JP3256301B2 - Power supply - Google Patents

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 provided with a secondary battery charged from a solar cell, and more particularly to a means for detecting the charging operation.

[0002]

2. Description of the Related Art Various semi-permanent power supply systems that do not require battery replacement have been proposed by providing a solar battery and a secondary battery and charging the secondary battery by electromotive force of the solar battery. In such a power supply system, the charging operation of the secondary battery cannot be performed if the amount of light incident on the solar cell is small, so it is important to display whether or not the charging operation of the secondary battery is performed in the current environment. It becomes.

[0003] In particular, when this power supply system is incorporated in a camera, the camera is used in various environments. For example, when a number of images are taken in an environment of low illuminance where there is no charging operation from a solar cell, secondary shooting is performed. The batteries will be quickly consumed. At this time, if there is a display indicating that the battery is being charged, the photographer can recognize that the display has disappeared under low illuminance, and that the secondary battery is not being charged and is being consumed. In addition, when the remaining amount is displayed using a conventional temporary battery, for example, in the case of a camera, a battery check is performed when a shooting 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 photographed, and the remaining amount of the battery changes. Need to do.

As described above, in a power supply system using a solar battery and a secondary battery, it is necessary to detect the presence or absence of a charging operation for various purposes. As a conventional means for detecting a charging operation, a voltage drop across a backflow preventing diode connected in series in a charging loop from a solar cell to a secondary battery is detected. FIG. 4 shows a specific circuit configuration.

In FIG. 4, reference numeral 10 denotes a solar cell, 12 denotes a secondary battery, and 14 denotes a diode for preventing backflow. A comparator 16 has a positive input connected to the anode terminal of the backflow preventing diode, and a negative input connected to the cathode terminal. Reference numeral 18 denotes a booster circuit that boosts the output voltage of the secondary battery 12 and supplies the boosted voltage as a power source for the comparator 16. The reason why the power supply voltage of the comparator 16 is higher than the voltage of the secondary battery 12 is as follows. That is, since the anode voltage of the diode for preventing backflow during charging is higher than the positive voltage of the secondary battery, using a secondary battery as the power supply of the comparator 16 causes a malfunction of the comparator 16,
The boosted output is used as a power supply. Also, a method of stepping down the voltage of the anode and cathode of the diode for preventing backflow by the resistance voltage division between the ground terminals without using the booster circuit is conceivable, but this resistance wastes the solar cell and the secondary battery. It is not preferable because it causes power consumption.

[0007]

As described above, the conventional charging operation detecting circuit provided as the detecting means of the charging operation is complicated since the boosting circuit must be operated to perform the detecting operation. Was. Further, there is wasteful power consumption in the booster circuit itself, which is not preferable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional drawbacks. The gist of the present invention is to detect the voltage across the backflow prevention diode to detect the charging operation from the solar cell to the secondary battery. The purpose of the present invention is to provide a simple circuit configuration.

[0009]

In order to achieve the above object, a power supply according to the present invention is charged from a solar cell.
Power supply device having secondary battery and battery check circuit
In the above, the transistor for charging operation detection is
Installed between the battery and the secondary battery, the base-
The emitter junction forms a diode for backflow prevention, and
Detect charging operation from the collector terminal of the transistor
A charging operation detecting means is provided, and charging is performed by the charging operation detecting means.
When the battery is detected to be
-A power supply characterized by operating a check circuit
It is.

[0010]

With the above arrangement, the circuit configuration is simplified, and the current consumption when there is no charging operation is extremely reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments.

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 of charging operation detection.
A PNP transistor having 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 cell, and the diode 22 and the resistor 24 connected in series are connected between the collector and the ground terminal. . 26 is a CMOS (C
The input of the buffer circuit 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 denotes a light emitting diode (LED) connected to the collector of the transistor 28.

The operation of the embodiment constructed as described above will now be described.

When there is no charging operation from the solar cell 10 to the secondary battery 12, since the emitter-base of the PNP transistor 20 is reverse-biased, the PNP transistor 20 is off. Therefore, the collector current does not flow, and 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, the 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. If the resistance value of the resistor 24 is sufficiently large, the transistor 20 is saturated. Therefore, the input voltage Vin of the buffer circuit 26 is represented by the following equation.

