JPH0775458B2 - Solar battery charger - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solar battery charging device that charges a secondary battery using a solar battery.

(B) Conventional Technology Conventionally, in devices using a solar cell as a power source, a circuit for charging a secondary battery with an electromotive force of the solar cell is provided in order to stabilize the power source voltage regardless of fluctuations in illuminance. A secondary battery is used as a power source together with the battery. Further, in a device that charges a secondary battery with a generator, a solar cell may be used as an auxiliary charging device for the secondary battery.

Second example of a typical secondary battery charging circuit using solar cells
Shown in the figure. In FIG. 2, S is a solar cell and B is a secondary battery. R1 is a charging current limiting resistor and D1 is a backflow prevention diode. The transistor Q1 is connected in parallel with the charging current limiting resistor R1 and controls the charging current that bypasses the resistor R1 and flows. Resistor R8 is the transistor Q1 base bias resistor. Further, R6 and R7 form a resistance voltage dividing circuit together with R1, and the transistor Q4 receives the output voltage of the resistance voltage dividing circuit at its base to control the base potential of the transistor Q1.

The operation of the entire circuit shown in FIG. 2 is as follows. That is, when the illuminance on the solar cell S is a certain value or more, the charging current I1 flows through the resistor R1 and the diode D1 to the secondary battery B due to the starting force. At this time, the transistor Q4 determines the base potential of the transistor Q1 according to the divided voltage by R6 and R7, and the charging current I2 flows through the transistor Q1 accordingly. As a result, a charging current of I1 + I2 flows through the secondary battery B. When the secondary battery B becomes fully charged and the voltage becomes high, the divided voltage of R6 and R7 rises and the transistor Q4 lowers the base potential of the transistor Q1. Therefore, the on-resistance of Q1 increases and Q1 increases. The current I2 flowing through the device decreases. This limits the charging current for the secondary battery B and prevents overcharging. On the contrary, when the voltage of the secondary battery B is low, the charging voltage for the secondary battery B is large, so that the electromotive voltage of the solar battery S is lowered, and accordingly, the partial voltage of R6 and R7 is lowered, and Q4 is Increase the base potential of Q1. This reduces the on resistance of Q1 and increases the current I2.

As described above, the secondary battery is charged according to the secondary battery voltage and the illuminance of the solar battery.

(C) Problems to be Solved by the Invention However, as shown in FIG. 2, in the conventional solar battery charging device, the backflow prevention diode D1 is provided in the charging current path for the secondary battery, and the voltage stabilization is performed. Since the base bias of the transistor Q1 that conducts switching is given by the bias resistor R8 connected between the collector and the base, even when the on-resistance of the transistor Q1 is the lowest, the collector-emitter voltage is PN between the base and emitter. It does not become lower than the junction potential (about 0.7V). Therefore, the voltage drop in the voltage stabilizer is about 1.6V together with the drop voltage of the backflow prevention diode, and the charging current does not flow unless the electromotive voltage of the solar battery S is at least 1.6V or more than the voltage of the secondary battery B. , Could not be charged efficiently. Of course, if the number of cells of the solar battery S is increased, the overall electromotive voltage can be increased, but not only the solar battery becomes larger, but also the loss due to the voltage stabilizing transistor Q1 increases, and efficient charging cannot be performed.

An object of the present invention is to provide a solar cell charging device in which the voltage drop in the voltage stabilizer is reduced by adding a small number of parts to solve the above problems.

(D) Means for Solving the Problems The solar battery charger of the present invention connects the reference potential ends of the solar battery and the secondary battery with each other, and connects the charging current limiting resistor and the backflow prevention diode in series with the first circuit. A voltage stabilization circuit in which a parallel circuit with the first transistor is connected between the output terminal of the solar cell and the input terminal of the secondary battery, and the second transistor that applies a base bias to the first transistor is the base of the first transistor. A base bias circuit provided between the reference potentials, a voltage dividing resistor that divides the voltage of the secondary battery, and a divided voltage change that is inverted and applied to the base of the second transistor.
And a charging voltage detecting circuit provided with the transistor.

(E) Action In the solar battery charger of the present invention, the reference potential terminals of the solar cell and the secondary battery are connected to each other, and the voltage stabilizing circuit is connected between the output terminal of the solar cell and the input terminal of the secondary battery. ing. This voltage stabilization circuit is composed of a series circuit of a charging current limiting resistor and a backflow prevention diode, and a parallel circuit of a first transistor. In addition, the second transistor provided in the base bias circuit is provided between the base of the first transistor and the reference potential and applies a bias voltage to the base of the first transistor. Further, the voltage dividing resistor provided in the charging voltage detecting circuit divides the voltage of the secondary battery, and the third transistor inverts the divided voltage change and applies it to the base of the second transistor.

As described above, since the backflow prevention diode is not connected in series to the first transistor, the voltage drop due to the voltage stabilizer does not become larger than the collector-emitter voltage of the first transistor. Further, the base bias voltage of the first transistor is given from the second transistor, and the base bias resistor is not connected between the collector and the base.
The emitter-to-emitter voltage becomes lower than the PN junction potential in the lowest on-resistance state. Therefore, the voltage drop in the voltage stabilizing circuit can be remarkably reduced as compared with the conventional device, and efficient charging can be performed even in low illuminance.

