JP2006197688A - Charge control circuit of lithium-ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a reference voltage of a charge control circuit by a simple constitution. <P>SOLUTION: In order to obtain a charging current or a charging voltage matched to a charging sequence, a current control means 12 or a voltage control means 13 that change pulse widths by feeding values of the current and the voltage back to an AC/DC converter so that the values reach target values. When charging a battery CE up to a charge limit voltage, the charging voltage appearing at a terminal T is used as a reference voltage of the A/D converter 16, meanwhile a reference voltage from a setting circuit 11 is determined whether it can be read as a voltage in a certain range, and when it can be read as the voltage in the certain range, the A/D converter 16 is determined to be normally operated, and the acquisition of variety of data can be made effective. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a charge control circuit for a lithium ion battery (also referred to simply as a battery) that is used in large quantities as a power source for various portable devices, and more particularly to a charge control circuit having an improved method for forming its internal reference voltage.

  The charging control of the lithium ion battery is performed by monitoring the charging current and voltage. In particular, the application of overvoltage deteriorates the battery, so strict voltage management is required. The voltage at full charge is 4.2 V ± 25 mV for a battery of 4.2 V type at charge (if the rate of change is ± 0.6%) is required. The battery is commercialized in a packed state, and there are one (4.2V, n parallel) and several in series. Below, the case where it uses with one battery is demonstrated.

An example of a conventional charge control circuit is shown in FIG. Although the reference voltage of the A / D (analog / digital converter) 16a is not shown in FIG. 1, this is shown in FIG.
Since the operation of the circuit shown in FIG. 9 is the same as that of the circuit shown in FIG. 1 to be described later, the description thereof is omitted here. However, in such a configuration, the charging voltage setting reference voltage and the A / D converter reference voltage are 2 Here, the reference voltage for charging voltage setting is generated by the reference voltage setting circuit 11, and the reference voltage for A / D converter is generated by the amplifier Am that multiplies the output of the circuit 11 by A.

JP 2004-248476 A (page 3-9, FIG. 1)

By the way, in the configuration as shown in FIG. 9, the adjustment by trimming or the like is performed with reference voltage setting circuit 11 for setting the charging voltage with reference to the output voltage, and the output is multiplied by A to the reference voltage of the A / D converter. Must be applied to both amplifiers Am. In particular, the amplifier Am to be multiplied by A has not only variations in resistance values for providing offset and gain of the amplifier alone, but also variation in the charging voltage setting circuit of the setting circuit 11 in favor of the charging voltage. Since the adjustment is performed first, there arises a problem that the A / D reference voltage is gradually shifted.
An object of the present invention is to enable setting of a reference voltage in a circuit with a simple configuration.

In order to solve such a problem, the invention of claim 1 uses the rectified and smoothed DC voltage on the secondary side of the output transformer of the AC / DC converter as the charging voltage of the lithium ion battery and the power source for the controller. In order to obtain a charging current or a charging voltage corresponding to a sequence, the current / voltage value is fed back to the AC / DC converter so that the current or voltage value matches a target value, and the feedback output is provided. In the charge control circuit of the lithium ion battery, which controls the DC voltage on the secondary side of the transformer to be finally equal to the charge upper limit voltage of the battery,
While the charging voltage is input as a reference voltage of an A / D converter used for reading the voltage and current value inside the controller, there is a period in which the charging voltage generated during rapid charging decreases. Only when the converter can read the internal reference voltage as a predetermined value, the constant voltage charging period (including preliminary charging) is determined, and reading of various control data by the A / D converter is enabled. .

In the second aspect of the invention, the rectified / smoothed DC voltage on the secondary side of the output transformer of the AC / DC converter is used as the charging voltage of the lithium ion battery and the power supply for the controller, In order to obtain a charging voltage, it is provided with current control means and voltage control means for feeding back the current or voltage value to the AC / DC converter so as to match a target value, and the DC voltage on the secondary side of the output transformer to be fed back In a charge control circuit for a lithium ion battery that ultimately controls the battery so as to be equal to the charge upper limit voltage of the battery,
Comparing means for comparing the output voltages of the current control means and the voltage control means is provided, and when the current control operation is judged from the comparison result, reading of the voltage and current by the A / D converter is invalidated It is characterized by.

