JPH0787671B2 - Small electronic devices with solar cells - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a small electronic device with a solar cell using a solar cell as an operating power source in, for example, a quartz oscillator type wristwatch or a pocket calculator.

[Prior Art and Its Problems] Generally, in a small electronic device of a so-called battery-less system using a solar cell, charging can be performed comparatively frequently because only a few dozen hours of operation can be obtained by one charging. I need to do it. That is, when the device using the solar cell as a power source is, for example, a wristwatch, the frequency of use of the solar cell of this watch is extremely low, and if the solar cell of this watch is not exposed to light for a long time, the voltage generated by the solar cell is low. The charging voltage of the capacitor that charges is completely discharged, and the timekeeping function of this watch stops. In this case, the user has to perform a function recovery operation such as setting the time each time it is used again, and although there is an advantage that a battery is not required, a continuous operation for a longer time is obtained by the charging voltage of the capacitor. Is desired.

Therefore, in order to increase the charging capacity of the capacitor, it is only necessary to use one with a large capacity value.
Since the external dimensions of the capacitor increase as the capacitance value thereof increases, it is impossible to realize the capacitor, especially in the above-mentioned wristwatch or calculator, which hinders miniaturization.

However, with the recent technological innovation, the capacitors have been greatly improved, and for example, capacitors having a capacitance of 1 (F) have been developed even if the external dimensions are about 20Φ × 1.6 mmt. Therefore, it is conceivable to configure the power supply unit of the solar cell-equipped device by using the above-mentioned small-sized and large-capacity capacitor. However, if the capacity of the capacitor is large, it takes a long time to charge the capacitor. Almost all of the voltage generated by the solar cell is consumed to charge the capacitor after the function stops due to complete discharge,
The watch function cannot be restored at least until the charging voltage reaches the operating voltage of the watch circuit (for several minutes).

[Object of the Invention] The present invention has been made in view of the above problems.
For example, a small electronic device with a solar cell that can operate the main body circuit immediately without requiring a long time even when the function is restored by irradiating light again after the large-capacity capacitor is completely discharged. The purpose is to do.

[Summary of the Invention] That is, a small electronic device with a solar cell according to the present invention,
Connect a transistor element in series with a large-capacity capacitor, and if the charging voltage is extremely low, turn off this transistor element so that most of the voltage generated from the solar cell is directly supplied to the main circuit section. Also, when the charging voltage reaches a predetermined value or higher, the transistor element is turned on to directly connect the solar cell and the capacitor.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit configuration when the present invention is applied to, for example, a liquid crystal wristwatch, and this circuit includes a solar cell E. This solar cell E has a large-capacity charging capacitor C1.
Are connected in parallel. A small and large-capacity (for example, 0.7F) capacitor that has been recently developed is used as the capacitor C1, and a power transistor Tr1 is connected in series to the large-capacity capacitor C1. The series circuit including the power transistor Tr1 and the capacitor C1 is in parallel with the solar cell E, and the gate signal of the transistor Tr1 is controlled by the output signal of the comparator CP1. A reference voltage signal from the ground potential line VDD via the reference voltage diode ZD and a power supply voltage signal from the power supply line VCH are supplied to the positive (+) negative (-) comparison input terminals of the comparator CP1. On the other hand, a series circuit composed of transistors Tr2 and Tr3 is connected in parallel to the power transistor Tr1, and the gate signal of each transistor Tr2 and Tr3 is connected to the comparator C.
It is controlled by the output signal of P2. The power supply voltage VCH and the output voltage Vc of the large-capacity capacitor C1 are supplied to the positive (+) negative (-) comparison input terminals of the comparator CP2. Here, the circuit formed by the transistors Tr1 to Tr3, the comparators CP1 and CP2, and the reference voltage diode ZD surrounded by a broken line is referred to as a quick start circuit 11.

In addition, the solar cell E includes an overcharge prevention transistor.
Tr4 is connected in parallel and the gate signal of this transistor Tr4 is controlled by the output signal of the comparator CP3. To the positive (+) negative (-) comparison input terminals of the comparator CP3, a reference voltage signal from the ground potential line VDD via a reference voltage circuit 12 composed of a Zener diode or a MOS transistor, and the high voltage It supplies the output voltage Vc of the capacitor C1. Here, the circuit surrounded by the broken line, which includes the transistor Tr4, the comparator CP3, and the reference voltage circuit 12, is referred to as an overcharge prevention circuit 13 for the large-capacity capacitor C1. This overcharge prevention circuit
Power supply line VC between 13 and the above quick start circuit 11
Between H and the ground potential line VDD, a smoothing capacitor C2 having a small capacity of, for example, about 0.3 (μF) is connected in parallel with the solar cell E, and this capacitor C2 and the solar cell E are connected.
A backflow prevention diode D is interposed in a power supply line VCH between the and. Then, the power supply voltage signal set between the respective lines VCH-VDD is supplied to the timepiece main body circuit section 14. Here, for example, the minimum operating voltage of the watch LSI 15 in the watch body circuit unit 14 is set to -1.1.V, and the output voltage Vss of the voltage stabilizing circuit 16 including the transistor Tr5 and the comparator CP4 is set to -1.3V. To do. Then, the reference voltage Vzd by the reference voltage diode ZD is set to −1.3 to −1.4 V based on each set voltage in the main body circuit section 14, and the reference voltage V1 by the reference voltage circuit 12 in the overcharge prevention circuit 13 is set. To −2.2V.

