GB2433359A

GB2433359A - Protection method and device for lithium battery

Info

Publication number: GB2433359A
Application number: GB0619836A
Authority: GB
Inventors: Jing-Yih Cherng; Wei-Chen Wu; Samual Chen; Steven Hou
Original assignee: Amita Technologies Inc Taiwan
Current assignee: Amita Technologies Inc Taiwan
Priority date: 2005-12-16
Filing date: 2006-10-06
Publication date: 2007-06-20
Anticipated expiration: 2026-10-06
Also published as: KR20070064399A; GB0619836D0; DE102006059368A1; KR100887053B1; JP2007165324A; FR2895163A1; GB2433359B

Abstract

A protecting method for lithium battery and device thereof are applied for the control of a battery's charged or discharged procedure in order to prevent it from being overcharged or over-discharged. This protecting device of lithium battery 4 is comprised of abnormality-detecting circuit 2, photo-coupling circuit 3, balance circuit 9, and identity circuit 8. The abnormality-detecting circuit checks voltage value of a charged battery and outputs a measuring signal. If the signal is normal, then the charge or discharge will be continued. If the signal is abnormal, the charge or discharge will be cut off. Next, the balance circuit will judge if the measuring signal is an overcharging signal in order to decide that the battery will be discharged or not. In the meantime, if the signal is abnormal, the photo-coupling circuit will adjusts its-impedance to cut off the connection between the charged battery and an external circuit, and the identity circuit will provide the location of the battery that sends out the abnormal signal.

Description

PROTECTING METHOD FOR LITHIUM BAJTERY AND DEVICE THEREOF

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a control circuit parallel-connected to a battery series-connected to other battery, in particular, to a protecting method for lithium battery and device thereof.

Description of Prior Art

The category of chargeable battery is divided into Nickel-Cadmium (Ni-Cd) battery and Nickel-Metal Hydride (Ni-MB) battery. Ni-Cd battery is a product of last generation and hardly seen in current market. Its fatal drawbacks are that the battery has memory effect and short usage life. Besides, cadmium is a sort of heavy metal that easily causes environmental pollution.

The development of Ni-MB battery aims to overcome these shortcomings of Ni-Cd battery. Its advantAges include: reduction of memory effect, enhancement of charging capacity, endurance of overcharge or over-discharge, prolongation of recycling usage life, shorter time of charge, and most important of all, without the usage of poisonous metal, such that the problem of environmental pollution won't occur. Of course, the Ni-MR battery is not one hundred percents perfect. For example, its environmental adaptability is poor. It is almost useless under specific environment where temperature is higher than 45 C or lower than 000. Therefore, in extremely hot or extremely cold place, Ni-MI-i battery is unable to provide power to electronic equipment.

hi addition, after being charged and idle for a period of time, its power will be decayed significantly unless it is recharged again.

When lithium battery is charged, if charging voltage is too high, there will be a risk of explosion occurred in the battery. On the other hand, when the lithium battery is under discharge, if discharging voltage is too low, whereby the voltage of lithium battery is lower than a basic voltage, then the usage life of lithium battery will be influenced. Therefore, during charge and discharge, a protecting device as shown in Fig. 1 is attached.

In Fig. 1, four series-connected lithium batteries are exemplified for illustration. A protecting device 100 includes: a protecting IC 101 special for four series-connected batteries; and a circuit switch 103. During practical design, appropriate protecting IC 101 will be chosen, according to the number of series-connected lithium battery 102. When voltage abnormality of lithium battery 102 is detected, the protecting IC 101 will send out signal to circuit switch 103, thereby circuit switch 103 being jumped off in order to cut off the charging or discharging current.

Therefore, when the number of series-connected lithium battery 102 is different from four, it is necessary to reproduce new set of protecting device 100. Currently, manufacturers can only provide the protecting IC 101 for no more than 4 pieces of lithium battery connected in series.

