Charging circuit using an operational amplifier

Abstract

To provide a charging circuit using an operational amplifier of an inexpensive and simple configuration suitable for charging of a CC-CV method without using a dedicated IC.SOLUTION: A charging circuit has a first electric path, a second electric path, and a third electric path. A FETPch and a constant-current diode are provided in series on the first electric path, an operational amplifier is provided on the second electric path, and a first resistor and a second resistor are provided on the third electric path. A gate of the FETPch and an output terminal of the operational amplifier are connected through a fourth electric path. A positive electrode of a secondary battery and an input on a positive electrode side of the operational amplifier are connected through a fifth electric path. A position between the first resistor and the second resistor on the third electric path, and an input on a negative electrode side of the operational amplifier are connected through a sixth electric path. A position between the second resistor and the other end on the third electric path, and a position between the operational amplifier and the other end on the second electric path are connected through a seventh electric path.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a charging circuit using an operational amplifier for charging a secondary battery. [Background technology]

[0002] One charging method for secondary batteries that allows the stored power to be repeatedly discharged and charged is CC-CV (constant current-constant voltage) charging, which controls the current and voltage.

[0003] Figure 2 shows ideal current (I) and voltage (V) trends during CC-CV charging. As shown in Figure 2, in this CC-CV charging, initially (in Figure 2, "CC" on the horizontal axis representing time t), a constant current (in Figure 2, "I const Then, when the voltage of the secondary battery reaches a predetermined value (in Fig. 2, "CV" on the horizontal axis representing time t), the secondary battery is charged at a constant voltage (in Fig. 2, "V const In this way, the secondary battery is charged to full charge while avoiding overcharging.

[0004] CC-CV charging requires precise control, so it was common to develop a dedicated IC or similar device.

[0005] For example, Patent Document 1 discloses a charging structure for a lithium-ion battery that is equipped with a structure that stops charging of a lithium-ion battery installed in a mobile terminal before the battery is fully charged outside the mobile terminal, thereby mitigating battery degradation by terminating charging before full charge, when temperature degradation is significant. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Utility Model Registration No. 3215361

[0007] However, using a dedicated IC, etc., often results in an expensive and complicated configuration. Therefore, the applicant created a charging circuit that does not require a dedicated IC and uses an operational amplifier with an inexpensive and simple configuration, as shown in Figure 3. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0008] However, in the case of a charging circuit using an operational amplifier configured as shown in Figure 3, if the difference between the reference voltage applied to the - (negative) input of the operational amplifier and the battery voltage of the secondary battery applied to the + (positive) input of the operational amplifier to be charged is small, the operational amplifier will output a voltage proportional to the difference, and the voltage applied to the constant current diode will be small. If the applied voltage is too low, the constant voltage diode will not operate normally, and the output will not be stable. As a result, a constant current is supplied to the secondary battery to be charged, that is, in the CC period in Figure 2, "I const " cannot be provided.

[0009] Furthermore, the input voltage (V CC If the reference voltage is low (for example, 5 V), the difference between the reference voltage and the battery voltage will also be small accordingly.

[0010] Therefore, in order to solve the above-mentioned problems, the present invention aims to provide a charging circuit that is suitable for CC-CV charging, does not require a dedicated IC, and uses an operational amplifier with an inexpensive and simple configuration. [Means for solving the problem]

[0011] The invention of claim 1 is as follows: A charging circuit for charging a secondary battery using an operational amplifier, a first current path having one end connected to a power source and the other end connected to a positive electrode of a secondary battery; a second electric circuit having one end connected to the power source and the other end connected to ground; a third electric circuit having one end connected to the power source and the other end connected to the negative electrode of the secondary battery; a field effect transistor Pch and a constant current diode are respectively provided in series on the first electric path in order from the closest to the power supply; The field effect transistor Pch has a source connected to a voltage upper side and a drain connected to a voltage lower side, an operational amplifier is provided on the second electric path; The operational amplifier has a positive terminal of a power supply voltage connected to a voltage upper side and a negative terminal of the power supply voltage connected to a voltage lower side, a first resistor and a second resistor are provided on the third electric path in order from closest to the power supply; the gate of the field-effect transistor Pch and the output terminal of the operational amplifier are connected through a fourth current path; The positive terminal of the secondary battery and the positive input of the operational amplifier are connected through a fifth circuit; a point on the third electrical path between the first resistor and the second resistor and a negative input of the operational amplifier are connected through a sixth electrical path; The point on the third electric path between the second resistor and the other end and the point on the second electric path between the operational amplifier and the other end are connected via a seventh electric path, forming a charging circuit using an operational amplifier. [Effects of the Invention]

