KR200330442Y1 - Charging circuit for a secondary battery - Google Patents

Abstract

Disclosed is a charging circuit of a secondary battery having a precharge part and using lithium for performing charging by raising the voltage of the battery to a voltage suitable for normal charging before normal charging. The charging circuit includes a control unit for controlling charging start or stop, a reverse current prevention unit for preventing reverse current from an output terminal to an input terminal, determining an operation of the controller in the constant current mode, and detecting whether the battery is fully charged in the constant voltage mode. The charging current sensing unit and the pre-charge unit to continuously supply current even when the battery is below a predetermined voltage level to increase the voltage of the battery to enable normal charging. Normal charging can be performed by the continuous current supply of the precharge unit even if the initial voltage of the battery is lower than a predetermined level due to overdischarge, overcharge, overcurrent, or aging of the battery.

Description

Charging circuit for a secondary battery

The present invention relates to a charging circuit of a secondary battery, and more particularly to a charging circuit of a lithium ion battery and a lithium polymer battery having a precharge part.

Secondary batteries have the advantage that even if the charged electrical energy is consumed, they can be recharged and reused. There are two types of secondary batteries, which include nickel cadmium (NiCd) batteries and batteries using lithium.

Nickel cadmium batteries, which have been used conventionally, have a feature of charging with a constant current. Nickel cadmium batteries undergo chemical reactions at the positive and negative electrodes during charging and discharging to change active materials. When overcharged, water decomposes, but when the negative electrode active material is more than the positive electrode active material, only oxygen gas is generated at the positive electrode and absorbed at the negative electrode. At this time, a drop in battery voltage occurs and full charge is possible by detecting this.

In contrast, in lithium ion batteries, movable ions travel between the positive electrode and the negative electrode during charging and discharging, and electrical energy is generated by a redox reaction. When the battery voltage rises after full charge, the solvent starts to decompose instead of water, but it is impossible to design a battery that absorbs the decomposed gas such as nickel cadmium battery. It is necessary not to.

A lithium ion battery is a battery using lithium transition metal oxide as a cathode active material without using lithium metal as a negative electrode active material, reversibly inserting lithium ions.

Lithium polymer batteries use lithium alloy as a negative electrode active material and SPE (Solid Polymer Electrolyte) as an electrolyte.

In the case of a lithium ion battery, since the constant voltage charging method is used, the voltage is determined to be an absolute value. Usually, the charge control voltage employs two types of control voltages, 4.1V / cell and 4.2V / cell. The accuracy in the case of measuring the voltage relatively is only a minimum resolution, and the difference by the quantity of batteries connected in series is not a problem. In the case of absolute measurements, however, both measurement range and minimum resolution are problematic. Therefore, the charge control circuit of the lithium ion battery requires a high-precision constant voltage circuit corresponding to the battery voltage.

In general, a lithium ion battery is charged with a constant current until the battery voltage becomes 4.1V or 4.2V, and when such a voltage is reached, the battery is switched to the constant voltage method and charged while the charging current gradually decreases from the maximum charging current value.

There are three types of charging methods for the lithium ion battery and the lithium polymer battery.

First, the step-down method, characterized in that the input voltage is higher than the output voltage.

The second is a step up and down method where the input voltage may be higher or lower than the output voltage.

Thirdly, the step-up method is characterized in that the input voltage is lower than the output voltage.

In general, a step down method is used, and the step down method is divided into a pulse width modulation (PWM) and a linear method. In the PWM method, the control element changes the duty ratio of the transistor or the FET of the switching unit at a predetermined frequency, and controls the output voltage and the output current. The linear method is controlled by the output of the comparator inside the control unit regardless of the fixed frequency. It is a method of controlling transistors or FETs.

Charging in this step-down method is measured by the open circuit voltage of the battery before charging is performed. When the open circuit voltage of the battery is measured and this voltage is about 2V or more, the charging circuit is activated and fast charging occurs.

