Cell voltage detecting system and drive voltage maintaining method

A method of maintaining a drive voltage for a cell voltage detector that detects voltages of cells in a fuel cell connected in series, using voltages of the fuel cell and an auxiliary power supply, wherein the auxiliary power supply comprises a DC-DC converter, wherein the voltage detector that detects voltages of the cells and includes positive and negative drive terminals, and wherein the voltage detector comprises a multiplexer for selecting a positive terminal of one of the cells in the fuel cell to detect a potential of the selected positive terminal and applying the detected potential to a differential amplifier, wherein the differential amplifier calculates a voltage differential between the voltage potential of the selected positive terminal of the cell and a reference potential and multiplies the difference by a predetermined value, the method comprising the steps of:

• supplying the voltage of the fuel cell to the cell voltage detector when the voltage of the fuel cell is greater than the voltage of the auxiliary power supply;
• supplying the voltage of the auxiliary power supply to the cell voltage detector when the voltage of the fuel cell is not greater than the voltage of the auxiliary power supply;
• and
• determining the voltage of the auxiliary power supply to be equal to or greater than a minimum voltage necessary for driving the voltage detector between positive and negative terminals thereof,
• wherein the DC-DC converter comprises a plurality of isolated DC-DC converting devices that belong to respective blocks, each of the isolated DC-DC converting devices including primary and secondary sides isolated, including the negative terminal of the DC-DC converter on the secondary side, and generating the voltage between the positive and negative terminals on the secondary side;
• wherein the voltage detector comprises a plurality of voltage detecting devices that belong to respective blocks, each detecting voltages of the cells in the block and including the positive and negative drive terminals, and
• wherein the negative terminal on the secondary side of the isolated DC-DC converting device, and the negative drive terminal of the voltage detecting device in the block are equalized to a potential of the negative terminal of the block, and the primary side in each block is connected to the auxiliary power supply, and
• when an output voltage of the fuel cell is greater than the minimum voltage, supplying the voltage of the fuel cell to the voltage detector and when the voltage of the fuel cell is not greater than the minimum voltage, supplying the voltage of the auxiliary power supply to the voltage detector, comprising:
• providing a first diode connected to a positive terminal of the fuel cell and a positive drive terminal of the voltage detector in such a direction as to allow a current to flow therethrough from the positive terminal of the fuel cell to the positive drive terminal of the voltage detector;
• providing a second diode connected to the positive terminal of the auxiliary power supply and the positive drive terminal in such a direction so as to allow a current to flow therethrough from the positive terminal of the auxiliary power supply to the positive drive terminal;
• and
• connecting a negative terminal of a last cell in series of the fuel cell, a negative drive terminal of the voltage detector, a negative terminal of the auxiliary power supply, a negative drive terminal of the multiplexer and the reference potential of the differential amplifier to each other to have a same potential.