JP2010206910A - Charging unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging unit, having a simple configuration and available for charging a secondary battery to which a solar cell can be connected as an input power supply. <P>SOLUTION: The charger 40 for charging the secondary battery 3a using the solar cell 1 as an input power source includes a switching power supply circuit 8, an input voltage feedback circuit 7, a charging voltage feedback circuit 9 and a charging current feedback circuit 10. Error-detecting signals of the feedback circuits 7, 9 and 10 are composited with each other via an operational amplifier and the composited signal is fed back as a control signal to the switching power supply circuit 8, thereby controlling the charging voltage Vc and a charging current Ic of the secondary battery 3a so that the solar cell 1 is able to operate near the optimal output operation point (Vmax) of the output characteristics of the solar cell. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charging device for charging a secondary battery such as a lithium ion battery, a nickel metal hydride battery, or a nickel cadmium battery used as a power source of an electric tool by using a solar battery as a power source.

  In a cordless type electric tool such as a driver drill, a battery pack composed of a secondary battery such as a nickel cadmium battery (NiCad battery) or a lithium ion battery is generally used as a driving power source of the electric tool.

  Conventionally, a charging device for charging a secondary battery such as a nickel-cadmium battery or a lithium ion battery uses a commercial power source as an input power source. However, when the cordless power tool is used in a place where there is no commercial power supply equipment, it is necessary to prepare a large number of spare secondary batteries when the work volume is large. It may be difficult to carry the secondary battery to the site.

  Therefore, a charging device that can be charged from another power source other than a commercial power source has been proposed as an input power source of a charging device that charges a secondary battery. For example, Patent Document 1 below proposes a charging device that uses another power source other than a commercial power source.

JP 2005-245145 A

  Various power sources other than the commercial power source are conceivable as the input power source of the charging device, but the inventors of the present application do not need an existing power supply facility such as a commercial power source at the work site, and the environment in the process of power generation We focused on a charger that uses a solar cell that can prevent contamination as an input power source.

  In the voltage-current characteristic (output characteristic) of the solar cell, as shown in FIG. 3, at the time of light irradiation, the output voltage Voc when the output terminal is opened and the open current Isc when short-circuited, It has a maximum output operating point Amax that gives the maximum output power Pmax. In order to efficiently obtain power from the solar cell, it is necessary to operate the solar cell near the maximum output operating point Amax (hereinafter, the operating point Amax or an operating point in the vicinity thereof may be referred to as an “optimum output operating point”). is there. For this reason, when a load is connected to the solar cell, it is required to always keep the load viewed from the solar cell side near the optimum output operating point Amax.

  The reason why the load connected to the solar cell is held at the optimum output operating point (near Amax) will be further described with reference to FIG. For example, when a solar cell is used at the maximum output operating point Amax at “large irradiation amount”, the power is voltage × current. Therefore, when the voltage value at this point is Vmax and the current value is Imax, the power that can be extracted is Vmax. XImax. On the other hand, consider the case where a solar cell is used at the operating point Ah of the load. If the current value Ih at the operating point Ah is, for example, a current corresponding to half the voltage Vmax at the current value Imax at the maximum output point Amax, the voltage value at the operating point Ah is 1/2 Vmax. At this time, as apparent from the output characteristics, there is almost no change in the current value between the current value Imax and the current value Ih. That is, the current value Ih at the operating point Ah is substantially the same current value (Ih≈Imax) as the current value Imax at the maximum output point Amax. Therefore, the electric power Ph that can be extracted at the operating point Ah is ½ Vmax × Ih, which is about ½ of the electric power Pmax that can be extracted at the maximum output point Amax.

  Similarly, in the case of “medium irradiation amount” and “low irradiation amount” in the output characteristics of the solar cell, the output power is about half of the maximum output operating point. As described above, the operating point (for example, Amax) at which the electric power that can be extracted at a certain irradiation amount is maximum hits the output characteristic by drawing a vertical line from the line of voltage V (for example, Vmax) on the horizontal axis in the figure. The area of the rectangle surrounded by the horizontal axis, vertical axis, horizontal line, and vertical line when the horizontal line is drawn from the operating point (Amax) to the current I line (eg, Imax) as the vertical axis from that point is maximized. It is a place. That is, if the output power (P) of the voltage (V) × current (I) at a specific operating point (for example, Amax) on the output characteristics is the maximum from any other operating point (for example, Ah), The maximum output operating point Amax is reached, and the voltage Vmax and current Imax at that time become the maximum output operating point. The operating voltage V at the maximum output operating point Amax that gives the maximum output power Pmax of the solar cell is substantially constant regardless of the amount of irradiation such as “medium irradiation amount” or “low irradiation amount” shown in FIG. It becomes a voltage value (Vmax).