However, if the open circuit voltage of the battery is less than about 2V, the charging circuit does not work and the battery is considered abnormal. Thus no charging takes place and the charger is discarded.

Recently, a problem caused by over-discharge of a secondary battery is occurring because it requires long-term use with a single charge in a mobile phone, mp3, pda, etc. using a secondary battery using lithium. In particular, even if the battery is a normal battery according to a variety of usage forms a case where the open circuit voltage is less than 2V, there is a problem that recognizes this as an abnormal battery.

An object of the present invention for solving the above problems is to provide a fast charging unit, even when the charging control circuit is stopped, the precharge unit to supply a current to the battery to increase the open circuit voltage to 2V or more to perform fast charging To provide a charging circuit for a secondary battery.

1 is a block diagram schematically illustrating a charging circuit according to an embodiment of the present invention.

2 is a circuit diagram illustrating a charging circuit according to an embodiment of the present invention.

3 is a timing diagram showing an operation of a charging circuit during normal charging according to an embodiment of the present invention.

FIG. 4 is a timing diagram illustrating an operation in which the precharge unit increases the voltage of the battery to cause normal charging according to an embodiment of the present invention.

The present invention for achieving the above object, the charging control unit for starting the charge and stop charging in accordance with the charge control signal; A switching unit for transmitting an input signal of an input terminal to an output terminal according to a charging start signal of the charging control unit; A reverse current prevention unit for blocking a reverse current from the output terminal to the input terminal; Charge current detection unit for detecting whether the battery is fully charged; And a precharge unit formed in parallel with the switching unit and configured to increase the voltage of the battery by supplying power to the battery even in an open state of the switching unit due to the low voltage of the battery. Provided is a charging circuit for a secondary battery.

According to the present invention, the discharged secondary battery is charged even under a predetermined voltage, thereby enabling normal fast charging. It also has two charging paths, enabling faster charging.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Example

1 is a block diagram schematically illustrating a charging circuit according to an embodiment of the present invention.

Referring to FIG. 1, a controller for starting charging, a switching unit for opening or shorting a charging path according to a control signal of the controller, a reverse current prevention unit for preventing reverse current of an output terminal, and a precharge for performing precharge The charging unit, the charging current sensing unit for sensing the charging current, the input filter unit and the output filter unit are shown.

The control unit is for controlling the output voltage and the output current of the charging circuit to a constant current or a constant voltage. It consists of an OP-AMP, a transistor, and a resistor, and is currently commercially available in the form of a semiconductor chip.

In the present embodiment will be described by applying the Japanese Mitsumi MM1333D, but those skilled in the art can variously change the control unit according to the use form.

The control unit operates according to the charge control signal, and starts charging when the charge control signal is low, and stops charging when the charge control signal is high. In addition, it detects the output voltage from the output terminal and outputs a full charge output signal according to the amount of charge current detected by the charge current detector. In addition, the controller controls the amount of charging current from the input terminal to the output terminal according to the charge control signal and the sensed output current.

The switching unit is composed of a resistor and a transistor. The charging path from the input terminal to the output terminal may be opened or shorted according to the control signal of the controller.

The reverse current prevention unit prevents current from flowing into the charging circuit from the output terminal when the voltage of the signal passing through the switching unit is lower than the voltage of the output terminal. This connects the diode in series between the switching part and the output terminal, and connects the diode such that the output part of the switching part becomes the positive electrode and the output terminal part of the charging circuit becomes the negative electrode. If the voltage of the signal passing through the switching unit is higher than the output terminal, forward bias is applied to the diode, so the diode is turned on to charge. Since the diode is turned off, the reverse current from the output terminal to the switching unit is cut off.

The precharge unit is located in parallel with the switching unit, and serves to increase the voltage of the battery by supplying power to the battery even in an open state of the switching unit due to the low voltage of the battery.

In general, a charging circuit performs charging immediately when an input power is applied without checking a voltage state of a battery. However, this is a state in which the state of the battery to be charged is not confirmed, resulting in a rapid chemical change of the battery, which shortens the battery life. In addition, when the voltage of the battery is less than 2V, charging is not performed and the charging path is blocked.

