JP2016057762A - Charge circuit of secondary battery as power source of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve charging at a low illuminance when a secondary battery is charged with a solar cell as a power source.SOLUTION: When a control circuit 5 for MPPT (Maximum Power Point Tracking)-controlling a DC-DC converter 2 is provided, unless a quantity of light becomes a threshold quantity of light corresponding to the maximum power point of 0.5 Sun, charging is not started. Thus, if the lower limit of the MPPT control which is equal to or more than a threshold value of 0.05 Sun, a control circuit 4 for intermittently giving a reset trigger to the converter 2 is provided. Since the converter 2, when reset, separates a load (after the converter 2) from a solar battery 10, the load of the solar battery 10 becomes light-weighted and is recovered from a shut-down state, and an open end voltage rises to the maximum voltage. Even if the risen voltage does not become equal to or more than the threshold value of 0.5 Sun, when it becomes equal to or more than the threshold value of 0.05 Sun, the DC-DC converter 2 is recovered from the shut-down state, and spontaneously start operation. In so doing, even if at a low illuminance, energy can be efficiently fetched.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a circuit for charging a secondary battery using a solar battery as a power source, and particularly relates to a circuit including a DC-DC converter that can be charged with a stable voltage by stepping up or down.

  As described above, a secondary battery charging circuit using a solar battery as a power source is provided with a DC-DC converter so that it can be charged with a stable voltage by stepping up or down. The DC-DC converter control circuit includes MPPT (Maximum Power Point Tracking) control capable of following an optimum operation (maximum power) point that fluctuates due to changes in weather conditions or the like in order to obtain higher power generation and charging efficiency. Etc. are installed.

  For example, in Patent Document 1, when a secondary battery is charged with the output power using a solar battery as a power source, if the input (solar battery output) voltage is equal to or higher than a threshold value, the voltage is boosted to a full charge voltage, and is lower than the threshold value. The MPPT control with a simple configuration and low power consumption is realized by lowering the charging voltage according to the voltage difference from the threshold.

JP 2008-90672 A

  Here, FIG. 7 shows the MPPT control operation. As described above, the MPPT control is a control for operating the solar cell at the maximum power point, and when the predetermined threshold light amount A exceeds a predetermined value from the standby (shutdown) state, the DC-DC converter is activated, and the second When the amount of light is less than the threshold light amount B, the DC-DC converter is stopped and waited (shut down). The threshold light amount A depends on the power generation capability of the solar cell and is a light amount sufficient to drive the DC-DC converter sufficiently. The threshold light amount B is a light amount that can maintain the operation of the DC-DC converter at a minimum, for example. . When the solar cell has a small capacity, for example, the threshold light amount A is the maximum power point, and when the amount of light in the midsummer day is 1 Sun, it is 0.5 Sun, and the threshold light amount B is 0.05 Sun. .

  And the hysteresis by such two threshold light quantity A and B is provided for the stability of operation | movement. However, if the power generation capacity of the solar cell is sufficiently high, there is no substantial problem because it is possible to supply enough energy to remove the DC-DC converter from the shutdown state with a little light, but the solar cell has a small capacity. For example, if direct sunlight is not applied, the threshold light amount A cannot be exceeded, and charging cannot be started. In other words, once the light amount does not exceed the threshold light amount A due to the hysteresis, charging cannot be performed even if the light amount is in the range of the threshold light amounts A to B. In particular, when the solar cell is a dye-sensitized solar cell (DSC), although power generation with low illuminance is possible, the generated power is small at the low illuminance, and such a phenomenon is remarkable.

  An object of the present invention is a low illuminance light amount that does not exceed a threshold light amount for activation in MPPT control of a DC-DC converter in a charging circuit that uses a solar cell as a power source and charges a secondary battery with its output power. Also, it is to provide a charging circuit that can effectively take in energy.

  The charging circuit of the present invention is a charging circuit that uses a solar battery as a power source to charge a secondary battery with its output power, and converts the output power of the solar battery into a charging voltage and a charging current that are predetermined for the secondary battery. A DC-DC converter to be applied and MPPT control for monitoring the output voltage of the solar cell and operating the DC-DC converter so that the output voltage is constant, thereby operating the solar cell at a maximum power point And a second converter control circuit that resets the DC-DC converter at predetermined time intervals to release the load from the solar cell.

  According to the above configuration, when charging the secondary battery by using the solar battery as a power source, the DC-DC converter converts the output power of the solar battery into a charging voltage and a charging current predetermined for the secondary battery. When the first converter control circuit for MPPT-controlling the DC-DC converter is provided, the output voltage of the solar cell once rises to a sufficient first threshold voltage corresponding to, for example, the maximum power point. The first converter control circuit starts MPPT control. Thereafter, the MPPT control is performed with a predetermined hysteresis, and when the voltage becomes lower than the sufficiently low second threshold voltage, the DC-DC converter is stopped. For example, if the illuminance of sunlight during midsummer day is 1 Sun, the first threshold voltage corresponds to a threshold light amount of 0.5 Sun, and the second threshold voltage corresponds to a threshold light amount of 0.05 Sun.

  On the other hand, the DC-DC converter can operate by itself using the output power of the solar cell as a power source, and even if it is less than the second threshold voltage of 0.05 Sun, a voltage is output from the solar cell. If so, the operation, that is, the connection between the solar battery and the secondary battery as a load is attempted. Therefore, a second converter control circuit is provided, and the DC-DC converter is reset every predetermined time, and the load is disconnected from the solar cell by the reset.

  The disconnection of the load differs depending on the structure of the DC-DC converter. For example, when the enable terminal EN is reset, the oscillation of the DC-DC converter is completely stopped, and the input current from the solar cell is only 0. 0. At 3 mA, the DC-DC converter as a load and the secondary battery are disconnected from the solar battery, and the output terminal of the solar battery becomes an open end.

  As a result, the load on the solar cell is reduced, and the solar cell recovers from the shutdown state. For example, the voltage at the open end rises to the maximum voltage. Even if the rising voltage does not become the first threshold voltage or more, if the voltage becomes the second threshold voltage or more during reset, the DC-DC converter returns from the shutdown state and operates spontaneously. become.

  Therefore, even if the low illuminance state where the sunlight illuminance exceeds 0.05 Sun, for example, continues, the DC-DC converter can be activated and energy can be taken in effectively.

  In the charging circuit of the present invention, the second converter control circuit monitors the output voltage of the DC-DC converter, and when the output voltage becomes equal to or higher than the stable operation voltage of the DC-DC converter, The reset of the DC converter is stopped.

  According to the above configuration, when the DC-DC converter is started as described above and the output voltage becomes equal to or higher than the stable operation voltage and the secondary battery is normally charged, the second converter control circuit The reset operation of the DC-DC converter is stopped.

  Therefore, it is possible to realize normal MPPT control and prevent a situation in which the DC-DC converter is undesirably reset and restarted repeatedly in a state where it can be stably charged, and it becomes more effective continuously. Can be charged.

  Furthermore, the charging circuit of the present invention further includes an illuminance sensor that monitors the illuminance and stops the operation of the second converter control circuit if the illuminance is a level lower than the second threshold voltage. Features.

