Charge/discharge control circuit and battery device
View Patent ↗Provided is a battery device for controlling charge/discharge of a secondary battery by a single bidirectionally conductive field effect transistor, a charge/discharge control circuit with which a leakage current of the bidirectionally conductive field effect transistor is reduced to perform stable operation. The charge/discharge control circuit includes: a switch circuit for controlling a gate of the bidirectionally conductive field effect transistor based on an output of a control circuit for controlling the charge/discharge of the secondary battery; and two MOS transistors for preventing back-flow of a charge current and a discharge current. The first MOS transistor has a drain and a back gate which are connected to each other, and a source connected to a drain of the bidirectionally conductive field effect transistor. The second MOS transistor has a drain and a back gate which are connected to each other, and a source connected to a source of the bidirectionally conductive field effect transistor.
1. A charge and discharge control circuit for controlling charge and discharge of a secondary battery by a single bidirectionally conductive field effect transistor,
the charge and discharge control circuit comprising:
a control circuit connected to both ends of the secondary battery, and configured to determine whether the secondary battery is in a charge-inhibited or a discharge-inhibited state;
a switch circuit including a first terminal connected to a back gate of the bidirectionally conductive field effect transistor and a second terminal, for controlling a gate of the bidirectionally conductive field effect transistor based on an output of the control circuit, wherein the switch circuit comprises:
a P-channel MOS transistor including a gate connected to a first output terminal of the control circuit, a drain connected to the gate of the bidirectionally conductive field effect transistor, and a source connected to the second terminal; and
an N-channel MOS transistor including a gate connected to the first output terminal of the control circuit, a drain connected to the gate of the bidirectionally conductive field effect transistor and to the drain of the P-channel MOS transistor to provide a drain-to-drain connection of the P-channel MOS transistor and N-channel MOS transistor, wherein a voltage at the drain-to-drain connection is provided to the gate of the bidirectionally conductive field effect transistor, and a source connected to the first terminal;
a first transistor including a drain connected to a drain of the bidirectionally conductive field effect transistor, and a source and a back gate which are connected to the first terminal of the switch circuit; and
a second transistor including a drain connected to a source of the bidirectionally conductive field effect transistor, and a source and a back gate which are connected to the first terminal of the switch circuit.
2. A charge and discharge control circuit according to claim 1 , further comprising:
a first PN junction element connected between the drain and the source of the first transistor; and
a second PN junction element connected between the drain and the source of the second transistor.
3. A charge and discharge control circuit according to claim 1 , wherein:
the first transistor comprises an N-channel MOS transistor including a gate connected to a second output terminal of the control circuit; and
the second transistor comprises an N-channel MOS transistor including a gate connected to a third output terminal of the control circuit.
4. A charge and discharge control circuit according to claim 1 , wherein the control circuit includes a negative power supply terminal connected to the first terminal of the switch circuit.
5. A battery device, comprising:
a chargeable and dischargeable secondary battery;
a single bidirectionally conductive field effect transistor serving as a charge and discharge control switch, which is provided in a charge and discharge path of the chargeable and dischargeable secondary battery; and
the charge and discharge control circuit according to claim 1 , for monitoring a voltage of the chargeable and dischargeable secondary battery to open/close the charge and discharge control switch, to thereby control charge and discharge of the chargeable and dischargeable secondary battery.
6. A charge and discharge control circuit according to claim 1 , wherein,
the control circuit is configured to determine whether the secondary battery is in a charge-inhibited state or a discharge inhibited state, and
responsive to a determination that the secondary battery is in a charge-inhibited state, the control circuit is further configured to turn OFF the first transistor and turn ON the second transistor,
responsive to a determination that the secondary batter is in a discharge-inhibited state, the control circuit is further configured to turn ON the first transistor and turn OFF the second transistor.
7. A charge and discharge control circuit for controlling charge and discharge of a secondary battery by a single bidirectionally conductive field effect transistor, comprising:
a control circuit connected to both ends of the secondary battery, and configured to determine whether the secondary battery is in a charge-inhibited or a discharge-inhibited state;
a switch circuit including a first terminal connected to a back gate of the bidirectionally conductive field effect transistor and a second terminal, for controlling a gate of the bidirectionally conductive field effect transistor based on an output of the control circuit, wherein the switch circuit comprises:
a P-channel MOS transistor including a gate connected to a first output terminal of the control circuit, a drain connected to the gate of the bidirectionally conductive field effect transistor, and a source connected to the first terminal of the switch circuit; and
an N-channel MOS transistor including a gate connected to the first output terminal of the control circuit, a drain connected to the gate of the bidirectionally conductive field effect transistor and to the drain of the P-channel MOS transistor to provide a drain-to-drain connection of the P-channel MOS transistor and N-channel MOS transistor, wherein a voltage at the drain-to-drain connection is provided to the gate of the bidirectionally conductive field effect transistor, and a source connected to the second terminal of the switch circuit;
a first transistor including a drain connected to a drain of the bidirectionally conductive field effect transistor, and a source and a back gate which are connected to the first terminal of the switch circuit; and
a second transistor including a drain connected to a source of the bidirectionally conductive field effect transistor, and a source and a back gate which are connected to the first terminal of the switch circuit,
wherein, responsive to a determination that the secondary battery is in a charge-inhibited state, the control circuit is configured to turn OFF the first transistor and turn ON the second transistor, and
responsive to a determination that the secondary batter is in a discharge-inhibited state, the control circuit is configured to turn ON the first transistor and turn OFF the second transistor.
8. A charge and discharge control circuit according to claim 7 , wherein:
the first transistor comprises a P-channel MOS transistor including a gate connected to a second output terminal of the control circuit; and
the second transistor comprises a P-channel MOS transistor including a gate connected to a third output terminal of the control circuit.
9. A charge and discharge control circuit according to claim 7 , wherein the control circuit includes a positive power supply terminal connected to the first terminal of the switch circuit.