Method and semiconductor device for monitoring battery voltages

A method of monitoring voltages of a plurality of unit batteries having respective positive and negative terminals, the unit batteries being connected in series, the method comprising:

• using a plurality of switching elements to select one of the unit batteries and output a first voltage obtained from the positive terminal of the selected unit battery and a second voltage obtained from the negative terminal of the selected unit battery;
• using a first buffer amplifier having a first high-impedance input terminal for receiving the first voltage from the selector switch and blocking flow of current from the selector switch to output a voltage corresponding to the first voltage from a first output terminal;
• using a second buffer amplifier having a second high-impedance input terminal for receiving the second voltage from the selector switch and blocking flow of current from the selector switch to output a voltage corresponding to the second voltage from a second output terminal;
• and
• using a level shifter connected to the first output terminal of the first buffer amplifier and the second output terminal of the second buffer amplifier to output a shifted voltage corresponding to a difference between the first voltage and the second voltage.

A semiconductor device for receiving a first potential of first terminals of a plurality of battery cells being connected in series and a second potential of second terminals of a plurality of the battery cells through a filter having capacitor means, the semiconductor device detecting a voltage of a selected battery cell that is selected from a plurality of the battery cells on basis of a difference of the first potential of the first terminal and the second potential of the second terminal of the selected battery cell, comprising:

• a first cell selection switch connected to the first terminal of each of a plurality of the battery cells through the filter, for outputting the first potential of the first terminal of the selected battery cell;
• a second cell selection switch connected to the second terminal of each of a plurality of the battery cells through the filter, for outputting the second potential of the second terminal of the selected battery cell;
• a first buffer amplifier including a first transistor, wherein the first potential of the first terminal of the selected battery cell is input from the first cell selection switch to a gate of the first transistor and a first voltage based on the first potential of the first terminal is output from the first buffer amplifier;
• a second buffer amplifier including a second transistor, wherein the second potential of the second terminal of the selected battery cell is input from the second cell selection switch to a gate of the second transistor and a second voltage based on the second potential of the second terminal is output from the second buffer amplifier;
• and
• a difference output means for outputting a first differential potential that is a difference between the first voltage and the second voltage.