Method for detecting battery removal or absent battery condition in a constant current charger

[0002] 1. Field of the Invention

[0003] This invention relates generally to battery charging systems and methods, and more particularly to a method for detecting battery removal or absent battery conditions for a constant current charger.

[0004] 2. Description of the Prior Art

[0005] Current state of the art commercially available battery charge control IC's do not offer a means to distinguish between an absent battery or battery removal conditions without use of additional external stimulus. Typical solutions qualify battery presence with a thermistor or data input from the battery. U.S. Pat. No. 6,104,303, issued Aug. 15, 2000 to Katada, et al., entitled Battery detecting device for a radio pager, for example, uses a secondary battery and additionally requires a third electrode to sense removal or absence of a primary battery.

[0006] In view of the foregoing, a need exists for a means to efficiently detect battery absence or removal from a charging unit without use of external stimulus such as a thermistor, EEPROM, or additional pins (electrodes), and which can be used to correctly annunciate the current state of the charger to a host or end-user.

[0007] The present invention is directed to a technique that provides an efficient means to detect a battery removal from a battery charger, or otherwise distinguish between the condition when a battery is not present in the charger without the use of external stimulus. According to one embodiment, the techniques comprises a circuit having a series of logic gates arranged in a manner to produce a signal (NOBAT), that is indicative of an absent battery or battery removal state. The circuit is applied such that information provided by only the charger positive and negative terminals can be used to correctly annunciate the current state of the charger to a host or end-user. The circuit is implemented as part of a battery charger control integrated circuit (IC) that interrogates the charger output, including the current flowing through the charger to either provide a status signal or otherwise provide an input to a state machine capable of controlling the charger.

[0008] In one aspect of the invention, a technique is implemented to detect a battery removal from a charger without use of external stimulus.

[0009] In another aspect of the invention, a technique is implemented to distinguish between the condition when a battery is not present in a charger without use of external stimulus.

[0010] In yet another aspect of the invention, a technique is implemented to distinguish between the absent battery or battery removal conditions associated with a charger via information provided only by the charger positive and negative terminals.

[0011] In still another aspect of the invention, a technique is implemented to correctly annunciate the current state of a charger to a host or end-user without use of external stimulus.

[0012] Other aspects and features of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

[0013] FIG. 1 is a schematic diagram illustrating a circuit for detecting battery removal or absent battery condition in a charger according to one embodiment of the present invention;

[0014] FIG. 2 illustrates representative timing control signals for portions of the circuit shown in FIG. 1;

[0015] FIG. 3 is a timing diagram depicting operation of the circuit shown in FIG. 1;

[0016] FIG. 4 is a diagram illustrating one embodiment of a charging control system using the battery removal detection circuit shown in FIG. 1;

[0017] FIGS. 5aand 5billustrate battery charger voltage and current waveforms during normal charging and during a battery removal for the charging control system shown in FIG. 4; and

[0018] FIG. 6 illustrates timing relationships between various signals for the charging control system shown in FIG. 4 during a battery removal.

[0019] While the above-identified drawing figure sets forth a particular embodiment, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.

[0020] FIG. 1 is a schematic diagram illustrating a detection circuit 10 for detecting battery removal or absent battery condition in a charger according to one embodiment of the present invention. A timing signal input 12 provides a 1-second clock to operate the detection circuit 10. The use of a 1-second clock signal is arbitrary, and other clocking signal periods can just as well be utilized to operate the detection circuit 10. A 1-second clock signal is used only for explanatory purposes and to more easily describe the functionality of the detection circuit 10. The ΔVCH signal input 14 is connected to the charger (not shown) output to monitor the charger output voltage signal. The ΔGone signal input 16 is used to monitor the current flowing through the charger. The Pwrdwn signal input 18 is a global controller power down signal that is used by the charger controller IC (not shown) to reset the detection circuit 10 during turn-on. Once connected to a battery charger, and following a Pwrdwn reset, operation of the detection circuit 10 is best explained with reference to FIGS. 2 and 3.

[0021] FIG. 2 illustrates representative timing control signals for portions of the detection circuit 10 shown in FIG. 1. When the ΔVCH signal input 14 receives a trigger pulse ΔVCH 19, a re_cv pulse 20 is produced. The re_cv pulse 20 is most preferably a 20-60 second pulse generated via a resettable 1-shot timer comprising inverter 22 and nor gate 23, where tplh=tphl=60-seconds.

