Title of Invention	RECTIFIER DEVICE
Abstract	In a rectifier device 2 designed for full-wave rectification of output power of an AC generator 1 mounted on a motor vehicle, schottoky diodes each based on silicon carbide are used as rectifier semiconductor elements for the full-wave rectification of the AC power as generated.

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TECHNICAL FIELD The present invention relates to a rectifier device which is employed in an AC generator for a motor vehicle and in which Schottoky barrier diodes are used as semiconductor rectifier elements with a view to decreasing an amount of heat generation and mitigating influence of noise to electronic apparatus/instruments by suppressing surge voltage making appearance upon current commutation. BACKGROUND TECHNIQUE Figure 7 is a view showing a configuration of a prior art or conventional AC generator for a motor vehicle. The conventional system is comprised of an AC generator 1 constituted by a field coil 102 driven by an engine (internal combustion engine) of a motor vehicle (not shown) for generating a rotating magnetic field and an armature winding 101 for generating as the output voltage an AC voltage under the action of the rotating magnetic field as generated, a rectifier device 2 for rectifying the voltage generated by the AC generator 1 to thereby supply the rectified power to a battery 4 or an electric load 6 from a main terminal 201, a voltage regulator 3 for regulating or adjusting the voltage generated by the AC generator 1 by controlling an exciting current of the field coil 102 in dependence on an terminal voltage .of the battery 4 or the electric load 6 to which the terminal voltage is supplied, a load switch 7 for turning on/off a path for supplying the voltage generated by the AC generator 1 to the electric load, and a key switch 5 for allowing the exciting current to flow to the field coil 102 from the battery 4 by way of the voltage regulator 3 upon starting of the internal combustion engine. Further, the rectifier device 2 is provided with an auxiliary output terminal 203 for outputting an exciting current to the field coil 102 to allow the AC generator 1 to generate an AC power through self-excitation. Figure 8 is a diagram showing a configuration of a conventional AC generator for a motor vehicle in which the rectifier device 2 is provided with no auxiliary terminal. With regard to the other respects, this AC generator system is same as that shown in Fig. 7. Further, prior art AC generator systems for a motor vehicle shown in Figs. 9 and 10 are each equipped with a rectifier device of neutral point diode type. In other respects, the structures of these AC generator systems are essentially same as those shown in Figs. 7 and 8. Figure 11 shows a structure of a pn-junction diode implemented as a silicon diode to constitute a semiconductor rectifying element employed in the rectifier device 2. The pn-junction diode is implemented by bonding together P-type semiconductor made of silicon and an N-type semiconductor of silicon, wherein an electrode El is mounted on the P-type semiconductor to serve as an anode terminal A while an electrode E2 is mounted on the N-type semiconductor to serve as a cathode terminal K. Figure 12 shows a forward voltage drop characteristic versus a forward current in a pn-junction diode on the assumption, by way of example, that the forward voltage drop of the pn-junction diode is 1.0 V (volt) when the maximum output current of the AC generator 1 is 90 A (ampere). However, in case the pn-junction diodes are employed in the rectifier device 2 for the AC generator 1, there occurs power loss of 180 W (watt) = 90 W + 90 W as a total sum of power loss of 90W - 90A x 1.0 in the diode array of positive polarity and power loss of 90W = 90A.x 1.0 in the diode array of negative polarity when the AC generator 1 outputs the maximum current. Such being the circumstances, the rectifier device 2 has to be provided with a heat sink of large capacity for dissipating heat generated due to the power loss for protecting the diodes. The present invention has been made with the aim of solving the problems such as mentioned above and it is contemplated as an object to provide a rectifier device which is capable of reducing power loss of the AC generator for a motor vehicle while reducing the amount of heat generation and which is further capable of mitigating influence of noise to electronic apparatus/instruments, inclusive of car radio, by suppressing surge voltage making appearance upon current commutation among the diodes. DISCLOSURE OF THE INVENTION According to the present invention, there is provided a rectifier device for full-wave rectification of the output of an AC generator in which Schottoky