JP2001327095A - Charging control circuit for lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform charge control stably, while ensuring a constant power supply voltage through a simple and inexpensive arrangement. SOLUTION: When a PWM control AC/DC converter is used for charging a lithium ion battery, and a command for bringing primary conduction to zero is delivered in order to stop charging operation upon completion thereof, a secondary voltage also goes zero and thereby a control voltage goes zero to cause hunting. In order to prevent hunting at the time of stopping charging operation, a conventional current/voltage control loop (amplifiers 3, 4) for controlling the battery voltage at a constant level is provided with a control loop (amplifier 5) which although unable to perform charging operation can perform minimum control operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge control circuit for a lithium ion battery which has been widely used as a power source for various portable devices.

[0002]

2. Description of the Related Art A charge control of a lithium ion battery is performed by monitoring a charge current and a voltage. Since the application of overvoltage deteriorates the battery, the voltage at the time of charging is 4.2V ± 30mV (± 0.7% in terms of the variation rate) of the battery at the time of full charge of 4.2V, and the voltage management with high accuracy. Is required. When one battery is used, the voltage is 4.1 V or 4.2 V.

FIG. 4 shows a general A as a power source for charging a battery.
3 shows a C / DC converter. This is to double-wave rectify the AC power supply 24, switch the smoothed voltage at a high frequency, and rectify and smooth the voltage induced on the secondary side via the transformer 25 for battery charging. The charging control circuit section 22 on the AC line side and the secondary side is insulated by the transformer 25 and the photocoupler 23. The secondary side voltage control is
This is performed by transmitting the signal to the controller 21 on the primary side through the photocoupler 23. The controller 21 on the primary side is a photocoupler 23
The secondary-side voltage is controlled by changing the pulse width of high-frequency switching (PWM control: changing the current supply period) according to the amount of light obtained from. That is, the primary side controls so that the output voltage is low when the light emission amount is large and the output voltage is high when the light emission amount is small according to a command from the secondary side. At the time of start-up, the control power supply on the secondary side is 0 V, and there is no feedback (no light emission) by the photocoupler 23, so the command is to increase the output voltage. As a result, the controller 22 on the secondary side can obtain the operating voltage and execute the control.

In the configuration shown in FIG. 4, it is most natural that the power supply for the controller 22 on the secondary side is obtained from the secondary winding, but there are the following problems. 1) Ensuring the voltage required by the controller When charging the battery, the voltage on the secondary side is slightly higher than the battery voltage (= battery voltage + 0.3 V to 0.5 V: forward voltage drop of reverse blocking diode D + Voltage drop across the current detection resistor R). If an attempt is made to charge an excessively discharged battery, it is necessary to consider a battery voltage of at least about 2 V. When charging such a low-voltage battery, the voltage obtained by rectifying and smoothing the voltage of the secondary winding of the transformer (hereinafter also referred to as charging voltage) is 2.5 V (= 2 V (battery voltage) +0.5 V). Only occurs to the extent. Therefore, the charging voltage becomes 2.5 V, but this voltage is too low to be used as the power supply voltage of the controller. Although it may be good for the purpose of pursuing low-voltage operation, a normal analog / digital mixed controller requires a stabilized voltage of 3 to 5V. From this, to stabilize, 1
To allow for a V margin, a voltage of at least 4 to 6 V is required. However, when a single battery is charged and the battery voltage is about 2 V, the voltage required for the controller (4 to
6V) cannot be secured. Therefore, it is necessary to consider a method for securing the voltage.

[0005] 2) Occurrence of hunting The controller monitors the state of charge of the battery, cuts (0 V) the secondary output voltage at the end of charging or when an abnormality occurs, and operates to end the charging operation (photocoupler). The switching operation of the primary-side controller is stopped by maximizing the current supplied to the controller. As a result, the charging can be stopped by setting the charging voltage to 0V.
Since the power supply to the controller is also cut off, the current that has been flowing through the photocoupler at maximum is cut off, so that the primary-side switching circuit is restarted and the power supply to the secondary side is restarted. This voltage rise causes the controller to start again. The controller has the same malfunction (or end operation) as before.
And the above operation is repeated to cause a hunting operation.