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

V + = Vs−Vbe (2) where Vbe is a voltage between the base and the emitter of the transistor 20. In a normal silicon transistor and diode, Vbe is used.
Since ≒ Vf is satisfied and Vce is a low value, Vin becomes a value slightly lower than V + from the expressions (1) and (2). Therefore, the output of the buffer circuit 26 becomes HIGH level, the transistor 28 is turned on and the LED 30 is turned on to indicate that the solar cell is being charged. As described above, the buffer circuit 26
Is shifted to a value slightly lower than its power supply voltage, so that the buffer circuit 26 can operate normally.

In the conventional example shown in FIG.
6 detects the presence or absence of a charging operation, so that it is necessary to operate the booster circuit 18 and supply power to the comparator 16 even when there is no charging operation, so that wasteful power is consumed. Contrary to this, in the present embodiment shown in FIG. 1, when no charging operation is performed, the PNP transistor 20 is off, so that there is no power consumption here. The power consumption of the buffer circuit itself is very small. As described above, in this embodiment, there is an advantage that the power consumption of the detection circuit itself when there is no charging operation can be reduced to substantially zero, with a simple configuration.

Next, a second embodiment is shown in FIG. FIG.
FIG. 5 is an electric circuit diagram showing a main part of a second embodiment of the present invention. In the drawing, reference numeral 34 denotes a PNP transistor for detecting a charging operation (hereinafter, referred to as a detecting 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 of the diode 14 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 switching transistor controlled by the output of the microcomputer 38, 42 is a battery check circuit,
Reference numeral 44 denotes a liquid crystal display device for displaying the remaining battery capacity. The connection point between 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 the embodiment constructed as described above will now be described. When there is no charging operation from the solar cell 10 to the secondary battery 12, the diode 14 for backflow prevention is reverse-biased, and 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 battery 10 to the secondary battery 12 is performed, the diode 14 for backflow prevention is forward-biased. Accordingly, a 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 operation, and turns on the power switching transistor 40. As a result, power is supplied to the battery-check circuit 42, and a battery check operation is performed. The check voltage is transferred to the microcomputer 38, and the microcomputer 38 converts this voltage into A / 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
This is performed while the charging operation for the secondary battery 12 is being performed.

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 updating of the liquid crystal display is limited to when the secondary battery is being charged. However, when the liquid crystal display is used for a camera, for example, it is very easy to perform the updating also during the shooting operation of the camera. Also, in this embodiment, as in the first embodiment, when there is no charging operation to the secondary battery, the detection transistor 34 is off, and the microcomputer 38 is in the hold state and the power switching transistor 40 is off. Therefore, the current consumption of this electric circuit is suppressed to almost zero.

Since the resistor 36 connected to the base of the detecting transistor 34 is intended only to limit 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 therebetween, which also has a function of a backflow prevention diode. 52 is an NPN phototransistor whose emitter is connected to the ground. 54
Is a switching PNP transistor, the base of which is connected to the collector of the phototransistor 52, and the collector of the transistor 54 is connected to a resistor 58. A resistor 5 is connected between the base and the emitter of the transistor 54.
6 are connected. Phototransistor 52 is LED
A resistor 60 is provided at a position capable of receiving the light emitted from the light source 50 and between the collector of the phototransistor 52 and the base of the PNP transistor 54.

The operation of the embodiment constructed 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 the LED 50 is reverse-biased, so that 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 HIGH level. This HIGH level signal becomes a charge detection signal, and this signal is used as in the first or second embodiment and is input to a microcomputer or the like (not shown). Also,
Also 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 has been described in detail based on the above embodiments, the present invention provides a simple circuit for detecting the charging operation from the solar cell to the secondary battery by detecting the voltage across the backflow preventing diode. Since the current consumption when there is no charging operation can be minimized and a simple circuit configuration is sufficient, the effect is significant.

[Brief description of the 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 charging circuit for a secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Solar cell 12 Secondary battery 20 PNP transistor 22 Diode 24 Resistance 26 Buffer circuit 28 Transistor 30 Light emitting diode 32 Resistance

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J ^7/ 00-7/12 H02J ⁷ /34-7/36

Claims (1)

(57) [Claims] A secondary battery charged from a solar battery and a battery.
In a power supply device having a terry check circuit, a transistor for detecting a charging operation is provided between the solar cell and the secondary battery, and the base-emitter junction of the transistor is reversed.
A charging operation detection device which constitutes a diode for preventing current flow and detects a charging operation from a collector terminal of the transistor;
Means, and the charging operation is performed by the charging operation detecting means.
Battery check
A power supply device for operating a road .