Abstract:
A compulsory charging and protective circuit for secondary battery after being over discharged is disclosed. The circuit includes a circuit conducting switch, a releasing unit, a triggering unit and a comparing unit. When the secondary battery is over discharged, a temporary electrical connection is provided by the present invention. The loop of the secondary battery and a charger keeps. When the secondary battery recovers from abnormal status, the temporary electrical connection is called off so that the secondary battery can keep normal operation. Thus, when the secondary battery is under over-discharge, it doesn&#39;t have to be unloaded for repair to settle the issue. Maintenance costs can be saved.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a compulsory charging and protective circuit. More particularly, the present invention relates to a compulsory charging and protective for secondary batteries after being over discharged. 
     BACKGROUND OF THE INVENTION 
     Secondary batteries are so-called rechargeable batteries, widely used in many products, such as notebooks, tablets, mobile phones, and even large electric vehicles and robots. Although a rechargeable battery is composed of a number of rechargeable battery cells linked in series or parallel, according to different power supply targets, there are different specifications of output current and voltage. 
     Since each cell has its unique characteristics when the secondary battery is assembled, it leads to an unbalance problem for the cells of the secondary battery in use no matter it is charging or discharging. Abnormal operations will cause the temperature of the secondary battery to be high, reduce life time of the battery, and even make the battery explode. Reduced life time of the secondary battery mainly suffer from overcharging or over-discharging operations. Therefore, general secondary batteries will have a battery management chip to settle the problems above. 
     Please see  FIG. 1 . A structure of a conventional secondary battery  1  is shown. There is a battery management chip  2 . A source for storing and providing power for the secondary battery  1  are several cells  3  linked to each other in series. The battery management chip  2  is linked to the group of the cells  3  and can detect the status of each cell  3  effectively. Dynamic balance of the cells  3  is available. In addition, the battery management chip  2 , the charging control switch  4  and the discharging control switch  5  from a protective circuit for charging and discharging. The charging control switch  4  and the discharging control switch  5  are composed of a field effect transistor and a parasitic diode. The protective circuit further connected to a terminal unit  6 . The terminal unit  6  has a positive terminal  6   a , a negative terminal  6   b  and a data transmission terminal  6   c . The terminal unit  6  may be in the form of a plug. Depending on the target linked, the secondary battery  1  can decide to charge or discharge. The battery management chip  2  can send the status of the cells  3  to an external control system outside the secondary battery  1  through the data transmission terminal  6   c . The battery management chip  2  can also receive instructions from the control system via the data transmission terminal  6   c  to manage the cells  3 . 
     When the target which the terminal unit  6  is linked to is a charger, the current goes from the positive terminal  6   a , to the cells  3 , the discharging control switch  5  and the charging control switch  4 , sequentially. Last, is passes the negative terminal  6   b  and returns back to the charger. Now, the charging control switch  4  and the discharging control switch  5  stay turned on. The battery management chip  2  knows the direction of the current by the resistor  7 , further being aware of the status of charging. When the target which the terminal unit  6  is linked to is a load, the current flows from the cells  3 , to the positive terminal  6   a  and the load. The load also has current flows to the negative terminal  6   b , the charging control switch  4  and the discharging control switch  5 , going back to the cells  3 . The loop completes. At this moment, the charging control switch  4  and the discharging control switch  5  also in the status of turned on. The battery management chip  2  knows it is discharging depending on the direction of current through the resistor  7 . 
     When the secondary battery  1  is charged, if an over-charged situation comes out (namely, the voltage of the secondary battery  1  is over its maximum rating voltage when in charging), the battery management chip  2  will turn off the charging control switch  4  to protect the secondary battery  1  from damage due to keeping charging. Similarly, when the secondary battery  1  discharges, if an over-discharged situation comes out (namely, the voltage of the secondary battery  1  is lower than a minimum allowable voltage value when discharging), the battery management chip  2  turns off the discharging control switch  5  to protect the secondary battery  1  from losing its rechargeability due to keeping discharging. When the over-charged protection is going on, since the voltage of the secondary battery  1  drops with time, as it is lower than the maximum rating voltage, the battery management chip  2  can work again to turn on the charging control switch  4 , thus, the secondary battery  1  can also function well. However, when the over-discharged protection is going on, since the voltage of the secondary battery  1  is not able to come back to the normal operating voltage, unless a compulsory action takes place out of the battery for recovery, the secondary battery  1  can not function normally. 
     For end users, if the secondary battery is protected due to over-discharge and cannot come back to normal operations, they must think the secondary battery is damaged. The vendor of the secondary battery is asked for exchange. Even the vendor is willing to exchange a good secondary battery for with the original one, the cost for transportation is a lost to the vendor. Therefore, a design for relative circuit to effectively reboot the secondary battery for normal operations after the secondary battery is protected for being over discharged is desired. 