[0012] By applying and using a charging circuit using the operational amplifier according to the present invention, it is possible to charge a secondary battery using the CC-CV method with an inexpensive and simple configuration that does not require a dedicated IC.

[0013] Furthermore, by applying and using the field effect transistor Pch, a stable constant current can be supplied to the secondary battery, and the secondary battery 2 can be charged by the CC-CV method with more ideal control. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a configuration diagram of a charging circuit using an operational amplifier according to a first embodiment of the present invention. [Figure 2]FIG. 1 is an explanatory diagram showing ideal changes in current (I) and voltage (V) during CC-CV charging. [Figure 3] FIG. 1 is a diagram illustrating the configuration of a conventional charging circuit using an operational amplifier. DETAILED DESCRIPTION OF THE INVENTION

[0015] (Embodiment Example 1) First, the configuration of a charging circuit A using an operational amplifier according to the first embodiment of the present invention will be described with reference to Fig. 1. The charging circuit A using an operational amplifier is a circuit that charges a secondary battery.

[0016] <Configuration of charging circuit A using an operational amplifier> As shown in Figure 1, a charging circuit A using an operational amplifier includes a first electric circuit 31 having one end connected to a power source 1 and the other end connected to the positive electrode 21 of a secondary battery 2, a second electric circuit 32 having one end connected to the power source 1 and the other end connected to ground (GND), and a third electric circuit 33 having one end connected to the power source 1 and the other end connected to the negative electrode 22 of the secondary battery 2.

[0017] Power supply 1 is a DC power supply (V CC ) and, for example, 5 (V) is applied. The secondary battery 2 is an electricity storage device that can repeatedly discharge and charge stored electricity.

[0018] On the first electric circuit 31, a field effect transistor Pch (=P-channel FET) 4 and a constant current diode (CRD) 5 are respectively provided in series in order from the closest to the power supply 1.

[0019] The field effect transistor Pch4 has its source (indicated as "S" in Figure 1) connected in the voltage direction upward and its drain (indicated as "D" in Figure 1) connected in the voltage direction downward.

[0020] An operational amplifier 6 is provided on the second circuit 32, with a positive terminal 61 of the power supply voltage of the operational amplifier 6 connected in the upper voltage direction and a negative terminal 62 of the power supply voltage of the operational amplifier 6 connected in the lower voltage direction.

[0021] A first resistor 71 and a second resistor 72 are provided on the third electric circuit 33 in order from the closest to the power source 1 .

[0022] The gate (indicated as "G" in FIG. 1) of the field effect transistor Pch4 and the output terminal 63 of the operational amplifier 6 are connected via a fourth current path .

[0023] The positive electrode 21 of the secondary battery 2 and the positive input terminal (non-inverting input terminal) 64 of the operational amplifier 6 are connected through a fifth electrical path 35. A resistor 74 is provided on the fifth electrical path 35.

[0024] A point on the third electric circuit 33 between the first resistor 71 and the second resistor 72 and the negative input terminal (inverting input terminal) 65 of the operational amplifier 6 are connected through a sixth electric circuit 36. A resistor 74 is provided on the sixth electric circuit 36. The resistors 74 provided on the fifth electric circuit 35 and the sixth electric circuit 36 ​​have a high resistance of, for example, 10 (KΩ), and are intended to eliminate the influence of noise, which is easily affected by the input terminals of the operational amplifier.

[0025] A point on the third electric circuit 33 between the second resistor 72 and the other end and a point on the second electric circuit 32 between the operational amplifier 6 and the other end are connected via a seventh electric circuit 37 .