The precharge part becomes a new charging path in addition to the charging path composed of the switching part and the reverse current prevention part, and is composed of a resistor or a resistor and a diode.

If the voltage of the battery itself is less than 2V due to various reasons such as over discharge and aging of the battery, the path of the switching part of the charging circuit is opened and the current flowing to the switching part becomes 0, but the precharge part supplies the current to the battery and the potential of the battery Slowly increase.

In addition, since the current supplied through the precharge unit is 100 uA or less, the risk of damaging the charging circuit itself due to the destruction of the battery is reduced. Even when normal charging is performed, the precharge unit continuously supplies current to the battery, and in addition to charging by the switching unit, the precharge unit supplies current in parallel so that fast charging occurs.

The charging current detector is positioned between the ground of the input terminal and the ground of the output terminal and is composed of a resistor. This fully detects whether the battery is fully charged and sends a signal to the controller, and the controller amplifies the detected signal and outputs a full charge output signal. According to the embodiment, the full charge output signal may be input to a light emitting diode (LED) to allow the user to visually check whether the battery is charged. In addition, it detects the charging current during the initial charging and serves to input the amount of charging current to the controller so that charging occurs in the form of a constant current.

The input filter part is composed of a capacitor located between the input terminal and the input ground to remove ripple or noise at the input. Since the capacitor is open for the DC component of the input signal and has a predetermined impedance according to the frequency for the AC component, a signal supplied to the precharge unit and the switching unit is transmitted to the precharge unit and the switching unit by sending a ripple or the like from the input to the input ground. Have a bay.

The output filter part is located between the output terminal and the output ground to eliminate ripple or noise at the output and is composed of a capacitor.

2 is a circuit diagram illustrating a charging circuit according to an embodiment of the present invention.

Referring to FIG. 2, the control unit may be variously applied to those skilled in the art as described in FIG. 1. In the present embodiment, the control unit MM1333D manufactured by Mitsumi, Japan, will be described.

The switching section consists of a resistor R ₁ and a transistor Q ₁ . Preferably, R ₁ is 100? In addition, Q ₁ should select a device that can pass a current of 2A or less. Such a device is suitable to use a transistor consisting of a Bipolar Junction Transistor (BJT) or a Field Effect Transistor (FET).

The reverse current protection part consists of diode D ₁ . In addition to the diode, the base of the BJT and the collector terminal may be connected to perform a diode function.

The precharge part consists of the resistor R ₂ . It is preferable to set R <_2> to 100 kPa-1 kPa. Since the input voltage range of the input terminal is 4.75V to 6V, the current passing through the resistor constituting the precharge portion is up to 60uA, thereby reducing the risk of damage to the charging circuit itself due to the destruction of the battery. Since uA is sufficient to protect the charging circuit, the consumption of the charged battery is negligible. As described above with reference to FIG. 1, when the voltage of the battery immediately before charging is 2V or less, the control unit continuously supplies current to the battery so that the voltage of the battery reaches 2V or more as compared with the switching unit opening the charging path. Operate the switch to allow normal charging to occur. In addition, even in the case of an additional minute current, the charging circuit has two charging paths as a whole, thereby enabling faster charging than in the related art.

In addition, the precharge unit may be configured by connecting a diode in series with the resistor R ₂ . At this time, the diode blocks the reverse current flowing from the output terminal to the input terminal. Therefore, the anode of the diode is connected to R ₂ , the cathode of the diode should be configured to face the output terminal.

The charging current detector is composed of a resistor R ₃ . During initial charging, the charging circuit performs charging with a constant current. The resistor R ₃ senses a current between the output ground terminal and the input ground terminal to supply a signal to the controller so that the controller operates in a constant current state. In addition, when the battery is fully charged, the full charge state is detected and the detection signal is input to the controller to output the full charge output signal. The resistance R ₃ is preferably 0.1 k? To 0.3 k ?.

