1. Field of the Invention
The present invention provides a voltage regulator for a direct current (DC) power supply, and more particularly, a voltage regulator for stabilizing an output voltage of a fuel cell.
2. Description of the Prior Art
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When the AC power source 120 is not accessible, the AC/DC converter 110 cannot provide the DC power to the conventional battery 130 and the portable electronic device 140. Meanwhile, the portable electronic device 140 only operates by discharging the power stored in the conventional battery 130.
Generally, the ability of the conventional battery 130 to discharge has a ceiling. That is, the discharging period of the conventional battery 130 is limited. For example, the discharging period of a lithium cell for a notebook computer is about two hours. Therefore, when the portable electronic device 140 has to operate for more than two hours, the conventional battery 130 cannot provide enough power to the portable electronic device 140, which is a great inconvenience.
The present invention provides a voltage regulator of a DC power supply comprising a current-limiting circuit coupled to an output end of the DC power supply for limiting a current output from the DC power supply, and a storage circuit coupled between the current-limiting circuit and a ground end of the DC power supply for storing power output from the DC power supply.
The present invention further provides a fuel cell comprising a power output end for providing power, a ground end, a current-limiting circuit coupled to the power output end of the fuel cell for limiting a current from the power output end, and a storage circuit coupled between the current-limiting circuit and the ground end for storing the power output from the fuel cell.
The present invention further provides a portable electronic device using a fuel cell. The fuel cell comprises a power output end for providing power, a ground end, a current-limiting circuit coupled to the power output end of the fuel cell for limiting a current from the fuel cell, and a power-storing circuit coupled between the current-limiting circuit and the ground end of the fuel cell for storing the power. The portable electronic device is coupled between the power output end of the fuel cell and the ground end of the fuel cell for receiving a power regulated by the power-storing circuit.
The present invention further provides a portable electronic device using a fuel cell. The fuel cell comprises a power output end for providing power, and a ground end. The portable electronic device is coupled between the power output end of the fuel cell and the ground end of the fuel cell for receiving the power of the fuel cell. The portable electronic device comprises a current-limiting circuit coupled to the power output end of the fuel cell for limiting a current from the fuel cell, and a storage circuit coupled between the current-limiting circuit and the ground end of the fuel cell for storing the power output from the fuel cell.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
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The fuel cell 210 can be a direct methanol fuel cell or a proton exchange membrane fuel cell. The direct methanol fuel cell is characterized by high power density and ease of transport. When the power stored in the direct methanol fuel cell runs out, a user can add methyl alcohol, and then the direct methanol fuel cell can continue outputting power.
One drawback of the direct methanol fuel cell is unstable output power which is hard for the portable electronic device 140 and the conventional battery 130 to use. Therefore, another voltage regulator 220 is necessary to stabilize the output power of the direct methanol fuel cell.
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Because the power consumption of the portable electronic device 140 increases as the number of tasks the portable electronic device 140 is operating on increases, and the fuel cell 210 cannot provide stable power in time to the portable electronic device 140 when the portable electronic device 140 suddenly becomes busy, the storage capacitor C1 is disposed between the fuel cell 210 and the portable electronic device 140. Therefore, when the portable electronic device 140 is not busy, the storage capacitor C1 can store power, and when the portable electronic device 140 is abruptly busy, the storage capacitor C1 can release the stored power to the portable electronic device 140 and maintain the voltage V2 shown in
Before the fuel cell 210 is coupled to the voltage regulator 220, the storage capacitor C1 is completely discharged. Once the fuel cell 210 is coupled to the voltage regulator 220, the storage capacitor C1 starts charge and sink current. To prevent the output voltage of the fuel cell 210 from being lowered because the storage capacitor C1 sinks the current, the voltage regulator 220 is designed with a resistor R1 between the output end of the fuel cell 210 and the storage capacitor C1 for limiting the current of the fuel cell 210 and preventing the components of the fuel cell 210 and the voltage regulator 220 from being damaged.
After the storage capacitor C1 has charged for a while, the storage capacitor C1 sinks only a little current. Therefore, we do not have to limit the output current of the fuel cell 210. In other words, the resistor R1 becomes useless and wastes power. Consequently, the voltage regulator 220 of the present invention comprises a switch S1 across the resistor R1 for shorting the ends of the resistor R1 after the storage capacitor C1 is charged so that the current passes through the switch S1 rather than the resistor R1. In this way, the resistor R1 does not waste power.
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If the switch S1 is realized with a MOS (metal oxygen semiconductor, MOS) transistor, the predetermined value is the threshold voltage of the MOS transistor.
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The voltage regulation circuit 530 can be realized with a switching regulator, a linear regulator, or a capacitor. Please refer to
The portable electronic device 140 can be realized with a notebook PC, a personal digital assistant, or any electronic device that is easy to carry. Also, in
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Number | Date | Country | Kind |
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95136681 A | Oct 2006 | TW | national |
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3757200 | Cohen | Sep 1973 | A |
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6377033 | Hsu | Apr 2002 | B2 |
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1082213 | Feb 1994 | CN |
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1770526 | May 2006 | CN |
Number | Date | Country | |
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20080079412 A1 | Apr 2008 | US |