[0026] The field effect transistor Pch4 is a p-channel MOS-FET. The field effect transistor Pch4 is configured with a junction of "p-type semiconductor → n-type semiconductor → p-type semiconductor" between the source (S) and drain (D). When a voltage with source (S) + polarity (positive polarity) is applied between the drain (D) and source (S), and when a voltage with gate (G) - polarity (negative polarity) is applied between the gate (G) and source (S), current flows from the source (S) to the drain (D).

[0027] The constant current diode 5 has an anode (indicated as "A" in FIG. 1) connected to the upper voltage side and a cathode (indicated as "K" in FIG. 1) connected to the lower voltage side. The constant current diode 5 is characterized by being less susceptible to fluctuations in the applied voltage, and outputs a predetermined current when a voltage is applied.

[0028] The operational amplifier 6 is a differential amplifier that amplifies the difference between a reference voltage applied from the negative input terminal 65 and the battery voltage of the secondary battery 2 applied from the positive input terminal 64, and outputs the amplified result from the output terminal 63. The operational amplifier 6 is connected to the positive terminal 61 of the power supply voltage on the second current path 32, and to the negative terminal 62 of the power supply voltage of the operational amplifier 6 in the voltage direction downward, and operates by receiving voltage from the power supply 1. Therefore, the operational amplifier 6 cannot output a voltage from the output terminal 63 that is greater than the supplied power supply voltage; it can only output a voltage that is equal to or less than the supplied power supply voltage.

[0029] The voltage from the power supply 1 is divided by resistors 71 and 72 and applied to the negative input terminal 65 of the operational amplifier 6. This voltage is compared with the battery voltage of the secondary battery 2 and is a reference voltage (V ref ) The reference voltage is determined by the values ​​of resistors 71 and 72. Setting the reference voltage sets the upper limit of the charging voltage for the secondary battery 2. In other words, it sets the reference value for the full charge voltage of the secondary battery 2. When the voltage reaches or exceeds the full charge voltage, the voltage output of the operational amplifier 6 turns OFF, and the field effect transistor Pch4 turns OFF. When the field effect transistor Pch4 turns OFF, charging stops.

[0030] <Operation of charging circuit A using an operational amplifier> Next, the operation of the charging circuit A using the operational amplifier of the first embodiment of the present invention will be described. As described above, the voltage from the power supply 1 is divided by resistors 71 and 72 and applied as a reference voltage to the negative input terminal 65 of the operational amplifier 6. The battery voltage related to the secondary battery 2 is applied to the positive input terminal 64 of the operational amplifier 6 via the fifth electrical circuit 35. The operational amplifier 6 compares the reference voltage with the battery voltage. If the battery voltage is lower than the reference voltage, the differential voltage is output from the output terminal 63 of the operational amplifier 6. When a negative voltage relative to the source is applied to the gate via the fourth electrical circuit 34, the field-effect transistor Pch4 turns ON, and current flows from the source (S) to the drain (D). When the field-effect transistor Pch4 turns ON and a voltage is applied from the power supply 1, the constant current diode 5 outputs a predetermined current. As a result, the secondary battery 2 is charged with a predetermined current via the first electrical circuit 31. This corresponds to the "CC" period shown in FIG. 1.

[0031] As charging progresses and the battery voltage approaches the reference voltage, the difference between the battery voltage and the reference voltage becomes smaller, and the differential voltage output from output terminal 63 also becomes smaller, reducing the current flowing from the source (S) to the drain (D) of field-effect transistor Pch4. As a result, the voltage applied from power supply 1 also becomes smaller, the current output from constant current diode 5 also becomes smaller, and the power charged to secondary battery 2 also becomes smaller. This corresponds to the "CV" period shown in Figure 1, and plays the role of supplementary charging to compensate for self-discharge of secondary battery 2.

[0032] This will be explained in detail below. The secondary battery 2 constantly self-discharges the power it has stored. As a result, the battery voltage of the secondary battery 2, which is applied to the positive input terminal 64 of the operational amplifier 6 via the fifth current path 35, becomes slightly lower than the reference voltage applied to the negative input terminal 65 of the operational amplifier 6. This also reduces the voltage output from the operational amplifier 6, driving the gate of the field-effect transistor Pch4 and increasing the current flowing from the source (S) to the drain (D). This also increases the current output from the constant current diode 5, and the power charged to the secondary battery 2 increases to compensate for the self-discharge.