     SUMMARY OF THE INVENTION 
     This paragraph extracts and compiles some features of the present invention; other features will be disclosed in the follow-up paragraphs. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims. 
     In order to settle the problems mentioned above, a compulsory charging and protective circuit for secondary battery after being over discharged is provided. The circuit includes: a circuit conducting switch, connected in parallel with a charging control switch and a discharging control switch which are connected in series in a secondary battery at two ends, opening to electrically conduct the two ends; a releasing unit, for connecting to the grounding after a releasing voltage is received; a triggering unit, connected to the circuit conducting switch and the releasing unit, for electrically conducting a connection between the circuit conducting switch and the releasing unit after a triggering signal is received; and a comparing unit, electrically connected to the secondary battery, for comparing a value of a voltage difference between an anode and a cathode of the secondary battery with a minimum allowable voltage value; when the value of the voltage difference is greater than the minimum allowable voltage value, a normal voltage is provided to the releasing unit; when the value of the voltage difference is smaller than the minimum allowable voltage value, the releasing voltage is provided to the releasing unit. When the releasing unit is connected to the grounding and the triggering unit conducts electrical connection between the circuit conducting switch and the releasing unit, the circuit conducting switch turns on. 
     Preferably, the triggering unit is further connected to a triggering switch; when the triggering switch is turned on, the triggering signal is sent to the triggering unit. 
     Preferably, the triggering unit is a silicon controlled rectifier. 
     Preferably, a gate of the silicon controlled rectifier is connected to the triggering switch; when the triggering switch turns on, the gate receives a high level voltage. 
     Preferably, the compulsory charging and protective circuit further includes a power, connected to the circuit conducting switch, for providing power for operation of the circuit conducting switch. 
     Preferably, the comparing unit is a comparator. 
     Preferably, an input of the comparator is connected to a circuit signal source of the secondary battery. 
     Preferably, the circuit signal source is a discharging control switch pin or a working voltage pin (VDD) of the battery management chip of the secondary battery. 
     Preferably, the releasing unit comprises a field effect transistor and a parasitic diode. 
     Preferably, the circuit conducting switch is a MOS relay. 
     When the secondary battery is over discharged, a temporary electrical connection is provided by the present invention. The loop of the secondary battery and a charger keeps. When the secondary battery recovers from abnormal status, the temporary electrical connection is called off so that the secondary battery can keep normal operation. Thus, when the secondary battery is under over-discharge, it doesn&#39;t have to be unloaded for repair to settle the issue. Maintenance costs can be saved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a conventional structure of a secondary battery. 
         FIG. 2  shows a compulsory charging and protective circuit and a secondary battery linked thereby according to the present invention. 
         FIG. 3  is a structure of the compulsory charging and protective circuit. 
         FIG. 4  illustrates a triggering unit and a releasing unit in the compulsory charging and protective circuit. 
         FIG. 5  illustrates a comparing unit in the compulsory charging and protective circuit. 
         FIG. 6  is a time table for some elements in the compulsory charging and protective circuit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiment. 
     Please see  FIG. 2  to  FIG. 6 . An embodiment is illustrated.  FIG. 2  shows a compulsory charging and protective circuit  200  according to the present invention. The compulsory charging and protective circuit  200  is linked to a secondary battery  100 . Before the compulsory charging and protective circuit  200  is illustrated, the secondary battery  100  that the compulsory charging and protective circuit  200  is applied to should be explained first. 
     Secondary batteries in the market can be divided to many categories due to different components and application objects. For the secondary battery that used by the present invention, no matter what the materials and the specifications of the cells for storing power are (it should be a Ni—Cd battery, a Ni-MH battery, a Li-ion battery or a Li-polymer battery), there must be a battery management chip for managing the secondary battery. In addition, the battery management chip can protect the secondary battery from over-charge and over-discharge. Namely, when the secondary battery is in a status of over-charge or over-discharge, the battery management chip can stop operation of the secondary battery. Thus, in the description for  FIG. 2 , a structure of the secondary battery  100  mainly contains a number of cells  110  linked to one another in series and/or in parallel, a battery management chip  120  complied with the above requirements, a charging control switch  130 , a discharging control switch  140  and a terminal unit  150 . 