  Here, in order to charge the secondary battery with the output voltage of the solar battery, considering the case where the secondary battery is directly connected to the solar battery and charged, the output voltage of the solar battery is It will drop to the charging voltage of the battery. For example, when a secondary battery having a voltage of 1/2 Vmax is directly connected to the solar battery having the characteristics shown in FIG. 3, the voltage of the solar battery is also reduced to 1/2 Vmax. Assuming that “the irradiation amount is large”, the charging current that flows is Imax. Therefore, although the maximum value Pmax of the power that can be extracted is Vmax × Imax as described above, when the secondary battery is directly connected, only a power of ½ Vmax × Imax can be extracted. In view of the efficiency reduction of the output power, if a charge control circuit is provided between the solar battery and the secondary battery so that the output voltage of the solar battery becomes a predetermined value near the maximum output operating point (Vmax), The output power of the solar battery can be brought close to the maximum output power Pmax, and the secondary battery can be efficiently charged by the solar battery.

  Accordingly, an object of the present invention is to provide a charging device that includes a charge control circuit that operates a solar cell as an input power source at an optimum output operating point, and thereby can efficiently charge a secondary battery from the solar cell. It is in.

  Another object of the present invention is to provide a charging device including a charge control circuit that is simple and inexpensive to operate a solar cell as an input power source at an optimum output operating point.

  To achieve the above object, typical features of the invention disclosed in the present application will be described as follows.

  According to one aspect of the present invention, there is provided a charging device that supplies output power of a solar cell as a charging power source for a secondary battery via a charging control circuit, wherein the charging control circuit includes an output voltage of the solar cell. Is fed back to the switching control circuit and a control signal for controlling the charging voltage to a set voltage value based on the charging voltage of the secondary battery. A charging voltage feedback circuit, a charging current feedback circuit for feeding back a control signal for controlling the charging current to a set current value based on a charging current of the secondary battery to the switching control circuit, and the sun A control signal for controlling the input voltage of the switching control circuit to a set input voltage value based on the output voltage of the battery is switched An input voltage feedback circuit for feeding back to the control circuit, the switching control circuit based on a feedback control signal from the input voltage feedback circuit and a feedback control signal from the charging current feedback circuit, The charging current value controlled by the switching control circuit is controlled so that the input voltage of the switching control circuit becomes the set input voltage value of the input voltage feedback circuit.

  According to another aspect of the present invention, the input voltage feedback circuit includes an input voltage detection circuit for detecting an input voltage of the switching control circuit, and an input voltage for determining an input voltage reference value at a predetermined value. A reference setting circuit; and a first comparison amplifier having the input voltage detection circuit and the input voltage reference setting circuit as inputs. The charging current feedback circuit includes a charging current detection circuit for detecting a charging current; A first comparison amplifier that constitutes the input voltage feedback circuit and a second comparison amplifier that receives the output of the charging current detection circuit as inputs; and the first comparison amplifier via the first comparison amplifier. The error output signal of the comparison amplifier is synthesized with the charge current detection signal.

  According to still another aspect of the present invention, the charging current detection circuit receives a charging current detection resistor inserted in the output side charging path of the switching control circuit and a potential difference generated in the charging current detection resistor. And a third comparison amplifier, and the output of the third comparison amplifier is cascaded to the input of the second comparison amplifier.

  According to still another aspect of the present invention, the charging voltage feedback circuit includes a charging voltage detection circuit for detecting a charging voltage of the switching control circuit, and a charging for determining a charging voltage reference value at a predetermined value. A voltage reference setting circuit; and a fourth comparison amplifier having the charging voltage detection circuit and the charging voltage reference setting circuit as inputs. An output signal of the fourth comparison amplifier is an output of the second comparison amplifier. Configured to be combined with the signal.

  According to still another feature of the present invention, each of the first comparison amplifier, the second comparison amplifier, the third comparison amplifier, and the fourth comparison amplifier includes an operational amplifier.

