JPS5922458B2 - power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply device equipped with a solar cell and a secondary battery charged by the solar cell, and in particular to a power supply device equipped with a solar cell and a secondary battery charged by the solar cell. It is something to control.

Traditionally, power supplies used in electronic devices such as desktop computers and electronic wristwatches have used a combination of secondary batteries and solar cells, and the electrical energy converted by the solar cells when exposed to light is For charging secondary batteries or
These solar cells are used to drive electronic devices, but when the solar cells are exposed to strong light such as direct sunlight, the converted electrical energy greatly exceeds the voltage of the secondary battery, and in this state When electrical energy from a solar cell is supplied to a secondary battery for a long time, the secondary battery becomes overcharged, which impairs the performance of the secondary battery, and also causes damage inside the battery due to overcharging. There was a risk that the secondary battery would explode due to gas generation. Therefore, conventionally, a voltage regulator diode is connected in parallel to a secondary battery that uses the output of a solar cell as a charging power source, and when the output voltage of the solar cell exceeds the operating voltage set by the voltage regulator diode and resistor, A method has been proposed that prevents overcharging current from flowing to the secondary battery by breaking down the constant voltage diode and bypassing the charging current.

However, in the conventional circuit system described above, a resistor connected in series with a constant voltage diode is required to set the operating voltage of the bypass circuit that prevents overcharging current to the secondary battery. Therefore, as the number of circuit components increases, the mounting space also increases, and problems arise with the layout when mounting in devices with limited space such as electronic wristwatches. This will impede the formation. 5 In addition, when a voltage regulator diode breaks down, a considerable amount of bypass current flows, so if there are circuit elements that are airtight, densely packed, and easily affected by heat, such as a wristwatch, the voltage regulator diode is Therefore, the capacity and size (shape) of the constant voltage diode to be mounted are limited, and it is not applicable to circuits that bypass large currents due to heat generation. It may not be possible.

Furthermore, in general, voltage regulator diodes with low Zener voltages exhibit constant voltage characteristics in the large current region with a soft current rise. As a voltage regulator circuit for solar battery powered power supplies such as watches and calculators used in
This is not very desirable because the constant voltage diode exhibits a soft rise before reaching its operating point, making it unstable.

The present invention was made in view of the above points, and includes a photoconductive element whose conductivity changes depending on the illuminance of light, which is connected to the output side of a solar cell, and which is irradiated to the photoconductive element and the solar cell. By creating a relative difference in the illuminance of the light, the illuminance-resistance characteristic of the photoconductive element can be set to an arbitrary characteristic suitable for charging the secondary battery, and thereby the low illuminance region and the high illuminance region The electrical energy generated from the solar cell can be used to charge the secondary battery in a specified illuminance range except for Furthermore, it is an object of the present invention to provide a power supply device that can be used regardless of whether the current is low or high, and that can be easily and inexpensively mounted at high density in a limited space.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the principle of the power supply device according to the present invention, in which a photoconductive circuit 2 whose conductivity changes depending on the illuminance of light is connected to the output side of a solar cell 1, and this The conductive circuit 2 is irradiated with the same light as the solar cell 1, and when the power generated by the solar cell 1 changes depending on the illuminance of the light, the photoconductive circuit 2
The conductivity of the solar cell 1 is changed by the irradiation light, and at the same time, a part of the output from the solar cell 1 is shunted to the photoconductive circuit 2. The power to the load 5 such as an electronic circuit driven by the battery 4 is controlled to be almost constant. FIG. 2 shows an example of a specific circuit of the present invention based on the above block diagram, in which the solar cell 1 is connected to a predetermined circuit, that is, a secondary battery 4 and a load 5.
A plurality of CdS are connected in series and parallel to obtain the voltage and current capacity required for the photoconductive circuit 2.
The photoconductive element 2 is connected to the solar cell 1 through a current limiting resistor 6 to prevent a large current from flowing when the solar cell 1 is irradiated with strong light such as direct sunlight. Two rechargeable batteries 4 and a load 5 are connected in parallel to both ends of the battery 1, and further connected in parallel to both ends of the photoconductive element 2 via diodes forming a backflow prevention circuit 3.

