JP3187454B2 - Charging circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit for charging a storage battery or the like, and more particularly to a charging circuit capable of charging a small current to a large current with a constant current.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional charging circuit.
FIG. 5 is a time chart. The conventional charging circuit rectifies the AC power supply 1 and guides the rectified AC power supply 1 to a switching transformer T, and controls the on / off switching of a switching element 3 connected in series to a primary coil of the transformer T at a high speed to output an AC output to a secondary coil. And the secondary AC output is rectified and smoothed and supplied to the storage battery B as a charging current. Further, an operational amplifier OP and a photocoupler PC which take in the voltage across the detection resistor R1 connected in series to the charging current supply line, amplify and generate a feedback output according to the voltage across the detection resistor R1, and feed back to the primary side.
1 and receives the output of the photocoupler PC1 to perform PWM
The control circuit 8 adjusts the on-duty of the switching pulse to the switching element 3, and thereby controls the output current from the transformer T at a constant current.

Further, the temperature measured by the temperature sensor 5 for detecting the temperature of the storage battery B is detected by a battery temperature detection circuit 6,
The program is taken into the microcomputer 7. During charging, the microcomputer 7 operates the operational amplifier OP and the photocoupler PC1 to perform charging control. When the microcomputer 7 determines that the battery is fully charged by ΔT control performed based on the temperature measured by the temperature sensor 5, the microcomputer 7 operates the photocoupler PC2. Then, the current is switched to a required minute current (end-stage current) and supplied to the storage battery B.

[0004] Such terminal current is used for supplementary charge after full charge, and for activation of a battery by charging for a long time before normal charging of an inactive battery that has been left for a long time. Therefore, the microcomputer 7 is a photocoupler PC
2, a predetermined control signal is transmitted to operate the switching element at a predetermined on-duty, thereby generating and supplying a terminal current when required. This terminal current is set to about 0.1 C to 0.2 C, for example, 120 C.
In the case of a 0 mAh battery, 1200 × 0.1 to 0.2
= 120 to 240 mAh.

On the other hand, FIG. 6 is a circuit diagram of a main part of a conventional charging circuit in which a single photocoupler controls a charging current or a minute current at a constant current. That is, in FIG. 6, the transistor Q1 is turned off during the charging period, the gain of the operational amplifier is set by the resistance value of only the resistor R21, and the charging current is controlled at a constant current. By reducing the parallel combined resistance value of the resistors R21 and R22 in this way, the gain of the operational amplifier OP1 is increased to make the current small, and the constant current control is performed.

[0006]

In the conventional charging circuit shown in FIG. 4, the ground of the secondary-side charging control circuit is located on the secondary coil side of the transformer T, that is, the detection is made based on the magnitude of the charging current. Since the voltage between both ends of the resistor R1 changes and the ground of the microcomputer 7 and the ground of the temperature sensor 5 change, there is a problem that a signal input to the microcomputer 7 changes and an error occurs.

In addition, when the terminal current is supplied, the switching element is operated at a predetermined on-duty without detecting the battery voltage or performing feedback control of the terminal current, so that a pulse having a constant pulse duty is supplied from the PWM control circuit 8. Therefore, the current value greatly varies depending on the magnitude of the battery voltage. For this reason, for example, in a general-purpose universal charger, as shown in FIG.
The above current flows. On the other hand, when an assembled battery having 10 batteries is set, the current becomes 0.1 C or less, which makes it impossible to achieve the supplementary charging and the activation of the battery. become.

Further, in the charging circuit of FIG. 6 which performs feedback control of the terminal current, the loss due to the charging current of the detection resistor R1 is suppressed, and the amount of current changes with the heat generation of the detection resistor R1 (temperature characteristic). In general, a low resistance of about 10 mΩ is used in order to suppress the deterioration of the constant current control characteristic due to the above-mentioned condition. For example, when the terminal current is 120 mAh, the voltage across the detection resistor R1 is 120 mAh × 10 mΩ =
It becomes a very small voltage such as 1.2 mV. That is, in order to handle such a minute voltage, the supply current output greatly fluctuates even with a fluctuation of several mV due to the influence of V _{CEsat of the} transistor Q1 for switching the gain of the operational amplifier OP1 and the influence of the temperature characteristic. Is extremely difficult to control.