diodes made of silicon carbide as a basic material are employed as the semiconductor elements for realizing full-wave rectification so that not only the heat generation due to power loss can be suppressed but also influence of noise to the electronic apparatus/instruments mounted on a motor vehicle can be mitigated by suppressing the surge voltage occurring upon current commutation among the diodes. By using as the rectifier semiconductor the silicon diode formed of silicon carbide as the basic material elements for performing full-wave rectification of the output power of the AC generator, not only the capacity of a heat sink can be rated lower owing to the capability of reducing the heat generation due to power loss but also the influence of noise to the electronic apparatus/instruments mounted in the motor vehicle can be mitigated owing to the capability of suppressing the surge voltage making appearance upon current commutation among the diodes. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view showing a configuration of an AC generator system for a motor vehicle in which a rectifier device provided with an auxiliary output terminal according to an implementation mode or embodiment of the present invention is employed. Figure 2 is a view showing a configuration of an AC generator system for a motor vehicle in which a rectifier device provided with no auxiliary terminal according to another implementation mode of the invention is employed. Figure 3 is a view showing a configuration of an AC generator system for a motor vehicle in which a neutral-point connection type diode rectifier device provided with an auxiliary output terminal according to yet another embodiment of the invention is employed. Figure 4 is a view showing a configuration of an AC generator system for a motor vehicle in which a neutral-point connection type diode rectifier device provided with no auxiliary output terminal according to still another embodiment of the invention is employed. Figure 5 is a sectional view showing a structure of a Schottoky barrier diode. Figure 6 is a view showing a forward voltage drop characteristic versus a forward current in a Schottoky barrier diode. Figure 7 is a view showing a configuration of a conventional AC generator for a motor vehicle- Figure 8 is a view showing a configuration of a conventional AC generator system for a motor vehicle in which a rectifier device provided with no auxiliary terminal is employed. Figure 9 is a view showing a configuration of a AC generator system for a motor vehicle in which a conventional neutral-point connection type diode rectifier device provided with an auxiliary output terminal is employed. Figure 10 is a view showing a configuration of a AC generator system for a motor vehicle in which a conventional neutral-point connection type diode rectifier device provided with an auxiliary output terminal. Figure 11 is a view showing a structure of a pn-junction diode. Figure 12 is a view showing a forward voltage drop characteristic versus a forward current in a pn-junction diode. BEST IMPLEMENTATION MODES FOR CARRYING OUT THE INVENTION In the following, implementation modes for carrying out the instant invention will be described by reference to the drawings. Figure 1 is a diagram showing a configuration of an AC generator system for a motor vehicle in which Schottoky barrier diodes are used as semiconductor rectifier elements in a rectifier device provided with an auxiliary output terminal are employed. At this juncture, it should be mentioned that the structure of the AC generator system for the motor vehicle according to the instant implementation mode of the invention differs from that of the conventional AC generator for the motor vehicle in the respect that the Schottoky barrier diodes are employed as the semiconductor rectifier elements of the rectifier device 2. Except for this difference, the structure of the former is essentially same as the latter. Further, Fig. 2, 3 and 4 show AC generator systems for a motor vehicle which correspond to the prior art or conventional motor vehicle destined AC generator systems shown in Figs. 8, 9 and 10, respectively, except that the Schottoky barrier diodes are employed as the semiconductor rectifier elements in place of the pn-junction diodes. Before entering into description of operation of the rectifier device according to the instant embodiment of the invention, brief explanation will be made of the Schottoky barrier diode. The Schottoky barrier diode is a diode including a metal-semiconductor junction having Schottoky barrier with electrode terminals being attached to metal and semiconductor, respectively. The Schottoky barrier diode exhibits a current-versus-voltage characteristic which is very similar