     When the secondary battery  100  is working, the charging control switch  130  and the discharging control switch  140  are both turned on so that current can pass through. When the target which the terminal unit  150  is connected to is a charger (not shown), the current goes through a positive terminal  150   a , the group of the cells  110 , the discharging control switch  140  and the charging control switch  130  sequentially. Finally, it returns to the charger through a negative terminal  150   b . Now, all cells  110  are charged. When the target which the terminal unit  150  is connected to is a load (not shown), the current goes through the negative terminal  150   b , the charging control switch  130 , the discharging control switch  140  and the group of the cells  110 . Finally, it returns to the load through the positive terminal  150   a . Now, all cells  110  discharge. The battery management chip  120  is able to judge if the secondary battery  100  is in the status of charging or discharging by the direction the current goes through the resistor  127 . 
     The battery management chip  120  has a number of pins. A working voltage pin (VDD)  121  is connected to a node  100   a  in the charging or discharging loop. Because the node  100   a  is close to a positive terminal of the group of the cells  110 , it can obtain a high potential from the group of the cells  110 . Relatively, a grounding pin (VSS)  122  is connected to a node  100   b  in the charging or discharging loop. Since the node  100   b  is close to a negative terminal of the group of the cells  110 , it can obtain a low potential from the group of the cells  110 . Differential value between the high potential and the low potential is roughly the working voltage value of the secondary battery  100  at that moment. The charging control switch pin  123  and the discharging control switch pin  124  are used to turn on or off the charging control switch  130  and the discharging control switch  140 , respectively. When the secondary battery  100  is working properly, the charging control switch pin  123  and the discharging control switch pin  124  are both turned on. The battery signal pin  125  is used to transmit the status of the secondary battery  100  to a device (not shown) connected to a signal terminal  150   c  of the terminal unit  150 , or operate the secondary battery  100  according to instructions from the device. 
     When the secondary battery  100  functions well, the compulsory charging and protective circuit  200  only links to the secondary battery  100  and doesn&#39;t take any action. Only when the secondary battery  200  encounters over-discharged situation, the compulsory charging and protective circuit  200  starts to function. The compulsory charging and protective circuit  200  includes a circuit conducting switch  210 , a releasing unit  220 , a triggering unit  230 , a comparing unit  240 , a triggering switch  250  and a power  260 . The circuit conducting switch  210  is connected in parallel with the charging control switch  130  and the discharging control switch  140  which are connected in series in the secondary battery  100  at two ends, namely, electrically connection between to the nodes  100   c  and  100   d  in  FIG. 2 . When the circuit conducting switch  210  turns on, electrical connection between the nodes  100   c  and  100   d  (two ends) takes place immediately. The circuit conducting switch  210  may be an electronic switch of a general type. A MOS relay is recommended. The power  260  and the circuit conducting switch  210  are connected. The power  260  is used to provide necessary power for operating the circuit conducting switch  210 . A power circuit  261  between the power  260  and the circuit conducting switch  210  to ensure the power is well transferred to the circuit conducting switch  210 . Preferably, the power circuit  261  has a design to prevent countercurrent from the battery to protect the power  260 . 
     The releasing unit  220  is used to connect to the grounding after receiving a releasing voltage. When a normal voltage is received, the releasing unit  220  stops grounding. In fact, the normal voltage may be any value other than the value fell in a tolerance of the releasing voltage. The releasing unit  220  is an electronic switch. As shown in  FIG. 4 , the releasing unit  220  is a switch composed of a field effect transistor and a parasitic diode. Its gate is electrically connected to the comparing unit  240 . On-and-off of the releasing unit  220  is controlled by the comparing unit  240 . The triggering unit  230  is connected to the circuit conducting switch  210  and the releasing unit  220 , for electrically conducting the connection of the circuit conducting switch  210  and the releasing unit  220  after receiving a triggering signal. In the present embodiment, the triggering unit  230  is a silicon controlled rectifier. For a convenient control, the triggering unit  230  further connects to a triggering switch  250 . The triggering switch  250  is turned off when the secondary battery  100  functions well. When the triggering switch  250  turns on, the mentioned triggering signal us sent to the triggering unit  230 . This triggering switch  250  may be a button switch, controlled manually; the triggering switch  250  may also be an electronic switch, turned on by a specific issue, e.g. the secondary battery  100  stops working for 30 minutes due to over discharge. A gate of the silicon controlled rectifier is linked to the triggering switch  250 . When the triggering switch  250  turns on, the gate receives a high level voltage, the triggering signal. When the releasing unit  220  is connected to the grounding and the triggering unit  230  conducts an electrical connection between the circuit conducting switch  210  and the releasing unit  220 , the circuit conducting switch  210  turns on. 