In addition, the input filter portion is composed of a capacitor C ₁ , preferably 0.1uF to 100uF.

The output filter part is composed of a capacitor C ₂ , preferably 1uF to 220uF.

3 is a timing diagram showing an operation of a charging circuit during normal charging according to an embodiment of the present invention.

Referring to FIG. 3, the input signal V _cc is applied to the input terminal of the charging circuit. V _cc of the input signal, it is preferable to be a 4.75V to 6V. The controller does not operate while the charge control signal is high, but when it is in the low state, the charging circuit starts operation to perform charging. However, this normal charging occurs when the initial voltage of the battery is more than 2V.

When the input is applied and charging starts by the charge control signal, the charging circuit initially operates in the constant current mode. When the output signal reaches about 4.2V by the supply of a constant current, the charging circuit performs the charging in the constant voltage mode. The full charge output signal remains low during charging, and when charging is complete, it goes high to indicate that charging is complete. Even in this static state of charge, the precharge unit supplies a maximum of several hundred uA of current to the battery to allow fast charging.

FIG. 4 is a timing diagram illustrating an operation in which the precharge unit increases the voltage of the battery to cause normal charging according to an embodiment of the present invention.

4, the input signal V _cc is applied to the input terminal of the charging circuit. V _cc of the input signal, it is preferable to be a 4.75V to 6V. The controller does not operate while the charge control signal is high, but when the controller is in a low state, the charging circuit should start operation, but when the voltage of the battery is 2V or less, the controller detects an output signal and blocks the charging path. Therefore, the flow of current through the transistor of the switching unit is blocked, and the controller stops the operation. However, with the input signal applied, the precharge unit continuously supplies current to the battery. Therefore, even when the voltage of the battery is less than 2V at the beginning of charging, since the current is supplied through the precharge unit, the voltage of the output signal gradually increases. When the output signal is 2V or more, the controller performs an operation and conducts fast charging by conducting a transistor of the switching unit. Therefore, the full charge output signal goes low to indicate that the charging circuit has entered a normal charging state. When charging in the constant current and constant voltage mode is performed and the charging is completed, the charging current detector detects whether the battery is fully charged and causes the controller to output a high charging output signal having a high state.

According to the present invention as described above, by the aging, overcurrent, overcharge or over-discharge of the battery, the voltage of the initial battery of the charge is below a predetermined level to prevent the charging is started, and to continuously supply the current through the precharge unit The voltage of the battery is raised above a predetermined level to allow normal charging to occur.

Although the above has been described with reference to the preferred embodiment of the present invention, those skilled in the art various modifications of the present invention without departing from the spirit and scope of the present invention described in the utility model registration claims below And can be changed.

Claims (6)

A charging control unit for starting charging and stopping charging according to a charging control signal; A switching unit comprising a first resistor and a transistor for transmitting an input signal of an input terminal to an output terminal according to a charging start signal of the charging controller; A reverse current prevention unit formed of a first diode to block reverse current from the output terminal to the input terminal; Charge current detection unit for detecting whether the battery is fully charged; And Located in parallel with the switching unit, including a pre-charge unit consisting of a second resistor or a second diode to supply power to the battery to increase the voltage of the battery even in the open state of the switching unit due to the low voltage of the battery Charging circuit of a secondary battery, characterized in that. The output circuit of claim 1, wherein the charging circuit of the secondary battery removes ripple or noise at an input filter or output positioned between the input terminal and an input ground to remove ripple or noise at an input. And an output filter positioned between the output ground and the secondary battery. The secondary battery charging circuit according to claim 1, wherein the second resistor of the precharge part is 100 kW to 1 kW. The charging circuit of claim 1, wherein the voltage of the input signal is 4.75V to 6V. The charging circuit of claim 1, wherein the voltage at the output terminal is about 4.2V. The charging circuit of claim 1, wherein the charge current preventing unit includes a third resistor, and the third resistor is 0.1Ω to 0.3Ω.