In the circuit with the above configuration, the voltage-current characteristics of the solar cell when the solar cell 1 is irradiated with light and the illuminance L is doubled, tripled, etc. are shown in Figure 3. become.

In addition, when the solar cell 1 is sufficiently activated, the current 1 (L) generated by the solar cell 1 with respect to the illuminance L of light is
Since it is proportional to , 1(L)=KL (K: constant of proportionality). When a load, that is, a photoconductive element 2 whose resistance value changes depending on the illuminance L (having a characteristic that the resistance value decreases as the illuminance L increases) is connected to the solar cell 1 in parallel, both ends of the photoconductive element 2 The potential difference V(L) appearing at is (L}=i(L
)・R(L) (R(L): resistance value of photoconductive element 2 depending on illuminance, i(L): resistance value of photoconductive element 2 depending on illuminance)
The current flowing through, i(LKI(L).

Now, the illuminance L of the light irradiated to the solar cell 1 is L in Fig. 3,
2L, 3L, etc., in order to keep the potential difference (L) between both ends of the photoconductive element 2 at a constant value E as shown by the broken line 10 in FIG. The resistance value R(L) of the photoconductive element 2 depending on is R(L)=E/1(L
) must be satisfied. In other words, if the resistance value R(L) of the photoconductive element 2 changes according to E/i(L) with respect to the illuminance L, the potential difference between both ends of the photoconductive element 2 is constant regardless of the magnitude of the illuminance L. can be kept. That is, by utilizing the fact that the conductivity of the photoconductive element 2 changes depending on the intensity of light, some of the electric power generated by the solar cell 1 is absorbed by the electronic device (load).
The photoconductive element 2 consumes excess electrical energy other than the electrical energy required to drive the photoconductive element 5 and the electrical energy required to appropriately charge the secondary battery.

The curve 11 in FIG. 4a is curved by keeping the potential constant at the connection point A', which is under the same potential as point A shown in FIG. Next battery 4
This characteristic curve 1 shows the change in resistance value R(1) with respect to illuminance L so that the charging current becomes zero.
1, the charging current to the secondary battery 4 is zero, but when the resistance value R(L) of the photoconductive element 2 changes as shown in characteristic curve 12, which is slightly larger than the characteristic curve 11, the charging current of the photoconductive element 2
The potential at the connection point A, that is, point A', rises above the potential of the secondary battery 4, and current flows to the secondary battery 4 side.
will be charged. In the characteristic curve 11, the resistance value R(L) increases rapidly in the low illuminance area because the solar cell 1 cannot generate a sufficient voltage in the low illuminance area.
Furthermore, the reason why the resistance value R(L) is approximately constant in the high illuminance region is that the current limiting resistor 6 is provided.

When a CdS photoconductive cell is used as the semiconductor element,
Its illuminance-resistance characteristic is approximately inversely proportional to the illuminance L, as shown by the straight line 13 in Figure 4a, and if the CdS photoconductive cell 2 is placed in the same illuminance atmosphere as the solar cell 1, it can be used as a semi-permanent power source. cannot perform its functions, and therefore,
The properties 13 of the CdS photoconductive cell 2 must match the properties 12.

