Electronic device, and system for DC voltage conversion

• US 7,816,812 B2
• Filed: 11/20/2007
• Issued: 10/19/2010
• Est. Priority Date: 01/30/2007
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Yokota, Koichi, Nakashima, Yoshiyasu, Kazama, Satoshi
• Primary Examiner(s): Fureman; Jared J
• Assistant Examiner(s): AMAYA, CARLOS DAVID
• Application Number:
  US11/986,081
• Publication Number:
  US 20080179955A1
• Time in Patent Office: 1,064 Days
• Field of Search: 307/25, 307 44- 45, 307/48, 307/64, 307/66
• US Class Current: 307/44
• CPC Class Codes: B60L 58/30 for monitoring or controlling fuel cells
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence
• CPC Class Codes: Y02T 90/40 Application of hydrogen technology to transportation, e.g. using fuel cells

Abstract

An electronic device includes: a first input terminal to which a first DC supply voltage of a fuel cell system having a controllable supply voltage is provided; a second input terminal to which a second DC supply voltage of a rechargeable secondary battery is provided; a DC voltage conversion circuit which receives the first and second DC supply voltages from the first and second input terminals, and supplies a current of a desired voltage to a load; a charging circuit which receives the first DC supply voltage from the first input terminal, and supplies a DC supply voltage for charging to the second input terminal; and a control circuit which determines a desired value of the first DC supply voltage in accordance with a value of the second DC supply voltage of the secondary battery, and provides the determined desired value to the fuel cell system.

Claims

1. An electronic device comprising:

a first input terminal to which a first DC supply voltage of a fuel cell system having a controllable supply voltage is provided;

a second input terminal to which a second DC supply voltage of a rechargeable battery is provided;

a DC voltage conversion circuit for receiving the first and second DC supply voltages from the first and second input terminals, and supplying a current of a desired DC voltage to a load, wherein a power efficiency of voltage conversion of the DC voltage conversion circuit becomes higher as a difference between the received DC supply voltage and the desired DC voltage becomes lower;

a charging circuit for receiving the first DC supply voltage from the first input terminal, and supplying a DC supply voltage for charging to the second input terminal; and

a control circuit for receiving, from the rechargeable battery, a value of the second DC supply voltage of the rechargeable battery, and determining a desired value of the first DC supply voltage to be a sum of the received value of the second DC supply voltage of the rechargeable battery and a given value, and providing the determined desired value to the fuel cell system.

2. The electronic device according to claim 1, further comprising a load state determination unit for determining a state of the load,

wherein the control circuit determines the desired value of the first DC supply voltage in accordance with the received value of the second DC supply voltage of the rechargeable battery and the state of the load determined by the load state determination unit.

3. The electronic device according to claim 1, further comprising a load state determination unit for determining a state of the load,

wherein the control circuit looks up a table which defines a relation between the state of the load and the given value, and the control circuit determines the given value so that the given value corresponds to the state of the load in the table based on the state of the load determined by the load state determination unit.

4. The electronic device according to claim 3, wherein the state of the load is a CPU occupancy.

5. The electronic device according to claim 3, wherein the state of the load is a load power in the electronic device.

6. The electronic device according to claim 1,

wherein when the rechargeable battery is not full and can be charged by the first DC supply voltage of the fuel cell system, the control circuit determines the desired value of the first DC supply voltage to be a value higher than a voltage required for charging the rechargeable battery.

7. The electronic device according to claim 1,

wherein when the rechargeable battery is not full and can be charged by the first DC supply voltage of the fuel cell system, the control circuit determines the desired value of the first DC supply voltage to be a value not less than a maximum DC supply voltage of the rechargeable battery.

8. The electronic device according to claim 1,

wherein the control circuit allows the charging circuit to start charging the rechargeable battery when a remaining power of the rechargeable battery is lower than a given percentage of full remaining power of the rechargeable battery.

9. The electronic device according to claim 1, wherein

a communication between the fuel cell system and the control circuit is performed through the first input terminal in a superimposed manner.

10. The electronic device according to claim 1, wherein

a communication between the fuel cell system and the control circuit is performed by wireless communication.

11. A DC voltage conversion system comprising:

a first input terminal to which a first DC supply voltage of a fuel cell system having a controllable supply voltage is provided;

a second input terminal to which a second DC supply voltage of a rechargeable battery is provided;

a DC voltage conversion circuit for receiving the first and second DC supply voltages from the first and second input terminals, and supplies a current of a desired DC voltage to a load, wherein a power efficiency of voltage conversion of the DC voltage conversion circuit becomes higher as a difference between the received DC supply voltage and the desired DC voltage becomes lower;

a charging circuit for receiving the first DC supply voltage from the first input terminal, and supplies a DC supply voltage for charging to the second input terminal; and

a control circuit for receiving, from the rechargeable battery, a value of the second DC supply voltage of the rechargeable battery, and determining a desired value of the first DC supply voltage to be a sum of the received value of the second DC supply voltage of the rechargeable battery and a given value, and providing the determined desired value to the fuel cell system.