     The comparing unit  240  is electrically connected to the secondary battery  100 . It can compare voltage difference between an anode and a cathode of the secondary battery  100 , namely the working voltage of the secondary battery  100 , with a minimum allowable voltage value. When the voltage difference is greater than the minimum allowable voltage value, a normal voltage is provided to the releasing unit  220 ; when the voltage difference is smaller than the minimum allowable voltage value, a releasing voltage is provided to the releasing unit  220 . In practice, the comparing unit  240  may be a comparator. Please refer to  FIG. 5 . The comparator not only connects to the working voltage (please notice that the working voltage of the secondary battery  100  may not the same as that of the compulsory charging and protective circuit  200 ) and grounding, but also two inputs and one output. The minimum allowable voltage value is used to evaluate if the secondary battery  100  is over-discharged. If the voltage difference between the abode and the cathode of the secondary battery  100  is lower than the minimum allowable voltage value, the secondary battery  100  is considered in a status of over discharge. The minimum allowable voltage is a reference voltage and imputed from an input (−). The other input (+) of the comparator is connected to a circuit signal source of the secondary battery  100 , fetching a working voltage of the secondary battery  100  or the voltage difference between the anode and the cathode immediately. The circuit signal source may be the discharging control switch pin  124  of the battery management chip  120  of the secondary battery  100 . It can also be the working voltage pin  121 . It depends on the design of the battery management chip  120  where the pin can provide the mentioned working voltage or voltage difference when the secondary battery  100  stops functioning. It should be noticed in the present embodiment that due to selection of the inputs, the normal voltage has a voltage level higher than that of the releasing voltage. If the inputs of the reference voltage and the working voltage are exchanged, the normal voltage will have a voltage level higher than that of the releasing voltage. 
     Please refer to  FIG. 6 . Description of operations of the compulsory charging and protective circuit  200  are illustrated below. In  FIG. 6 , the statuses off working voltage of the secondary battery  100 , H (High) and L (Low), represent the secondary battery  100  is under normal working and over discharge, respectively. H and L of the output voltage of the comparing unit  240  represent the normal voltage and the releasing voltage outputted from the comparing unit  240 , respectively. H and L of the voltage of the power  260  represent the statuses of power provided and power not provided by the power  260 , respectively. 
     When the compulsory charging and protective circuit  200  and the secondary battery  100  are connected under normal working status, the outputted voltage from the comparing unit  240  is the normal voltage. The releasing unit  220  turns off. The triggering switch  250  turns off. The circuit conducting switch  210  turns off. It should be noticed that the power  260  is all turned on to provide power when the compulsory charging and protective circuit  200  and the secondary battery  100  are connected. Thus, the compulsory charging and protective circuit  200  can function well. 
     When time comes to t 1 , the secondary battery  100  is in the status of over discharge and the discharging control switch  140  turns off. When the secondary battery  100  discharges, the loop is opened at the discharging control switch  140 . The line linked by the compulsory charging and protective circuit  200  between the node  100   c  and the node  100   d  forms a bypass connection. Now, a value of the voltage difference provided by the circuit signal source is lower than the minimum allowable voltage value. The comparing unit  240  changes the outputted voltage to be a low level voltage, the releasing voltage, to the releasing unit  220 . The releasing unit  220  is connected to the grounding. However, since the triggering switch  250  is turned off so that the triggering unit  230  has not received the triggering signal, the circuit conducting switch  210  doesn&#39;t connect to the releasing unit  220 . The circuit conducting switch  210  is off. When time comes to t 2 , the triggering switch  250  turns on. The circuit conducting switch  210  and the releasing unit  220  are electrically connected. At this moment, the circuit conducting switch  210  turns on, a short circuit forms between the node  100   c  and the node  100   d , the charger can compulsorily charge the secondary battery  100  via the terminal unit  150 . 
     When the voltage difference between the anode and the cathode of the secondary battery  100  has increased by charging after a period of time, the bypass connection should be called off. Operations of the secondary battery  100  return back to the battery management chip  120 . At t 3 , a value of voltage difference provided by the circuit signal source is greater than the minimum allowable voltage value. The comparing unit  240  provides the normal voltage to the releasing unit  220 . The releasing unit  220  is not connected to the grounding. As a result, the circuit conducting switch  210  turns off. The electrical connection between the node  100   c  and the node  100   d  cannot be held by the bypass connection. If the secondary battery  100  keeps charged by the charger, the battery management chip  120  will turn on the discharging control switch  140  since the secondary battery  100  has a normal working voltage, so that the voltage difference between the anode and the cathode of the secondary battery  100  keeps going up. The triggering switch  250  is not necessary to be turned off at t 3 . It can be turned off later (t 4 ). Because the releasing unit  220  is not connected to the grounding, status of the triggering switch  250  during t 3  and t 4  doesn&#39;t affect the status of the circuit conducting switch  210  to be off. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.