[0009] The present invention has been made in view of the above,
An object of the present invention is to provide a charging circuit in which a first operational amplifier and a second operational amplifier are configured in a two-stage configuration and the gain of the second operational amplifier is switched so that constant current can be controlled accurately from a small current to a large current. And

[0010]

According to the present invention, a secondary-side charging current is detected, and a control signal corresponding to the charging current is fed back to the primary side to adjust the on / off duty of the switching element. A charging resistor of an inverter type for performing constant current control by means of a detection resistor connected in series to a charging current supply line, a first operational amplifier for amplifying a voltage across the detection resistor, and an output of the first operational amplifier. And a gain switching means for switching the gain of the second operational amplifier, wherein the detection resistor is connected in series to the return path of the charging current supply line,
The first operational amplifier is used for inverting amplification, and the second operational amplifier is used for non-inverting amplification, and a voltage between both ends of the detection resistor is extracted with a negative polarity and guided to the first operational amplifier.

According to the present invention, the voltage across the detection resistor connected in series to the charging current supply line is input to the first operational amplifier and amplified. Further, the output of the first operational amplifier is input to the second operational amplifier and amplified. Then, the output from the second operational amplifier is fed back to the primary side, and the on / off duty of the switching element is adjusted according to the amount of the feedback, thereby performing constant current control.

The gain of the second operational amplifier is switched by a switching signal from gain switching means. At this time, since the input signal to the second operational amplifier is a signal amplified by the first operational amplifier, its level is large,
Therefore, even if a minute voltage fluctuation occurs in the gain switching means, the fluctuation of the amplified signal with respect to the fluctuation is substantially ignored.

The voltage across the detection resistor is input to the input terminal of the inverting operational amplifier having a negative polarity, inverted and amplified, and input to the input terminal of the second non-inverting operational amplifier to be amplified. Then, the output signal of the second operational amplifier is fed back to the primary side, and constant current control is performed. At this time,
Since the detection resistor is connected in series to the return path of the charging current supply line, the output terminal of the charging current supply line becomes the ground of the control circuit on the secondary side, so that a potential difference does not occur due to the voltage across the detection resistor.

[0014]

FIG. 1 is a circuit diagram showing an example of a charging circuit according to the present invention. In FIG. 1, 1 is an AC power supply such as a commercial power supply, 2 is a diode bridge for rectification, and C1 is a capacitor for smoothing the rectified current. T is a switching transformer, and a switching element 3 is connected in series to the primary coil L1. Reference numeral 4 denotes a snubber circuit including a diode, a resistor, and a capacitor for removing noise.

Diodes D1 and D2 for rectifying the induced AC secondary output, a choke coil Lc for smoothing, and a capacitor C2 are connected to the secondary coil L2 of the transformer T, and a charging current rectified and smoothed by such a circuit is connected. Is to be generated. B is a charging storage battery connected between the output terminals P (+) and P (−) of the charging current supply line, and a return resistor of the charging current supply line converts the charging current into a voltage and detects the voltage. R1 is interposed in series.

The secondary-side control circuit for charging control includes an O
P1, OP2, a temperature sensor 5, a battery temperature detection circuit 6, a microcomputer 7, and the like. And the detection resistor R
The output terminal P (−) of the positive electrode 1 is set to the ground of the secondary side control circuit.