to that of the pn-junction diode. However, in the Schottoky diode, the voltage rise in the forward direction is generally low because of low internal potential. Furthermore, the Schottoky barrier diode is a majority carrier device whose operation is governed by majority carriers and which exhibits no minority carrier storing effect at the pn-junction. Thus, the Schottoky barrier diode enjoys a high switching speed with reverse recovery time being short on the order of ns (nanosecond). By contrast, the reverse recovery time of the pn-junction diode is on the order of ps (microsecond). In the past, difficulty was encountered in manufacturing the Schottoky barrier diode having high voltage withstanding capability by using Si (silicon) as the semiconductor. At present, however, it is possible to manufacture the Schottoky barrier diode having a wide band gap and exhibiting high dielectric breakdown strength, high voltage withstanding capability and small current leakage by using SiC (silicon carbide) as the semiconductor material. Figure 5 is a sectional view showing a structure of a Schottoky barrier diode. As can be seen from the figure, the Schottoky barrier diode is implemented by bonding together barrier metal BM and n-type semiconductor of SiC (silicon carbide). An anode terminal A is mounted on the barrier metal BM through interposition of an electrode El with a cathode terminal K being mounted on the n-type semiconductor through interposition of an electrode E2. Figure 6 shows a forward voltage drop characteristic versus a forward current in the Schottoky barrier diode. According to this characteristic, the forward voltage drop of the Schottoky barrier diode is 1.0 V (volt) on the assumption, by way of example only, that the maximum output current of the AC generator 1 is 90 A (ampere). Thus, when the Schottoky barrier diodes are used in the rectifier device 2 of the AC generator 1, the power loss in the diodes array positive polarity is 45 W = 90 A x 0.5 at the maximum current output of the AC generator 1. Similarly, the power loss in the diode array of the negative polarity is 45 W = 90A x 0.5. As is apparent from the above, when compared with the rectifier device in which the pn-junction diode is employed as the semiconductor rectifier element, the power loss can be reduced to 90 W, a half of the power loss in the rectifier device using the pn-junction diodes, which contributes to increasing the output power of the AC generator 1 in correspondence to the reduction in the power loss. Besides, the capacity of the heat sink for dissipating heat generated due to the power loss can be lowered correspondingly, which in turn means that the package area of the rectifier device can be decreased correspondingly. Furthermore, because the reverse recovery time is as short as on the order of \xs (microsecond) when compared with the pn-junction diode, the surge voltage generated upon current commutation for the rectification can be suppressed, whereby influence of noise to the electronic apparatus/instruments, inclusive of car radio, can be mitigated. INDUSTRIAL UTIL1ZABIL1TY As is apparent from the foregoing description, in the rectifier device according to the present invention in which the Schottoky barrier diode is employed as the semiconductor rectifier element, the power loss can be decreased when compared with the conventional rectifier device in which the pn-junction diode is used as the semiconductor rectifier element. Besides, because of short reverse recovery time, the commutation surge voltage can be suppressed, which is effective for suppressing the influence of noise to the electronic apparatus/instruments. 1. A rectifier device for full-wave rectification of an output power of an AC generator, characterized in that Schottoky diodes each based on silicon carbide are used as rectifier semiconductor elements for said full-wave rectification. 2. A rectifier device set forth in claim 1, characterized in that the Schottoky diodes each based on silicon carbide are used as rectifier semiconductor elements for full-wave rectification of the output power of an AC generator for a motor vehicle. * . 3. A rectifier device for full-wave rectification of an output power of an AC-generator substantially as herein described with reference to the accompanying drawings.

Documents:

1574-mas-1998-abstract.pdf

1574-mas-1998-claims duplicate.pdf

1574-mas-1998-claims original.pdf

1574-mas-1998-correspondence others.pdf

1574-mas-1998-correspondence po.pdf

1574-mas-1998-description complete duplicate.pdf

1574-mas-1998-description complete original.pdf

1574-mas-1998-drawings.pdf

1574-mas-1998-form 1.pdf

1574-mas-1998-form 26.pdf

1574-mas-1998-form 3.pdf

1574-mas-1998-other documents.pdf

1574-mas-1998-pct.pdf