Battery pack protective circuit for detecting overcharge or wire disconnect

A protective circuit of a battery pack and a method of operating the protective circuit prevents the battery cells from being overcharged by directly detecting overcharge or detecting disconnection of sensing wires, which sense the voltage of battery cells, and instantly shuts off the high current being applied to the battery cells when the sensing wires are disconnected. The protective circuit includes at least one battery cell, and a cell voltage detecting unit adapted to detect the voltage of the battery cell. The protective circuit also includes a switch unit, and a control unit adapted to receive a signal from the cell voltage detecting unit and generate a predetermined control signal based on the signal of the cell voltage detecting unit in order to turn off the switch unit when the battery cell is overcharged or the sensing wire is disconnected.

This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0098834, filed on Nov. 29, 2004, in the Korean Intellectual Property Office, the entire content of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a protective circuit of a battery pack. More particularly, the present invention relates to a protective circuit of a battery pack, capable of detecting disconnection of a sensing wire, which senses a voltage of a battery cell, while preventing overcharge of the battery cell.

2. Description of the Related Art

As generally known in the art, a battery cell is typically not used as a power source for a notebook personal computer and the like because the battery cell has low capacity and operational voltage. Thus, a battery pack or a battery cell module including a plurality of battery cells coupled to each other in series is used as a power source for the notebook personal computer.

Such a battery pack is assembled with a protective circuit in order to control the charge/discharge state of the battery cell while protecting the battery pack from various hazards derived from the overcharge or over-discharge of the battery cell. In addition, a sensing wire is coupled to the protective circuit in order to detect the voltage of each battery cell. For instance, when the battery pack includes three battery cells coupled to each other in series, four sensing wires are required. In this case, a first sensing wire is coupled to a negative electrode of a first battery cell in order to detect a minimum voltage, a second sensing wire is coupled between a positive electrode of the first battery cell and a negative electrode of the second battery cell so as to detect a maximum voltage of the first battery cell (or, a minimum voltage of the second battery cell), a third sensing wire is coupled between a positive electrode of the second battery cell and a negative electrode of the third battery cell so as to detect a maximum voltage of the second battery cell (or, a minimum voltage of the third battery cell), and a fourth wire is coupled to a positive electrode of the third battery cell in order to detect a maximum voltage of the third battery cell.

According to the circuit structure having the above construction, the voltage of the first battery cell is detected by means of first and second wires, the voltage of the second battery cell is detected by means of second and third wires, and the voltage of the third battery cell is detected by means of third and fourth wires, respectively.

Therefore, the voltage of each battery cell can be detected, so the overcharge of all battery cells or a specific battery cell can be detected. If the overcharge of the battery cell is detected, the charge operation for the battery cell is instantly stopped.

However, the conventional protective circuit presents a problem in that there is no apparatus or method for detecting disconnection of a specific sensing wire. For instance, if the second wire is disconnected, the total voltage of the battery cells can be detected by means of the first and fourth wires, but the voltage of the first battery cell cannot be detected. That is, an average voltage value of the first and second battery cells is only detected by means of the first and third wires. In this case, it is impossible to precisely detect the overcharge of the first battery cell even if the first battery cell has been subject to the overcharge state. Accordingly, the first battery cell may be continuously overcharged, thereby causing explosion or ignition of the first battery cell. In addition, it is also difficult to precisely detect the voltage of the second battery cell, so that the secondary battery cell may also be subject to the overcharge.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to address one or more of the above-mentioned problems occurring in the prior art, and embodiments of the invention provide a protective circuit of a battery pack, capable of detecting disconnection of a sensing wire, which senses a voltage of a battery cell, while preventing overcharge of the battery cell by shutting off a high current being applied to the battery cell.

In order to accomplish the above, the present invention provides a protective circuit of a battery pack having at least one battery cell, which is coupled in series. A cell voltage detecting unit is coupled to negative and positive electrodes of the battery cell through a sensing wire so as to detect a voltage of the battery cell. A switch unit is coupled to a high current line in series between one terminal of the battery cell and an external terminal. A control unit receives a signal from the cell voltage detecting unit and generates a predetermined control signal based on the signal of the cell voltage detecting unit in order to turn off the switch unit when the battery cell is overcharged or the sensing wire is disconnected.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As shown inFIG. 1, a protective circuit100of a battery pack according to the present invention includes at least one battery cell111,112or113, a cell voltage detecting unit120for detecting the voltage of the battery cell111,112or113, a switch unit130coupled to a high current line in series, and a control unit140adapted to operate the switch unit130based on a signal of the cell voltage detecting unit120. The switch unit130may be adapted to shut off the high current upon overcharge of the battery cell111,112or113or upon disconnection of sensing wires w1, w2, w3or w4coupled with the battery cell111,112or113.

Although three battery cells111,112and113are shown inFIG. 1, they are illustrative purposes only. That is, according to another embodiment of the present invention, two battery cells or more than four battery cells can be used. In addition, according to the present invention, the battery cells111,112and113are coupled to external terminals P+ and P−, i.e., positive and negative electrode terminals, respectively, and a current detecting unit150for detecting the charge current is coupled to the high current line in series.

