Patent Application
20080003462
The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:
The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
The present invention is directed to a converter for supplying a desire output to a load from a fuel cell, e.g., a direct hydride fuel cell (DHFC), and a process for adjusting current from the fuel cell to maintain the fuel cell voltage within an optimum target range. According to the invention, the present converter saves power, i.e., consumes small power out, and is highly efficient, i.e., about 90%, which is not available in the market. Of course, it is understood that other fuel cell chemistries can be utilized without departing from the scope and spirit of the invention, e.g., PEM, DMFC, AFC, etc. A block diagram of converter 10 is illustrated in
The multiplied voltage from multiplier 14 is applied to boost converter 15 in order to boost the voltage to levels required by the load. Thus, depending upon the load, the output voltage of boost converter 15 is generally between 3.5 and 5.5 V. Converter 10 can be utilized to supply power for charging lithium ion (Li-ion) batteries for cell phones and the like. Boost converter 15, which can be formed, e.g., by a conventional integrated circuit chip, is provided to vary the output voltage, whereby input voltage Vcel can remain constant at about 0.6 V.
Boost converter 15 is coupled to a switch 16, e.g., a p-channel MOSFET, which is OFF at start up and remains closed until the voltage output of boost converter 15 is sufficient for the requirements of the powered device or charging device. Once the required voltage is achieved by boost converter 15, e.g., 5.4-5.5 V, switch 16 turns ON to supply this voltage as output voltage Vo of converter 10 to the load, i.e., a powered device or charging device.
A tune and shut down 17 receives input voltage Vcel, the output voltage of multiplier 14 and the output voltage of boost converter 15 in order to, if necessary, instruct control and driver 13 to shut down and tune boost converter 15. Tune and shut down 17 is also coupled to switch 16, which closes to connect converter 10 to the load Vo, e.g., a powered device such as a cell phone, laptop computer, PDA, chargers, etc., through a parallel capacitor. Tune and shut down 17 monitors input voltage Vcel and regulates it for output and current variations due to the load. Thus, tune and shut down 17 monitors the voltage levels to ensure that the voltage required by the load is attained before switch 16 is turned ON, and that input voltage Vcel is maintained constant while the requirements of the load vary. As a result, output power is almost constant during all charge cycles until the output voltage exceeds 5.4 V. Moreover, when the output voltage of multiplier 14 exceeds, e.g., 2.4 V at no load, tune and shut down 17 can instruct control and driver 13 to shut down the MOSFET gate pulses of multiplier 14 in order to save power. To ensure proper control, tune and shut down 17 receives a reference voltage of, e.g., 1.2 V from Vref 18, which is a sufficient voltage to tune boost converter 15, to shut down control and driver 13, and to activate switch 16.
Accordingly, converter 10 provides maximum allowable current to the load, but does not reduce output voltage below 3.2 V. However, the current from converter 10 is preferably limited so that not more than 1 W of power can be taken from the cell.
Thus, by way of example of operation, at steady state, the load on converter 10 is 1 W, and, during operation, Vcel drops to 0.6 V, is multiplied to 2.4 V and boosted to 5.5 V for the load. Converter 10 supplies the maximum current to the load based upon the load's requirements, and varies the boost voltage accordingly to ensure maximum current supply. However, if more than 1 W is drawn from the cell, voltage can be reduced until 3.2 V. Thereafter, the amount of current supplied will have to be adjusted while the boosted voltage remains at the minimum level of 3.2 V.
As is known, charging of Li-ion batteries is strictly regulated due to their instability, i.e., such batteries charged above 4.2 V or below 2.7 V can explode. For this reason, converter 10 supplies a minimum voltage of 3.2 V and a maximum voltage of 4.2 V to the batteries during charging. Of course, due to voltage drops within the phone, generally 4.8 V are supplied to the phone in order to charge the Li-ion battery.
A schematic illustration of the controller 20 of the instant invention is shown in
In a further exemplary embodiment, driver and multiplier circuit 24 can be formed by the multiplier circuit 70 shown in
The first phase is connected to the gates of MOSFETs Q1, Q2, Q6, Q7, and Q8 via inputs 1, 2, and 3, while the second phase is connected to the gates of MOSFETs Q3, Q4, Q5, Q9, and Q10 via inputs 4, 5, and 6. At steady state, capacitor C1 is charged to Vin, capacitor C2 is charged to 2Vin, capacitor C3 is charged to 3Vin, and Cout, i.e., the output capacitor, is charged to 4Vin, as required by the multiplier.
Multiplier circuit 70 operates as follows. When phase 1 is initiated, MOSFETs Q1 and Q2 are turned on to charge capacitor C1 to input voltage Vin, and when phase 2 is initiated, MOSFETs Q3, Q4, and Q5 are turned on to charge capacitor C2 to 2Vin (Vin+VC1). When phase 1 returns, MOSFETs Q6, Q7, and Q8 are turned on to charge capacitor C3 to 3Vin (Vin+VC2), and when phase 2 returns, MOSFETs Q9 and Q10 are turned on to charge capacitor Cout to 4Vin (Vin+VC3).
As shown in the schematic diagram of
It is contemplated that controller 20 can be integrated onto a single chip, which is either fixed or programmable, or into a VLSI module. Moreover, controller 20 can be built into or external to the fuel cell, and the chip on which controller 20 is integrated can include other controllers or converters.
By connecting the modules in parallel as shown in
It is noted that the circuits depicted in the Figures are for the purposes of illustration and should not be considered as limiting. Thus, is it to be understood that other circuits and arrangements for monitoring the standby mode/no load condition of a fuel cell and for drawing an intermittent pulse from the fuel cell in order to relieve membrane blocking in accordance with the invention can be utilized without departing from the scope and spirit of the invention.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