According to the present invention, by simplifying the internal control circuit and making the power supply common by setting the internal reference circuit to be set to the charging voltage and allowing the reference (charging) voltage fluctuation. It becomes possible.
Since a battery is connected to the outside and a large filter is added as a power source, it is expected to obtain a stable reference voltage.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
As shown in the figure, the charging control circuit 1 has a reference voltage setting circuit 11, comparators 12 and 13, a current detection differential amplifier 15, an A / D converter 16, a controller 17, and a reference that does not particularly require adjustment of trimming and the like. The voltage generating circuit E is configured. The controller 17 is composed of, for example, a computer. Although the comparators 12 and 13 and the current detection differential amplifier 15 are indicated by the same circuit symbol, the comparators 12 and 13 are operational amplifiers according to the image of the symbol, whereas the current detection differential amplifier 15 Assumes a subtraction circuit with several resistors connected to an operational amplifier. The capacitor C is connected to stabilize the output of the AC / DC converter (AC / DC) or the input to the charge control circuit 1. SW1 to SW3 are switches for connecting and releasing the battery CE.

  As shown in FIG. 1, the charging voltage (battery charging voltage: voltage after charging current detection resistor R = voltage at terminal T) is connected to the reference voltage terminal of A / D converter 16 to charge the voltage setting. The A / D converter 16 requires the voltage from the reference voltage setting circuit 11 (nominal 1V reference voltage: for calibration of the A / D converter). It will be read from time to time according to.

  The charging control circuit 1 is activated when AC power is turned on, and the light emission amount of the photocoupler PC is controlled so that the charging voltage becomes 4.2 V. At that time, the charging control circuit 1 is in a waiting state for charging. In this charging waiting state, the charging switches SW2 and SW3 are off, the charging current is 0, the current command value indicates about 1A of the rapid charging setting, and the output of the current control comparator 12 swings to “H”. ing. Therefore, since the output of the voltage control comparator 13 is lower than the output of the current control comparator 12, the voltage control is dominant and the charge voltage is controlled preferentially to 4.2V. . That is, as shown in FIG. 2, switching between current control and voltage control has a configuration in which the outputs of the comparators 12 and 13 are diode-connected, and the lower one of the output voltages is controlled with priority.

Charging is started by detecting that a battery is attached. When the battery CE is connected, first, SW1 is turned on and the voltage of the battery is measured. If it is determined that the battery can be charged and needs to be precharged, as shown by the dotted line in FIG. The battery is charged with a current of about C), and the battery voltage is measured. When the voltage rises within a certain period of time and reaches a voltage for shifting to the rapid charge, the rapid charge operation is started.
FIG. 3 shows a case where the battery is initially unconnected, the voltage of the connected battery is detected thereafter, and preliminary charging is determined to be unnecessary, and rapid charging is performed.
In the quick charging operation, the output of the current control comparator 12 is lower than the output of the voltage control comparator 13 in order to adjust the charging current to a set current value (a constant value), and the charging voltage is maintained during the current control period. It becomes a state lower than 4.2V.

  FIG. 4 shows the outputs of the comparators 12 and 13. The solid line shows the output of the comparator 12, and the dotted line shows the output of the comparator 13, respectively. The output of the comparator 12 is smaller than the output of the comparator 13 in the current control range, and the output of the comparator 13 is smaller than the output of the comparator 12 in the voltage control range. It can be seen that control is performed.

  As shown in FIG. 3, the battery is charged at a constant current in a state where the battery voltage is lower than the set voltage at the end of battery charging. The charging voltage at this time is lower than the charging end voltage of the battery, and when that voltage reaches the charging end voltage (for example, 4.2V for a single battery of 4.2V type), this voltage. Is fixed at the upper limit and shifts to constant voltage charging. As time elapses in the constant voltage charging state, the battery is charged, and the charging current gradually decreases as shown by the dotted line in FIG. When the current value decreases to a constant value (for example, 1/10 of the constant current charge value), it is determined that the charging is finished.

This will be described in more detail with reference to FIG.
Pre-charging is a method of charging with a current of about 1 / 10C of the battery, but this is averagely charged with this current value, so there is no practical problem. In this method, the battery is not connected (= constant voltage charging) The on / off period of SW3 connected in series with the resistor Rb shown in FIG. 1 is adjusted as shown in FIG. 5B (pulse width modulation) while the charging voltage is set to the current voltage (4.2V). Thus, the charging current is adjusted to be approximately 1 / 10C. As the precharge proceeds, the battery voltage increases as shown in FIG. 5 (a), but the current peak value decreases as shown in FIG. 5 (c) (Rb indicates the resistance and V _CE indicates the battery voltage). The change in the battery voltage is measured by an A / D converter, the on / off period is reviewed, and the energization period is adjusted to be adjusted to 1 / 10C.

SW2 shown in FIG. 1 is a quick charge switch, which is off as shown in FIG. 5 (d) during the precharge period, and is turned on during the quick charge to generate a current i _Q as shown in FIG. 5 (e). Supply to battery CE. SW3 is used as an on / off period adjustment switch during preliminary charging.
By doing as described above, the reference voltage of the A / D converter is ensured even during the preliminary charging period, so that the A / D operation during this period can be guaranteed.