[0033] In this way, by applying and using the charging circuit A using the operational amplifier of embodiment 1 of the present invention, it is possible to charge the secondary battery 2 using the CC-CV method with an inexpensive and simple configuration that does not require a dedicated IC.

[0034] Furthermore, by applying and using the field effect transistor Pch4, a stable constant current can be provided to the secondary battery 2, and the secondary battery 2 can be charged by the CC-CV method with more ideal control.

[0035] In particular, the voltage values ​​of the power storage device such as the secondary battery 2 and the power supply 1 are close to each other. Also, the operational amplifier 6 used is not rail-to-rail with respect to the power supply 1. That is, the operational amplifier 6 does not have a maximum voltage (V CC ) to the minimum value (GND). Even in these cases, by using the field effect transistor Pch4, the secondary battery 2 can be charged using the CC-CV method with more ideal control.

[0036] Furthermore, as shown in FIG. 3, in a configuration in which the constant current diode 5 is operated by the output voltage of the operational amplifier 6, if the difference between the reference voltage applied to the negative input terminal 65 of the operational amplifier 6 and the battery voltage related to the secondary battery 2 applied to the positive input terminal 64 of the operational amplifier 6 is small, the operational amplifier 6 outputs a voltage proportional to the difference, and the voltage applied to the constant current diode 5 becomes small. If the applied voltage is too low, the constant voltage diode 5 will not operate normally. However, by using the field-effect transistor Pch4, a negative feedback circuit is activated, allowing the constant current diode 5 to operate normally even if the difference between the reference voltage and the battery voltage related to the secondary battery 2 applied to the positive input terminal 64 of the operational amplifier 6 is small.

[0037] Although the preferred embodiments of the present invention have been described above, it goes without saying that the charging circuit using the operational amplifier according to the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. [Explanation of symbols]

[0038] A: Charging circuit using an operational amplifier, 1: Power supply, 2: secondary battery, 21: positive electrode of secondary battery, 22: positive electrode of secondary battery, 31: 1st electrical circuit, 32: 2nd electrical circuit, 33: 3rd electrical circuit, 34: 4th electrical circuit, 35: 5th electrical circuit, 36: 6th electrical circuit, 37: 7th electrical circuit, 38: 8th electrical circuit, 4: Field effect transistor Pch, 5: constant current diode, 6: operational amplifier, 61: positive terminal of power supply voltage of the operational amplifier, 62: negative terminal of power supply voltage of the operational amplifier, 63: output terminal of the operational amplifier, 64: positive input terminal of the operational amplifier, 65: negative input terminal of the operational amplifier, 71:Resistance, 72:Resistance, 74:Resistance

Claims

[Claim 1] A charging circuit for charging a secondary battery using an operational amplifier, a first electric circuit having one end connected to a power source and the other end connected to a positive electrode of a secondary battery; a second electric circuit having one end connected to the power source and the other end connected to ground; a third electric circuit having one end connected to the power source and the other end connected to the negative electrode of the secondary battery; a field effect transistor Pch and a constant current diode are respectively provided in series on the first electric path in order from the closest to the power supply; The field effect transistor Pch has a source connected to a higher voltage side and a drain connected to a lower voltage side, an operational amplifier is provided on the second electric path; The operational amplifier has a positive terminal of a power supply voltage connected to a voltage upper side and a negative terminal of the power supply voltage connected to a voltage lower side, a first resistor and a second resistor are provided on the third electric path in order from closest to the power source; the gate of the field-effect transistor Pch and the output terminal of the operational amplifier are connected through a fourth current path; The positive terminal of the secondary battery and the positive input of the operational amplifier are connected through a fifth circuit; a point on the third electrical path between the first resistor and the second resistor and a negative input of the operational amplifier are connected through a sixth electrical path; A charging circuit using an operational amplifier, characterized in that a point on the third electrical path between the second resistor and the other end and a point on the second electrical path between the operational amplifier and the other end are connected through a seventh electrical path.

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