The more pieces of lithium battery series-connected, the more complicated circuit design of the protecting IC 101 will be. Because of the complicacy of circuit design and unbalance problem caused by the uneven aging and decay with respect to each series-connected battery, it is very difficult to produce the protecting circuit for more than 5 pieces of lithium batteries that are connected in series.

SUMMARY OF THE INVENTION

The main objective of the present invention is to solve the drawbacks mentioned inabove prior arts. In order to avoid the existing shortcomings, the invention is to redesign the entire protecting device for a chargeable battery, and it is characterized as follows: first, it is unnecessary to consider the number of lithium batteries connected in series; second, each series-connected lithium battery is also parallel-connected to an individual circuit board, which has interface for the interconnection with other circuit board; third, when any lithium battery is abnormal, its corresponding circuit board will generate signal to notify the system about the location of this abnormal battery, then jump off the circuit switch to cut off the charging or discharging current.

Another main objective of the present invention is to provide a protecting device wherein, when any series-connected lithium battery is abnormal, its parallel-connected circuit board will first judge if the lithium battery is overcharged, then process discharging procedure to the battery if necessary, such that the balance of each series-connected lithium battery may be micro-adjusted simultaneously.

The further main objective of the present invention is to provide a protecting device foi multiple series-connected lithium batteries wherein, when the number of series-connected lithium batteries is increased or decreased, it is unnecessary to reproduce any new circuit board, because the circuit board is changeable through external wiring.

In order to achieve abovementioned objectives, the protecting device for lithium battery according to the present invention is to prevent a chargeable battery from being overcharged or over-discharged by means of the control of an external circuit that charges or discharges the battery. The protecting device is comprised of abnormality-detecting circuit, photo-coupling circuit, balance circuit, and identity circuit. The abnormality-detecting circuit checks the voltage value of charged battery and outputs a measuring signal. If the signal is normal, then the charging or discharging action is continued, otherwise being cut off. Next, the balance circuit will judge if the measuring signal is an overcharging signal, then decide that the charged battery should be discharged or not In the meantime, according to the status of measuring signal, the photo-coupling circuit adjusts its impedance for cutting off the connection between charged battery and external circuit, while the identity circuit provides the system with the position of the battery, which sends out the abnormal signal.

In order to achieve abovementioned objectives, the present invention provides a protectin method for lithium battery to prevent the charged battery from being overcharged -or over-discharged by means of the control of an external circuit that charges or discharges the lithium battery. The protecting method for lithium battery includes following steps: First, check that the battery is under charge or discharge; when the checked battery is under charge, examine if its average voltage is larger than the maximal charging voltage of one single battery; if the answer is yes, the charging loop is opened and the charging procedure is stopped; if the answer is no, check whether the output signal of protecting device is normal or abnormal; if the output signal is abnormal, the battery will be charged with lower current, otherwise normal charging procedure is continued.

When the checked battery is under discharge, check if its average voltage is lower than the minimal discharging voltage of one single battery, if the answer is yes, the discharging loop is opened and the discharging procedure is stopped; if the answer is no, check if the output signal of protecting device is normal after several seconds of further discharge; if the judged signal is normal, discharge is continued, otherwise discharging action is cut off.

BRIEF DESCRIPTION OF DRAWING

Fig. lis a circuit illustration of the protecting device for lithium battery according to the

prior arts.

Fig. 2 is a circuit illustration of one parallel-connected module of protecting device for lithium battery according to the present invention.

Fig. 3 is a circuit illustration, which shows one parallel-connected module of protecting device for lithium battery according to the present invention, wherein the protecting device is connected to chargeable battery in parallel manner.

Fig. 4 is a circuit illustration, which shows the protecting device for multiple series-connected lithium batteries according to the present invention.

Fig. 5 is a circuit illustration, which shows another protecting device for multiple series-connected lithium batteries according to the present invention.

Fig. 6 is a circuit illustration, which shows the protecting device for multiple series-connected lithium batteries according to the present invention, wherein an external circuit is included.

Fig. 7 is another embodiment illustration of the protecting device for lithium battery according to the present invention.

