Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
1999-06-30
2001-08-07
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C307S086000, C307S140000
Reexamination Certificate
active
06271605
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed toward the field of battery protection systems. In particular, the invention is directed to a battery disconnect system for disconnecting a battery from its load during long periods of inactivity to reduce the likelihood that the battery will become damaged due to excessive battery discharge.
Many batteries such as rechargeable batteries may be irreparably damaged if they are discharged too deeply. Lithium-based batteries are especially susceptible to this hazard.
Many devices having built-in rechargeable batteries can expose their rechargeable battery to this excessive discharge hazard. Even when not in use, the rechargeable battery remains connected to the device's load. The small load the device presents to the rechargeable battery during inactive periods will cause the rechargeable battery to slowly discharge, potentially damaging the battery.
This problem is amplified when devices having rechargeable batteries are transferred from a manufacturer to a retailer. Prior to being sold to an end-user, the device may be warehoused or placed on shelves for weeks or months before the end-user first uses the device. The period of time that the device remains in the warehouse or on the retailer's shelf may be sufficient to allow the battery to become over-discharged and damaged. To alleviate this problem, it is desirable to have a method of preventing the device from over-discharging during periods of long inactivity.
One method of addressing this problem has been for manufacturers to position plastic tabs between the battery and the power terminal to physically disconnect the load from the battery. Upon purchase of the device, the customer is then instructed to remove the tab thereby reconnecting the load to the device.
This method has many disadvantages. One disadvantage is that it poses significant impediments to the manufacturer's quality assurance program. During a quality assurance inspection, the tab must be removed to allow the inspector to test whether the product functions, and then must be reinstalled in the product, which may be extremely difficult. This method also can reduce the product's overall reliability due to the addition of mechanical controls. Another shortcoming is that the end-user has to ensure that the rechargeable battery is properly installed and connected after removal of the tab.
Other proposed methods include adding mechanical switches that can add significant resistance to the battery path thereby degrading performance. Also, the mechanical nature of the switches often results in a reduction of overall product reliability.
Another method of addressing the problem has been the use of commercially available Lithium battery pack protection circuits. These battery pack protection circuits measure the lithium cell voltage and disconnect the battery from the load if the battery voltage drops below 2.5 volts or other predetermined thresholds. One disadvantage of this method is that several hours are required for the battery to be charged back to a useable state after the battery pack protection circuit has disconnected the battery from the load—an unacceptable result for electronic devices that are designed to function with little, if any perceived downtime. Another disadvantage is that disconnecting the load after the battery voltage has dropped to a pre-determined level such as 2.5 volts does not guarantee that the battery will not be damaged. The battery will continue to discharge as a result of self-discharge and power drain from the protection circuit. Lithium cells become damaged if they are discharged below a low voltage level (typically 2.5 volts) for more than a few minutes. Consequently, the battery may still over-discharge when utilizing a load-disconnecting method that does not compensate for self-discharge and power drain and thereby does not protect against damage to the lithium cell.
Therefore, there remains a need in this art for a battery protection system that can disconnect the load from the battery to prevent the battery from over-discharging without the use of a removable mechanical interlock device. There remains a further need for a system that can disconnect the load from the battery before the battery has been significantly discharged.
SUMMARY OF THE INVENTION
The present invention overcomes the problems noted above and satisfies the needs in this field for a battery disconnect system that includes the feature of disconnecting a battery from its load while the battery is almost fully charged. The present invention provides a method for protecting the internal rechargeable battery in a device by electrically disconnecting the internal rechargeable battery from the load when the device will not be needed for a long time. The present invention further provides a method for quickly reconnecting the battery to the load in a manner that requires little action by the end-user.
The present invention is particularly useful for products that charge an internal, non-removable rechargeable battery from a primary user-replaceable battery or other user-connected external power source. This invention can conceal the fact that the product uses an internal non-removable rechargeable battery because the product can be constructed to appear to turn on and off when the primary user-replaceable battery is inserted or removed.
The present invention provides many advantages over the presently known battery protection systems. Not all of these advantages are simultaneously required to practice the invention as claimed, and the following list is merely illustrative of the types of benefits that may be provided, alone or in combination, by the present invention. These advantages include: (1) disconnecting the rechargeable battery based on a primary battery or external power source not being available for a programmed period of time; (2) disconnecting the rechargeable battery from a charging source when the rechargeable battery is nearly fully charged; (3) reconnecting the battery based on a primary battery or external power source being made available; (4) providing a method whereby a manufacturer can ship a device with an internal rechargeable battery fully charged and ready for use but with the rechargeable battery electrically disconnected from the load, and in which the user can electrically connect the rechargeable battery to the load in a few seconds by simply installing a primary battery or plugging in an external power source; (5) increasing the shelf life of a device having the invention; and (6) providing an over temperature safety disconnect.
In accordance with the present invention, a battery disconnect system is provided for a device having a battery and load. The battery disconnect system includes a switch that is operative to connect the battery to the load when the switch is in a closed state. The switch is also operative to disconnect the battery from the load when the switch is in an open state. The battery disconnect system also includes a switch controller that is coupled to the switch. The switch controller is operative to cause the switch to enter the closed state in response to receipt of a first signal from a first external source. The switch controller is also operative to cause the switch to enter the open state in response to receipt of a second signal from a second external source.
In one embodiment, the first external source is an external battery, the first signal is a pre-defined level of power generated by the external battery, the second signal is a logic signal, and the second external source is the load. In an alternate embodiment, the first external source is an AC power source instead of an external battery, and the first signal is either the actuation of a reset switch or the presence of an adequate power supply from the AC power source.
In accordance with the present invention a device is provided. The device includes a battery for providing power, a load configured to consume power provided by the battery, and a switch coupled between the
Carkner Steven
Fischer Daniel
Lowles Robert
Luong Quang
Malton Jonathan
Fleming Fritz
Jones Day Reavis & Pogue
Meyer, Esq Charles B.
Pathiyal, Esq. Krishna K.
Research In Motion Limited
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