  According to still another aspect of the present invention, a value of a predetermined input voltage determined by the input voltage feedback circuit is set as an optimum output operating point of a solar cell used as an input power source of the switching control circuit.

  According to the above feature of the present invention, the charge control circuit uses a solar cell as an input power source, and is configured to control the charge current and the charge voltage in accordance with the output voltage of the solar cell. An optimum operating point can be set for the output characteristics of a solar cell connected as an input power source, and charging power can be efficiently obtained from the solar cell.

  For example, referring to the output characteristic diagram of FIG. 3, when the secondary battery is charged with a voltage of 1/2 Vmax in the “irradiation amount” state, the charging current I is (Secondary battery charging power P = efficiency × maximum power Pmax of solar cell) = (secondary battery charging voltage 1/2 Vmax × secondary battery charging current I = efficiency × solar cell output voltage Vmax × solar cell Output current Imax) = (1/2 Vmax × secondary battery charging current I = efficiency × solar cell output voltage Vmax × solar cell output current Imax) From the following, assuming that the efficiency of the charging control circuit is 85%, for example: The charging current I of the secondary battery is I = 2 × 0.85Imax = 1.7Imax, which is approximately 1.7 times the charging current Imax when the secondary battery is directly connected to the solar battery. Can be charged with Thus, charging efficiency can be improved.

  According to the above feature of the present invention, the charging control circuit includes a switching control circuit, a charging voltage feedback circuit, a charging current feedback circuit, and an input voltage feedback circuit, and the input voltage feedback circuit includes a plurality of input voltage feedback circuits. An input voltage setting means capable of setting a set input voltage value, wherein a value of a charging current controlled by the switching control circuit based on a control signal from the charging current feedback circuit is determined by the input voltage of the switching control circuit; Since the control is performed so that a predetermined voltage value selected based on the signal from the input voltage setting means of the input voltage feedback circuit is obtained, it is possible to set an optimum output operating point for each characteristic of the plurality of solar cells, Charging power can be efficiently obtained from the battery.

  Further, since the charging voltage feedback circuit, the charging current feedback circuit, and the input voltage feedback circuit can be configured by an operational amplifier, a simple and inexpensive charging control circuit can be achieved.

  The above and other objects, and the above and other features of the present invention will become more apparent from the following description of the present specification and the accompanying drawings.

  Hereinafter, a charging device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a charging apparatus according to an embodiment of the present invention, and FIG. 2 is a control flowchart for operating the charging apparatus shown in FIG. Note that in the drawings for describing the embodiments, the same reference numerals are given to the portions indicating the same functions or elements, and repeated description thereof is omitted.

<About the configuration of the charging device>
A solar cell 1 serving as an input power source is constituted by a battery cell constituted by, for example, a PN junction of crystalline silicon. The solar cell 1 is detachably connected to the main body of the charging device 40 via the connecting portion 41, and can be replaced with another solar cell 1 of the same kind prepared in advance if necessary.

  The auxiliary power supply unit 2 is a power supply unit that steps down the voltage Vi of the solar cell 1a and supplies a power supply voltage Vcc such as a microcomputer 11 and operational amplifiers 7g, 9e, 10g, and 10h described later. The auxiliary power supply unit 2 includes a DC converter (switching power supply circuit) 2a, a P-channel insulated gate field effect transistor (hereinafter referred to as “P-channel FET”) 2b, a rectifier diode 2c, a coil 2d, The capacitor 2e and the resistors 2f and 2g constitute a step-down switch power supply circuit, and step down the voltage Vi of the solar battery to generate the power supply voltage Vcc for the microcomputer 11 and the like.

  That is, the DC converter 2a constitutes a step-down converter, and the P-channel FET 2b is set so that the value obtained by dividing the output voltage by the potentiometers of the resistors 2f and 2g becomes a predetermined value set in the DC converter 2a. By switching, a desired power supply voltage Vcc is output. The resistance values of the resistors 2f and 2g are set so that a value obtained by dividing the desired power supply voltage Vcc by the resistors 2f and 2g becomes a comparison value set in a comparison circuit (not shown) of the DC converter 2a.

  The battery pack 3 is a battery pack to be charged, and includes a battery set 3a to which a secondary battery of one cell or more is connected, and a battery type discrimination including a discrimination resistor for discriminating the type or number of cells of the battery set 3a. It comprises an element 3b and a temperature sensitive element 3c such as a thermistor set in the vicinity of the battery set 3a for monitoring the battery temperature. The battery set 3a is composed of, for example, a lithium ion secondary battery.

