JPH06165410A - Power device - Google Patents

Abstract

PURPOSE:To perform charging operation to a secondary battery from a solar battery with simple circuit constitution and to prevent power consumption from wasteful use. CONSTITUTION:A power device is constituted of a solar battery 10, a secondary battery 12, a reverse-current preventing diode 20 and a PNP transistor using both functions of charging operating detection. An emitter of the transistor is connected to a plus terminal of the solar battery, a base is connected to a plus terminal of the secondary battery, a diode 22 connected to a collector in series, and a resistance is connected between ground terminals. Input of a buffer circuit 26 formed of a CMOS is connected to a partial pressure point of the diode 22 and resistance 24. A switching transistor 28 is connected to the output of the buffer circuit 26 through a resistance 32. A light emission diode 30 is connected to the collector of the transistor 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply system equipped with a secondary battery charged from a solar cell, and more particularly to means for detecting the charging operation thereof.

[0002]

2. Description of the Related Art Various semi-permanent power supply systems that do not require battery replacement have been proposed by including a solar battery and a secondary battery, and making the secondary battery chargeable by the electromotive force of the solar battery. In such a power supply system, the rechargeable battery cannot be charged if the amount of light incident on the solar battery is small, so it is important to display whether or not the rechargeable battery is charged in the current environment. Is becoming.

In particular, when this power supply system is incorporated in a camera, the camera is used in various environments. For example, when many images are taken in a low illuminance environment where there is no charging operation from a solar cell, the secondary Batteries will be exhausted rapidly. At this time, if there is a display during charging, the photographer can recognize that the display disappears under low illuminance and the secondary battery is being consumed without being charged. Further, when displaying the remaining amount with a conventional temporary battery, for example, in the case of a camera, a battery check is performed when the photographing operation is performed, and the remaining amount display is updated from the battery voltage at that time.

On the other hand, in a power supply device provided with a secondary battery, the charging operation of the secondary battery is performed even when the camera is not photographing, and the remaining amount of the battery changes. Therefore, this charging operation is detected and the remaining amount display is updated. Need to do.

As described above, in the power supply system using the solar cell and the secondary battery, it is necessary to detect the presence or absence of the charging operation for various purposes. Then, as a conventional means for detecting a charging operation, a voltage drop across a diode for preventing reverse current, which is connected in series in a charging loop from a solar cell to a secondary cell, is detected. The specific circuit configuration is shown in FIG.

In FIG. 4, 10 is a solar cell, 12 is a secondary battery, and 14 is a diode for preventing backflow. Reference numeral 16 denotes a comparator, the plus input of which is connected to the anode terminal of the backflow prevention diode and the minus input of which is connected to the cathode terminal thereof. A booster circuit 18 boosts the output voltage of the secondary battery 12 and supplies it as a power source of the comparator 16. The reason why the power supply voltage of the comparator 16 is set higher than the voltage of the secondary battery 12 is as follows. That is, since the anode voltage of the diode for backflow prevention becomes higher than the positive voltage of the secondary battery during charging, using the secondary battery as the power source of the comparator 16 causes malfunction of the comparator 16.
The boost output is used as the power supply. It is also conceivable to reduce the voltage of the anode and cathode of the diode for backflow prevention by a resistance partial voltage between the ground terminals without using a booster circuit, but this resistance causes waste of solar cells and secondary batteries. It is not preferable because it causes power consumption.

[0007]

As described above, the charging operation detection circuit provided as the conventional means for detecting the charging operation is complicated because the booster circuit needs to be operated to perform the detection operation. It was In addition, there is wasted power consumption in the booster circuit itself, which is not preferable.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and its main purpose is to detect the voltage across the backflow preventing diode in order to detect the charging operation from the solar battery to the secondary battery. By doing so, it is an object to provide a simple circuit configuration.

[0009]

In order to achieve the above object, the power supply device of the present invention is characterized in that in claim 1, a transistor for detecting a charging operation is provided between the solar cell and the secondary battery, and The base-emitter junction constitutes the diode for preventing backflow, and means for detecting a charging operation from the collector terminal of the transistor is provided, and a transistor for detecting a charging operation is provided in claim 2, A base and an emitter of the transistor are connected to both ends of the backflow prevention diode, and means for detecting a charging operation from the collector terminal of the transistor is provided. A light-emitting diode connected between the secondary batteries and a photo diode arranged at a position where it can receive the luminous flux of the light-emitting diode. A transistor provided, is provided with a means for detecting the charging operation from the output terminal of the photo transistor.

[0010]

With the above structure, the circuit structure is simplified, and the current consumption when there is no charging operation is extremely small.

