DC/DC converter, power supply circuit, and semiconductor device

Patent metadata

Field	Value
Publication number	US-9543835-B2
Application number	US-201414262965-A
Country	US
Kind code	B2
Filing date	Apr 28, 2014
Priority date	Jun 10, 2010
Publication date	Jan 10, 2017
Grant date	Jan 10, 2017

Abstract

Provided is a DC-DC converter with improved power conversion efficiency. A transistor which is incorporated in the DC-DC converter and functions as a switching element for controlling output power includes, in its channel formation region, a semiconductor material having a wide band gap and significantly small off current compared with silicon. The transistor further comprises a back gate electrode, in addition to a general gate electrode, and a back gate control circuit for controlling a potential applied to the back gate electrode in accordance with the output power from the DC-DC converter. The control of the potential applied to the back gate electrode by the back gate control circuit enables the threshold voltage to decrease the on-state resistance when the output power is high and to increase the off-state current when the output power is low.

First claim

The invention claimed is:

1. A semiconductor device comprising:
a DC-DC converter comprising:
a first transistor comprising a gate, a back gate and a channel formation region comprising an oxide semiconductor; and
a constant-voltage generation circuit electrically connected to one of a source and a drain of the first transistor;

wherein a potential applied to the back gate of the first transistor is controlled according to a magnitude of a power output from the constant-voltage generation circuit.

2. The semiconductor device according to claim 1 , wherein a threshold voltage of the first transistor is controlled by controlling the potential applied to the back gate of the first transistor.

3. The semiconductor device according to claim 2 ,
wherein the threshold voltage is shifted in a negative direction when the power output from the constant-voltage generation circuit exceeds a predetermined value, and
wherein the threshold voltage is shifted in a positive direction when the power output from the constant-voltage generation circuit is equal to or smaller than the predetermined value.

4. The semiconductor device according to claim 1 , wherein the DC-DC converter further comprises a second transistor comprising a channel formation region comprising silicon.

5. The semiconductor device according to claim 4 ,
wherein the second transistor is over a substrate,
wherein an insulating film is over the second transistor, and
wherein the first transistor is over the insulating film.

6. A semiconductor device comprising:
a DC-DC converter comprising:
a first transistor comprising a gate, a back gate and a channel formation region comprising an oxide semiconductor;
a diode;
a coil;
a capacitor; and
a back gate control circuit configured to control a potential applied to the back gate of the first transistor,

wherein one of a source and a drain of the first transistor is electrically connected to a first terminal of the DC-DC converter,
wherein the other of the source and the drain of the first transistor is electrically connected to a cathode of the diode,
wherein a first terminal of the coil is electrically connected to the cathode of the diode,
wherein a second terminal of the coil is electrically connected to a second terminal of the DC-DC converter,
wherein a first electrode of the capacitor is electrically connected to the second terminal of the DC-DC converter,
wherein an anode of the diode is electrically connected to a third terminal of the DC-DC converter,
wherein a second electrode of the capacitor is electrically connected to a fourth terminal of the DC-DC converter, and
wherein the back gate control circuit is electrically connected to the cathode of the diode.

7. The semiconductor device according to claim 6 , wherein the DC-DC converter is a step-down DC-DC converter.

8. The semiconductor device according to claim 6 , wherein the DC-DC converter further comprises a second transistor comprising a channel formation region comprising silicon.

9. The semiconductor device according to claim 8 ,
wherein the second transistor is over a substrate,
wherein an insulating film is over the second transistor, and
wherein the first transistor is over the insulating film.

10. A semiconductor device comprising:
a DC-DC converter comprising:
a first transistor comprising a gate, a back gate and a channel formation region comprising an oxide semiconductor;
a diode;
a coil;
a first capacitor; and
a back gate control circuit configured to control a potential applied to the back gate of the first transistor,

wherein a first terminal of the coil is electrically connected to a first terminal of the DC-DC converter,
wherein a second terminal of the coil is electrically connected to an anode of the diode,
wherein one of a source and a drain of the first transistor is electrically connected to the anode of the diode,
wherein a cathode of the diode is electrically connected to a second terminal of the DC-DC converter,
wherein a first electrode of the first capacitor is electrically connected to the second terminal of the DC-DC converter,
wherein the other of the source and the drain of the first transistor is electrically connected to a third terminal of the DC-DC converter,
wherein a second electrode of the first capacitor is electrically connected to a fourth terminal of the DC-DC converter, and
wherein the back gate control circuit is electrically connected to the cathode of the diode.

11. The semiconductor device according to claim 10 , wherein the DC-DC converter is a step-up DC-DC converter.

12. The semiconductor device according to claim 10 , further comprising:
a photodiode;
a switch;
a second capacitor; and
an inverter,
wherein a first terminal of the photodiode and a first electrode of the second capacitor is electrically connected to the first terminal of the DC-DC converter,
wherein a second terminal of the photodiode and a second electrode of the second capacitor is electrically connected to the third terminal of the DC-DC converter,
wherein the inverter is configured to convert a voltage between the second terminal and the fourth terminal of the DC-DC converter to an AC voltage.

13. The semiconductor device according to claim 10 , wherein the DC-DC converter further comprises a second transistor comprising a channel formation region comprising silicon.

14. The semiconductor device according to claim 13 ,
wherein the second transistor is over a substrate,
wherein an insulating film is over the second transistor, and
wherein the first transistor is over the insulating film.

Assignees

• Semiconductor Energy Lab

Inventors

• Takahashi Kei
• Koyama Jun
• Ishii Masato

Classifications

• H02M3/156 Primary

  with automatic control of output voltage or current, e.g. switching regulators · CPC title

• H02M3/155

  using semiconductor devices only · CPC title

• Y02B70/1483

  Cross-Sectional Technologies · mapped topic

• H01L27/1225

  Electricity · mapped topic

• H01L27/1251

  Electricity · mapped topic