On the other hand, the comparator CP5
A charge notification control circuit 17 is provided. A reference voltage signal Vzd set by the reference voltage diode ZD and an output voltage signal Vc from the large-capacity capacitor C1 are connected to the positive (+) negative (-) comparison input terminals of the charge notification control circuit 17, respectively. To supply the output signal to the timepiece LSI 15. The timepiece LSI 15 is operated by the constant voltage VSS from the voltage stabilizing circuit 16, supplies time information or other various information to the liquid crystal display device 18, and boosts a voltage doubler circuit (voltage bra) 19 as well. A timing signal for use is supplied, and the liquid crystal display device 18 is dynamically driven by the boosted voltage (-2.6V to -2.8V) from the voltage doubler circuit 19. Where C3 and C4 are 0.1 (μ
F) is a boosting capacitor, and C5 is a small-capacity smoothing capacitor of, for example, about 0.1 (μF) that is used for preventing malfunction when an instantaneous voltage drop occurs.

Next, the operation of the clock circuit thus configured will be described.

FIG. 2 shows the operating voltage of each part in the above clock circuit. First, when the solar cell E is exposed to light from the initial state of the large-capacity capacitor C1 in the completely discharged state,
The generated voltage is supplied to the power supply line VCH via the backflow prevention diode D. In this case, in the initial state, the comparator CP1 of the quick start circuit 11 inevitably outputs the L level signal, so that the transistor Tr1 is set to a high resistance. As a result, most of the power supply voltage VCH is supplied to the voltage stabilizing circuit 16 of the watch body circuit section 14, and the capacitor C1 is in the high resistance state of the transistor Tr1.
Is charged very slowly via. Therefore the power supply voltage
The constant voltage VSS from the VCH and the voltage stabilizing circuit 16 reaches the LSI operation minimum voltage indicated by the point P1 in a few seconds, for example, and the clock LSI 15 immediately starts its operation. At the same time, the charging voltage Vc of the large capacity capacitor C1 gradually rises. That is, since the quick start circuit 11 is provided, all the generated voltage from the solar cell E is not supplied to the capacitor C1 side even in the initial state of charging start, so that the charging completion of the capacitor C1 is completed for several minutes. Even without waiting, it is possible to quickly recover the timekeeping function.

After this, a few minutes later, as indicated by point P2, the power supply voltage VC
When H and the charging voltage Vc of the large-capacity capacitor C1 match and both of them start to rise, the power supply voltage VCH becomes equal to or higher than the reference voltage Vzd set by the reference voltage diode ZD, and the comparator CP1 outputs an H level signal. To do. This causes the transistor Tr1 to turn on and the capacitor C
1 and the solar cell E are directly connected to each other to be in a normal charge state. In this case, the voltage stabilization circuit 16 operates in the same manner as above with the constant voltage Vs.
Continue to output s. Here, the charging voltage Vc of the capacitor C1 further rises, and the reference voltage V1 set by the reference voltage circuit 12 of the overcharge prevention circuit 13 as shown by a point P3.
When it reaches (-2.2V in this case), comparator CP3 goes high.
Output level signal. As a result, the overcharge prevention transistor Tr4 is turned on, and the supply voltage of the reference voltage V1 or higher to the capacitor C1 is all consumed by this transistor Tr4. That is, by providing this overcharge prevention circuit 13, it is possible to prevent the large-capacity capacitor C1 from being destroyed by overcharge.

Next, when the light irradiation is stopped while the capacitor C1 is fully charged, the watch body circuit section 14 is directly driven by the discharge output voltage Vc from the capacitor C1 and the voltage Vc (= VC
H) gradually begins to decline. In this case, the action of the backflow prevention diode D prevents the discharge voltage Vc of the capacitor C1 from backflowing and destroying the solar cell E. In a circuit drive state where there is no electromotive force from the solar cell E and only the discharge output voltage Vc of the capacitor C1, for example, due to noise or contact with another member, the power supply voltage VC
When H is momentarily lowered to the ground potential VDD, the comparator CP1 is inverted and the transistor Tr1 is turned off.
At the same time, the comparator CP2 outputs an H level signal to turn on the transistors Tr2 and Tr3. In this case, the output voltage Vc from the capacitor C1 is
Voltage stabilization circuit 16 of the watch main circuit 14 via Tr2 and Tr3
Will be supplied to. As a result, the power supply voltage VCH
Capacitor instantly drops to the ground potential VDD, the capacitor C
As long as 1 has a certain charge voltage Vc, the watch main circuit 1
A stable voltage supply will be made to 4.

