Voltage sensing circuit and battery pack monitoring system
A voltage sensing circuit includes a difference voltage sensing circuit and a leakage cancelling circuit. The difference voltage sensing circuit includes two sensing capacitors, a first sensing switch, a second sensing switch, and a third sensing switch. A first group including the first sensing switch and the second sensing switch and a second group including the third sensing switch are complementally turned on and turned off. The leakage cancelling circuit includes two compensation capacitors, a first compensation switch, a second compensation switch, and a third compensation switch. A third group including the first compensation switch and the second compensation switch and a fourth group including the third compensation switch are complementally turned on and turned off.
1. A voltage sensing circuit sensing a voltage difference between two input nodes, comprising:
a difference voltage sensing circuit sensing the voltage difference by sampling voltages of the two input nodes; and
a leakage cancelling circuit generating a compensation charge that is used to compensate a charge leaked from the two input nodes due to an operation of the difference voltage sensing circuit, by using a cancelling voltage, wherein
the difference voltage sensing circuit has a differential configuration, where two sensing capacitors that are a pair, a first sensing switch that connects and disconnects a wiring between one of the two sensing capacitors and one of the two input nodes, a second sensing switch that connects and disconnects a wiring between the other one of the two sensing capacitors and the other one of the two input nodes, and a third sensing switch that connects and disconnects a wiring between the two sensing capacitors are arranged,
a first group including the first sensing switch and the second sensing switch and a second group including the third sensing switch are complementally turned on and turned off,
the leakage cancelling circuit has a differential configuration, where two compensation capacitors that are a pair, a first compensation switch that connects and disconnects a wiring between one of the two compensation capacitors and one of the two input nodes, a second compensation switch that connects and disconnects a wiring between the other one of the two compensation capacitors and the other one of the two input nodes, and a third compensation switch that connects and disconnects a wiring between the two compensation capacitors are arranged, and
a third group including the first compensation switch and the second compensation switch and a fourth group including the third compensation switch are complementally turned on and turned off.
2. The voltage sensing circuit according to claim 1 , wherein
when the cancelling voltage is expressed as ΔVd, a capacity of one of the sensing capacitors is expressed as Csh, a capacity of one of the compensation capacitors is expressed as Clc, and a voltage difference that is a difference between voltages of the two input nodes, the cancelling voltage ΔVd and the capacity Clc of one of the compensation capacitors are set based on a formula that ΔVd=((Csh+Clc)/(2×Clc))×ΔVi.
3. The voltage sensing circuit according to claim 1 , wherein
the two sensing capacitors are in a pair state.
4. The voltage sensing circuit according to claim 1 , wherein
the two sensing capacitors are in a pair state.
5. The voltage sensing circuit according to claim 1 , wherein
the leakage cancelling circuit includes a switch circuit that charges and discharges the two compensation capacitors by using the cancelling voltage, and
the switch circuit includes two switches that are a first circuit switch and a second circuit switch which connect and disconnect a wiring between one of two cancelling nodes to which the cancelling voltage is applied and the two compensation capacitors, and two switches that are a third circuit switch and a fourth circuit switch which connect and disconnect a wiring between the other one of the tow cancelling nodes and the two compensation capacitors.
6. The voltage sensing circuit according to claim 1 , wherein
the leakage cancelling circuit directly uses a sensing voltage outputted from the difference voltage sensing circuit as the cancelling voltage.
7. The voltage sensing circuit according to claim 1 , wherein
the leakage cancelling circuit uses a voltage in response to a sensing voltage outputted from the difference voltage sensing circuit as the cancelling voltage.
8. The voltage sensing circuit according to claim 1 , wherein
the leakage cancelling circuit executes a correction of a sensing voltage outputted from the difference voltage sensing circuit, and then uses a voltage that is corrected as the cancelling voltage.
9. The voltage sensing circuit according to claim 1 , further comprising:
a control circuit controlling an operation of the difference voltage sensing circuit and an operation of the leakage cancelling circuit, wherein
the control circuit controls the first sensing switch, the second sensing switch, the third sensing switch, the first compensation switch, the second compensation switch, and the third compensation switch, so as to control the difference voltage sensing circuit and the leakage cancelling circuit to operate in phases opposite to each other.
10. The voltage sensing circuit according to claim 1 , further comprising:
a control circuit controlling an operation of the difference voltage sensing circuit and an operation of the leakage cancelling circuit, wherein
the control circuit controls the first sensing switch, the second sensing switch, the third sensing switch, the first compensation switch, the second compensation switch, and the third compensation switch, so as to control the difference voltage sensing circuit and the leakage cancelling circuit to operate in phases same as each other.
11. The voltage sensing circuit according to claim 1 , further comprising:
a control circuit controlling an operation of the difference voltage sensing circuit and an operation of the leakage cancelling circuit, wherein
the control circuit controls the first sensing switch, the second sensing switch, the third sensing switch, the first compensation switch, the second compensation switch, and the third compensation switch, so as to execute the operation of the leakage cancelling circuit in plural cycles while executing the operation of the difference voltage sensing circuit in one cycle.
12. A battery pack monitoring system monitoring a voltage of each of battery cells that constitute a battery pack, the battery pack monitoring system comprising:
the voltage sensing circuit according to claim 1 ;
a filter arranged at a position between voltage terminals of each of the battery cells and the two input nodes of the voltage sensing circuit, the voltage terminals including a high voltage terminal and a low voltage terminal; and
an A-D converter converting a sensing voltage outputted from the difference voltage sensing circuit into a digital data, wherein
the voltage sensing circuit senses the voltage difference by using an oversampling from a sensing target that is the battery cells.