As shown inFIG. 2, the first, second and third battery cells111,112and113are coupled to each other in series. In addition, the first sensing wire w1is coupled to a negative electrode of the first battery cell111, the second sensing wire w2is coupled between a positive electrode of the first battery cell111and a negative electrode of the second battery cell112, the third sensing wire w3is coupled between a positive electrode of the second battery cell112and a negative electrode of the third battery cell113, and the fourth sensing wire w4is coupled to a positive electrode of the third battery cell113, respectively. In addition, the voltage of the first battery cell111is detected by means of first and second wires w1and w2, the voltage of the second battery cell112is detected by means of second and third wires w2and w3, and the voltage of the third battery cell113is detected by means of third and fourth wires w3and w4, respectively.

The cell voltage detecting unit120includes a number of voltage-dividing resistors R1to R6and a number of comparators121,122and123. The voltage-dividing resistors R1and R2are coupled to the first battery cell111in a row, in which the voltage-dividing resistor R1is grounded. In addition, a reference voltage is supplied through a ground terminal of the voltage-dividing resistor R1. A reference voltage source is coupled to a non-inverting terminal of the comparator121. In addition, an inverting terminal of the comparator121is coupled between the voltage-dividing resistors R1and R2. Accordingly, if the charge voltage of the first battery cell111is higher than the reference voltage, that is, when the voltage VR1applied to the voltage-dividing resistor R1is higher than the reference voltage, the comparator121sends an inverting signal to the control unit140, so that the control unit140can recognize the overcharge state of the first battery cell111. Similarly, the voltage-dividing resistors R3and R4and the comparator122are coupled to the second battery cell112, and the voltage-dividing resistors R5and R6and the comparator123are coupled to the third battery cell113in order to perform the above-mentioned operation. The voltage-dividing resistors R1and R2, the voltage-dividing resistors R3and R4, and the voltage-dividing resistors R5and R6may each have voltage values different from each other. The reason for this will be described below later.

The cell voltage detecting unit120can be fabricated in the form of an integrated circuit (IC) together either with the control unit140or separately from the control unit140. Since the cell voltage detecting unit120is an analog circuit and the control unit140is a logic circuit, an analog signal processing unit and a logic signal processing unit can be designed to be integrally installed in one semiconductor chip or to be separately installed in two semiconductor chips.

The switch unit130is coupled to the high current line between the positive electrode of the third battery cell113and the external positive electrode terminal P+. In more detail, the switch unit130may include a charge FET device131and a discharge FET device132. In addition, the charge FET device131and the discharge FET device132may be provided with parasitic diodes in which a gate of each of the FET devices receives a control signal from the control unit140. Herein, the charge FET device131becomes an off state when the battery cell is overcharged and the discharge FET device132becomes an off state when the battery cell is over-discharged.

In addition, the switch unit130may further include a self control protector. The self control protector may include a fuse133coupled to the high current line in series, a coil134for melting the fuse133, and an FET device135for applying current to the coil134. By way of example, the coil134may be a resistive heating coil. A gate of the FET device135may also receive an output signal of the control unit140. According to the self control protector having the above structure, the high current is applied to the coil134when the control unit140outputs a predetermined electric signal to the FET device135so that the coil134generates heat and the fuse133is melted as a result of the heat generated from the coil134.

The control unit140may include a typical IC, a logic circuit, or a microcomputer. Upon receiving information related to the overcharge of the battery cells111,112and113or disconnection of the sensing wires w1to w4from the cell voltage detecting unit120, the control unit140operates the switch unit130so as to prevent the battery cells111,112and113from being overcharged.

In addition, the control unit140can receive a signal from the current detecting unit150, which is coupled to the high current line in series. In this case, the control unit140operates the switch unit130in such a manner that the overcharge current is not applied to the battery cells111,112and113. For instance, since the current detecting unit150is a resistance device, and the control unit140already knows the resistance value of the current detecting unit150, the control unit140can calculate the current value applied to the current detecting unit150by sensing the voltage applied to both ends of the current detecting unit150.

The operation of the protective circuit100of the battery pack according to the present invention, when a battery cell is overcharged or a sensing wire is disconnected, will now be described.

Herein, VB1means the voltage of the first battery cell111. When the first battery cell111is overcharged, the voltage (VR1=[R1/(R1+R2)]*VB1) is applied to the voltage-dividing resistor R1coupled to the first battery cell111in a row and the voltage value is inputted into the inverting terminal of the comparator121. At this time, the reference voltage is being applied to the non-inverting terminal of the comparator121. The reference voltage has been set to a level lower than the overcharge voltage of the first battery cell111.

If the first battery cell111is overcharged, the voltage VR1applied to the voltage-dividing resistor R1is higher than the reference voltage. Accordingly, the comparator121sends a state-inverting signal to the control unit140.