Fig. 8 is further embodiment illustration of the protecting device for lithium battery according to the present invention.

Fig. 9 is a flowchart diagram of the protecting method for the charge and discharge of lithium battery according to the present invention.

DETAILED DESCRIPTION OF ThE INVENTION

In cooperation with attached drawings, the technical contents and detailed description of the present invention will be as follows.

Please refer to Fig. 2 and Fig. 3, which respectively are a circuit illustration for one parallel-connected module of the protecting device for lithium battery and a circuit illustration of one parallel-connected module of chargeable battery's protecting device parallel-connected to lithium battery according to the present invention. In this embodiment according to the present invention, the protecting device is comprised of an abnormality-detecting circuit 2 and a photo-coupling circuit 3.

First, the abnormality-detecting circuit 2 checks the voltage of the charged battery 4, then outputs a measuring signal to the photo-coupling circuit 3, which adjusts an impedance thereof according to the status of signal in order to cut off the connection between protecting device 11 and external circuit or continuously charge/discharge the chargeable battery 4.

The photo-coupling circuit 3 includes light-emitting diode (LED) 31 and transistor 32.

The LED 31 is electrically coupled to the abnormality-detecting circuit 2 in such a manner that it may decide to light or not depending upon the voltage value of the chargeable battery 4. On the other hand, the transistor 32 is electrically coupled to an external circuit that will be connected or cut off according to the lighting status of LED 31, which in turn determines the impedance value of the transistor 32.

In this embodiment, when the battery 4 is in normal condition, the abnormality-detecting circuit 2 will send a measuring signal of the voltage of battery 4 to the LED 31 of photo-coupling circuit 3. After receiving the measuring signal, the LED 31 starts to emit light, which is incident upon another side of the transistor 32, such that the impedance between two sides of the transistor 32 will be lowered down.

When the battery 4 is in abnormal condition, the abnormality-detecting circuit 2 won't send any signal to the LED 31, which won't light either, so the impedance between two sides of the transistor 32 is increased so large as to make the photo-coupling circuit 3 become a (broken) open circuit, because there is no light incident upon another side of the transistor 32.

By the light incidence, two sides of the photo-coupling circuit 3 are communicated without any electrical contact, so there is very high intensity of insulation between these two sides.

Thereby, as shown in Fig. 4, many series-connected lithium batteries 4 may be parallel-connected with this kind of protecting module. Two sides of the transistor 32 of each module is interconnected to one another by series-connecting manner, such that there is completely no electric contact between the transistor 32 string and the lithium battery 4 string.

In Fig. 4, if there is any abnormal situation occurring in a series-connected lithium battery 4, as described above, its abnormality-detecting circuit 2 will send a measuring signal to make corresponding LED 32 stop lighting. Because there is no light incident upon another side of the transistor 32, the impedance between two sides of transistor 32 is increased so large that the transistor 32 becomes an almost open circuit. Furthermore, since every transistor 32 is series-connected to one another, the impedance of entire transistor 32 string becomes so high that there is no current passing between its two sides.

On the other hand, if every lithium battery is under normal condition, the impedance between two sides (i.e., A and B) of entire transistor 32 string is very small. As soon as any abnormality occurred in any series-connected lithium battery 4, the impedance between A, B sides will instantly rise to become an almost open circuit.

Furthermore, on the base of this impedance variation between A, B sides of transistor 32 string, another embodiment of protecting device for multiple series-connected lithium batteries.

according to the present invention may be provided, as shown in the circuit illustration of Fig. 5 In this embodiment, a circuit switch 5 and a switch control circuit 6 are further designed in the protecting device. Wherein, the switch control circuit 6 is electrically coupled to the last level of photo-coupling circuit 3. Depending upon the impedance of entire string of transistor 32, a control signal may be output from this switch control circuit 6, to which the circuit switch 5 is electrically coupled. By judging from the status of this control signal, the charging or discharging current will be cut off or continued. . Therefore, when the impedance between A, B sides is low, the circuit switch 5 is conducted; on the other hand, when the impedance between A; B sides is high, the circuit switch 5 will jump off, then the charging or discharging current is cut off.