  According to the above configuration, if the illuminance is lower than the second threshold voltage, the DC-DC converter does not start even if the second converter control circuit resets the DC-DC converter. In such a situation, the second converter control circuit is stopped by the illuminance sensor.

  Therefore, unnecessary power consumption from the secondary battery during standby of the second converter control circuit that resets the DC-DC converter can be suppressed.

  In the charging circuit of the present invention, the rise of the output voltage due to the start of the solar cell is detected, and the MPPT control by the first converter control circuit is set to the minimum load state over a predetermined time from the rise timing. And a third converter control circuit.

  According to the above configuration, when charging the secondary battery by using the solar battery as a power source, the DC-DC converter converts the output power of the solar battery into a charging voltage and a charging current predetermined for the secondary battery. When a first converter control circuit that performs MPPT control on the DC-DC converter is provided, the DC-DC converter starts operating when the output voltage of the solar cell rises, and the first converter control circuit performs MPPT control. The MPPT control operates under a relatively large load, and when the load is connected to the solar cell via the DC-DC converter, the output voltage of the rising solar cell rapidly decreases, As a result, the DC-DC converter is locked out (cannot start up).

  Therefore, a third converter control circuit is provided to detect the rise of the output voltage due to the activation of the DC-DC converter, and the MPPT control by the first converter control circuit is performed for a predetermined time from the rise timing. Set to the minimum load state. Specifically, even if the illuminance of sunlight is different, the voltage at the point where the solar cell is the maximum power point is substantially equal, and a difference in output power is generated between the output currents. The DC converter is operated to have a minimum output (charge) current.

  Therefore, even if the charging circuit starts operating with weak sunlight, the DC-DC converter can be started up normally (the operation is started) without being locked out.

  Preferably, the third converter control circuit includes a monostable multivibrator circuit. Specifically, for example, a first capacitor that detects activation of the DC-DC converter as a pulse, and turns on in response to a detection pulse by the first capacitor, and the MPPT control by the second converter control circuit In response to a detection pulse generated by the first capacitor and the first capacitor that artificially grounds the input terminal of the output voltage of the solar cell in the second converter control circuit. The third converter control circuit includes a second capacitor that starts charging, performs a time-limited operation over the predetermined time, and turns off the first switch element when charging is completed. .

  Furthermore, the charging circuit of the present invention includes a first reference voltage circuit that creates a first reference voltage determined in advance from an output voltage of the DC-DC converter, and the first reference voltage and the secondary battery. A fourth converter control circuit having a first comparator for performing an overcharge protection operation for comparing the charging voltage and stopping the DC-DC converter when the charging voltage becomes equal to or higher than the first reference voltage; A second reference voltage circuit that creates a second reference voltage that is predetermined higher than the first reference voltage from the output voltage of the DC converter, and the second reference voltage and the charging voltage of the secondary battery. A fifth comparator having a second comparator for performing a no-load detection operation for invalidating the overcharge protection operation by the fourth converter control circuit when the charging voltage is equal to or higher than the second reference voltage. And further comprising a converter control circuit.

  According to the above configuration, when the fourth converter control circuit performs the overcharge protection operation of the DC-DC converter, the fifth converter control circuit is provided, and the charge voltage is supplied to the first converter for the overcharge protection. If it is higher than the second reference voltage higher than the reference voltage, it is determined that the load (secondary battery) is not connected, and the overcharge protection operation by the fourth converter control circuit is invalidated.

  Therefore, in the no-load state, when the fourth converter control circuit performs the overcharge protection operation of the DC-DC converter and stops or reduces the output, the charge voltage at the open end immediately decreases and the overcharge protection operation is released. When the fifth converter control circuit is unloaded, the overcharge protection operation is performed while the DC-DC converter starts operation and the overcharge protection operation is performed again. Such a problem can be prevented by invalidating.

  In the charging circuit of the present invention, the solar cell is a dye-sensitized solar cell.

  According to said structure, when the said solar cell is a dye-sensitized solar cell (DSC), although electric power generation with low illuminance is attained, in the said low illuminance, generated electric power is also small, and the low illuminance at the time of starting etc. The present invention, which can sometimes stabilize the operation of the DC-DC converter, is particularly suitable.

  Furthermore, in the charging circuit of the present invention, the solar cell has a light-receiving surface formed with a design based on a difference in pigment.

  According to said structure, the design can be formed in a light-receiving surface using the difference in a pigment | dye by making the said solar cell into a dye-sensitized solar cell (DSC).

  As described above, the charging circuit according to the present invention uses a solar battery as a power source, and in the charging circuit that charges the secondary battery with the output power, the first converter control circuit that performs MPPT control of the DC-DC converter is provided. Provided with a second converter control circuit, the second converter control circuit resets the DC-DC converter at a predetermined time, and by the reset, the load is disconnected from the solar cell, for example, the output of the solar cell Make the terminal open.

  Therefore, the load on the solar cell is lightened and recovered from the shutdown state. For example, since the open-circuit voltage rises to the highest voltage, it becomes easy to start the DC-DC converter even when the low illumination state continues. Energy can be taken in effectively.

It is a block diagram which shows the electric constitution of the charging circuit which concerns on one Embodiment of this invention. It is a graph which shows the output characteristic of a solar cell. It is a wave form diagram for demonstrating operation | movement of the monostable multivibrator circuit in the said charging circuit. It is a block diagram which shows typically only the structure which performs MPPT control in the said charging circuit, and its lockout prevention control. It is a wave form diagram for demonstrating the said MPPT control and a lockout prevention control function. It is a block diagram which shows typically only the structure which performs the prohibition control by the overcharge protection function in the said charging circuit, and its battery absence (no load) detection. It is a figure for demonstrating the said MPPT control. It is a block diagram which shows typically only the structure which performs the intermittent reset trigger operation | movement in the said charging circuit. It is a wave form diagram for demonstrating operation | movement of the oscillation part which implement | achieves the said intermittent reset trigger operation | movement.

  FIG. 1 is a block diagram showing an electrical configuration of a charging circuit 1 according to an embodiment of the present invention. The charging circuit 1 uses the solar battery 10 as a power source and charges the secondary battery 11 with the output power. In the present embodiment, the solar cell 10 is a dye-sensitized solar cell (DSC) that can generate power at low illuminance and can be used indoors, and the secondary battery 11 is a nickel-hydrogen battery. . The secondary battery 11 is assumed to connect two AAA sizes in series. Therefore, the rated voltage is 1.2V × 2 = 2.4V.

  The charging circuit 1 generally includes a DC-DC converter 2 that converts the output power of the solar cell 10 into a predetermined charging voltage and charging current for the secondary battery 11 and gives the DC-DC converter 2. The control circuit 3-7, 9 and the illuminance sensor 8 are provided.

  The DC-DC converter 2 includes a DC-DC module 21, an input circuit 22, a constant voltage circuit 23, diodes D20 and D24, and resistors R20 and R28. The input circuit 22 includes an input voltage limiting circuit 24, a diode D21, a resistor R21, and a smoothing capacitor C21.

