Selector circuit

• US 8,044,639 B2
• Filed: 10/23/2008
• Issued: 10/25/2011
• Est. Priority Date: 10/23/2007
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Yokomizo, Ichiro, Tamegai, Yoichi, Nakahara, Hironori
• Primary Examiner(s): Tso; Edward
• Assistant Examiner(s): Ramadan; Ramy
• Application Number:
  US12/256,797
• Publication Number:
  US 20090102427A1
• Time in Patent Office: 1,097 Days
• Field of Search: 320/103, 320/138, 320/163, 320/164, 307/43
• US Class Current: 320/138
• CPC Class Codes: H02J 2207/40 adapted for charging from various sources, e.g. AC, DC or multivoltage
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters

Abstract

A selector circuit outputs one of a first input voltage or a second input voltage via an output terminal. A first transistor and a second transistor are provided in series between a first input terminal and the output terminal. A third transistor and a fourth transistor are provided in series between a second input terminal and the output terminal. A control unit controls the ON/OFF operations of the first transistor through the fourth transistor. The back gates of the first transistor and the second transistor are connected such that at least one body diode of the first transistor M1 and at least one body diode of the second transistor are arranged in opposing directions. The back gates of the third transistor and the fourth transistor are connected in the same way.

Claims

1. A selector circuit including:

a first input terminal via which a first input voltage is input from an external source;

a second input terminal via which a second input voltage is input from another external source;

an output terminal which outputs one of the first input voltage or the second input voltage;

a first MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and a second MOSFET, which are provided in series between the first input terminal and the output terminal;

a third MOSFET and a fourth MOSFET, which are provided in series between the second input terminal and the output terminal; and

a control unit which controls the ON/OFF operations of the first MOSFET and second MOSFET pair and the third MOSFET and fourth MOSFET pair,

wherein a connection of a back gate of the first MOSFET and a connection of a back gate of the second MOSFET are formed such that at least one body diode of the first MOSFET and at least one body diode of the second MOSFT are arranged in opposing directions,

wherein a connection of a back gate of the third MOSFET and a connection of a back gate of the fourth MOSFET are formed such that at least one body diode of the third MOSFET and at least one body diode of the fourth MOSFET are arranged in opposing directions; and

wherein the control unit comprises;

a first charge pump circuit configured such that, when an instruction is given to switch the first and second MOSFETs to the ON state, the first charge pump circuit steps up the first input voltages and outputs the first input voltage thus stepped up to the gates of the first and second MOSFETs; and

a second charge pump circuit configured such that, when an instruction is given to switch the third and fourth MOSFETs to the ON state, the second charge pump circuit steps up the second input voltage, and outputs the second input voltage thus stepped up to the gates of the third and fourth MOSFETs.

2. A selector circuit according to claim 1, wherein, in a case in which the first input voltage is within a predetermined first voltage range, the control unit switches the first and second MOSFETs to the ON state,

and wherein, in a case in which the first input voltage deviates from the first voltage range, and in a case in which the second input voltage is within a predetermined second voltage, the control unit switches the third and fourth MOSFETs to the ON state.

3. A selector circuit according to claim 2, wherein each of the upper limit level of the first voltage range and the upper limit level of the second voltage range is set to a threshold voltage for overvoltage protection.

4. A selector circuit according to claim 2, wherein each of the lower limit level of the first voltage range and the lower limit level of the second voltage range is set to a low-voltage lockout voltage.

5. A selector circuit according to claim 1, wherein each of the first MOSFET through the fourth MOSFET is an N-channel MOSFET.

6. A selector circuit according to claim 5, wherein the first charge pump circuit performs a voltage step-up operation using the gate capacitance of the first MOSFET and the gate capacitance of the second MOSFET as output capacitors,

and wherein the second charge pump circuit performs a voltage step-up operation using the gate capacitance of the third MOSFET and the gate capacitance of the fourth MOSFET as output capacitors.

7. A selector circuit according to claim 1, wherein, in a case in which the temperature exceeds a predetermined threshold value, the control unit switches the first MOSFET through the fourth MOSFET to the OFF state.

8. A selector circuit according to claim 1, which is integrally formed on a single semiconductor substrate.

9. An electronic device including:

a first connector which allows a first external power supply to be detachably connected;

a second connector which allows a second external power supply to be detachably connected;

a secondary battery;

a selector circuit according to claim 1, configured such that the first connector is connected to the first input terminal, and such that the second connecter is connected to the second terminal; and

a charging circuit which charges the secondary battery using the output voltage of the selector circuit.