(F) Example FIG. 1 shows a circuit diagram of a solar cell charging device according to an example of the present invention. In FIG. 1, S is a solar cell and B is a secondary battery. As shown in the figure, the positive terminal of the solar cell S and the positive terminal of the secondary battery B are commonly connected as a reference potential. Then, the negative terminal (output terminal) of the solar cell S and the negative terminal of the secondary battery B
A voltage stabilizing circuit 1 is provided between terminals (input terminals). The voltage stabilizing circuit 1 comprises a series circuit of a charging current limiting resistor R1 and a backflow prevention diode D1 and a parallel circuit of a first transistor Q1. In the figure, 2 is a base bias circuit, and the second transistor Q2 is connected between the base of the first transistor Q1 and the reference potential via a resistor R2. 3 is a charging voltage detection circuit, and resistors R4 and R5 are resistors R1
At the same time, the voltage of the secondary battery B is divided. The third transistor Q3 inverts the output voltage change of the resistance voltage dividing circuit and supplies the voltage to the base of the second transistor Q2.
The resistor R3 is a load resistor of the transistor Q3.

The operation of the entire circuit shown in FIG. 1 is as follows. First, when the secondary battery B is not fully charged and the solar cell S is provided with standard illuminance, the current I1 flows through the diode D1 and the resistor R1. Also, the transistor Q3
The voltage across the resistor R4 is added to the base potential of, and the corresponding collector current of Q3 flows through the resistor R3 to determine the base potential of the transistor Q2. As a result, the collector current of Q2, that is, the base current of Q1 is determined, and the current I2 flows through the transistor Q1. Therefore, the charging current of I1 + I2 flows through the secondary battery B.

When the secondary battery B approaches the fully charged state, its voltage increases. As a result, the base potential with respect to the emitter of Q3 decreases (absolute value increases), and the base current of Q3 increases and R3 increases.
The collector current of Q3 flowing through the gate increases and the base potential of Q2 rises (absolute value decreases). As a result, the collector current of Q2, that is, the base current of Q1 decreases, and the collector current I2 flowing through Q1 also decreases. As a result, the charging current flowing through the secondary battery B is limited.

Conversely, when the voltage of the secondary battery B decreases, the base potential of the emitter of Q3 as a reference increases, the collector current of Q3 flowing through R3 decreases, and the base potential of Q2 decreases. This increases the collector current of Q2, that is, the base current of Q1, and increases the collector current I2 of Q1. In this way, the charging current of the secondary battery is adaptively controlled according to the voltage of the secondary battery B.

In FIG. 1, even if the electromotive voltage of the solar cell S is 0, a current does not flow in the reverse direction in the transistor Q1, so a backflow prevention diode is not necessary in the current path of Q1. In addition, the base potential of Q1 is applied from the reference potential side via transistor Q2 and resistor R2, so it is not limited to the PN junction voltage between the base and emitter as in the past, and the ON resistance of Q1 is the lowest. Therefore, the collector-emitter voltage becomes about 0.1V. Therefore, the charging can be started from the state where the electromotive voltage of the solar cell S exceeds the voltage of the secondary battery B by more than 0.1 V, and the charging current at standard illuminance can be increased compared to the conventional case. For example, when the circuit is configured with the same capacity for the solar battery S and the secondary battery B, the charging current at standard illuminance was 90 mA in the conventional device shown in FIG. 2, whereas it was 130 mA in the device shown in FIG. ~ 140mA, charging efficiency improved by about 40%.

(G) Effect of the Invention According to the present invention, since the voltage drop in the voltage stabilizing unit for preventing overcharge of the secondary battery is significantly reduced, charging can be started from low illuminance, and standard illuminance is maintained. Can ensure a sufficient charging current. This enables efficient charging.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a solar battery charging device according to an embodiment of the present invention. FIG. 2 is a circuit diagram of a conventional solar battery charging device. 1 ... Voltage stabilization circuit, 2 ... Base bias circuit, 3 ...
… Charging voltage detection circuit, Q1 …… First transistor, Q2…
… Second transistor, Q3 …… Third transistor, R1
...... Charging current limiting resistance, R4, R5 ...... Voltage resistance, D1 ...... Backflow prevention diode, S ...... Solar cell, B ...... Secondary battery.

Claims (1)

[Claims] 1. A solar cell and a secondary battery are connected at their respective reference potential terminals, and a series circuit of a charging current limiting resistor and a backflow prevention diode and a parallel circuit of a first transistor are connected to the output terminal of the solar cell. A voltage stabilization circuit connected between the input terminals of the secondary battery; a base bias circuit in which a second transistor for applying a base bias to the first transistor is provided between the base of the first transistor and a reference potential; A voltage dividing resistor for dividing the voltage and a third resistor for inverting the divided voltage change and giving it to the base of the second transistor.
A charging device for a solar cell, comprising: a charging voltage detection circuit provided with the transistor.