[0022] FIG. 3 is a timing diagram depicting operation of the detection circuit 10 shown in FIG. 1 when a re_cv pulse 20 is produced. An output signal at NOBAT 24 is produced if a rising edge of ΔVCH 19 is detected; and if, within one minute following the rising edge of ΔVCH 19, a rising edge of a signal received at the ΔGone signal input 16 (charger current falls below a predetermined level, i.e. 10 mA) is latched via combinatorial element 26 to produce a reset signal rst_nobat 30 for a falling edge of ΔVCH 19 that lasts greater than 20-seconds. Other timing sequences can also be formulated in accordance with the present invention; although detection circuit 10 operates as described above since the propagation delay through inverter 32 is established as tplh=tphl=10-seconds, and the propagation delay through combinatorial element 34 is established as tplh=tphl=tilh=tihl=20-seconds. The combinatorial element 34 is shown as an “or” gate in which the inherent propagation and inertial delay is 20-seconds. The present invention is not so limited however, and it shall be understood the other combinatorial elements can just as easily be implemented to provide the requisite functionality according to the principles of the present invention.

[0023] FIG. 4 is a diagram illustrating one embodiment of a charging control system 100 using the battery removal detection circuit 10 shown in FIG. 1. The charging control system can be seen to include a charger 102 and a state machine charger control unit 104. As stated herein before, the battery removal detection circuit 10 can also be seen to provide a control signal (NOBAT) 24 to the state machine control unit 104 using only two input sensing nodes 106 and 108 to generate ΔGone at input node 16 and ΔVCH 19 at input node 14 respectively.

[0024] Operation of the charging control system 100 is further explained below with reference to FIGS. 5 and 6 wherein FIG. 5aillustrates battery charger voltage and current waveforms during normal charging and FIG. 5billustrates charger voltage and current waveforms during a battery removal. As seen in FIG. 5a, when the charging voltage 110 is increasing, the charging current 112 remains steady at a predetermined value until the charging voltage 110 begins to attain a predetermined maximum value. As the charging voltage 110 comes closer to the predetermined maximum value, the charging current 112 begins reduce until charging current 112 is no longer flowing at some predetermined point in time. As seen in FIG. 5b, when the charging voltage 110 is increasing and the battery (enumerated as 150 in FIG. 4) is removed from the system 100 during the charging process (enumerated as 114), the charging voltage 110 very abruptly jumps to its maximum predetermined value. Simultaneously, the charging current 112 drops to zero, since charging current 112 is no longer flowing into the battery 150.

[0025] FIG. 6 illustrates timing relationships between various signals for the charging control system 100 shown in FIG. 4 during a battery 150 removal. The re₁₃cv pulse 20 transitions high when ΔVCH 19 transitions high (V_CHG110>V_ΔVCH130). The ΔGone pulse 140 at input node 16 must transition high (indicating the charging current I_CHG112 <10 mA), during the 1-minute re_cv pulse 20. Otherwise, the NO₁₃BAT output signal 135 will not be asserted to a logic 1 state. The timing delay intervals 136, 138 are implemented solely to provide noise immunity for the battery charger detection circuit 10.

[0026] In summary explanation of the foregoing, a battery charger detection circuit 10 architecture is implemented in a way that detects battery removal from the charger 102, or distinguishes between the condition when a battery 150 is not present in the charger 102 without using external stimulus such as a thermistor, EEPROM, or an additional pin. The detection circuit 10 requires signal information provided solely by the charger 102 positive and negative terminals to correctly annunciate the current state of the charger 102 to a host or end-user.

[0027] In view of the above, it can be seen the present invention presents a significant advancement in the art of battery charger control technology. Further, this invention has been described in considerable detail in order to provide those skilled in the data communication art with the information needed to apply the novel principles and to construct and use such specialized components as are required. In view of the foregoing descriptions, it should further be apparent that the present invention represents a significant departure from the prior art in construction and operation. However, while particular embodiments of the present invention have been described herein in detail, it is to be understood that various alterations, modifications and substitutions can be made therein without departing in any way from the spirit and scope of the present invention, as defined in the claims which follow. For example, although various embodiments have been presented herein with reference to particular functional architectures and characteristics, the present inventive structures and characteristics are not necessarily limited to particular detection circuit architectures or sets of characteristics as used herein. It shall be understood the embodiments described herein above can easily be implemented using diverse combinations of combinatorial elements so long as the combinations achieve charger information according to the inventive principles set forth herein above.