After this, the output voltage Vc of the capacitor C1 further decreases,
Supply voltage VCH and regulated output voltage V as indicated by P4
When SS falls below the reference voltage Vzd together, the comparator CP5 of the charge notification control circuit 17 outputs an H level signal and outputs a clock L signal.
Supply to SI15. As a result, the LSI 15 becomes the liquid crystal display device 1.
A charge warning display signal is output to 8 to display on the liquid crystal display that the charging voltage Vc of the capacitor C1 has dropped extremely. That is, by providing the charge notification control circuit 17,
It is possible to prompt the user to irradiate the solar cell E with light immediately. In other words, if the user sees this charging warning display and illuminates the solar cell E before the stabilization voltage Vss (= VCH) falls below the minimum operating voltage of the timepiece LSI 15, then after the point P1. The charging operation of the capacitor C1 as described above is repeated. In this case, since the charging capacitor C1 has a large capacity of 0.7 (F), it takes a long time of several days from the above fully charged state to the charging warning state. That is,
Even if the user does not use this watch for a few days, for example, there is no need to perform a recovery operation when it is reused without causing a malfunction.

Therefore, according to the clock circuit thus configured,
By providing the quick start circuit 11, for example, even in the initial charging state after the stop of the function, all the electromotive force of the solar cell E is not supplied to the capacitor C1 side,
After a few seconds, the watch body circuit section 14 can be operated immediately.

In addition, since this watch circuit is provided with the large-capacity capacitor C1, the overcharge prevention circuit 13 and the backflow prevention diode D, not only the continuous operation time after the full charge is significantly extended, but also the overcharge Destruction of capacitor C1 due to
And solar cell E due to backflow from large-capacity capacitor C1
You can also prevent the destruction of.

In the above embodiment, the case where the present invention is applied to a wrist watch has been described, but other than that, for example, an electronic game, a wireless device,
It goes without saying that it can be applied to various electronic devices such as cameras and electronic IC cards.

[Effects of the Invention] As described above, according to the present invention, a transistor element is connected in series with a large-capacity capacitor, and when the charging voltage is extremely low, the transistor element is turned off to control the voltage generated from the solar cell. Most of them are directly supplied to the main body circuit section, and when the charging voltage reaches a predetermined value or more, the transistor element is turned on to directly connect the solar cell and the capacitor. , For example, even after the above large-capacity capacitor is completely discharged, even if the function is restored by irradiating light again, it is possible to immediately operate the main circuit section within a few seconds without requiring a long time. It is possible to provide an attached small electronic device.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a case where a small electronic device with a solar cell according to an embodiment of the present invention is applied to a wrist watch,
FIG. 2 is a diagram showing the operating voltage of each part of the clock circuit in FIG. 11 …… Quick start circuit, 14 …… Clock body circuit,
E ... Solar cell, C1 ... Large-capacity capacitor for charging, Tr1
...... Transistor, ZD …… Reference voltage diode, CP1…
…comparator.

Claims (1)

[Claims] 1. A large-capacity charging capacitor (C1), a transistor element (Tr1) connected in series to this capacitor, and a backflow prevention means (D) in a series circuit composed of the capacitor and the transistor element. Voltage stabilizing circuit means (16) for stabilizing the voltage (VCH) supplied from the connection point between the solar cell (E) connected in parallel via the solar cell (E) and the backflow prevention means and the transistor element to a constant voltage. And a constant voltage (Vss) from the voltage stabilizing circuit means is applied as a drive voltage to the main body circuit section (15) to operate.
And a predetermined reference voltage (Vzd) above the certain voltage
When the reference voltage circuit means (ZD) set to and the solar cell starts to be exposed to light and the voltage applied to the voltage stabilizing circuit means does not reach the reference voltage set by the reference voltage circuit means, The transistor element is turned off, the voltage of the solar cell is supplied to the voltage stabilizing circuit means, the capacitor is charged, and the voltage applied to the voltage stabilizing circuit means is set by the reference voltage circuit means. When the voltage reaches the reference voltage, the transistor element is turned on to rapidly charge the capacitor with the voltage of the solar cell, and when the solar cell is not exposed to light, the discharge voltage of the capacitor is adjusted to the voltage stabilizing circuit means. A small electronic device with a solar cell, comprising: an ON / OFF control unit (CP1) for supplying the transistor described above;