  The output voltage of the solar cell 10 is output between the high-side power supply line K1 and the common GND line K2. The power supply line K1 includes a backflow prevention diode D21 and an input resistor R21, and an input voltage limiting circuit 24 and a smoothing capacitor C21 are connected to the GND line K2 downstream of the input resistor R21. Is done. The input voltage limiting circuit 24 is composed of a series circuit of a Zener diode D22 and a diode D23. Thus, the power supply input terminal VIN of the converter IC 25 in the DC-DC module 21 is limited to a maximum voltage of 5.5 V and stabilized against lightning and the like, and the output voltage of the solar cell 10 is stabilized. Is entered.

  The DC-DC module 21 includes the converter IC 25, resistors R22 to R27, capacitors C22 to C26, and an inductor L21. The high-side input voltage from the smoothing capacitor C21 is input to the power supply input terminal VIN of the converter IC25 via the resistor R22, and pulls up the enable terminal EN of the converter IC25 via the resistor R27. The high-side input voltage from the smoothing capacitor C21 is given to the terminal L of the converter IC25 through the inductor L21. Further, a resonance capacitor C22 is provided between the input side of the inductor L21 and the GND line K2. Between the power input terminal VIN and the GND line K2, there is provided a capacitor C23 for removing noise caused by resonance, which will be described later.

  The converter IC 25 performs a step-up / step-down operation on the input voltage to the power input terminal VIN using the inductor L21 and the capacitors C22 and C23, and the noise removing capacitor C25 from the output terminal Vout for driving a large-capacity load. A voltage is output to the power supply line K3 via the voltage, and the voltage is applied as a charging voltage to the secondary battery 11 via the diode D24 and the resistor R28. The output voltage from the output terminal Vout to the power supply line K3, including the drop of the diode D24, is set such that the charging voltage of the secondary battery 11 is 2.4 V at the minimum and 3.0 V at the maximum. 3 to 2.7V. The output voltage of the output terminal Vout is also input to the feedback terminal FB via the voltage dividing resistors R25 and R26 and the capacitor C24.

  The converter IC 25 supplies control power from the external power output terminal Vaux serving as its own power source to the power supply line K4 via the noise removing capacitor C26, the diode D20, and the resistor R20. The constant voltage circuit 23 that supplies the control power to the other control circuits 5 to 7 includes a smoothing capacitor C27, voltage dividing resistors R29 and R30, and a shunt regulator D25. A smoothing capacitor C27 is interposed between the power supply line K4 and the GND line K2, and the shunt regulator D25 is controlled according to the voltage divided by the voltage dividing resistors R28 and R29. The control power supply supplied to the other control circuits 5 to 7 is stabilized at 3.9V.

  The input voltage to the power supply input terminal VIN of the converter IC 25 is also divided by the resistors R23 and R24 and applied to the low voltage lock terminal LVLO. The converter IC 25 operates when the input voltage of the low voltage lock terminal LVLO is 250 mV or higher, stops when the input voltage is lower than that, and stops the voltage output to the load (secondary battery 11).

  On the other hand, the control circuit 3 performs an overcharge protection operation on the DC-DC converter 2, and includes a reference voltage circuit 31, a comparator 32, resistors R31 to R37, capacitors C31 to C33, a switch element Q31, A transistor Q32, a switch SW1, and a light emitting diode D31 are provided. The reference voltage circuit 31 includes resistors R38 to R40 connected in series between the lines K4 and K2, and a shunt regulator D32. The shunt regulator D32 controls the voltage at the connection point between the resistors R38 and R39 according to the voltage at the connection point between the resistors R39 and R40, and thus the reference voltage circuit 31 is supplied from the control power supply of 3.9V. A reference voltage of 1.65 V corresponding to 3.0 V of full charge is created with the voltage of the secondary battery 11 and applied to the non-inverting input terminal of the comparator 32 through the input resistor R31 and the capacitor C31.

  The comparator 32 is supplied with power from the power supply line K4 and outputs a charging (output) voltage of the secondary battery 11 output between a power supply line K5 and a GND line K2, which will be described later, input to the inverting input terminal to the resistor R32. , R33 and the capacitor C32 and the reference voltage of 1.65V are compared, and when the charging (divided) voltage becomes equal to or higher than the reference voltage, the DC-DC converter 2 is stopped. Perform charge protection operation. The overcharge protection operation is performed by setting the output terminal of the comparator 32 connected to the power supply line K4 to a low level (short circuit to the GND line K2) by the pull-up resistor R34. The output terminal of the comparator 32 is set to high level (open). A feedback resistor R35 is provided between the output terminal and the non-inverting input terminal of the comparator 32, and the comparator 32 is composed of a Schmitt circuit having hysteresis.

  The output of the comparator 32 is also applied to the gate of the switch element Q31. The drain of the switch element is connected to the power supply line K4 via the resistor R36, and is connected to the base of the transistor Q32, and the source is the above-mentioned. Connected to the GND line K2. The collector of the transistor Q32 is connected to the enable terminal EN of the converter IC25, and the potential is held by the capacitor C33. The emitter of the transistor Q32 is connected to the GND line K2.

  Therefore, when the charge (output) voltage of the secondary battery 11 is low and the comparator 32 outputs a high level, the switch element Q31 is turned on, the base voltage of the transistor Q32 is lowered, and the transistor Q32 is turned off. The enable terminal EN of the converter IC 25 becomes high level, and the converter IC 25 operates. On the other hand, when the charging voltage increases to an overcharge level (over 3.0 V), the comparator 32 outputs a low level, the switch element Q31 is turned OFF, and the base voltage of the transistor Q32 is pulled by the resistor R36. The transistor Q32 is turned on, the enable terminal EN of the converter IC25 becomes low level, the converter IC25 stops its operation, and the load (the power supply line K3 to the secondary battery 11) is disconnected to protect the overcharge. Operation is performed.

  The control circuit 3 is provided with a light emitting diode D31 as a display element capable of displaying the state of charge. The light emitting diode D31 is connected between the lines K3 and K2 by a series circuit of a current limiting resistor R37, the light emitting diode D31, and the switch SW1. Accordingly, during charging, a high level is output from the output terminal Vout of the converter IC 25 to the power supply line K3. When the switch SW1 is turned on in this state, the light emitting diode D31 is lit and it is confirmed that charging is in progress. can do. The configuration related to these light emitting diodes D31 is not particularly provided in an actual product as it is connected only at the time of charging confirmation at the time of assembly.

  In addition to the basic charging circuit configured as described above, in the charging circuit 1 of the present embodiment, first, the output voltage of the solar cell 10 is monitored, and the DC-DC converter is configured so that the output voltage becomes constant. 2 is provided, and a control circuit 5 that performs MPPT control for operating the solar cell 10 at the maximum power point is provided. Further, in connection with the control circuit 5, the DC-DC converter 2 is activated. A control circuit 6 is provided for detecting the rise of the output voltage and setting the MPPT control by the control circuit 5 to the minimum load state for a predetermined time from the rise timing.