In the case of a defective battery, the precharge is judged as a defective battery that does not increase in voltage even after 2 hours, so there is no guarantee that this time is short. Also, during this period, the SW3 on / off cycle is adjusted (if the battery voltage is low, if 30% of the voltage is the energization period, if the battery voltage rises, this energization period is changed to 60 to In order to be able to increase it to 80 to 100%), it is necessary to measure the battery voltage, and it is necessary to read the battery voltage correctly.
The relationship between the above periods and the on and off of SW1 to SW3 is summarized as follows.
Precharge SW2 …… off
SW3 ... on / off (energization angle adjustment: energization with Rb (Ω))
SW1 …… on
Quick charge SW2 …… on
SW3 …… off
SW1 …… on
Battery voltage reading SW2 …… off
SW3 …… off
SW1 ... on (battery voltage read if necessary)

  With the series of operations as described above, the charging voltage during the constant voltage charging (including the precharging and battery unconnected states) can be set as the predetermined reference voltage of the A / D converter 16, but charging (reference) During the quick charge (constant current charge) period in which the voltage fluctuates, correct conversion cannot be performed as an A / D converter. Therefore, the value obtained by reading and converting the output of the reference voltage setting circuit 11 by the A / D converter 16 deviates from the reference value as shown in FIG. . Therefore, although the operation status cannot be monitored during the quick charging period, there is no particular problem because time monitoring is performed during this period.

  FIG. 7 shows such an operation as a flow. The A / D converter 16 reads the reference voltage from the circuit 11 (see step S1), and determines whether or not it can be read as a predetermined range in step S2. Only in the case (YES), it is assumed that the A / D converter 16 can operate normally, and data is taken in and judgment and processing are executed based on the data (see steps S3 and S4). It should be noted that if it cannot be read as a certain range in step S2, data is not taken in.

FIG. 8 is a circuit diagram showing a second embodiment of the present invention.
As is clear from FIG. 8, the reference voltage from the setting circuit 11 is not input to the A / D converter 16 with respect to that shown in FIG. A feature is that a comparator 14 for comparison is added. When the output of the comparator 12 is lower than the output of the comparator 13, the comparator 14 determines that the quick charging period is in progress, and prohibits reading of the code of the A / D converter 16.

Circuit diagram showing an embodiment of the present invention Circuit diagram showing voltage control circuit and current control circuit Explanatory drawing explaining the charge sequence example of a battery Switching operation explanation of current control and voltage control Operation explanatory diagram for explaining the operation of FIG. Explanatory diagram of relationship between A / D conversion code and A / D conversion reference voltage Flowchart for explaining the operation of FIG. Circuit diagram showing another embodiment of the present invention Circuit diagram showing conventional example of charge control circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Charge control circuit, 11 ... Reference voltage setting circuit, 12, 13, 14 ... Comparator, 15 ... Differential amplifier, 16 ... A / D converter, 17 ... Controller, AC / DC ... AC / DC converter, E Reference voltage generating circuit, Tr ... Transformer, PC ... Photocoupler, R ... Resistance, T ... Terminal, C ... Capacitor, SW1-SW3 ... Switch, CE ... Battery.

Claims (2)

The rectified and smoothed DC voltage on the secondary side of the output transformer of the AC / DC converter is used as the charging voltage for the lithium ion battery and the power source for the controller, and these currents are obtained in order to obtain the charging current or charging voltage according to the charging sequence. Or a current control means and a voltage control means for feeding back the voltage value to the AC / DC converter so as to coincide with a target value, and the DC voltage on the secondary side of the output transformer to be fed back is finally charged to the battery. In a charge control circuit for a lithium ion battery that is controlled to be equal to the upper limit voltage,
The charging voltage is input as a reference voltage of an A / D converter used to read the voltage and current value inside the controller, and the internal reference voltage is used during a voltage drop period that occurs during rapid charging. The lithium ion battery charging control circuit is characterized in that only when the A / D converter can be read as a predetermined value, it is determined that the A / D converter operates normally, and reading of various control data by the A / D converter is enabled. . The rectified and smoothed DC voltage on the secondary side of the output transformer of the AC / DC converter is used as the charging voltage for the lithium ion battery and the power source for the controller, and these currents are obtained in order to obtain the charging current or charging voltage according to the charging sequence. Or a current control means and a voltage control means for feeding back the voltage value to the AC / DC converter so as to coincide with a target value, and the DC voltage on the secondary side of the output transformer to be fed back is finally charged to the battery. In a charge control circuit for a lithium ion battery that is controlled to be equal to the upper limit voltage,
Comparing means for comparing the output voltages of the current control means and the voltage control means is provided, and when the current control operation is judged from the comparison result, reading of the voltage and current by the A / D converter is invalidated A charge control circuit for a lithium ion battery.

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