  The battery type discriminating means 4 has a function of discriminating the type of secondary battery of the battery set 3a from the battery type discriminating element 3b of the battery pack 3, and is composed of a resistor 4a. The battery type of the secondary battery 3a is a value obtained by dividing the power supply voltage Vcc by the resistor 4a and the battery type discrimination resistor 3b set in the battery pack 3, and an A / D port (analog- It is determined by inputting to the digital conversion port) 11d. Here, the battery type is, for example, the difference in the type of the secondary battery itself such as a lithium ion secondary battery, a nickel-cadmium secondary battery, a nickel hydride secondary battery, or the number of cells in the same type of secondary battery such as a lithium ion battery. (For example, a difference between 4 cells, 5 cells, etc.). The reason for determining the battery type is that the charge control method differs depending on the battery type, and accordingly, it is necessary to perform appropriate charging for each battery type.

  The battery temperature detection means 5 is a battery temperature detection means composed of resistors 5a and 5b. As the battery temperature, a value obtained by dividing the power supply voltage Vcc by the resistor 5a and the parallel resistance of the resistance value of the resistor 5b and the temperature sensing element 3c in the battery pack 3 is input to an A / D port 11d of the microcomputer 11 described later. Detect by.

The smoothing capacitor 6 is a smoothing capacitor connected in parallel to the solar cell 1.
The input voltage feedback circuit 7 is connected to the operational amplifier (comparison amplifier) 7e, the voltage dividing resistors 7a and 7b connected to the non-inverting input part (+) of the operational amplifier 7e, and the inverting input part (-) of the operational amplifier 7e. It comprises voltage dividing resistors 7c and 7d. The voltage dividing resistors 7a and 7b divide the output voltage Vi of the solar cell serving as an input power source, and the divided value is input to the non-inverting input part (+) of the operational amplifier 7e. Further, the voltage dividing resistors 7c and 7d divide the power supply voltage Vcc and invert the operational amplifier 7e with a set voltage for holding the output voltage Vi of the solar battery, that is, the input voltage Vi to the charge control circuit at a predetermined voltage value. It has a function of supplying to the input unit (-).

  The output voltage Vi of the solar cell 1 is divided by the detection resistors 7a and 7b, input to the non-inverting input part (+) of the operational amplifier 7e, and input to the inverting input part (-) (input voltage setting value). And the optimum output operating voltage (for example, Vmax) that can output the maximum power Pmax corresponding to the output characteristics of the solar cell 1. Thereby, the output voltage Vi of the solar cell 1 is controlled to a voltage value at which the maximum power Pmax of the solar cell 1 can be taken out.

  The switching power supply circuit 8 constitutes a power supply for controlling the charging voltage Vc and the charging current Ic. The switching power supply circuit 8 includes a DC converter 8a, a P-channel FET 8b, a rectifier diode 8c, a coil 8d, and a smoothing capacitor 8e. In the present embodiment, a step-down switching power supply circuit that steps down the output voltage Vi of the solar cell 1 to generate the charging voltage Vc is used. The DC converter 8a controls the charging voltage Vc and the charging current Ic based on a feedback control signal from a charging current feedback circuit 10 in which error control signals of a charging voltage feedback circuit 9 and an input voltage feedback circuit 7 described later are combined. .

  The charging voltage feedback circuit 9 includes resistors 9a, 9b, 9c and 9d, an operational amplifier 9e, and a diode 9f. The battery charging voltage Vc is divided by resistors 9a and 9b and input to the non-inverting input (+) of the operational amplifier 9e. The set value Vsc of the charging voltage is generated by dividing the power supply voltage Vcc by the resistors 9c and 9d, and is input to the inverting input section (−) of the operational amplifier 3e.

  The DC converter 8a switches the switching FET 8b based on the output control signal of the operational amplifier 9e so that the charging voltage divided by the resistors 9a and 9b becomes the charging voltage setting value Vsc set by the resistors 9c and 9d. Control. Based on the output control signal of the operational amplifier 9e, the charging voltage setting value Vsc set by the resistors 9c and 9d is set to a limit voltage value for preventing the secondary battery voltage Vc from rising to a voltage equal to or higher than this setting value. Switching control of the drive signal of the switching FET 8b is performed by the converter 8a. That is, when the secondary battery voltage Vc is lower than the set value Vsc, switching control is performed to increase the battery voltage Vc. Conversely, when the secondary battery voltage Vc is higher than the set value Vsc, the secondary battery voltage is Switching control is performed so as to decrease Vc. Thus, a predetermined secondary battery voltage Vc that is equal to or lower than the set value Vsc can be maintained. The secondary battery voltage Vc is controlled to a voltage equal to or lower than the voltage Vi output from the solar battery 1 to the switching power supply circuit 8.