  The control circuit 5 includes a voltage dividing circuit 51, a reference voltage circuit 52, resistors R51 to R53, an operational amplifier 53, and capacitors C51 and C52. The voltage dividing circuit 51 is configured by resistors R54 and R55 connected in series between the lines K1 and K2. The voltage dividing circuit 51 divides the output voltage of the solar cell 10 at a predetermined voltage dividing ratio and passes through the input resistor R51. To the inverting input terminal of the operational amplifier 51. The reference voltage circuit 52 includes resistors R56 to R58 connected in series between the lines K4 and K2 and a shunt regulator D51, similarly to the reference voltage circuit 31 described above. The shunt regulator D51 controls the voltage at the connection point between the resistors R56 and R57 according to the voltage at the connection point between the resistors R57 and R58. Thus, the reference voltage circuit 52 is supplied from the control power supply of 3.9V. A reference voltage of 2.0 V corresponding to 4.0 V is created by the voltage of the solar cell 10 and applied to the non-inverting input terminal of the operational amplifier 53.

  The operational amplifier 53 is supplied with power from the power supply line K4, and its output is output between the resistors R25 and R26 connected in series between the lines K3 and K2 in the DC-DC converter 2 via the output resistor R53. Given to connection points. The connection point is connected to the feedback terminal FB of the converter IC 25, and the converter IC 25 controls the voltage of the output terminal Vout so that the input voltage to the feedback terminal FB becomes 500 mV. A capacitor C24 for stabilizing the voltage at the connection point is provided in parallel with the resistor R25. The output of the operational amplifier 53 is negatively fed back from the output resistor R53 via a feedback capacitor C51 and a feedback resistor R52.

  Here, FIG. 2 shows the output characteristics of the solar cell. The MPPT control is generally control for operating a solar cell at a maximum power point, and changes a load in accordance with the intensity of illumination light. And even if the output power is different, the voltage that becomes the maximum power point is substantially constant, so that a large amount of load current flows when the illumination light is strong, and a load current when the illumination light is weak. By reducing the size, the solar cell can be operated at the maximum power point. Specifically, the operational amplifier 53 compares the divided voltage of the output voltage of the solar cell 10 from the voltage dividing circuit 51 with the divided voltage of the internal power supply voltage from the reference voltage circuit 52 so that they are equal. Then, the voltage of the feedback terminal FB of the converter IC 25 is changed.

  However, once the MPPT control is activated, charging of the secondary battery 11 can continue even if the intensity of illumination light changes to some extent, but the solar battery 10 is connected to the secondary battery 11 (DC-DC converter 2). Since the DC-DC converter 2 starts at a setting with high power when the illumination light is weak, a large load current flows suddenly and the output voltage of the solar cell 2 decreases. Therefore, the DC-DC converter 2 does not rise (locks out), and the MPPT control of the control circuit 5 does not work. Thereafter, when strong illumination light strikes, the DC-DC converter 2 starts to operate and the MPPT control of the control circuit 5 starts to function, but there is a problem that charging cannot be performed during that time.

  Therefore, the control circuit 6 is provided. The control circuit 6 is composed of a monostable multivibrator circuit. Specifically, the control circuit 6 includes transistors Q61 and Q62, a switch element Q63, capacitors C61 and C62, resistors R61 to R66, and diodes D61 and D62.

  The capacitor C61 detects the activation of the DC-DC converter 2 as a pulse from the voltage of the output terminal Vout. The output of the capacitor C61 is given to the base of the transistor Q61 via the diode D61. Between the connection point of the capacitor C61 and the diode D61 and the GND line K2, a discharge diode D62 for preventing a negative pulse from being applied to the transistor Q61 when the voltage of the output terminal Vout becomes 0V, and A resistor R61 for differential (= pulse) output of the capacitor C61 is provided.

  The base of the transistor Q61 is connected to the GND line K2 through the resistor R62, and is connected to the gate of the switch element Q63 through the resistor R63. The emitter of the transistor Q61 is connected to the GND line K2, and the collector is connected to the power supply line K4 via the resistor R64, and is connected to one end of the capacitor C62 for time limit operation. The other end of the capacitor C62 is connected to the power supply line K4 via the resistor R65 and is also connected to the base of the transistor Q62. The emitter of the transistor Q62 is connected to the GND line K2, and the collector is connected to the power supply line K4 via the resistor R66 and also to the gate of the switch element Q63. The drain of the switch element Q63 is connected to the connection point between the resistors R54 and R55 in the control circuit 5, that is, the inverting input terminal of the operational amplifier 53 via the input resistor R51, and the source is connected to the GND line K2.

  FIG. 3 is a waveform diagram for explaining the operation of the control circuit 6 functioning as the monostable multivibrator circuit. In the stable state, as shown in FIG. 3 (d), the base of the transistor Q62 is pulled up by the resistor R65, the transistor Q62 is turned on, and its collector voltage is low as shown in FIG. 3 (e). At the level, the switch element Q63 is OFF. Therefore, in this state, the divided voltage of the output voltage of the solar cell 10 is applied to the voltage dividing point in the voltage dividing circuit 51 in the control circuit 5, that is, the inverting input terminal of the operational amplifier 53.

  As a result, the operational amplifier 53 outputs a voltage corresponding to the difference between the divided voltage of the output voltage of the solar cell 10 and the divided voltage of the reference voltage to the feedback terminal FB of the converter IC 25, and the DC-DC converter. The normal MPPT operation for controlling the load state (output current) 2 in a relatively large state can be performed. During this time, when the transistor Q62 is turned on, a charging current flows through the path of the resistor R64-capacitor C62-transistor Q62. The capacitor C62 reduces the voltage Vbe of the transistor Q62 from 0.6 V to 3.9 V which is the voltage of the power supply line K4. It is charged to 3.3V after subtraction.

  On the other hand, when the output voltage of the solar cell 10 rises during startup and the DC-DC converter 2 starts operating and the output voltage Vout rises as shown in FIG. As shown in b), a starting pulse is output from the capacitor C61. When this starting pulse exceeds the ON voltage of the transistor Q61 of 0.6V, the transistor Q61 is turned ON, and the collector voltage is reduced to approximately 0V as shown in FIG. Thus, as shown in FIG. 3D, the base voltage of the transistor Q62 is -3.3 (-(3.9- 0, 6)) After decreasing to V, the voltage increases as the capacitor C62 is discharged. The time constant of the rise is set to τ = C62 · R65, for example, 90 msec, and becomes the time limit of this monostable multivibrator circuit.

  During the time limit in which the base voltage of the transistor Q62 is lower than 0.6V, the transistor Q62 is turned off, and its collector voltage becomes high level as shown in FIG. Element Q63 is turned on. Therefore, the voltage dividing point in the voltage dividing circuit 51 in the control circuit 5, that is, the voltage at the inverting input terminal of the operational amplifier 53 is reduced to approximately 0V. As a result, the operational amplifier 53 outputs a high level, the input voltage to the feedback terminal FB of the converter IC 25 increases, and the converter IC 25 operates in the minimum load state.

  When the time limit elapses, the base voltage of the transistor Q62 reaches 0.6V, the transistor Q62 is turned on, the switch element Q63 is turned off, and charging of the capacitor C62 is started. In this way, the control circuit 6 can realize the monostable multivibrator as described above. FIG. 4 schematically shows only the configuration for performing such MPPT control and its lockout prevention control in the charging circuit 1.

