JPH10248176A - Battery charger - Google Patents

Abstract

(57) Abstract: In a charging device for charging a rechargeable secondary battery, an influence of an offset voltage of an operational amplifier generated in a process of amplifying a detected charging current is eliminated to eliminate a charging current error. That is. A circuit consumption current other than a charging current, that is, a circuit consumption current flowing through a microcomputer, an inverting amplification unit, a phase control signal transmission unit, a zero-cross signal detection unit, and the like, flows through a charging current detection resistor. Assume that the output offset voltage of the amplifying means 7 is positive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging a secondary battery such as a nickel-cadmium battery.

[0002]

2. Description of the Related Art In order to perform accurate charging, a charging device is used.
Constant current charging is performed in which the charging current is detected, amplified by an operational amplifier and read by a microcomputer, and the charging current is controlled to a predetermined value. FIG. 3 shows an example of the current detecting means.
In FIG. 3, the current detection resistor is Rs, and the output voltage is Vop. In this case, the gain of the operational amplifier G is represented by Rf / Ri. FIG. 4 shows characteristics of the output voltage Vop of the operational amplifier G with respect to the charging current Ij.

In the case of an ideal operational amplifier, the output voltage Vo
pA is expressed as VopA = Ij × Rs × Rf / Ri, and its output characteristic is indicated by characteristic a in FIG. However, strictly speaking, the operational amplifier G is affected by the input offset voltage and the input offset current. Assuming that the input offset voltage of the operational amplifier G is VosG and the input offset current of the operational amplifier G is IosG, the offset voltage ± Vos appearing in the output voltage is ± Vos = (VosG × (Rf / Ri)) + (IosG
× Rf). Under the influence of the offset voltage ± Vos, the output characteristic of the operational amplifier G becomes the characteristic b or the characteristic −b, and the output voltage Vo
pB (−VopB) is as follows: VopB = Ij × Rs × Rf / Ri ± Vos

That is, the variation of the output voltage Vop of the operational amplifier G is greatly affected by the offset voltage of the operational amplifier G, and the charging current I.sub.
j also has a large variation. For example, if the value for controlling the charging current, that is, the charging current control value S is fixed on the premise of the ideal operational amplifier G having the characteristic a, the charging current controlled based on the value S is in the range from Ij1 to Ij2. It is greatly affected by the performance of the operational amplifier G. If the operational amplifier G is a single-supply operational amplifier, the output voltage of the operational amplifier G in which a negative offset voltage as shown by the characteristic -b occurs becomes 0 V up to the charging current Ij0. For this reason, in the conventional charging device, for example, as shown in FIG. 6, a positive voltage (for example, a divided voltage by the resistors R1 and R2) corresponding to the offset voltage is input to the non-inverting terminal of the operational amplifier G, and Make the output voltage always positive,
The output voltage of the operational amplifier G when the charging current Ij is 0, that is, the offset voltage, is taken in by the microcomputer and subtracted from the output voltage of the operational amplifier G when the charging current Ij is flowing, thereby eliminating the influence of the offset voltage and thereby reducing the charging current. Ij variation was eliminated. In addition to the above method, there is a method of eliminating the offset voltage by adjusting the offset voltage to 0 using an operational amplifier capable of adjusting the offset voltage.

[0005]

However, according to the above-described method, the resistance R is reduced to eliminate the negative offset voltage.
1, R2 needs to be added, and the number of parts increases. Further, the method of eliminating the offset voltage by adjusting the offset voltage to 0 has a problem in that an operation of manually adjusting the variable resistor is required and the operation is troublesome. In addition to the above method, there is a method using a low offset type operational amplifier having a small offset voltage, but it is more expensive than a general-purpose operational amplifier. SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks of the prior art, to easily eliminate the influence of the offset voltage of the operational amplifier without using additional components and the like, and to eliminate a charging current error.

[0006]

The above object can be achieved by supplying a circuit consumption current other than the charging current to the charging current detecting resistor and making the output offset voltage of the operational amplifier positive.