  The charging current feedback circuit 10 includes a first stage operational amplifier 10g and a subsequent stage operational amplifier 10h. The first stage operational amplifier 10g constitutes an inverting amplifier circuit together with the shunt resistor 10a for detecting the charging current Ic, the input resistors 10b and 10c, and the feedback resistor 10d, and can detect a relatively small charging current. A highly sensitive current amplifier is constructed. The post-stage operational amplifier 10h constitutes a comparison amplifier circuit, and the output of the first-stage operational amplifier 10g is input to the non-inverting input section (+) of the post-stage operational amplifier 10h via the input resistor 10e, and the inverting input section (-). The feedback signal (output of the operational amplifier 7g) from the input voltage feedback circuit 7 is input via the input resistor 10f. The output of the post-stage operational amplifier 10h is fed back to the DC converter 8a of the switching power supply circuit 8 through the diode 10i.

  According to this embodiment, the output via the diode 10i of the post-stage operational amplifier 10h is commonly connected to the output via the diode 9f of the operational amplifier 9e constituting the charge voltage feedback circuit 9 described above. That is, the output of the operational amplifier 9e and the output of the operational amplifier 10h are commonly connected in a wired OR format. Thus, the input voltage Vi by the solar cell 1 is controlled in accordance with the magnitude of the charging current Ic while suppressing the charging voltage Vc to a voltage equal to or lower than the predetermined voltage value Vsc (Vsc <Vsi). In general, operational amplifiers 10g and 10h used in each stage are incorporated in one package (DIP or SOP package) by a semiconductor integrated circuit technology. Since an operational amplifier incorporated in one package may include an operational amplifier circuit connected in multiple stages, if such an operational amplifier circuit connected in multiple stages is adopted as the previous operational amplifier 10g, the detection sensitivity of charging current is further increased. Can be improved.

  According to such a feedback circuit 10, when a charging current Ic flows through the shunt resistor 10a, a negative potential of charging current (Ic) × shunt resistor (10a) × (−1) is applied to the non-inverting input portion of the operational amplifier 10g ( -). Since the operational amplifier 10g constitutes an inverting amplifier circuit together with the resistors 10b, 10c, and 10d, the voltage is 10d / 10c times the negative voltage value proportional to the charging current Ic input to the non-inverting input part (−) of the operational amplifier 10g. The value is output from the operational amplifier 10g and can be detected with high sensitivity even with a relatively small charging current. The output of the operational amplifier 10g is input to the non-inverting input part (+) of the operational amplifier 10h. On the other hand, since the feedback signal from the input voltage feedback circuit 7 is input to the inverting input section (−) of the operational amplifier 10h, the operational amplifier 10h is connected to the detection signal output of the charging current Ic and the input voltage (output voltage of the solar cell). ) Operates as a comparison amplifier circuit that compares Vi.

  Here, when the input voltage (output voltage of the solar cell 1) Vi of the charging device 40 rises or falls below the input voltage setting Vsi set in the input voltage feedback circuit 7, the switching power supply circuit is based on the feedback output from the operational amplifier 7e. 8, the charging voltage Vc and the charging current Ic are controlled. That is, a virtual short circuit (imaginary short) in which the input potential difference between the non-inverting input unit (+) and the inverting input unit (−) in the operational amplifier 10h is zero within a range where the charging voltage Vc does not exceed the predetermined setting voltage Vsc. Thus, switching control is performed by the switching power supply circuit 8.

  In such switching control, if the input voltage Vi rises above the input voltage setting Vsi, the input voltage Vi rises, so that the input voltage feedback circuit 7 has both input portions (+) and (−) of the operational amplifier 7e. Unbalanced. Further, since the output of the operational amplifier 7e is input to the non-inverting input part (+) and the inverting input part (-) of the operational amplifier 10h of the charging current feedback circuit 10, both input parts (+) (-) of the operational amplifier 10h. There is no balance between them. Then, the switching power supply circuit 8 performs switching so that the input portions of the operational amplifiers 7e and 10h are balanced based on the feedback signal from the operational amplifier 10h. By performing this switching, the charging current Ic is increased so that the input voltage Vi decreases to the input voltage set value Vsi.