  FIG. 5 is a diagram for explaining the MPPT control of the DC-DC converter 2 and its lockout prevention control function by the control circuits 5 and 6. (A) shows the output voltage of the solar cell 10, (b) shows the output of the DC-DC converter 2, and (c) shows the operation of the monostable multivibrator. Note that the drain potential of the switch element Q63, which is the output of the monostable multivibrator, is opposite to (c).

  Therefore, when the control circuit 5 that performs MPPT control of the DC-DC converter 2 is provided, the control circuit 6 that performs lockout prevention control is provided, and the rise of the output voltage due to the activation of the DC-DC converter 2 is detected. The MPPT control by the control circuit 5 is set to a minimum load state for a predetermined time from the rising timing (in this embodiment, the DC-DC converter 2 is operated to have a minimum output (charge) current. Thus, even if the charging circuit 1 starts to operate with weak illumination light, the DC-DC converter 2 can be started up normally (the operation is started) without being locked out.

  In addition, the charging circuit 1 of the present embodiment causes the DC-DC converter 2 to start operation by a control circuit 4 described later, and then to the DC-DC converter 2 by the control circuit 5 by the control circuit 6 at low illuminance. Therefore, the DC-DC converter 2 and the MPPT control can be started up more reliably at low illuminance.

  Furthermore, in the charging circuit 1 of the present embodiment, a control circuit 7 that performs battery-free (no load) detection is provided in association with the control circuit 3 that performs an overcharge protection operation. The control circuit 7 includes a voltage dividing circuit 71, a reference voltage circuit 72, a comparator 73, a resistor R71, a switch element Q71, and a capacitor C71.

  Similar to the reference voltage circuit 52, the reference voltage circuit 72 includes resistors R72 to R74 connected in series between the lines K4 and K2, and a shunt regulator D71. The shunt regulator D71 controls the voltage at the connection point between the resistors R72 and R73 according to the voltage at the connection point between the resistors R73 and R74. Thus, the reference voltage circuit 72 is supplied from the control power supply of 3.9V. A reference voltage of 1.88 V corresponding to 3.42 V is created with the voltage of the secondary battery 11 and applied to the inverting input terminal of the comparator 73. The voltage between the lines K5 and K2, that is, the charging voltage of the secondary battery 11 is applied to the non-inverting input terminal of the comparator 73 by being divided by the voltage dividing resistors R75 and R76 of the voltage dividing circuit 71. The output terminal of the comparator 73 is connected to the power supply line K4 via the pull-up resistor R71, and is connected to the gate of the switch element Q71. The drain of the switch element Q71 is connected to the base of the transistor Q32 in the control circuit 3. The source of the switch element Q71 is connected to the GND line K2.

  The reference voltage circuit 31 in the control circuit 3 creates the 1.65 V reference voltage at which the charging voltage of the secondary battery 11 is 3.0 V. On the other hand, the reference voltage circuit 72 in the control circuit 7 creates a reference voltage of 1.88V corresponding to the charging voltage of the secondary battery 11 of 3.42V. The comparator 73 outputs a low level when the charging voltage is lower than the reference voltage of the reference voltage circuit 72, and thereby the switch element Q71 is OFF. On the other hand, when the charging voltage becomes equal to or higher than the reference voltage of the reference voltage circuit 72, the comparator 73 determines that there is no load, that is, the secondary battery 11 is not connected, and outputs a high level. Overcharge protection operation by 3 is prohibited.

  Specifically, the switch element Q71 is turned off while the comparator 73 outputs a low level and the charging voltage is less than 3.42V. Therefore, the drain of the switch element Q71 is open, the switch element Q31 and the transistor Q32 operate as described above, and an overcharge protection operation is performed between 3.0 and 3.42V.

  On the other hand, when the comparator 73 outputs a high level and the charging voltage becomes 3.42 V or more, the switch element Q71 is turned on. Accordingly, the switch element Q32 remains OFF, and the enable terminal EN of the converter IC25 becomes high level, invalidating the overcharge protection operation of the converter IC25.

  Thus, if the charging voltage is higher than the reference voltage of 3.42V, which is higher than the specified 3.0V, the control circuit 7 determines that the load (secondary battery 11) is not connected, and the control circuit 7 Disable the overcharge protection operation by 3. Therefore, if the overcharge protection operation is activated in such a case, the control circuit 3 performs the overcharge protection operation of the DC-DC converter 2 and when the output is stopped or reduced, the charge voltage at the open end immediately decreases. Then, the overcharge protection operation is released, the operation of the DC-DC converter 2 is started, and the overcharge protection operation is performed again. can do. FIG. 6 schematically shows only the configuration for performing the overcharge protection function and the prohibition control based on the absence of battery (no load) detection in the charging circuit 1.

  By the way, the control circuit 9 functions as an operation control circuit for the comparator 32 for preventing overcharge and the comparator 73 for detecting no battery (no load). That is, the comparators 32 and 73 use the output voltage from the external power supply output terminal Vaux of the converter IC 25 as the power supply. Therefore, when the output voltage of the secondary battery 11 becomes higher than the output voltage from the output terminal Vaux at low illuminance, the voltage at the input terminal becomes higher than the power supply of the comparators 32 and 73. Therefore, in order to protect these comparators 32 and 73, this control circuit 9 is provided. For example, the output voltage from the external power supply output terminal Vaux, that is, the power supply voltage Vcc of the comparators 32 and 73 is 1 V or less at the time of the low illuminance such as at night, but the voltage at the input terminal is the output voltage of the secondary battery 11. For example, 1.2V, which is higher than the power supply voltage Vcc.

  Therefore, schematically, the control circuit 9 cuts off the power supply to the power supply line K5 when the output voltage from the external power supply output terminal Vaux of the converter IC25 via the power supply line K4 becomes 0V with low illuminance. . Specifically, the control circuit 9 includes resistors R91 to R94 and switch elements Q91 and Q92. The output voltage from the external power supply output terminal Vaux of the converter IC 25 via the power supply line K4 is divided by the voltage dividing resistors R91 and R92, and is given to the gate of the switch element Q91. The source of switch element Q91 is connected to GND line K2, and the drain is connected to the gate of P-type switch element Q92 via resistor R94. A resistor R93 is provided between the gate and source of the switch element Q92, and the source is connected to the positive electrode of the secondary battery 11.

  Therefore, when the output voltage from the external power supply output terminal Vaux becomes approximately 3 V or more, the switch element Q91 is turned on, causing a potential difference between the gate and the source of the switch element Q92, thereby turning on the switch element Q92. As a result, the voltage of the secondary battery 11 is output from the drain of the switch element Q92 to the power supply line K5. When the output voltage from the external power supply output terminal Vaux is less than about 3V, the operation is reversed and the power supply to the power supply line K5 is cut off.

