuit according to claim 1 , further comprising:

a power storage device electrically connected to the DC converter circuit,

wherein the power storage device comprises at least one of a photoelectric conversion device, a lithium ion secondary battery, and a lithium ion capacitor.

7. The DC converter circuit according to claim 1 , wherein the inductor comprises a coil.

8. The DC converter circuit according to claim 1 , wherein the rectifier comprises a diode.

9. 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 to which an output voltage of the DC converter circuit is input as an input signal, and

wherein the hysteresis comparator compares the input signal and a reference voltage, and outputs a pulse signal whose pulse width is set in accordance with a comparison result,

wherein the hysteresis comparator outputs the 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,

wherein the channel formation region contains a hydrogen concentration of less than or equal to 5×10 19 atoms/cm 3 , 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.

10. The DC converter circuit according to claim 9 ,

wherein the inductor is configured to generate electromotive force in accordance with a change in flowing current,

wherein the transistor is configured to control generation of the electromotive force in the inductor by being on or off,

wherein the rectifier is in a conducting state when the transistor is off, and

wherein the control circuit is configured to control on and off of the transistor.

11. The DC converter circuit according to claim 9 , wherein the rectifier comprises an oxide semiconductor with a hydrogen concentration of less than or equal to 5×10 19 atoms/cm 3 .

12. The DC converter circuit according to claim 9 , wherein the control circuit comprises an oxide semiconductor with a hydrogen concentration of less than or equal to 5×10 19 atoms/cm 3 .

13. The DC converter circuit according to claim 9 , further comprising a capacitor comprising:

a first electrode to which the voltage of the second terminal of the inductor is applied; and

a second electrode to which a low power supply voltage is applied.

14. The DC converter circuit according to claim 9 , further comprising:

a power storage device electrically connected to the DC converter circuit,

wherein the power storage device comprises at least one of a photoelectric conversion device, a lithium ion secondary battery, and a lithium ion capacitor.

15. The DC converter circuit according to claim 9 , wherein the inductor comprises a coil.

16. The DC converter circuit according to claim 9 , wherein the rectifier comprises a diode.

17. The DC converter circuit according to claim 5 ,

wherein the transistor further comprises a source electrode and a drain electrode,

wherein one of the source electrode and the drain electrode outputs a voltage to the first terminal of the inductor and the other of the source electrode and the drain electrode is applied with an input voltage, and

wherein the rectifier comprises an anode to which the low power supply voltage is applied and a cathode which is connected to the one of the source electrode and the drain electrode of the transistor.

18. The DC converter circuit according to claim 13 ,

wherein the transistor further comprises a source electrode and a drain electrode,

wherein one of the source electrode and the drain electrode outputs a voltage to the first terminal of the inductor and the other of the source electrode and the drain electrode is applied with an input voltage, and

wherein the rectifier comprises an anode to which the low power supply voltage is applied and a cathode which is connected to the one of the source electrode and the drain electrode of the transistor.

19. The DC converter circuit according to claim 1 , wherein the channel formation region contains a hydrogen concentration of less than or equal to 5×10 19 atoms/cm 3 .