Upon receiving the state-inverting signal from the comparator121, the control unit140operates the switch unit130. For instance, the control unit140sends a predetermined control signal to the gate of the charge FET device131, thereby turning off the FET device131. Since the charge FET device131is provided with the parasitic diode aligned in the direction reverse to the charge current, the high current being applied to the battery cells111,112and113can be instantly shut off. In the meantime, the charge current may be continuously applied to the battery cells111,112and113even if the charge FET device131does not operate. This means that the charge FET device131malfunctions. In this case, the control unit140sends a predetermined control signal to the gate of another FET device135, thereby operating the self control protector. Thus, a predetermined current is applied to the coil134, so that the fuse133is melted by means of heat generated from the coil134. In other words, the self control protector may operate when the charge FET device malfunctions in order to shut off the high current being applied to the battery cells111,112and113. Although the charge FET device131reversibly operates, the self control protector may irreversibly operate.

The voltage of the first battery cell111applied to the voltage-dividing resistor R1before the disconnection of the second sensing wire w2coupled to the positive electrode of the first battery cell111can be calculated as follows.

When it is assumed that the resistance value of each of the voltage-dividing resistors R1and R2is 4 kΩ, the resistance value of each of the voltage-dividing resistors R3and R4is each 3 kΩ the resistance value of each of the voltage-dividing resistors R5and R6is 2 kΩ, and the voltage of each of the first and second battery cells111and112is each 4V, the voltage VR1applied to the voltage-dividing resistor R1can be calculated as VR1=[4/(4+4)]*4=2, based on the above-described equation VR1=[R1/(R1+R2)]*VB1. In other words, the voltage of the first battery cell111applied to the voltage-dividing resistor R1before the disconnection of the second sensing wire w2is approximately 2V. Since the voltage 2V is lower than the reference voltage, the comparator121may not send the inverting signal to the control unit140.

However, if the second sensing wire w2is disconnected, the voltages of the first and second battery cells111and112are applied to the voltage-dividing resistor R1.

In this case, the voltage VR1applied to the voltage-dividing resistor R1is represented as VR1=[R1/(R1+R2+R3+R4)]*(VB1+VB2), wherein VB2is a voltage of the second battery cell112. In other words, the voltage VR1applied to the voltage-dividing resistor R1is VR1=[4/(4+4+3+3)]*(4+4)=2.28V.

Thus, if the second sensing wire w2is disconnected, the voltage (2.28V) applied to the voltage-dividing resistor R1is higher than the voltage (2V) applied to the voltage-dividing resistor R1before the second sensing wire w2is disconnected. The voltage (2.28V) applied to the voltage-dividing resistor R1when the second sensing wire w2is disconnected is higher than the reference voltage, so the comparator121sends the inverting signal to the control unit140in the same manner as when the first battery cell111is overcharged.

Therefore, the control unit140operates the switch unit130. That is, the control unit140operates the charge FET device131or the self control protector, thereby stopping the charge operation and completing the operation of the protective circuit of the battery pack according to the present invention.

The voltage of the second battery cell112applied to the voltage-dividing resistor R3before the disconnection of the third sensing wire w3coupled to the positive electrode of the second battery cell112can be calculated as follows.

The voltage applied to the voltage-dividing resistor R3can be calculated as VR3=[3/(3+3)]*4=2 based on the equation VR3=[R3/(R3+R4)]*VB2. In other words, the voltage of the second battery cell112applied to the voltage-dividing resistor R3before the disconnection of the third sensing wire w3is approximately 2V. Since the voltage 2V is lower than the reference voltage, the comparator122may not send the inverting signal to the control unit140.

However, if the third sensing wire w3is disconnected, the voltages of the second and third battery cells112and113are applied to the voltage-dividing resistor R3.

In this case, the voltage applied to the voltage-dividing resistor R3is represented as VR3=[R3/(R3+R4+R5+R6)]*(VB2+VB3), wherein VB3is a voltage of the third battery cell113. In other words, the voltage applied to the voltage-dividing resistor R3is VR3=[3/(3+3+2+2)]*(4+4)=2.4V.

Thus, if the third sensing wire w3is disconnected, the voltage (2.4V) applied to the voltage-dividing resistor R3is higher than the voltage (2V) applied to the voltage-dividing resistor R3before the third sensing wire w3is disconnected. The voltage (2.4V) applied to the voltage-dividing resistor R3when the third sensing wire w3is disconnected is set to be higher than the reference voltage, so the comparator122sends the inverting signal to the control unit140as if the second battery cell112is overcharged.

Therefore, the control unit140operates the switch unit130. That is, the control unit140operates the charge FET device131or the self control protector, thereby stopping the charge operation and completing the operation of the protective circuit of the battery pack according to the present invention.

As described above, the protective circuit of the battery pack according to the present invention can precisely detect the disconnection of the sensing wires, which sense the voltage of each battery cell, and instantly shut off the high current being applied to the battery cells when the sensing wires are disconnected, thereby preventing the battery cells from being overcharged.