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A power converter that can be used in a vehicle equipped with an electrical motor provides power to both the electrical motor and other, auxiliary loads, such as a headlamp, that require a different voltage. The power converter includes a first DC power supply that generates a first voltage equivale

A power converter that can be used in a vehicle equipped with an electrical motor provides power to both the electrical motor and other, auxiliary loads, such as a headlamp, that require a different voltage. The power converter includes a first DC power supply that generates a first voltage equivalent to the voltage required by the auxiliary loads and a second DC power supply, connected in series with the first DC power supply, that generates a differential voltage, where the sum of the differential voltage and the first voltage is the voltage required to drive the electrical motor. A DC-DC converter is connected to the second power supply and converts the differential voltage to the voltage required to drive the auxiliary loads.

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What is claimed is: 1. A method of supplying power using a main DC power supply for generating a predetermined voltage to supply a first output voltage substantially equal to the predetermined voltage and a second output voltage lower than the predetermined voltage, comprising the steps of: connect

What is claimed is: 1. A method of supplying power using a main DC power supply for generating a predetermined voltage to supply a first output voltage substantially equal to the predetermined voltage and a second output voltage lower than the predetermined voltage, comprising the steps of: connecting a first DC power supply for generating the same voltage as the second output voltage in series to a second DC power supply for generating a differential voltage between the first output voltage and the voltage from the first DC power supply, thereby forming the main DC power supply, connecting a DC-DC converter to the second DC power supply; and stepping down the voltage output from the second DC power supply to produce the second output voltage by using the DC-DC converter. 2. A power converting apparatus for generating a first output voltage and a second output voltage lower than the first output voltage, comprising: a first DC power supply for generating the same voltage as the second output voltage; a second DC power supply, connected in series to the first DC power supply, for generating a voltage corresponding to a difference between the first output voltage and the voltage from the first DC power supply; and a DC-DC converter, connected to the second DC power supply, for converting the voltage from the second DC power supply to the second output voltage. 3. The power converting apparatus according to claim 2, wherein the DC-DC converter includes a polarity-inverting type DC-DC converter, the second DC power supply is connected to an input of the polarity-inverting type DC-DC converter, and the first DC power supply is connected to an output of the DC-DC converter. 4. The power converting apparatus according to claim 2, wherein the DC-DC converter includes an insulated DC-DC converter, the second DC power supply is connected to an input of the insulated DC-DC converter, and the first DC power supply is connected to an output of the DC-DC converter. 5. A power converting method of supplying a first output voltage substantially equal to a voltage of a main battery and a second output voltage lower than the voltage of the main battery, comprising the steps of: forming the main battery by connecting a first battery for generating the same voltage as the second output voltage in series to a second battery for generating a voltage corresponding to a difference between the first output voltage and the voltage of the first battery; producing the first output voltage by adding the voltages of the first and second batteries; connecting a charge power supply for generating a voltage lower than the voltage of the main battery to a step-up DC-DC converter; stepping up the voltage of the charge power supply using the step-up DC-DC converter to produce a differential voltage between the voltage of the main battery and the voltage of the charge power supply; and charging the main battery with a sum of the differential voltage and the voltage of the charge power supply. 6. A power converting apparatus for generating a first DC voltage and a second DC voltage lower than the first DC voltage, comprising: a first battery for generating the same voltage as the second DC voltage; a second battery, connected in series to the first battery, for generating a differential voltage between the first DC voltage and the voltage of the first battery; and a polarity-inverting type DC-DC converter having an input connected to the second battery and an output connected to the first battery, the DC-DC converter including a first switching element and a first diode connected in parallel to each other, a second switching element connected between the output of the DC-DC converter and the first battery, and a second diode connected in parallel to the second switching element. 7. The power converting apparatus according to claim 6, wherein the first switching element and the first diode are a first MOSFET and the second switching element and the second diode are a second MOSFET. 8. A power converting apparatus for a motor driven vehicle, comprising: a main battery assembly, connected between a high-potential power supply and a low-potential power supply, for generating a main output voltage for driving the vehicle motor, the main battery assembly including a first battery cell for generating a first voltage lower than the main output voltage, and a second battery cell, connected in series to the first battery cell, for generating a second voltage corresponding to a difference between the main output voltage and the first voltage; and a DC-DC converter, connected to the second battery cell, for converting the second voltage to a low voltage substantially equal to the first voltage. 9. The power converting apparatus according to claim 8, further comprising: a first voltage sensor for detecting the main output voltage, and a second voltage sensor for detecting the low voltage; and wherein the DC-DC converter includes: a switching element responsive to a control signal; an inductance connected in series to the switching element; and a control circuit, connected to the switching element and the first and second voltage sensors, for supplying the switching element with the control signal for controlling ON and OFF actions of the switching element based on detection signals from the first and second voltage sensors. 10. The power converting apparatus according to claim 9, wherein the switching element includes a MOSFET. 11. The power converting apparatus according to claim 9, wherein the control circuit includes: a triangular wave oscillator for generating a triangular wave signal having a predetermined cycle; and a comparator for comparing a difference between detection signals from the first and second voltage sensors with the triangular wave signal and generating a pulse signal according to a comparison result, wherein the control circuit sends the pulse signal as the control signal to the switching element. 12. The power converting apparatus according to claim 11, wherein the control circuit controls a ratio of an ON time of the switching element to an OFF time thereof by changing a pulse width of the pulse signal, thereby adjusting a level of the low voltage. 13. The power converting apparatus according to claim 11, wherein the comparator generates a high-level pulse signal when the difference between the detection signals from the first and second voltage sensors is greater than the triangular wave signal and generates a low-level pulse signal when the difference between the detection signals from the first and second voltage sensors is smaller than the triangular wave signal.