  Referring to FIG. 7, the MPPT control by the control circuit 5 is a control for operating the solar cell at the maximum power point as described above, and the first threshold light amount (voltage) determined in advance from the standby (shutdown) state. This is an operation of starting the DC-DC converter 2 when A is greater than or equal to A, and stopping the DC-DC converter 2 when it is less than the second threshold light quantity (voltage) B and waiting (shut down). The threshold light amount A depends on the power generation capability of the solar cell 10 and is a light amount sufficient to drive the DC-DC converter 2 sufficiently. The threshold light amount B can maintain the operation of the DC-DC converter 2 at a minimum, for example. The amount of light.

  Such hysteresis due to the two threshold light quantities A and B is caused by whether or not the operational amplifier 53 is functioning (that is, MPPT is functioning). When the voltage of the power supply line K4 of the operational amplifier 53 is several hundred mV at low illuminance, the operational amplifier 53 does not function. Therefore, the DC-DC converter 2 needs to start up without assistance from the operational amplifier 53, and has a large energy ( Light quantity A or more). On the other hand, once the DC-DC converter 2 is started up and the operation up 53 is functioning, the MPPT function is activated and voltage is supplied to the feedback terminal FB of the converter IC 25. Therefore, with low energy (light quantity B or more). Can be started.

  On the other hand, the output voltage from the power supply line K4 of the operational amplifier 53, that is, the external power supply output terminal Vaux is reset to the normal voltage during the period when the converter IC 25 is reset even at low illuminance, so the converter IC 25 is reset. The functioning of MPPT by the operational amplifier 53 can be said to be an effective technique for performing MPPT control between threshold light amounts A to B as described later. When in the range of these threshold light amounts A to B, the control circuit 5 controls the converter IC 25. Specifically, as described above, the current is mainly adjusted according to the generated power, and the secondary battery 11 is adjusted. Can be charged.

  If the power generation capacity of the solar cell 10 is sufficiently high, there is no substantial problem because it is possible to supply energy for removing the DC-DC converter 2 from the shutdown state with a small amount of light, but the solar cell 10 is small. In the case of the capacity, for example, if the direct sunlight is not applied, the threshold light amount A cannot be exceeded, and charging cannot be started. That is, once the light quantity does not exceed the threshold light quantity A due to the hysteresis, charging cannot be performed even if the light quantity is in the range of the threshold light quantities A to B. When the solar cell 10 has a small capacity, for example, the threshold light amount A is the maximum power point, and when the light amount in the midsummer day is 1 Sun, it is 0.5 Sun, and the threshold light amount B is 0.05 Sun. is there.

  Therefore, the charging circuit 1 of the present embodiment further includes a control circuit 4 that intermittently performs the reset trigger operation of the DC-DC converter 2 as described above, and an illuminance sensor 8. In the charging circuit 1, only a configuration for performing a reset function described later and its prohibition control by detecting illuminance is schematically shown in FIG. 8. Note that the lockout prevention control by the control circuit 6 described above is such that, as described above, the load becomes too heavy immediately after the DC-DC converter 2 is started from the standby (shutdown) state once the threshold light quantity A is exceeded. In contrast, the intermittent reset trigger operation by the control circuit 4 periodically resets the DC-DC converter 2 so that the light intensity is set to a threshold value at the reset timing. If the amount of light is between A and B, the DC-DC converter 2 is started to operate, and the functions are different.

  With reference to FIG. 1, the control circuit 4 includes an oscillating unit 41, a trigger pulse generating unit 42, a reset unit 43, and a self-resetting unit 44. The charging (output) voltage of the secondary battery 11 is supplied to the control circuit 4 and the illuminance sensor 8 via the high-side power supply line K6 and the GND line K2.

  The oscillation unit 41 includes a comparator 45, resistors R411 to 415, and a capacitor C411. The charging (output) voltage of the secondary battery 11 via the power supply line K6 is input to the power supply line K7 via a switch element Q441 in a self-reset unit 44 described later, and is divided by resistors R411 and R412 to be compared with the comparator. It is input to 45 non-inverting input terminals. The output terminal of the comparator 45 is connected to the power supply line K7 via a pull-up resistor R413, and is connected to an inverting input terminal and a non-inverting input terminal via feedback resistors R414 and R415, respectively. The voltage at the inverting input terminal is held (integrated) by the capacitor C411.

  Therefore, as will be described later, in a state where the charging (output) voltage from the secondary battery 11 is being output to the power supply line K7, the capacitor C411 is discharged in the initial state, and as shown in FIG. As shown by the solid line, the voltage Vc, that is, the input voltage V− of the inverting input terminal of the comparator 45 is 0V, while the input voltage V + of the non-inverting input terminal is 0V or more, so FIG. The output of the comparator 45 indicated by () becomes the high level Vcc, and the voltage V + of the non-inverting input terminal of the comparator indicated by the broken line in FIG. 9A becomes the high level VH.

  The high level Vcc output of the comparator 45 advances the charging of the capacitor C411 as shown by the solid line in FIG. 9A, and the input voltage V− of the inverting input terminal is more than the input voltage V + = VH with the non-inverting input terminal. When it becomes higher, the output of the comparator 45 becomes 0V. As a result, the discharge of the capacitor C411 proceeds, and when the input voltage V− at the inverting input terminal becomes smaller than the input voltage V + = VL at the non-inverting input terminal, the comparator 45 sets the output terminal to the high level again.

  In other words, the feedback resistor R415 causes the comparator 45 to have hysteresis, and the oscillating unit 41 periodically outputs a rectangular wave pulse as shown in FIG. 9B. The hysteresis is a balance between the output of the comparator 45 and the feedback resistor R415, and the input voltage V + at the non-inverting input terminal is as follows.

V + = Vcc · Ra / (Ra + R411): At the time of VL output However, Ra = (R412 · R415) / (R412 + R415)
V + = Vcc · R412 / (R412 + R415): At the time of VH output The pulse width t of the rectangular wave (the period of the rectangular wave is 2 · t) is determined by the product of the feedback resistor R414 and the capacitor C411, that is, the time constant, It is obtained by expanding the following formula.
VH = (Vcc-VL). (1-exp (-t / (C411.R414))) + VL
For example, if Vcc = 2.4V, VH = 2.0V, VL = 0.2V, C411 · R414 = 10 μF · 1MΩ = 10,
2.0 = 2.2 · (1-exp (−t / 10)) + 0.2
0.82 = 1−exp (−t / 10)
exp (−t / 10) = 0.18
-T / 10 = ln (0.18) =-1.72
t = 17.2 sec
It becomes.

  This period 2 · t defines an interval for preventing the next reset pulse from being input before the rise of the DC-DC converter 2 is completed. That is, when the next reset pulse comes, if the DC-DC converter 2 is still in the middle of rising due to the previous reset pulse, a reset occurs again and a problem of repeating this occurs. Therefore, since the next reset pulse is not input until the DC-DC converter 2 starts up and outputs a charging output, whether or not the DC-DC converter 2 returns to the charging operation in this period 2 · t. It is necessary to have a length longer than the time for confirming. As will be described in detail below, since the negative pulse after t is not used for resetting, the next reset pulse comes after a period of 2 · t, and the time required to return the DC-DC converter 2 is, for example, If t, then it has a double margin.