In this case, by weakening the light irradiated to the CdS photoconductive cell 2 using a filter or a mask with aperture holes, the illuminance of the light irradiated to the solar cell 1 and the light irradiated to the CdS photoconductive cell 2 can be made to be different. By creating a difference in CdS
The illuminance-resistance characteristic of the photoconductive cell 2 is made to match the characteristic curve 12 which intersects the characteristic curve 11 at two points as shown in FIG. 4a,
This prevents the electrical energy from the solar cells in the low illuminance area below L1 and the high illuminance area above L2 from being supplied to the secondary battery 4 side, and at the same time prevents the supply of electrical energy from the solar cells to the secondary battery 4 side.
Only when the solar cell 1 is receiving illuminance between 2 and 3, current is passed to the secondary battery 4 side to charge the secondary battery 4 and drive the load 5. Figure 4b shows a characteristic diagram of the charging current flowing to the secondary battery 4 side at this time.As is clear from this diagram, the energy of light is small in the low illuminance area, so the solar cell 1 receives a sufficient charging current. In addition, in high-intensity areas such as direct sunlight, the electrical resistance of the photoconductive element 2 decreases, and the potential at the connection point A becomes lower than that at the point A'. Electrical energy from the battery 1 is consumed by the photoconductive element 2, and almost no charging current flows to the secondary battery 4 side. Furthermore, if the potential of the secondary battery 4 increases as the charge increases and the potential at point A' increases to the same level as or higher than the potential at point A, this is equivalent to a decrease in the resistance value of the photoconductive element 2. The supply of electrical energy from the solar cell 1 to the secondary battery 4 is stopped, and the secondary battery 4 is charged so that its potential is always constant. Furthermore, by changing the relative relationship between characteristics 11 and 12 in FIG. becomes possible.

Note that the photoconductive element used in the present invention is not limited to the CdS photoconductive cell, but may also be made of CdSe, PbS, PbSe, or the like. As described above, according to the device of the present invention, by creating a relative difference in the illuminance of the light irradiated to the solar cell and the photoconductive element connected to the output side thereof, the illuminance-resistance characteristic of the photoconductive element is created. can be set to characteristics suitable for charging a secondary battery or driving a load.
Even if solar cells are exposed to strong light such as direct sunlight,
The current generated thereby does not flow to the secondary battery side, and the charging current to the secondary battery can be controlled to be substantially constant, and the voltage of the secondary battery can be maintained at a constant voltage or less.

This prevents overcharging of the secondary battery, prevents performance deterioration and damage to the secondary battery due to conventional overcharging, and contributes to the realization of a semi-permanent power source for electronic watches, etc. be. In addition, the circuit that controls the charging current supplied from the solar cell to the secondary battery at a nearly constant level is constructed using a photoconductive element whose resistance value changes with changes in light.
Constant current and voltage can be achieved simply by adjusting the relationship between the amount of light incident on the photoconductive element and the amount of light incident on the solar cell, and unlike low voltage diodes, it can be used regardless of low or high current. can do. Furthermore, since the photoconductive element can be manufactured from the same material as the solar cell, it is advantageous in terms of cost and also in terms of characteristics when controlling the output voltage of the power supply device. Furthermore, since the output voltage of the power supply device can be adjusted by adjusting the incident light on the solar cell and photoconductive element, the power supply device can be easily mounted and laid out in wristwatches, etc., and costs can be reduced. .

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a power supply device according to the present invention, Fig. 2 is a circuit diagram showing a specific example of the inventive device, Fig. 3 is a voltage-current characteristic diagram of a solar cell, and Fig. 4a is a photoconductive element. Fig. 4b is a characteristic diagram of the current flowing to the secondary battery side. 1... Solar cell, 2... Photoconductive element,
3... Backflow prevention circuit, 4... Secondary battery, 5... Load, 6... Current limiting resistor.

Claims (1)

[Claims] 1. In a solar cell connected to at least a secondary battery, a photoconductive element whose conductivity changes depending on the illuminance of light is connected in parallel to the output side of the solar cell via a current limiting resistor. By connecting the photoconductive element and making the illuminance of light to the photoconductive element weaker than the illuminance to the solar cell, the resistance value of the photoconductive element rapidly increases in the low illuminance area, and the resistance value remains approximately constant in the high illuminance area. 1. A power supply device characterized in that the electric energy of the solar cell is not supplied to the secondary battery side above the low and high illuminance regions with a single resistance characteristic. 2. The power supply device according to claim 1, wherein the photoconductive element is a CdS photoconductive cell.