Please refer to Fig. 6 continuously, which is a circuit illustration of an embodiment of the protecting device for multiple series-connected lithium batteries with an external circuit according to the present invention. Wherein, A, B sides are electrically connected to an external circuit 7 that may be, for example, a system or a charger, but these are not exclusively included herein only.

In Fig. 6, the abnormality-detecting circuit 2 informs the external circuit 7 through the impedance variation between A, B sides. Therefore, when the external circuit 7 is informed that the impedance between A, B sides is low, the external circuit 7 will function as usual but, when the impedance is high, the external circuit 7 will stop normal job to cut off the charging or discharging current.

Please refer to Fig. 7, which shows another embodiment illustration of the protecting device for lithium battery according to the present invention. Wherein, an identity circuit 8 is electrically connected to the photo-coupling circuit 3 in the protecting device 1. The identity circuit 8 is a resistance with Rx value. When the photo-coupling circuit 3 adjusts an impedance thereof according to the status of measuring signal to cut off the electric connection between chargeable battery 4 and external circuit, the identity circuit 8 simultaneously outputs a signal (a resistance value) to the external circuit, such that the external circuit is informed which battery 4 is under abnormal situation. Taking the example in Fig. 4, the photo-coupling circuit 3 in each protecting device 1 is all electrically connected to an identity circuit 8, which is assigned a resistance value specifically, such as 5K, 1 OK, 15K, and 20 K, etc. When the photo-coupling circuit 3 of the second protecting device I is under a status of open circuit, the external circuit will receive a resistance value of 10 K, such that the abnormality occurred in second battery is notified.

Please refer to Fig. 8 continuously, which shows further embodiment illustration of the protecting device for lithium battery according to the present invention. In this embodiment, besides an identity circuit 8 is electrically connected to the photo-coupling circuit 3 of protecting device 1, a balance circuit 9 is also electrically connected to the abnormality-detecting circuit 2.

When the battery 4 is over-charged, the abnormality-detecting circuit 2 will output a measuring signal to the balance circuit 9, which may control the battery 4 to take a discharging action, such that battery damage caused by overcharge may be avoided.

Please refer to Fig. 9, which shows a flowchart diagram of the protecting method for charging and discharging lithium battery according to the present invention. In the charging procedure of battery 4, as shown in step 10, the charging or discharging status of the battery 4 is judged firstly; when the charging status of the battery 4 is confirmed, the process enters step I Oa to check whether the average voltage of battery 4 is larger than V (the maximal charging voltage of one single battery, for example, 4.2 V) or not; if the answer is yes, then the process enters step lOb, where the charging loop is opened, namely, charging procedure being stopped; on the other hand, if the average voltage of battery 4 is not larger than Vhjgh, then the process is switched to step 1 Oc, where the outputting signal of the protecting device for lithium battery is checked; if the signal is abnormal, then the process enters to step 1 Od, where the battery 4 is charged with low current (ii0); if the signal is normal, then the process enters step I Oe, where normal charging procedure is continued.

If the judged battery 4 is under discharged state, then the process enters step 1 Of, where the average voltage of the battery 4 is checked; if the checked value is smaller than V10 (the minimal discharging voltage of one single battery), then the process goes to step 1 Og, where the discharging loop is opened and the discharging process is stopped; on the other hand, if the checked voltage is larger than V, then the process goes to step 1 Oh and, after several seconds of discharge, the process goes to step 101 to check whether the outputting signal of the protecting device for lithium battery is OK or not; if the signal is normal, then the process goes to step lOj and the discharging procedure is continued; otherwise, the procedure going to step 10k, where the discharging action is cut off.

The present invention has been disclosed as aforementioned descriptions, which however are only preferable embodiments thereof, being not used to limit its executing scope. Any equivalent variation and small modification that are made according to appended claims by those who are skilled in such arts are all covered by the claims claimed by the present invention.