[0007]

FIG. 1 is a block circuit diagram showing an embodiment of the present invention. In the figure, 1 is an AC power supply, 2 is a transformer, 3 is diodes 3a to 3d and thyristor 3
e, full-wave rectifier circuit composed of 3f, diode 3
The voltages rectified by the a and 3b and the thyristors 3e and 3f are adjusted in conduction angle by the thyristors 3e and 3f, and the battery set 4 in which a plurality of rechargeable cells are connected in series is charged with the charging current I. The voltage rectified by the diodes 3a to 3d passes through a constant voltage power supply circuit 5 including capacitors 5a and 5b, a voltage regulator 5c, and a diode 5d. It serves as a power source for the zero-cross signal detection means 10, the display means 11, and the like. The charging current I is detected and converted by a charging current detecting means 6 having a low resistance, and is input to a microcomputer 8 via an inverting amplifying means 7. The inverting amplification means 7 includes a single power supply operational amplifier 7a (hereinafter referred to as an operational amplifier 7a), a resistor 7
b, 7c and a capacitor 7d.
As is well known, a CPU 81, a ROM 82, a RAM 8
3, timer 84, A / D converter 85, output port 8
6, an input port 87, a reset circuit 88 and the like. 821 in the ROM 82 is a charging current control value S storing means for storing a set value S for setting the charging current I to a predetermined value, and 831 in the RAM 83 stores the output of the inverting amplifying means 7 when not charging. Voltage, ie, operational amplifier 7a
Drift voltage storage means for storing the offset voltage and the voltage generated by the current consumption of the circuit such as the microcomputer 8 and the current amplification means. Reference numeral 9 denotes a phase control signal transmitting unit including a transistor 9a, a resistor 9b, a diode 9c, and the like, and transmits a phase control signal output from an output port 86 of the microcomputer 8 to the thyristors 3e and 3f. 10 is an operational amplifier 10
a, a transistor 10b, resistors 10c to 10g, and a capacitor 10h, a zero-cross signal detecting means for detecting a zero-cross signal near 0 V of the output voltage of the full-wave rectifier circuit 3 (a voltage determined by the resistors 10e to 10g). To enter. Reference numeral 11 denotes a display unit including an LED 11a and a resistor 11b, and displays a state of charge such as charging or completion of charging of the battery set 4. Reference numeral 12 denotes a battery voltage detecting means including resistors 12a and 12b, which detects the voltage of the battery set 4. The microcomputer 8 converts the charging current detected by the charging current detecting means 6 and the inverting amplifying means 7 and converted into a voltage every time a zero-cross signal is detected into A / A.
It is read via the D converter 85, and if it is smaller than the predetermined value, the phase control signal outputted from the output port 86 is advanced so as to increase the charging current. Conversely, if the charging current is large, control is performed to delay the phase control signal output from the output port 86 to reduce the charging current. In this way, the charging current I for charging the battery set 4 is maintained at a constant value.

Before describing the operation of the present invention, the principle of the present invention will be described. The inverting amplifying means 7 has the same configuration as that of the current detecting means of FIG. 3 and has the same output characteristics as those shown in FIG. That is, since the inverting amplifying means 7 uses the single power supply operational amplifier 7a, when a negative offset voltage is generated, the output voltage of the inverting amplifying means 7 becomes 0 V unless a charging current flows, and the offset voltage cannot be corrected. . Therefore, according to the present invention, as shown in FIG. 1, in addition to the charging current I, the circuit consumption current i flowing through the microcomputer 8, the phase control signal transmitting means 9, and the zero-crossing signal detecting means 10 also flows through the charging current detecting means 6 at the same time. By configuring the inverting amplifier 7a, the output voltage Vi can be detected based on the negative offset voltage and the circuit consumption current i, and the offset voltage can be corrected. According to FIG. 1, when the charging current is 0, the output voltage Vop of the inverting amplifying means 7 is Vop = Vi ± Vos, and the cause of the negative voltage is 0> Vi−Vos. Here, Vi is an output voltage of the inverting amplifier 7 generated by a circuit current consumed by the charging device, and Vos is an offset voltage of the inverting amplifier 7. That is, if Vi ≧ Vos is satisfied, the negative offset voltage (−Vos) of the operational amplifier 7a as shown by the characteristic −b in FIG. 4 rises toward the positive side by the output voltage Vi due to the circuit consumption current i. The characteristic -B shown in the output characteristic of the inverting amplification means 7 is obtained. That is, in any state, the output of the inverting amplification means 7 becomes a positive voltage, so that the detection by the A / D converter 85 becomes possible. Therefore, the output voltage Vop of the inverting amplifier 7 when the charging current I is not flowing, that is, the drift voltage is detected and added to the charging current control value S to add the charging current control value ΔS
If the charging current is controlled based on the value ΔS, even if the inverting amplifier 7 has the characteristic −b, it is always independent of the offset voltage Vos and the output voltage Vi due to the circuit consumption current. Charging with a predetermined charging current I becomes possible.