  Conversely, when the input voltage (solar cell voltage) Vi drops below the input voltage setting value Vsi set in the input voltage feedback circuit 7, the switching power supply circuit 8 sets the charging current Ic and the input voltage Vi sets the input voltage. Decrease to a value that increases to Vsi. In this way, when the irradiation amount increases and the voltage of the solar cell 1 increases, the charging current Ic is increased. Conversely, when the irradiation amount decreases and the voltage of the solar cell 1 decreases, charging is performed. The switching power supply circuit 8 is controlled so as to reduce the current Ic. As a result, the output voltage Vi of the solar cell 1 is controlled to a predetermined set value Vsi (a voltage near the optimum output operating point Vmax) having a voltage value higher than the charging voltage Vc.

  The microcomputer 11 includes a CPU 11a, output ports 11b and 11c, A / D ports 11d and 11e, and a memory unit such as a ROM and a RAM (not shown), and performs various controls based on various detection input signals. Output a signal. A memory unit (not shown) of the microcomputer 11 stores and holds battery type determination data, battery temperature data, charging voltage data, and the like of the battery pack 3, and stores data related to the battery type of the solar cell module 1. .

  The battery voltage detection circuit 12 includes resistors 12a and 12b connected in series across the charge output circuit, and inputs a voltage divided by the resistors 12a and 12b to the A / D port 11e of the microcomputer 11. To determine the battery voltage.

  The charging on / off circuit 13 is a circuit for turning on / off the charging path (ON / OFF), includes two semiconductor switching elements including a PNP transistor 13e and an NPN transistor 13f, and includes a bias resistor 13a of the NPN transistor 13f, 13b, and bias resistors 13c and 13d of the PNP transistor 13e.

  When charging, the NPN transistor 13f is turned on by outputting a high signal (H signal) from the output port 11b connected to the resistor 13a of the microcomputer 11. When the NPN transistor 13f is turned on, the PNP transistor 13e is also turned on, whereby the charging circuit including the switching power supply circuit 8 is electrically connected to the battery pack (secondary battery) 3 and the battery pack 3 is charged. On the contrary, when charging is terminated, the NPN transistor 13f is turned off by outputting a low signal (L signal) from the output port 11b connected to the resistor 13a of the microcomputer 11. By turning off the NPN transistor 13f, the PNP transistor 13e is also turned off, the charging path between the charging circuit and the battery pack 3 is cut off, and charging is terminated.

  The charge state display circuit 14 is a charge state display circuit for notifying the user whether or not charging is in progress. It comprises resistors 14a, 14b, 14c, an LED 14d, and an N-channel FET 14e. During charging, by outputting a high signal from the output port 11c connected to the resistor 14b of the microcomputer 11, the N-channel FET 14e is turned on and the LED 14d is turned on. Conversely, when the battery is not charged, a low signal is output from the output port 11c connected to the resistor 14b of the microcomputer 11, thereby turning off the N-channel FET 14e and turning off the LED 14d.

<About the operation of the charging device>
Next, the operation of the charging device 40 according to the embodiment of the present invention will be described with reference to the circuit block diagram of FIG. 1 and the control flowchart of FIG.

First, when the solar cell 1 as an input power source is connected to the charging device 40, the charging device 40 enters an operating state using the solar cell 1 as a power source.
In order to notify the user of a state in which charging is not performed before the secondary battery 3a of the battery pack 3 is mounted, the LED 14d of the charging state display circuit 14 is turned off (step 301). In this case, in order to turn off the LED 14d, a low signal is output from the output port 11c connected to the resistor 14b of the microcomputer 11 to turn off the FET 14e.

  Next, it is determined whether or not the battery pack 3 is mounted on the charging device 40. The connection of the battery pack 3 is determined by, for example, a change in the detection signal of the battery temperature detection means 4 input to the A / D port 11d of the microcomputer 11 (step 302).