  Further, since a larger amount of current flows when outputting a short pulse Vp described later, it is desirable to suppress the consumption of the secondary battery 11 by increasing the period 2 · t to some extent, that is, by suppressing the number of pulses. On the other hand, during the period of 2 · t, no attempt is made to restore the DC-DC converter 2, resulting in a loss of opportunity for charging. That is, since the cycle 2 · t is a trade-off between battery consumption and charging opportunity, it is desirable to set an optimal value in accordance with the installation environment, usage, and the like. For example, if C411 = 270 μF, then 2 · t = 15 minutes.

  This pulse is input to the trigger pulse generator 42. The trigger pulse generating unit 42 includes switch elements Q421 and Q422, a capacitor C421, resistors R421 to R423, and a diode D421. The capacitor C421 is a coupling capacitor that extracts a short pulse Vp as shown in FIG. 9C from a long-period rectangular wave pulse from the comparator 45. The output of the capacitor C421 is given to the gate of the switch element Q421. The gate of the switch element Q421 is used for the output of the differential (= pulse) of the discharge diode D421 and the capacitor C421 that prevents the negative pulse from being applied to the switch element Q421 when the output voltage of the comparator 45 becomes 0V. The resistor R421 is provided. The source of switch element Q421 is connected to GND line K2, and the drain is connected to the gate of switch element Q422 via resistor R422. The gate of the switch element Q422 is connected to the power supply line K7 via the pull-up resistor R423, the source is connected to the power supply line K7, and the output is derived from the drain to the reset unit 43. The pulse width tw of the short pulse Vp shown in FIG. 9C is determined by the time constants C421 and R421.

  The reset unit 43 includes a transistor Q431 and resistors R431 and R432. The short pulse Vp is converted into a current output by the switching elements Q421 and Q422, input to the reset unit 43, converted into a voltage by resistors R431 and R432, and applied to the base of the transistor Q431. The emitter of the transistor Q431 is connected to the GND line K2, and the collector is connected to the enable terminal EN of the converter IC25.

  Therefore, when the short pulse Vp is input from the trigger pulse generating unit 42, the reset unit 43 sets the enable terminal EN of the converter IC 25 to the GND level and resets the converter IC 25. The converter IC 25 uses the solar cell 10 as a power source, and the low level threshold value of the enable terminal EN becomes very low at low illuminance, but can be completely reset by dropping it to the GND level by the reset unit 43.

  Here, the operation of the converter IC 25 will be described in detail. In general, the converter IC 25 is provided with an enable terminal EN and a low voltage lock terminal LVLO in order to stop its operation. However, the low voltage lock terminal LVLO has a relatively low threshold value for stopping its operation. When the input voltage is less than 250 mV, the main function is stopped and the load (secondary battery 11) is disconnected. In the above, the operation is performed and the load (secondary battery 11) is connected. Further, the converter IC 25 intermittently performs an oscillation operation using the inductor L21 even when the low voltage lock terminal LVLO is less than 250 mV, and the current drawn (consumed) from the solar cell 10 side is 2.3 mA. .

  On the other hand, the enable terminal EN has a relatively high threshold value for stopping operation, and when the enable terminal EN is reset to a low level, the converter IC 25 completely stops the oscillation operation. The current drawn (consumed) from the solar cell 10 side is 0.3 mA. As a result, when the enable terminal EN is reset, not only the load (secondary battery 11) is disconnected from the solar battery 10, but also the converter IC 25 itself is effectively disconnected, and the load of the solar battery 10 is thus reduced. Is even lighter.

  Therefore, when the converter IC 25 is periodically reset as described above, the load (the converter IC 25 and the secondary battery 11) can be disconnected from the solar cell 10 regardless of the input voltage of the low voltage lock terminal LVLO. After the converter IC 25 is reset (stopped), the solar cell 10 recovers from the shutdown state, and the open end voltage rises to the maximum voltage. Therefore, even if there is an input voltage at the low voltage lock terminal LVLO by resetting the reset unit 43, the converter IC 25 is temporarily stopped and waits until the solar cell 10 reaches the maximum power.

  In this state, when the maximum power corresponds to light of the threshold light amount B or more, the DC-DC converter 2 starts operation and charging of the secondary battery 11 is started. Thus, energy can be taken in effectively even with a low light quantity. As the pulse width of the short pulse Vp, when the converter IC25 is reset, the load (the converter IC25 and the secondary battery 11) is disconnected from the solar cell 10 and a trigger is applied for a time when the solar cell 10 rises to the maximum power. Good.

  Further, the charging circuit 1 according to the present embodiment is provided with the control circuits 5 and 6, so that the operation of the DC-DC converter 2 can be performed even when the illuminance is low when the control circuit 5 and 6 are normally activated with the threshold light amount A or more. Stabilized. Therefore, although the silicon solar cell can be used as the solar cell 10, a dye-sensitized solar cell (DSC) advantageous for power generation at low illuminance can be preferably used, and particularly in a room with low illuminance. Suitable for use.

  In the dye-sensitized solar cell (DSC), a design can be formed on the light receiving surface by utilizing the difference in the dye. As an example of the use of the panel of the solar cell 10 in such a room, the present applicant can use it as an award, award, award for recognition, etc. as shown in Japanese Patent Application No. 2013-242109. The electric power stored in the battery 11 can be used as a lighting power source for the bag.

  On the other hand, if the light quantity is less than the threshold light quantity B in the MPPT control range after the converter IC 25 is reset, the shutdown state is entered again, and the recovery from the shutdown by the reset and the shutdown are repeated.

  However, the oscillation unit 41 and the trigger pulse generation unit 42 described above use the charging (output) voltage of the secondary battery 11 as a power source. Accordingly, when these circuits are operated with the threshold light amount B being less than the above, the secondary battery 11 is discharged. For this reason, the control circuit 44 is provided with a self-resetting unit 44 and an illuminance sensor 8 for the control.

  The illuminance sensor 8 includes a CdS 81 that is a photoelectric conversion element, a switch element Q81, and resistors R81 to R83. A CdS81 and a resistor R81 are connected in series between the lines K6 and K2, and the potential at the connection point is divided by the resistors R82 and R83 and applied to the gate of the switch element Q81. The source of the switch element Q81 is connected to the GND line K2.

  On the other hand, the self-resetting unit 44 includes switch elements Q441 and Q442 and resistors R441 to R444. The drain of the switch element Q81 is connected to the gate of the switch element Q441 through a resistor R441. The switch element Q441 is interposed in series between the power supply lines K6 and K7, and its gate is connected to the power supply line K6 together with the source via a pull-up resistor R442, and from the drain to the power supply line K7. Power can be supplied to the oscillating unit 41 and the trigger pulse generating unit 42 via.

  The gate of the switch element Q81 can be short-circuited to the GND line K2 via the switch element Q442. The gate of the switch element Q442 is connected to the power supply line K3, that is, the output from the output terminal Vout of the converter IC25. The voltage is divided and applied by resistors R443 and R444.