As a countermeasure for these, there are the following methods. Instead of taking control power from the battery charging power supply,
A configuration as shown in FIG. 5 for securing a stable voltage from another route is conceivable. This is because the secondary-side voltage control is not performed on the primary side, but the secondary-side voltage is rectified and smoothed.
A switching regulator 32 having a step-down configuration is provided based on the C voltage, and a DC voltage obtained by rectifying and smoothing the secondary voltage or a separate winding is provided as a power supply for the controller. . In this case, a controller on the primary side is not particularly required, and a power transformer configuration at a commercial power frequency can be considered. However, since the transformer is large and heavy, a high-frequency switching system is indispensable for this portion as well. As a result, a similar circuit 32 is prepared on the secondary side, causing problems such as an increase in cost and an increase in circuit size due to an increase in the number of components. 33 indicates a charge controller.

A method of mounting a switch A method of mounting a switch for cutting off the power supply to the charging circuit when charging is stopped can be considered. In this case, the secondary side voltage is determined to be 0 V, and the primary side is driven at the maximum duty. . Although there are some differences depending on the design specifications, the no-load output voltage in the state without feedback needs to be assumed to be a voltage two to three times (about 30 to 50 V) the voltage in a normal use state. . In many cases, the controller does not have a withstand voltage enough to withstand such a high voltage, and an overvoltage protection circuit for suppressing this voltage is required. Since this voltage is not generated in the transient state of the control but is generated continuously when the switch is turned off, the power consumption and size of the circuit tend to increase. Attention must also be paid to the transient characteristics of the controller when the switch is turned on at this high voltage (due to control delay, etc.).

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a charging control circuit which can avoid problems such as cost increase and circuit size increase due to an increase in the number of components, and which is stable and consumes less power. It is in.

[0009]

In order to solve such a problem, according to the first aspect of the present invention, a DC voltage on the secondary side of an AC / DC converter is used as a power supply for charging a lithium ion battery, and charge control is performed. A current control loop and a voltage control loop for detecting these values in order to obtain a charging current and a voltage according to a sequence and controlling a DC voltage so that each of them becomes a target value are provided. In a charge control circuit of a lithium ion battery that changes a pulse width by feeding back to a pulse width modulation controller, a DC voltage obtained by rectifying and smoothing a voltage on the secondary side of the power supply is received as a charge voltage, and based on this voltage, A DC / DC converter for producing a power supply voltage for control is provided, and a third control loop for controlling a DC voltage to be constant separately from the current and voltage control loop is provided. Is characterized by be higher than the minimum operating voltage of the third lower than the battery voltage setting voltage at the control loop, and the DC / DC converter. In the first aspect of the present invention, the voltage control loop and the third control loop can be shared (the second aspect of the invention), or the current control loop and the third voltage control loop are shared. (The invention of claim 3).

[0010]

1 is a block diagram showing an embodiment of the present invention, wherein 1 is a DC / DC converter, 2 is a control circuit power supply, 3 is a current control amplifier, 4 is a voltage control amplifier, Reference numeral 5 denotes an amplifier for controlling an idle mode, 6 denotes a photocoupler, 7A and 7B denote analog switches, 8 denotes an idle mode setting command terminal, E denotes a reference voltage, and 10 denotes a lithium ion battery.

This is because D is used as a power supply for the control circuit on the secondary side.
A current control loop including a normal current control amplifier 3 for providing a C / DC converter 1 to secure a power supply voltage and controlling a DC voltage according to a charging voltage and a current to a battery;
Outside the voltage control loop including the voltage control amplifier 4, DC
A third control (idle mode control) loop for controlling the voltage to be constant is added. When the set voltage in the third control is lower than the battery voltage and the DC / DC
By setting the voltage lower than the operation lower limit voltage (about 2 V) of the converter, the DC / DC converter 1 secures the control voltage (operation voltage) and prevents the hunting operation. Normally, the analog switches 7A and 7B set the reference voltage of the amplifier 5 to E, and divide the E to 2 V in the idle mode.
It is provided for the degree.

FIG. 2 is a view for explaining the principle of the present invention. FIG. 2A is a circuit diagram of a main part of FIG. 1, and FIG. Conventionally, the current control amplifier 3 shown in FIG.
The voltage and current control amplifier 4 compares the detected values of the current and the voltage with the command value, selects the lower one of the output voltages, and determines the current supplied to the light emitting diode D of the photocoupler 6. I have. In the battery voltage control, as shown in (b), when the battery voltage is low, constant current control is performed as shown by a dotted line, and the battery voltage is constant (for example, if the battery voltage is a 4.2 V type with one battery, 4.2V)
, Constant-voltage charging is performed. When the charging current becomes equal to or less than a fixed value (for example, 1/10 of the current at the time of constant-current charging), charging ends.