OP1 takes in the voltage between both ends of the detection resistor R1 on the secondary coil side, that is, with the negative polarity to the inverting input terminal,
The non-inverting input terminal is connected to the middle point of voltage dividing resistors R3 and R4 for applying a bias for canceling the offset voltage of the operational amplifier OP1. This means, for example, that the terminal current is 120
When the resistance value of the detection resistor R1 is 10 mΩ, the voltage between both ends is a very small voltage of 1.2 mV. If this voltage is directly input to the operational amplifier OP1, the offset voltage of the operational amplifier is about 7 mV at the maximum. ,
This is to prevent the output voltage from being generated in the operational amplifier OP1 and the control from becoming impossible. The resistors R5 and R6 are resistors for determining the gain of the operational amplifier OP1, and C3 is for relaxation.

OP2 is an operational amplifier for performing non-inverting amplification.
The inverted amplified output from the operational amplifier OP1 is input to the non-inverted input terminal, and the amplified output is amplified and output. Thus, the operational amplifier OP1 and the operational amplifier OP2 have a two-stage configuration.

R10, R20 and R2 are operational amplifiers OP
2 is a resistor for determining the gain, of which the resistor R2
Is a so-called open collector whose other end is connected to the output end P1 of the microcomputer 7 and is connected to the ground via the transistor Q1. This transistor Q1
Is turned on and off by the microcomputer 7. That is, while the transistor Q1 is turned off and the high signal (H) is output from the output terminal P1 of the microcomputer 7, the gain is set by the resistance value of only the resistor R20, and the normal charging current is controlled at a constant current. While the transistor Q1 is on and the low signal (L) is being output from the output terminal P1, the gain is set to a high gain by the parallel combined resistance value of the resistors R2 and R20, and the on-duty of the switching element 3 is narrowed down. The current is controlled and the constant current is controlled. In this case, the operational amplifier OP2 is several tens of meters amplified by the operational amplifier OP1 of the first stage.
V has been input. Therefore, V _CEsat by the transistor Q1 for switching the gain of the operational amplifier OP2.
And the voltage fluctuation due to the temperature characteristic is, for example, about several mV, which is considerably smaller than the signal level, so that the output of the operational amplifier OP2 is not affected by the fluctuation.

PC1 is a photocoupler composed of a light emitting diode and a phototransistor.
2 is fed back to the primary side.

Numeral 8 sends a periodic switching pulse to the switching element 3 and the photocoupler P
The pulse duty of the switching pulse is varied according to the level of the current signal from C1,
This is a PWM control circuit that performs constant current control on the next output current. The PWM control circuit 8 is designed so that the on-duty and / or the off-duty of the switching pulse can be switched according to the level of the current signal from the photocoupler PC1.

Reference numeral 5 denotes a temperature sensor, such as a thermistor, which is provided in contact with or close to the storage battery B, for example, for measuring the heat generation temperature of the storage battery B. The temperature measured by the temperature sensor 5 is detected by a temperature detection circuit 6 as an electric signal, and is taken into a microcomputer 7.
The microcomputer 7 includes a ROM in which a program for charge control is stored, a calculating means for calculating a temperature rise per unit time, and the like, and performs charge control described later from the detected temperature data. When the temperature rise per unit time reaches the control ΔT value, the microcomputer 7 determines that the battery is fully charged and switches the output level of the output terminal P1.

A circuit composed of the tertiary coil L3, diode D3 and capacitor C4 is a power supply for supplying power to the PWM control circuit 8. R7 is a current limiting resistor interposed in a power supply path for operating the PWM control circuit 8 normally at startup. The quaternary coil L4, the diode D4, the capacitor C5, and the three-terminal regulator 9 are a power supply unit for supplying power to the secondary control circuit unit.

FIG. 2 is a flowchart of the charge control operation of the charging circuit according to the present invention.
This will be described with reference to the time chart of FIG.

