JPH0480355B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a long-life electric timepiece that has a solar cell as a primary power source and stores the output current of the solar cell in a high-capacity capacitor that is a secondary power source to maintain the movement of the timepiece. This invention relates to charging current control to prevent a drop in solar cell voltage due to charging current of a high-capacity capacitor.

Traditionally, primary batteries, secondary batteries, and electric double layer capacitors have been known as clock maintenance backup power sources for solar-powered watches, but currently, they have better rapid charging and discharging characteristics than the former two, and are less prone to leakage. It is believed that the use of electric double layer capacitors, which are said to be highly reliable at liquid level, is advantageous in creating long-life watches that do not require battery replacement. Figure 1 shows a power supply circuit for a solar cell watch equipped with a conventional electric double layer capacitor. In FIG. 1, a solar cell 1 is directly connected to an electric double layer capacitor 3 and a clock load 4 via a reverse current blocking diode 2, and a constant voltage holding circuit 5 serves as a circuit that regulates the maximum charging voltage of the capacitor 3. ing. Therefore, even under illuminance conditions where the power generated by the solar cell exceeds the driving load of the clock circuit, the clock function will not start unless the electric double layer capacitor is charged to a level higher than the minimum operation starting voltage of the clock circuit. In other words, when a fully discharged solar cell watch is moved to a normal illumination environment such as an office room, the watch does not start operating for several hours or more.

The present invention eliminates such drawbacks, and its purpose is to immediately start the clock function when there is the minimum illuminance necessary for driving the clock, regardless of the charging voltage of the high-capacity capacitor, and when the illuminance is higher than necessary. The aim is to realize a solar cell watch that can be rapidly charged depending on the amount of power generated by the solar cell.

The present invention will be described in detail below based on Examples. FIG. 2 shows a power supply circuit according to the first embodiment of the present invention, in which 1 is a solar cell, 2 is a backflow blocking diode to the solar cell, 3 is an electric double layer capacitor, 4 is a clock load, and 5 is a constant voltage maintenance The circuit includes a discharging diode 6, a voltage detection circuit 7, a charging circuit 8, a diode 9 blocking reverse current to the charging circuit, a charging transistor 10, and a capacitor 11 for absorbing load fluctuations. When the voltage generated by the solar cell 1 exceeds the forward voltage of the diode 2 and the clock load 4 becomes equal to or higher than the minimum operation start voltage, the clock function is started. Here, the charging transistor 10 does not turn on until the voltage detected by the voltage detection circuit 7 becomes equal to or higher than the minimum operation start voltage of a clock circuit (not shown). When sufficient illuminance is maintained after starting the clock function, the charging circuit 8 is controlled according to the voltage increase corresponding to the illuminance.
Charging is performed using surplus current generated by the solar cells. After charging is completed, the constant voltage holding circuit 5 sets the voltage generated by the solar cell within the rated voltage determined by the circuit elements. In addition, if the illuminance is extremely low,
A clock circuit is driven by the charge accumulated in the electric double layer capacitor 3 via the discharge diode 6. Diode 9 is installed to prevent loss to the charging circuit during discharging.

The charging current characteristics described above preferably have ideal constant voltage characteristics near the minimum operation start voltage of the timepiece circuit.

FIG. 2 shows a second embodiment of the present invention, in which 12 is a Zener diode and 13 is a resistor for voltage adjustment to the load side. Figure 3 utilizes the constant voltage characteristics of a Zener diode, and the second
This power supply circuit is a simplified version of the first embodiment in which the voltage detection circuit 7 and charging circuit 8 shown in the figure are replaced with Zener diodes 12.

As shown in the two examples above, in a solar cell watch equipped with a high capacity capacitor or a secondary battery as a secondary power source, it is possible to prevent the watch load voltage from decreasing due to the charging current to the two receiving power sources, and to effectively use the solar cell output as a clock. By distributing the circuit to the charging circuit, we can provide the optimal product as a solar battery watch.

[Brief explanation of the drawing]

FIG. 1 shows a power supply circuit of a conventional solar battery watch, FIG. 2 shows a power supply circuit of a solar battery watch according to a first embodiment of the present invention, and FIG. 3 shows a power supply circuit of a solar battery watch according to a second embodiment of the present invention. This is a power supply circuit. 1... Solar cell, 2... Diode, 3... Electric double layer capacitor, 4... Clock load, 5... Constant voltage holding circuit, 6... Diode, 7... Voltage detection circuit, 8... Charging circuit , 9...diode, 1
0...Transistor, 11...Capacitor, 12
...Zener diode, 13...resistance.

Claims (1)

[Scope of Claims] 1. At least a solar cell, a driving clock circuit that is connected to the solar cell through a backflow prevention diode and starts driving when the clock load reaches a minimum operation start voltage, and the clock circuit. A capacitor for absorbing load fluctuations, a high-capacity capacitor connected to the clock circuit via a discharge diode, a constant voltage holding circuit for preventing overvoltage of the high-capacity capacitor, and a voltage for detecting the electromotive force of the solar cell. a detection circuit; and a charging circuit in which the high-capacity capacitor and the reverse current blocking diode are connected in series and charge the high-capacity capacitor with the voltage detected by the voltage detection circuit; A solar cell watch characterized in that charging of the high capacity capacitor starts when the voltage detected by the voltage detection circuit becomes equal to or higher than the minimum operation start voltage.