  Next, the battery type of the battery pack 3 is determined based on the detection signal from the battery type detection means 4 (step 303). The battery type of the battery pack 3 is set corresponding to the resistance value of the battery type discriminating element 3b in the battery pack 3. For example, the difference in the type of structure such as a lithium ion battery, a nickel metal hydride battery, a nickel-cadmium battery, etc. Even in the battery pack 3 having the same structure, the battery type discriminating element 3b based on the difference in the voltage range such as 14.4V or 18V or the number of battery sets in the battery pack 3 as in the case of the lithium ion secondary battery. The resistance value is set.

  Next, charging is started (step 304). Charging is started by outputting a high signal from the output port 11b connected to the resistor 13a of the microcomputer 11, thereby turning on the NPN transistor 13f and the PNP transistor 13e, and conducting the charging path connecting the switching power supply circuit 8 and the battery pack 3. This is done by setting a state.

  When charging is started, the LED 14d of the charging status display circuit 14 is lit in red, for example, in order to notify the user of the start of charging (step 305). To turn on the LED 14d, a high signal is output from the output port 11c connected to the resistor 14b of the microcomputer 11, and the FET 14e is turned on.

  After the start of charging, it is determined whether or not the battery is fully charged (step 306). A well-known method can be adopted as a method for determining full charge. In an example of the full charge determination method in the present embodiment, for example, when the battery pack 3 charges the lithium ion secondary battery 3a, when the battery voltage detected by the battery voltage detection circuit 12 reaches a predetermined value, the battery pack 3 is fully charged. Is determined.

  The predetermined value of the battery voltage determined as full charge at this time is based on the battery type detected in step 303, for example, 4 cells × 4.2V = 16.8V in the case of a 4 cell lithium ion secondary battery 3a. In the case of the 5-cell lithium ion secondary battery 3a, it may be set to 4.2 V per cell, such as 5 cells × 4.2 V = 21 V. The predetermined value to be set is not limited to such a voltage value. In the case of a nickel-cadmium battery, for example, a method can be adopted in which charging is determined to be full when the battery temperature detected by the battery temperature detecting means 5 reaches a predetermined temperature or higher during charging.

  If it is determined in step 306 that the battery is fully charged, charging is terminated (step 307). The end of charging is performed by turning off the NPN transistor 13f and the PNP transistor 13e by outputting a low signal from the output port 11b connected to the resistor 13a of the microcomputer 11 and blocking the charging path between the switching power supply circuit 8 and the battery pack 3. Is done by. When the charging is terminated in step 409, the LED 14d of the charging state display circuit 14 is turned off to notify the user that the charging is terminated (step 308). To turn off the LED 14d, a low signal is output from the output port 11c connected to the resistor 14b of the microcomputer 11 to turn off the FET 14e.

  Next, it is determined whether or not the battery pack 3 has been removed from the charging device 40 (step 309).

  As will be apparent from the above description of the embodiment, according to the present invention, a charging device (40) using a solar cell as an input power source can be provided, and according to the output characteristics of the solar cell (1). The operating point (output voltage Vi and output current Ii) in the output characteristics of the solar cell can be controlled to the optimum output operating point. Thereby, the charging efficiency by a solar cell can be improved.

  Further, the voltage setting (Vsi) and current setting (Isi) for obtaining the optimum output operating point of the solar cell are constituted by an input voltage feedback circuit (7) constituted by an operational amplifier (7e) and an operational amplifier (10g, 10h). Since the charging current feedback circuit (10) is employed, the charging efficiency can be improved with a relatively simple circuit configuration.

  Further, the charging current feedback circuit (10) includes an inverting amplifier using a first-stage operational amplifier (10g) for detecting and amplifying the charging current, a setting error signal of the charging current (Ii), and setting of the input voltage (Vi). Since a comparison amplifier using a post-stage operational amplifier (10h) that compares the error signal is connected in multiple stages, the combination circuit of the setting error signal of the charging current (Ii) and the setting error signal of the input voltage (Vi) is compared. It can be configured easily. In particular, even when the charging current is small, the charging current is detected by the front-stage operational amplifier, and is combined with the error signal of the input voltage setting by the rear-stage operational amplifier.

  In the description of the above embodiment, an example in which a lithium ion secondary battery is charged as a secondary battery of the battery pack has been described. However, in a battery pack charging device configured with another secondary battery such as a Nicad battery. The same effect can be obtained even if the above is applied.

  As mentioned above, the invention made by the present inventor has been specifically described on the basis of the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof. is there.

The circuit diagram of the charging device which concerns on one Embodiment of this invention. The control flowchart of the charging device shown in FIG. The output characteristic figure of a solar cell.