[0011]

EXAMPLES The present invention will be described in detail below based on examples.

FIG. 1 is an electric circuit diagram showing a main part of a first embodiment of the present invention. In the figure, 10 is a solar cell, 12 is a secondary battery, 20 is a backflow prevention diode and 2 for charging operation detection.
It is a PNP transistor that also has two functions. The emitter of this transistor is connected to the positive terminal of the solar cell, the base is connected to the positive terminal of the secondary battery, and the collector is connected in series with a diode 22 and a resistor 24 connected between the ground terminal. . 26 is a CMOS (C
a buffer circuit composed of an complementary MOS), the input of which is connected to the voltage dividing point of the diode 22 and the resistor 24. A switching transistor 28 is connected to the output of the buffer circuit 26 via a resistor 32. Reference numeral 30 is a light emitting diode (LED) connected to the collector of the transistor 28.

The operation of the present embodiment configured as above will be described below.

When there is no charging operation from the solar cell 10 to the secondary cell 12, the emitter-base of the PNP transistor 20 is reverse-biased, so the PNP transistor 20 is off. Therefore, since the collector current does not flow, the voltage at the connection point between the diode 22 and the resistor 24 becomes LOW level. Since the input level of the buffer circuit 26 is LOW, its output also becomes LOW level, the transistor 28 is turned off, and the LED 30 is not turned on.

On the other hand, when the charging operation from the solar cell 10 to the secondary cell 12 is performed, the base current of the PNP transistor 20 flows, so that the transistor 20 is turned on. Since the transistor 20 is saturated when the resistance value of the resistor 24 is sufficiently large, the input voltage Vin of the buffer circuit 26 is expressed by the following equation.

Vin = Vs-Vce-Vf (1) where Vs: electromotive voltage of solar cell 10 Vce: saturation voltage between collector and emitter of transistor 20 Vf: forward voltage of diode 22 If the voltage is V +, the following formula is established.

V + = Vs−Vbe (2) where Vbe: base-emitter voltage of the transistor 20 Vbe in a normal silicon transistor and diode
Since ≈Vf is satisfied and Vce is a low value, Vin becomes a value slightly lower than V + from the equations (1) and (2). Therefore, the output of the buffer circuit 26 becomes HIGH level, the transistor 28 is turned on, the LED 30 is turned on, and it indicates that the solar cell is being charged. As described above, due to the action of the diode 22, the buffer circuit 26
Since the input voltage at the HIGH level is shifted to a value slightly lower than the power supply voltage, the buffer circuit 26 can operate normally.

In the conventional example shown in FIG. 4, the comparator 1
Since 6 detects the presence or absence of the charging operation, it is necessary to operate the booster circuit 18 to supply the power to the comparator 16 even when the charging operation is not performed, resulting in wasting power. On the contrary, in the present embodiment shown in FIG. 1, since the PNP transistor 20 is off when the charging operation is not performed, there is no power consumption here, and since the input / output of the buffer circuit 26 is LOW level, the CMOS The power consumption of the buffer circuit itself is negligible. As described above, the present embodiment has the merit that the power consumption of the detection circuit itself when the charging operation is not performed can be reduced to substantially zero, and the like, with a simple configuration.

Next, a second embodiment is shown in FIG. Figure 2
It is an electric circuit diagram which shows the principal part of the 2nd Example of this invention. In the figure, 34 is a PNP transistor for detecting a charging operation (hereinafter referred to as a detection transistor), the emitter of which is connected to the anode of the diode 14 for preventing backflow and the base of which is connected to the cathode thereof via a resistor 36. The diode 22 and the resistor 24 are connected in series to the collector of the detection transistor 34. 38 is a one-chip microcomputer (hereinafter referred to as a microcomputer), 4
0 is a power supply switching transistor controlled by the output of the microcomputer 38, 42 is a battery check circuit,
Reference numeral 44 is a liquid crystal display device for displaying the remaining capacity of the battery. The connection point of the resistor 24 and the diode 22 and the output of the battery check circuit 42 are input to the microcomputer 38. The liquid crystal display 44 is driven by a liquid crystal driver in the microcomputer 38.

The operation of this embodiment having the above configuration will be described below. When there is no charging operation from the solar cell 10 to the secondary battery 12, the backflow prevention diode 14 is reversely biased, so the detection transistor 34 is off. Therefore, the voltage at the connection point between the resistor 24 and the diode 22 is at the LOW level, and the microcomputer 38 is in the hold state.