  Accordingly, when the illuminance is substantially equal to the threshold light amount B, for example, 1000 lux or more, the resistance of Cds 81 is low, the switch element Q81 is turned on, the switch element Q441 is also turned on, and the oscillation unit 41 and the trigger pulse generation unit 42 are turned on. Is fed. On the other hand, when the illuminance is low, the resistance of the Cds 81 is high, the switch element Q81 is turned off, the switch element Q441 is also turned off, and power is not supplied to the oscillating unit 41 and the trigger pulse generating unit 42.

  Further, when the converter IC 25 has already been operated and charging is started normally, the output voltage of the solar cell 10 becomes a control voltage for MPPT control, for example, 4 V or more, and this is detected from the voltage at the output terminal Vout. When the switch element Q442 is turned ON, the gate of the switch element Q81 becomes the GND level, the switch elements Q81 and Q441 remain OFF, and an unnecessary reset operation is not performed.

  In this way, the CdS81 is used to forcibly stop the circuit (41 to 43) at night, and when it becomes MPPT controllable light quantity (B or more) in the morning, this is detected and a reset operation is performed. It is possible to prevent the power consumption of the secondary battery 11 from being consumed in the dark at night. When the DC-DC converter 2 is started as described above and the secondary battery 11 is normally charged, the control circuit 4 stops the reset operation of the DC-DC converter. Therefore, in a state where normal MPPT control can be started and the battery can be stably charged, the situation in which the DC-DC converter 2 is undesirably reset and restarted repeatedly is prevented, and more effectively continuously. Charging can be performed.

  Here, if the threshold light quantity B can be accurately determined, the DC-DC converter 2 is started up with a single pulse, and when a voltage is generated from the output terminal Vout, the circuit (41 to 41) is stopped. There is almost no 11 consumption. However, even if the reset is started at an illuminance lower than the threshold light quantity B due to variations in Cds 81 and the startup fails, the reset operation is performed again after the period 2 · t. On the other hand, the amount of light surely increases in the morning, and the MPPT is activated and the circuits (41 to 41) can be stopped while the reset is repeated.

  In the above example, the self-reset unit 44 realizes a self-reset operation that stops the reset operation by the units 41 to 43 by stopping the power supply to the oscillation unit 41 and the trigger pulse generation unit 42. The current consumption of these circuits is about several μA. Therefore, the generation of the trigger pulse may be stopped by simply stopping the trigger, for example, by short-circuiting the capacitor C411 of the oscillation unit 41. In other words, if the converter IC 25 operates and a voltage is output from the output terminal Vout, the reset operation is not necessary. However, even if it is performed, current consumption due to it does not pose a problem.

DESCRIPTION OF SYMBOLS 1 Charging circuit 2 DC-DC converter 21 DC-DC module 22 Input circuit 23 Constant voltage circuit 24 Input voltage limiting circuit 25 Converter IC
3 Control circuit (fourth converter control circuit)
31 Reference voltage circuit (first reference voltage circuit)
32 Comparator (first comparator)
4 Control circuit (second converter control circuit)
41 Oscillator 42 Trigger Pulse Generator 43 Reset Unit 44 Self-Reset Unit 45 Comparator 5 Control Circuit (First Converter Control Circuit)
51 Voltage Dividing Circuit 52 Reference Voltage Circuit 53 Operational Amplifier 6 Control Circuit (Third Converter Control Circuit)
7 Control circuit (5th converter control circuit)
71 Reference voltage circuit (second reference voltage circuit)
72 Comparator (second comparator)
8 Illuminance sensor 9 Control circuit 10 Solar cell 11 Secondary battery C21 Smoothing capacitor D31 Light emitting diode D32, D51, D71 Shunt regulator K1, K3 to K7 Power supply line K2 GND line L21 Inductors Q31, Q421, Q422, Q441, Q442, Q63, Q81, Q91, Q92 Switch elements Q32, Q431, Q61, Q62 Transistors

Claims (10)

In a charging circuit that uses a solar battery as a power source to charge a secondary battery with its output power,
A DC-DC converter that converts the output power of the solar cell into a predetermined charging voltage and charging current for the secondary battery,
A first converter control circuit that monitors the output voltage of the solar cell and performs MPPT control for operating the solar cell at a maximum power point by operating the DC-DC converter so that the output voltage is constant. When,
A charging circuit for a secondary battery using a solar battery as a power source, comprising: a second converter control circuit that resets the DC-DC converter at predetermined time intervals to release a load of the solar battery.   The second converter control circuit monitors the output voltage of the DC-DC converter, and stops the reset of the DC-DC converter when the output voltage becomes equal to or higher than a stable operation voltage of the DC-DC converter. A charging circuit for a secondary battery using the solar battery according to claim 1 as a power source.   3. The illuminance sensor further comprising: an illuminance sensor that monitors the illuminance and stops the operation of the second converter control circuit if the illuminance is lower than the second threshold voltage. A charging circuit for a secondary battery using a solar battery as a power source.   A third converter control circuit for detecting a rise of the output voltage due to the start of the solar cell and setting the MPPT control by the first converter control circuit to a minimum load state for a predetermined time from the rise timing; The charging circuit of the secondary battery which used the solar cell of any one of Claims 1-3 as a power supply.   5. The charging circuit for a secondary battery using a solar battery as a power source according to claim 4, wherein the third converter control circuit is a monostable multivibrator circuit. The third converter control circuit includes:
A first capacitor for detecting activation of the DC-DC converter as a pulse;
The output voltage of the solar cell in the second converter control circuit is turned on in response to the detection pulse by the first capacitor, and the MPPT control by the second converter control circuit is set to the minimum load state. A first switch element that artificially grounds the input terminal;
A second capacitor that starts charging in response to a detection pulse by the first capacitor, performs a time-limited operation over the predetermined time, and turns off the first switch element when charging is completed. A charging circuit for a secondary battery using the solar battery as a power source according to claim 5.   After the DC-DC converter starts operating by the second converter control circuit in the charging circuit according to any one of claims 1 to 3, the illuminance is low. A secondary battery using a solar battery as a power source, wherein the MPPT control to the DC-DC converter by the first converter control circuit is set to a minimum load state by the third converter control circuit in the charging circuit described in the paragraph Charging circuit. A first reference voltage circuit that creates a first reference voltage determined in advance from an output voltage from the DC-DC converter, the first reference voltage and the charging voltage of the secondary battery are compared, and the charging voltage is A fourth converter control circuit having a first comparator that performs an overcharge protection operation to stop the DC-DC converter when the voltage becomes equal to or higher than the first reference voltage;
A second reference voltage circuit that creates a predetermined second reference voltage higher than the first reference voltage from an output voltage of the DC-DC converter; and charging the second reference voltage and the secondary battery. And a second comparator for performing a no-load detection operation for invalidating the overcharge protection operation by the fourth converter control circuit when the charging voltage is equal to or higher than the second reference voltage. The charging circuit of the secondary battery which used the solar cell of any one of Claims 1-7 for the power supply further.   The said solar cell consists of a dye-sensitized solar cell, The charging circuit of the secondary battery which used the solar cell of any one of Claims 1-8 for the power supply.   The secondary battery charging circuit using the solar battery as a power source according to claim 9, wherein the solar battery has a light receiving surface formed with a design based on a difference in pigment.

Images