The mode switching from the constant-current charging to the constant-voltage charging is such that the light emission amount of the photocoupler 6 is controlled in accordance with the lower control voltage in each control. If the output voltage of the voltage control amplifier 4 is set to be lower than the output voltage of the current control amplifier 3 when the battery voltage at the time becomes 4.2 V, the output of each amplifier is used for control switching. Since the cathodes of the diodes D1 to D3 are connected to each other and the anodes of the control switching diodes D1 to D3 are commonly connected to the cathode of the light emitting diode D, the voltage control which becomes lower than the current control output is automatically performed. Can be selected and executed.

An amplifier 5 is further provided for such a configuration, and the voltage to be set (in this case, 2
V: E3) and idle mode control in which a current detection terminal connected to the charging voltage is connected to the (-) input, and this mode is set when the charging operation is stopped. In the idle mode control, the charging voltage is set to 2 by setting the output voltage lower than that in the current / voltage control mode.
The voltage is set to about V so that the battery cannot be charged. However, a DC / DC converter of an up / down configuration that inputs this voltage is provided so that the supply of the voltage to the controller can be ensured even in the idle mode.

FIG. 3 is a block diagram showing another embodiment of the present invention. This is not to use amplifiers for current, voltage control and idle mode control, respectively, but to use two of them. In the figure, voltage control and idle mode control are used together. For example, in the case of voltage control, the output of the amplifier 12 is supplied to the (-) terminal.
The analog switches 7C to 7F are used to select the (+) terminal so that the reference voltage E0 is supplied thereto. Although the voltage control and the idle mode control are used in FIG. 3, it goes without saying that the current control and the idle mode control can be used in the same manner.

[0016]

According to the present invention, as a power supply circuit of a lithium-ion battery charger, the switching of the primary side of an AC / DC converter is PWM-controlled to control the charging voltage and control the charging of the battery. The power supply of the controller is secured by the DC / DC converter, and when charging is terminated (stopped), the charging voltage is not set to 0, but the voltage (DD) of the terminal to which the current detection resistor R is connected.
(The input voltage of the C / DC converter) is set to be lower than the battery voltage and higher than the operation lower limit voltage of 2 V of the DC / DC converter. In this state, the charging operation is stopped, but other monitoring functions and the like are operating, and the battery voltage measurement can be performed in this state.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the principle of the present invention.

FIG. 3 is a configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing an AC / DC converter as a battery charging power source.

FIG. 5 is a configuration diagram showing another example of a battery charging power supply.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC / DC converter, 3 ... Current control amplifier, 4
... voltage control amplifier, 5 ... idle mode control amplifier, 6 ... photocoupler, 7A-7F ... analog switch, 10 ... lithium ion battery, 11 ... voltage / idle control amplifier, 12 ... battery voltage detection amplifier.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H02M 3/28 H02M 3/28 H

Claims (3)

[Claims] 1. A DC voltage on a secondary side of an AC / DC converter is used as a power supply for charging a lithium ion battery, and these values are detected to obtain a charging current and a voltage according to a charging control sequence. DC to reach the target value
A charge control circuit for a lithium ion battery, comprising: a current control loop for controlling voltage; and a voltage control loop, the output of which is selectively fed back to a pulse width modulation controller on the AC side to change the pulse width. A DC / DC converter that receives a DC voltage obtained by rectifying and smoothing the voltage on the secondary side as a charging voltage and generates a power supply voltage for control based on the voltage is provided, and a DC voltage is generated separately from the current and voltage control loop. There is provided a third control loop for performing constant control, wherein the set voltage in the third control loop is lower than the battery voltage and the DC / DC
A charge control circuit for a lithium ion battery, wherein the charge control circuit is set to be higher than an operation lower limit voltage of the converter. 2. The charge control circuit for a lithium ion battery according to claim 1, wherein the voltage control loop and the third control loop are shared. 3. The charge control circuit according to claim 1, wherein the current control loop and the third voltage control loop are shared.