When charging is started, an H signal is sent from the output terminal P1 of the microcomputer 7 (step S1). This H
According to the signal, the operational amplifier OP2 changes the resistances of the resistors R10 and R20.
The constant current control is performed with the gain determined by ( ₁ ), and the normal charging current I ₁ (see FIG. 3) is supplied. Further, the microcomputer 7 calculates ΔT control, that is, calculates a temperature rise value of the battery B per unit time obtained from the measured temperature from the temperature sensor 5 and determines whether the value has reached the control ΔT value (step S2). ). When the charging is continued and the temperature rise value of the battery B per unit time reaches the control ΔT value (step S2).
It is determined that the battery is fully charged, and the output terminal P1 is switched from the H level to the L level (step S3). By this switching to the L level, the charging current is reduced to a minute terminal current I
₂ (see FIG. 3), and this terminal current I ₂ is controlled with a constant current.

In the above flow chart, the constant current control of the terminal current as the supplementary charge after the full charge is shown. However, when charging the inactive battery, the minute current is controlled by the constant current for a predetermined time prior to the charge. The battery may be supplied to activate the battery. In this case, a constant small current can be supplied regardless of the number of storage batteries B.

In this embodiment, the resistance of the resistor R2 (and the transistor Q) is used to switch the gain of the operational amplifier.
Although only 1) is used, the microcomputer 7 has a plurality of output terminals P
1, P2,..., And a plurality of similar charging circuits are connected to the corresponding output terminals in parallel with the resistor R2 (and the transistor Q1), thereby easily generating a plurality of types of charging currents. Can be. In this case,
The value of each resistor is set to obtain a desired charging current.

[0028]

As described above, according to the present invention,
A first operational amplifier for amplifying the voltage between both ends of the detection resistor interposed in series with the charging current supply line, and a second operational amplifier for amplifying the output of the first operational amplifier, having a two-stage configuration;
In addition, since the gain of the second operational amplifier is switched by the gain switching means to improve the accuracy of the set gain of the second operational amplifier, the constant current control can be accurately performed with respect to a wide range of charging current from a small current to a large current. I can do it.

In addition, a detection resistor is connected in series to the return path of the charging current supply line, the first operational amplifier is used for inverting amplification, and the second operational amplifier is used for non-inverting amplification,
Since the voltage at both ends of the detection resistor is extracted as negative polarity and led to the first operational amplifier, the output terminal of the charging current supply line is set to the ground of the secondary side control circuit unit. It is no longer a problem as an error,
High accuracy constant current control can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a charging circuit according to the present invention.

FIG. 2 shows a flowchart of a charging control operation of the charging circuit according to the present invention.

FIG. 3 is a time chart showing a charging current of the charging circuit according to the present invention.

FIG. 4 is a circuit diagram showing a conventional charging circuit.

FIG. 5 is a time chart showing a charging current of the circuit shown in FIG. 4;

FIG. 6 is a circuit diagram of a main part of a conventional charging circuit in which a single photocoupler controls both charging current and minute current at a constant current.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 AC power supply 2 Diode bridge 3 Switching element 5 Temperature sensor 6 Battery temperature detection circuit 7 Microcomputer 8 PWM control circuit T Transformer R1 Detection resistor OP1, OP2 Operational amplifier PC1 Photocoupler Q1 Transistor R2, R10, R20 Resistance determining the gain of operational amplifier OP2

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-24932 (JP, A) JP-A-1-190226 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02J 7/10 H02J 1/00

Claims (1)

(57) [Claims] An inverter that detects a secondary charging current and feeds back a control signal corresponding to the charging current to the primary side to adjust the on and / or off duty of the switching element to perform constant current control. A charging circuit of a system, a detection resistor connected in series to a charging current supply line,
A first operational amplifier for amplifying a voltage across the detection resistor;
A second operational amplifier for amplifying the output of the first operational amplifier; and gain switching means for switching a gain of the second operational amplifier , wherein the detection resistor is connected to a charging current supply line.
A first operational amplifier connected in series to a return path;
Is for inverting amplification, and the second operational amplifier is for non-inverting amplification.
To extract the voltage across the detection resistor with negative polarity
A charging circuit, wherein the charging circuit is led to the first operational amplifier .