Next, when the charging operation from the solar cell 10 to the secondary cell 12 is performed, the backflow preventing diode 14 is forward biased. Therefore, the base current flows from the emitter of the detection transistor 34 to the secondary battery via the resistor 36, and the detection transistor 34 is turned on, so that the voltage at the connection point between the resistor 24 and the diode 22 is inverted to the HIGH level. Triggered by this HIGH level signal, the microcomputer 38 returns from the hold state, starts operating, and turns on the transistor 40 for power supply switching. As a result, power is supplied to the battery-check circuit 42 and the battery check operation is performed. The check voltage is transferred to the microcomputer 38, and the microcomputer 38 uses this voltage as A /
D conversion is performed, and the display content of the liquid crystal display device 44 is updated based on the converted digital value. This update is for solar cell 10
Is performed during the charging operation from the secondary battery 12 to the secondary battery 12.

The purpose of the diode 22 in this embodiment is the same as that of the first embodiment shown in FIG. In the present embodiment, the update of the liquid crystal display is limited to the time when the secondary battery is being charged, but when it is used in a camera, for example, it is very easy to perform it during the photographing operation of the camera. Also in this embodiment, as in the first embodiment, when the rechargeable battery is not charged, the detection transistor 34 is off, and the microcomputer 38 is in the hold state and the power switching transistor 40 is also off. Therefore, the current consumption of this electric circuit is suppressed to almost zero.

Since the resistor 36 connected to the base of the detection transistor 34 is merely for limiting the base current, even if this resistor is short-circuited, it does not affect the operation of this embodiment.

Next, a third embodiment is shown in FIG. FIG. 3 is a circuit diagram of a main part showing a third embodiment of the present invention. In the figure, 10 is a solar cell, 12 is a secondary battery, and 50 is a light emitting diode (LED) connected between them, which also functions as a backflow prevention diode. 52 is an NPN phototransistor whose emitter is connected to the ground. 54
Is a PNP transistor for switching, the base of which is connected to the collector of the phototransistor 52, and the collector of the transistor 54 is connected to the resistor 58. A resistor 5 is placed between the base and the emitter of the transistor 54.
6 is connected. Phototransistor 52 is an LED
The resistor 60 is arranged at a position where the light emitted from the light source 50 can be received, and a resistor 60 is provided between the collector of the phototransistor 52 and the base of the PNP transistor 54.

The operation of this embodiment configured as described above will be described. When the charging operation from the solar cell 10 to the secondary battery 12 is not performed, the LED 50 does not emit light because it is reverse biased, so the phototransistor 52 is turned off and the transistor 54 is also turned off. Therefore, the collector voltage of the transistor 54 is at the ground level. Next, when the charging operation from the solar battery 10 to the secondary battery 12 is performed, the LED 50 is turned on, so that the phototransistor 52 is turned on and the transistor 54 is also turned on. Therefore, the collector voltage of the transistor 54 is inverted to the HIGH level. This HIGH level signal becomes a charge detection signal, and this signal is used as in the first or second embodiment and input to a microcomputer or the like (not shown). Also,
Even in this embodiment, when there is no charging operation, the phototransistor 52 and the transistor 54 are off, so that the current consumption is almost zero.

[0026]

As described above in detail based on the embodiments, the present invention provides a simple circuit for detecting the charging operation from the solar battery to the secondary battery by detecting the voltage across the backflow prevention diode. However, since the current consumption when there is no charging operation can be minimized and the circuit configuration is simple, the effect is great.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a main part of a first embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a main part of a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a main part showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional secondary battery charging circuit.

[Explanation of symbols]

 10 solar cell 12 secondary battery 20 PNP transistor 22 diode 24 resistor 26 buffer circuit 28 transistor 30 light emitting diode 32 resistor

Claims (3)

[Claims] 1. A power supply device having a secondary battery charged from a solar cell, wherein a transistor for detecting a charging operation is provided between the solar cell and the secondary battery, and a base-emitter junction of the transistor is for preventing the backflow. And a means for detecting the charging operation from the collector terminal of the transistor. 2. A power supply device having a secondary battery charged from a solar cell and a diode for preventing backflow connected between the solar cell and the secondary battery, wherein a transistor for charging operation detection is provided, and the transistor is provided. The power supply device is characterized in that a base and an emitter are connected to both ends of the diode for preventing backflow and a means for detecting a charging operation from the collector terminal of the transistor is provided. 3. A power supply device having a secondary battery charged from a solar cell, the light emitting diode being connected between the solar cell and the secondary battery, and arranged at a position capable of receiving the projected light flux of the light emitting diode. And a means for detecting the charging operation from the output terminal of the phototransistor.