BATTERY WITH PROTECTION CIRCUIT

Abstract: A battery apparatus (104) includes at least one cell (114) having a capacity. The battery apparatus (104) also includes a protection circuit (116) for directing the charging pattern of the at least one cell (114) to follow a predetermined format. The protection circuit (116) monitors the rate at which the battery apparatus (104) is charged and stops the charge when this rate falls below a predetermined rate.

Description: BATTERY WITH PROTECTION CIRCUIT Technical Field This invention relates generally to batteries and more specifically to batteries having current limiting protection. Background Rechargeable batteries capable of tolerating high number of recharge cycles are widely used in portable radio applications which demand safe and dependable energy sources. Some portable applications, in particular communication devices, demand high energy batteries due to their high power requirements and size limitations. New cell technologies are constantly being developed to handle the additional output power requirements of such devices. Some of these new technologies demand a particular charge pattern. In other words, charging a battery utilizing these new technologies at a rate other than desired may result in permanent battery damage. Continued use and charge of these batteries at undesired rates may produce gas evaporation which may lead to explosion. An approach to curtail cell damage is the use of dedicated chargers for each cell type. Several problems are obvious with dedicated chargers: high cost, unnecessary proliferation, maintenance, and storage are some of them. Batteries using these new cell technologies are desirable in that they can provide the desired additional power without a significant size increase. Therefore, a need is felt for a battery which can take advantage of these new cell technologies without the use of dedicated chargers. Summary of the Invention Briefly, according to the invention, a battery apparatus is provided having a cell and means for directing the charging pattern of the cell to follow a predetermined format. In other aspects of the present invention, the battery apparatus includes an inhibitor means for inhibiting the battery from being charged at lower than a predetermined rate. Brief Description of the Drawings FIG. 1 shows a battery coupled to a charger in a accordance with the present invention. FIG. 2 is a schematic diagram of a protection circuit in accordance with the present invention. FIG. 3 is a block diagram of a receiver in accordance with the present invention. Detailed Description of the Preferred Embodiment Referring to FIG. 1 , a block diagram coupling a charger 102 to a battery pack 104 is shown. The power generated by the charger 102 is coupled to the battery pack 104 via two power lines 106 and 108. The latter serves as the ground return for all signals communicated between the charger 102 and the battery pack 104. Internal to the battery packl 04 is at least one cell 114 having a cell capacity (C) and being coupled to the power line 106 via a protection circuit 116. The protection circuit 116 provides the inhibitor means for the battery pack 104. The cell 114 is preferably nickel metal hybrid type. As is known in the art, these battery cells can not be safely charged at or below a pre¬ determined rate. Specifically, it has been determined that rates lower than 1/3C must be avoided in order to prevent damage. The protection circuit 116 prevents the rate with which the cell 114 is charged to fall below a pre-determined level. In the preferred embodiment, this minimum rate is set at the cell capacity (C). Other rates may be used to suit other cells with charge rate limitations. Indeed, the protection circuit 116 may include circuits to dictate a desired charging pattern for the cell 114 in accordance with a charging pattern. In other words, the battery pack 104 may include a circuit for directing the charging pattern of the cell 114 to follow a predetermined format. This latter circuit would be suitable for applications where the battery cells are optimally charged when following a pre-determined charge pattern. Also included in the battery pack 104 is a thermistor 112 which is used to monitor the temperature of the cell 114 during charge up. This thermistor 112 provides for additional protection against damage caused by heat that may be the result of rapid charging a battery. The thermistor 112 communicates the temperature of the cell 114 to the charger 102, upon request. The charger 102 is a universal charger. Universal chargers are known for their versatility in charging a variety of batteries. In general, a universal charger is intended to charge batteries having similar packaging while using different technologies. These chargers are highly desired, for they limit the number of chargers needed to charge a variety of batteries that may be used by a user. It is the popularity of universal chargers that the protection circuit 116 is necessary in order to prevent damage to the variety of batteries they may potentially charge. The operation of chargers, and in particular universal chargers, is well known in the art. A battery placed in the charger 102 is first evaluated for its internal temperature. If within a pre-determined window, the charger proceeds to rapid charge the battery, often using a current source. The rapid charge of the battery is periodically interrupted for temperature measurements. Indeed, it is the temperature level or the rate of increase of the temperature of the battery which determines the charge rate. Upon determination that the battery temperature is above suitable level for rapid charge, a trickle charge state is entered. The protection circuit 116 takes advantage of this switching from rapid charge to trickle charge in order to prevent the battery pack 104 from being charged when trickle rate is applied. Referring now to FIG. 2, a schematic diagram of the preferred embodiment of the protection circuit 116 is shown. The charge input terminal 114 is branched to a regulator formed by a zener diode 210 and a resistor 222. The input terminal 114 is also coupled to the anode of a SCR 204. The cathode of the SCR 204 is coupled to the positive terminal ofthe cell 114. The gate of the SCR 204 is coupled to two switching transistors 208 and 220. The base of the latter is coupled to the resistor 222 via diodes 216 and 218. The base of the transistor 208 is coupled to the collector of the transistor 220 through a resistor 214. The rapid charge delivered by the charger 102 at the input terminal 118 turns the transistor 220 ON through diodes 216 and 218. The transistor 208 is consequently turned ON as its base is coupled to ground through resistor 214 and the ON transistor 220. The SCR 204 is turned ON as a high voltage is applied to its gate through the ON transistor 208. The SCR 204 subsequently applies the rapid charge current to the cell 114. The charging of the cell 114 continues along with periodic temperature checks. As the cell 114 reaches full charge the temperature increase communicated to the charger 102 causes the rapid charge to cease and be replaced with trickle charge. In the trickle charge mode the current supplied by the charger 102 produces a voltage across the resistor 222 insufficient to turn the transistor 220 ON. As a result, the transistor 208 and the SCR 204 do not turn ON preventing low current rates from trickle charging the cell 114. It can be seen that charge rates below a desired level, in this case one C, can be prevented from charging the cell 114 and hence preventing damage. By changing the values of the supporting components of transistors 208 and 220 other charge rates may be prevented from charging the cell 114. The circuit 116 demonstrates the principles of the present invention in relation to one specific battery cell. Other cells having different characteristics may require a different charging pattern which may be met with a different protection circuit. The presentation of the elements of the circuit 116 is not to imply, directly or indirectly, a limitation on the present invention. In summary, the protection circuit 116 is used to allow the cell 114 to be charged only in rapid mode. The circuit 116 breaks the current path from the charger 102 to the battery cell 114 when the rapid charge cease and is replaced with trickle charge. With this protection circuit 116 the cell 114 is protected from damage that may be caused by trickle charge, overcoming the deficiencies of the prior art battery packages. Referring to FIG. 3, a block diagram of a communication device is shown. A radio frequency signal is received via a receiver 304 through an antenna 302. The receiver 304 and other elements of the communication device 300 are powered via the battery 104. Audio signals received and decoded by the receiver 304 are presented on a speaker 308. Data signals are on the other hand, presented on a display terminal 306. A variety of batteries may be used with the communication device 300 so long as they include the protection circuit 116 which would prevent them from being trickle charged. With these batteries a single charger may be used eliminating the need for a multiplicity of chargers to accommodate various batteries. What is claimed is:

Claims: Claims 1. A battery apparatus, comprising: at least one cell having a cell capacity; and inhibitor means for inhibiting the at least one cell from being charged at a rate lower than a predetermined rate. 2. The battery apparatus as defined in claim 1, wherein the at least one cell includes a nickle metal hybrid. 3. The battery apparatus as defined in claim 1, wherein the inhibitor means includes means for inhibiting the at least one cell from being charged at a rate lower than one third of the cell capacity. 4. The battery apparatus as defined in claim 1 , wherein the inhibitor means includes means for inhibiting the at least one cell from being charged at a rate lower than a rate equal to the cell capacity. 5. A nickel metal hybrid battery apparatus, comprising: at least one cell having a cell capacity and a charging pattern; and means for directing the charging pattern to prevent the at least one cell from being trickle charged. 6. The battery apparatus of claim 5, wherein the means for directing includes means for directing the battery to be charged at the cell capacity. 7. A nickel metal hybrid battery apparatus, comprising: at least one nickel metal cell having a cell capacity; and means for preventing the at least one cell from being trickle charged. 8. The nickel metal hybrid battery of claim 7, further including a thermistor. 9. A communication device, comprising: a receiver; a battery apparatus, including: at least one cell having a cell capacity; and inhibitor means for inhibiting the at least one cell from being charged at a rate lower than a predetermined rate. 10. The communication device of claim 9, wherein the inhibitor means includes means for inhibiting the at least one cell from being charged at a rate lower than the cell capacity.

Inventors: HAWKINS LILBERT S III, MCCALEB FRANK D, HAWKINS, LILBERT, S., III, MCCALEB, FRANK, D.
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1992
Main classification: H02J7
IPC codes: H01M10, H02H7, H02J7