Electronic timepiece

Details Electronic timepiece Electronic timepiece

1999-08-09

2001-10-09

Miska, Vit (Department: 2859)

Horology: time measuring systems or devices

Power supply details

Electrical

C320S101000

Reexamination Certificate

active

06301198

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an electronic timepiece provided with a solar cell as a power source.
BACKGROUND TECHNOLOGY
An electronic timepiece (especially wristwatch) with solar cell, in which electric power generated by a solar cell is accumulated in an electric power accumulation device (referred to as “accumulator device” hereinafter), and time keep and time display are performed with the accumulated electric power, has recently become widespread.
From the above it has been supposed that the convenience of freedom from trouble of battery replacement and the recent requirements to prevent environmental pollution due to battery waste, are supported by users of wristwatches.
The most basic configuration of a conventional electronic timepiece with solar cell is shown in FIG.
8
.
In this electronic timepiece with solar cell, electric power generated by a solar cell
101
is accumulated in an accumulator device
104
and a time keeping means
105
is driven by the accumulated electric power. As the solar cell
101
, a plurality of cells (generally about four cells) made by vapor deposition of an amorphous silicon thin film onto a substrate and connected in series, are widely used. As the accumulator device
104
, a secondary cell (battery) is used.
The time keeping means
105
is an electronic timepiece module comprising a time keep counter circuit having a quartz oscillator circuit, an electric counter circuit (frequency dividing circuit) and the like, a digital display or hands and a drive mechanism thereof for displaying a time and the like, and so on.
A reverse flow preventing diode
802
is provided to prevent the accumulated electric power from decreasing due to a reverse flow of an electric current from the accumulator device
104
to the solar cell
101
in a state where the generated voltage by the solar cell
101
is low due to weak ambient light.
However, even if the reverse flow preventing diode
802
can serve to prevent leakage current in a state where the generated voltage by the solar cell
101
is low in low intensity of illumination as described above, it conversely has the disadvantage when the intensity of illumination is high and therefore the generated voltage by the solar cell
101
is high, a forward voltage drop of about 0.5 V due to the reverse flow preventing diode
802
produces a loss, which causes the charging efficiency of the accumulator device
104
to lower.
The influence of the voltage drop of about 0.5 V due to the reverse flow preventing diode
802
becomes a more significant problem in an electronic timepiece using a solar cell in which the number of cells connected in series (the number of divided surface electrodes) is few.
This is because the generated voltage by one cell of the solar cell is about 0.5 V, and it is multiplied by the number of cells connected in series to be a value of the generated voltage of the solar cell, therefore a solar cell having a small number of cells connected in series has a low output voltage. Especially in a single cell having the number of cells connected in series =1, almost all of the generated voltage by the solar cell
101
is consumed in a forward voltage drop of the reverse flow preventing diode
802
, thereby operational conditions for charging the accumulator device
104
are not established.
For the accumulator device in such an electronic timepiece with solar cell, an accumulation means having a large capacitance is used so as to drive its time keeping means for a long time even in a state where the solar cell does not generate electric power. Therefore, there is a disadvantage in that in a state where the accumulated electric power has been almost totally consumed, it takes a long time after illuminating the solar cell again before enough electric power is accumulated in the accumulator device to cause the time keeping means to start its operation.
To solve the above disadvantage, there exists a quick start type electronic timepiece having a configuration in which a large capacitance accumulator device and a small capacitance accumulator device are provided in parallel, and when light is emitted to a solar cell to start generating electric power in a state where the accumulated electric power in the accumulator device has been almost totally consumed as described above, the small accumulator device is first charged by the generated electric power and then the time keeping means can start its driving in a short time with the accumulated electric power.
An example of the configuration is shown in FIG.
9
. In the quick-start type electronic timepiece with solar cell, a small capacitance accumulator device (capacitor)
905
and a large capacitance accumulator device (secondary cell)
906
are connected in parallel to the solar cell
101
via reverse flow preventing diodes
901
and
902
in place of the accumulator device
104
shown in FIG.
8
.
The small capacitance accumulator device
905
is directly connected to the time keeping means
105
in parallel, and a switch
903
for selecting an object to be charged is inserted between the large capacitance accumulator device
906
and the diode
902
, and a switch
904
for selecting a power source is also inserted between the large capacitance accumulator device
906
and the time keeping means
105
.
Furthermore, a voltage detection means
907
is provided in the above timepiece to detect the value of the accumulated voltage Vb of the large capacitance accumulator device
906
and to electrically control the on-off states of the switches
903
and
904
in accordance with the detection result. More specifically, when the accumulated voltage Vb of the large capacitance accumulator device
906
is below a preset value, the control of bringing the switch
903
into the on-off states at a predetermined ratio is repeated, thereby the small capacitance accumulator device
905
is quickly charged and the large capacitance accumulator device
906
is gradually charged. At this time, the switch
904
is kept in the off-state, thereby the time keeping means
105
is instantly driven with the accumulated electric power in the small capacitance accumulator device
905
.
In a state where the accumulated voltage Vb of the large capacitance accumulator device
906
exceeds the preset value, the switches
903
and
904
are both kept in the on-states and the large capacitance accumulator device
906
is selected both as an object to be charged and as the power source of the time keeping means
105
.
Also in this electronic timepiece, there is a disadvantage that since reverse flow preventing diodes
901
and
902
are provided in the respective charging paths of the small capacitance accumulator device
905
and the large capacitance accumulator device
906
to prevent leakage currents via the solar cell
101
in a weak ambient light, voltage drops occur due to the reverse flow preventing diodes
901
and
902
when charging with the generated electric power by the solar cell
101
, which causes the charging efficiency for the respective accumulator devices
905
and
906
to be lower.
DISCLOSURE OF THE INVENTION
The present invention is made to solve the above disadvantages, and its object is to enhance the charging efficiency in an electronic timepiece with solar cell by eliminating a lowering of the charging efficiency by a reverse flow preventing diode while an accumulator device is charged by the solar cell.
The present invention, in an electronic timepiece having a solar cell and an accumulator device as described above, in which electric power generated by the solar cell is accumulated in the accumulator device and a time keeping means is driven with the accumulated electric power, comprises an electrically on-off controllable switch being provided in a circuit for charging the accumulator device by the solar cell to achieve the above object, in place of a conventional reverse flow preventing diode.
Moreover, provided is a voltage comparison means for comparing a generated voltage by the solar cell and an accumulated voltage in

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