1: Solar cell 2: Auxiliary power supply 2a: DC converter 2b: P channel FET 2c: Rectifier diode 2d: Coil 2e: Smoothing capacitor 2f, 2g: Resistance 3: Battery pack 3a: Battery set (secondary battery) 3b: Battery type Discriminating element (resistance)
3c: temperature sensing element (thermistor) 4: battery type discrimination means 4a: resistance 5: battery temperature detection means 5a, 5b: resistance 6: smoothing capacitor 7: input voltage feedback circuit 7a, 7b, 7c, 7d: resistance 7e: operational amplifier (Comparative amplifier) 8: Switching power supply circuit 8a: DC converter 8b: P-channel FET 8c: Rectifier diode 8d: Coil 8e: Smoothing capacitor 9: Charge voltage feedback circuits 9a, 9b, 9c, 9d: Resistor 9e: Operational amplifier (Comparative amplifier) )
9f: Diode 10: Charging current feedback circuit 10a: Shunt resistor 10b, 10c, 10d, 10f: Resistor 10g, 10h: Operational amplifier (comparative amplifier)
10i: Diode 11: Microcomputer 11a: CPU
11b, 11c: Output port 11d, 11e: A / D port 12: Battery voltage detection circuit 12a, 12b: Resistor 13: Charging ON / OFF circuits 13a, 13b, 13c, 13d: Resistor 13e: PNP transistor 13f: NPN transistor 14 : Charge state display circuits 14a, 14b, 14c: Resistance 14d: LED 14e: N-channel FET
40: Charger 41, 42: Connection part

Claims (6)

A charging device that supplies output power of a solar battery as a charging power source of a secondary battery via a charging control circuit, wherein the charging control circuit converts the output voltage of the solar battery into a charging voltage of the secondary battery A switching control circuit for controlling the charging voltage based on a charging voltage of the secondary battery, and a charging voltage feedback circuit for feeding back a control signal for controlling the charging voltage to a set voltage value to the switching control circuit; A charging current feedback circuit for feeding back a control signal for controlling the charging current to a set current value based on a charging current of a secondary battery to the switching control circuit; and the switching control based on an output voltage of the solar battery. A control signal for controlling the circuit input voltage to the set input voltage value is fed back to the switching control circuit. Comprising an input voltage feedback circuit because, the,
The switching control circuit inputs a value of a charging current controlled by the switching control circuit based on a feedback control signal from the input voltage feedback circuit and a feedback control signal from the charging current feedback circuit to the input of the switching control circuit. A charging apparatus configured to control so that a voltage becomes the set input voltage value of the input voltage feedback circuit.   The input voltage feedback circuit includes an input voltage detection circuit for detecting an input voltage of the switching control circuit, an input voltage reference setting circuit for determining an input voltage reference value to a predetermined value, and the input voltage detection circuit And a first comparison amplifier having an input voltage reference setting circuit as an input. The charging current feedback circuit includes a charging current detection circuit for detecting a charging current, and the first voltage constituting the input voltage feedback circuit. And a second comparison amplifier that receives the output of the first comparison amplifier and the output of the charging current detection circuit as inputs, and the error output signal of the first comparison amplifier is charged through the second comparison amplifier. The charging device according to claim 1, wherein the charging device is combined with a current detection signal.   The charging current detection circuit includes a charging current detection resistor inserted in an output side charging path of the switching control circuit, and a third comparison amplifier that receives a potential difference generated in the charging current detection resistor, 3. The charging device according to claim 2, wherein an output of the third comparison amplifier is cascaded to an input of the second comparison amplifier.   The charging voltage feedback circuit includes a charging voltage detection circuit for detecting a charging voltage of the switching control circuit, a charging voltage reference setting circuit for determining a charging voltage reference value at a predetermined value, and the charging voltage detection circuit And a fourth comparison amplifier having a charging voltage reference setting circuit as an input, and an output signal of the fourth comparison amplifier is combined with an output signal of the second comparison amplifier. Item 4. A charging device according to Item 3.   5. The charging device according to claim 4, wherein each of the first comparison amplifier, the second comparison amplifier, the third comparison amplifier, and the fourth comparison amplifier includes an operational amplifier. .   The predetermined input voltage value determined by the input voltage feedback circuit is set to an optimum output operating point of a solar cell used as an input power source of the switching control circuit. The charging device according to any one of 5.

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