Electricity: battery or capacitor charging or discharging – Wind – solar – thermal – or fuel-cell source
Patent
1998-08-06
1999-09-28
Tso, Edward H.
Electricity: battery or capacitor charging or discharging
Wind, solar, thermal, or fuel-cell source
H01M 1046
Patent
active
059594322
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a device for charging an electric accumulator including a photovoltaic cell power source, coupled to the accumulator and a voltage multiplier connected in series between the power source and the accumulator.
The invention also concerns an electronic timepiece, in particular a watch or an alarm clock, including such a charging device.
However, the applications of a charging device according to the invention are not limited to the horological field, but can concern any electronic apparatus including an electric accumulator and a photovoltaic cell power source intended for charging the accumulator, for example a pocket or table electronic calculator, a radio transmitter or receiver, an infrared signal remote control apparatus, a sensor, and generally any apparatus having an autonomous electric supply and storing electric power generated by solar cells.
Currently, one tends to operate low consumption electronic apparatus at as low a supply voltage as possible, of the order of 1.0 to 1.5 volts, which represents a current lower limit for the proper operation of certain electronic components. However, the photovoltaic cells currently preferred for supplying these devices, whether of the photochemical or semi-conductor type, generally only provide a lower voltage, typically of the order of 0.3 to 0.5 volts, so that it is necessary to connect at least three of these cells in series (see for example British Patent Document GB-A-2 149 942). These cells are generally juxtaposed on a visible face of the in order to benefit from the same lighting conditions. Such an arrangement can have drawbacks. On the one hand, in miniaturised apparatus, the manufacture of a small unit of several cells is more expensive than that of a single larger cell. On the other hand, in objects where aesthetic appearance is important, as in the horological field, the lines of separation between the juxtaposed cells are often inconvenient and would disappear if a single cell could be used, or two superposed quasi transparent cells as described in the Patent Document WO 93/19405.
In application to a wristwatch, a power source formed of several juxtaposed photovoltaic cells connected in series has the additional drawback of being liable to a shadow effect by clothes: if for example a sleeve puts one of the cells in shadow, the voltage provided by the latter drops significantly and thus the total output voltage of the cells can drop to a value insufficient for charging the accumulator.
German Patent Application DE-A-29 00 622 describes a device capable of charging an accumulator by means of a solar cell whose output voltage is lower than the voltage across the accumulator terminals, as a result of a voltage converter including an inductor and a diode connected in series between the electric power source and the accumulator. The junction between the inductor and the diode is cyclically connected to earth by a transistor controlled by a monostable device. The latter receives an input signal originating from a photoresistive sensor which measures the illumination to which the solar cell is exposed. When the illumination increases, the time constant of the monostable device increases, which decreases the charge resistance of the solar cell in order to optimise it.
However, the described device is liable to consume more energy than it generates when the illumination of the cell is relatively low, which can eventually lead to the accumulator being discharged. Furthermore, it is difficult to optimise the operation thereof because the illumination response features of the solar cell and the photoresistor are generally different. On the other hand, the presence of the photoresistor as an additional external element is disadvantageous in several respects, in particular in a watch, because of the space which must be reserved for it, the manufacturing cost, and the risk of it being subject to different illumination to the solar cell.
An object of the present invention is to avoid the aforementioned drawbacks, by providing an effi
REFERENCES:
patent: 3448575 (1969-06-01), Grohoski
patent: 4240021 (1980-12-01), Kashima et al.
Elektronik, vol. 39, No. 9, Apr. 27, 1990, pp. 150/151 XP000116206 Rittenbruch F-A: "Solar-Akkulader mit Nur einer Solarzelle".
Patent Abstracts of Japan vol. 009, No. 207 (P-382), Aug. 24, 1985 & JP 60 069589 A (Suwa Seikosha KK), Apr. 20, 1985.
Farine Pierre-Andre
Saurer Eric
Asulab S.A.
Tso Edward H.
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