Claims

WHAT IS CLAIMED IS

1. A protecting device for lithium battery is provided for the control of an external circuit that charges or discharges a chargeable battery, such that the overcharge or over-discharge of the chargeable battery may be prevented, the protecting device for lithium battery including: an abnormality-detecting circuit, which checks the voltage of said chargeable battery and outputs a measuring signal; and a photo-coupling circuit, which is electrically coupled to said abnormality-detecting circuit, and adjusts an impedance thereof depending the status of said measuring signal for the cut off of the connection between said chargeable battery and said external circuit, or for making said chargeable battery continuously discharged or charged.

2. The protecting device for lithium battery according to claim 1, wherein the photo-coupling circuit includes: a light-emitting diode (LED), which is electrically coupled to said abnormality-detecting circuit for making the decision of lighting or not depending upon the status of voltage signal measured by said abnormality-detecting circuit; and a transistor, which is electrically coupled to said external circuit for the decision of the impedance of said transistor depending upon the lighting situation of said LED and for the connection or disconnection of said external circuit.

3. The protecting device for lithium battery according to claim 2 wherein, when said chargeable battery is in normal condition, said LED will be lighted.

4. The protecting device for lithium battery according to claim 2 wherein, when said LED lights, the impedance of said transistor is in a condition of low value, such that the connectioti between said LED and said external circuit remains normal.

5. The protecting device for lithium battery according to claim 2 wherein, when said chargeable battery is in an abnormal condition, said LED will stop lighting.

6. The protecting device for lithium battery according to claim 5 wherein, when said LED stops lighting, the impedance of said resistor will possess an impedance of high value, such that the connection to said external circuit is cut off.

7. The protecting device for lithium battery according to claim I, wherein said protecting device is additionally arranged: a switch control circuit, which is electrically coupled to said photo-coupling circuit for the output of a control signal depending upon the impedance status of said photo-coupling circuit; and a switch, which is electrically coupled to said switch control circuit for making the decision of cutting off the charging or discharging current depending upon the status of said control signal.

8. The protecting device for lithium battery according to claim 1, wherein said protecting device is additionally arranged an identity circuit, which is electrically coupled to said photo-coupling circuit and, when said photo-coupling circuit is under a jump off condition, said identity circuit will output a signal to said external circuit, which will be informed the location o which battery is in abnormal condition.

9. The protecting device for lithium battery according to claim 8, wherein said output signal of said identity circuit is a resistance value.

10. The protecting device for lithium battery according to claim 1, wherein said protecting device is additionally arranged a balance circuit, which is electrically coupled to said abnormality circuit and said chargeable battery; when said battery is overcharged, said abnormality-detecting circuit will output a measuring signal to said balance circuit, which then processes discharging action to said battery.

11. A protecting method for lithium battery is provided for the control of an external circuit that charges or discharges a chargeable battery, such that the overcharge or over-discharge of thâ chargeable battery may be prevented, the protecting method for lithium battery including following steps: a) during the charging or discharging procedure of a battery, the first thing is to judge that said battery is under charged state or discharged state; when said battery is under charged state, check that the average voltage of charged battery is larger or smaller than the maximal charging voltage of one single battery; if said average voltage is larger than the maximal charging voltage, then the charging loop is opened and the charging procedure is stopped; b) in step a), if said average voltage is smaller than the maximal charging voltage of one single battery, then check whether the output signal of said protecting device for lithium battery is normal or abnormal; if said signal is abnormal, said battery will be charged with low current; if said signal is normal, then normal charging action is continued; t c) in step a), if judged battery-is under discharged state, then check the average voltag&of discharged battery; if checked average voltage is smaller than the minimal discharging voltage of one single battery, then the discharging loop is opened and the discharging procedure is stopped; and d) in step c), if checked average voltage is larger than the minimal discharging voltage of one single battery, then the discharging process is continued for several seconds; after that, check that said output signal from said protecting device for lithium battery is normal or abnormal; if checked signal is normal, then discharging process is continued; if checked signal is abnormal then discharging action is cut off.