Next, the operation of the present invention will be described with reference to the block circuit diagram of FIG. 1 and the flowchart of FIG. When the power is turned on, the microcomputer 8 determines the frequency of the AC power supply 1 based on the zero-cross signal of the zero-cross signal detecting means 10 (step 200), counts the timer 84 inside the microcomputer 8, and blinks the LED 11a of the display means 11 (step 200). 201). Next, the connection of the battery set 4 is awaited, and the connection of the battery set 4 is determined by the signal of the battery voltage detecting means 12 (step 202). When the battery set 4 is connected, the LED 11a is turned on to indicate that the charging state has been entered from the connection standby state (step 203). When the charging state is entered, the output voltage Vop of the inverting amplification means 7 is taken in through the A / D converter 85, and the drift voltage storage means 8
31 (step 204). The output voltage Vop of the inverting amplifying means 7 previously stored is added to a predetermined charging current control value S stored in the ROM 821 to add a charging current control value ΔS
Is calculated (step 205). When the charging current control value ΔS is calculated in step 205, the thyristors 3e and 3f are turned on at the minimum conduction angle from the output port 86 via the phase control signal transmitting means 9 to start charging (step 20).
6). Note that the minimum conduction angle is determined by the zero-cross signal detection means 10.
The timer 84 is counted based on the zero-cross signal detected in step (1), and a phase control signal is output after a predetermined period of time stored in the ROM 82 corresponding to the frequency of the AC power supply 1.
When the charging is started, the charging current flowing through the battery set 4 is detected by the current detecting means 6, and the charging current detecting process is performed by the A / D converter 85 via the inverting amplifying means 7 (step 207), and the calculation is performed at step 205. A comparison is made with the set charging current control value ΔS. As a result of the comparison, if the detected charging current is smaller than the calculated charging current control value ΔS (step 208), the conduction angle of the phase control signal output from the output port 86 is increased so as to increase the charging current. (Step 209). If the detected charging current is larger than the calculated charging current control value ΔS (step 210), the conduction angle of the phase control signal output from output port 86 is reduced so as to reduce the charging current (step 211). ). When the detected charging current is equal to the calculated charging current control value ΔS, the conduction angle of the phase control signal is not changed. Detected charging current and calculated charging current control value Δ
If S is equal, or after Steps 209 and 211, it is determined whether or not the battery is fully charged based on the voltage of the battery set 4 detected by the battery voltage detecting means 12. Returning to the charging current detection process of 207, the above process is repeated (step 212). If full charge is detected, the phase control signal output from the output port 86 is cut off, and charging of the battery set 4 is terminated (step 213). Thereafter, the LED 11a is turned on and off (step 214), a series of charging processes are completed, and the removal of the battery set 4 is waited for (step 215). If it is determined that the battery set 4 has been removed, the process returns to step 202 and returns to the next battery. Wait for connection of set 4.

[0010]

According to the present invention, variations in operational amplifiers generated in the process of converting and amplifying a charging current detected in a charging device for charging a rechargeable secondary battery are reduced by the circuit consumption of microcomputers, operational amplifiers and the like. It is possible to detect with an electric current and charge with high accuracy with a minimum number of components.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing one embodiment of the present invention.

FIG. 2 is a flowchart showing one embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of a current detection unit using an operational amplifier.

FIG. 4 is a graph showing output characteristics of an operational amplifier.

FIG. 5 is a graph showing the output characteristics of the inverting amplification means constituting the present invention.

FIG. 6 is a circuit diagram showing an example of an amplifier using an operational amplifier capable of correcting an offset voltage.

[Explanation of symbols]

6 is a charging current detecting means, 7 is an inverting amplifying means, and 8 is a microcomputer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiko Funabashi 1060 Takeda, Hitachinaka-shi, Ibaraki Prefecture Within Hitachi Koki Engineering Co., Ltd.

Claims (4)

[Claims] 1. A battery charging device in which a terminal voltage of a charging current detecting resistor connected in series with a secondary battery to be charged is amplified by an operational amplifier, and a charging current is controlled by an output of the operational amplifier. A battery charging device characterized in that a circuit consumption current other than the charging current flows through the charging current detection resistor, and the output offset voltage of the operational amplifier is made positive. 2. The battery charging device according to claim 1, wherein an output of the operational amplifier is sent to a microcomputer, and the charging current is controlled by the microcomputer. 3. The battery charging device according to claim 2, wherein the circuit consumption current is a current flowing through a microcomputer, a zero-cross signal detection circuit, and the like. 4. An operational amplifier for detecting an output voltage of an operational amplifier when a charging current is not flowing, storing a sum of a detected output voltage and a voltage corresponding to a charging current to be controlled, and operating the operational amplifier when a charging current flows. 4. The battery charging device according to claim 1, wherein the charging current is controlled so that the output voltage of the battery becomes equal to the sum.