Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
1998-05-21
2001-02-27
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S136000
Reexamination Certificate
active
06194869
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to portable phones and other electronic devices employing an external battery pack to provide power, and is particularly concerned with a protection circuit for preventing accidental short circuits of the exposed contacts of an external battery pack when disconnected from the phone or charging unit.
The back of a portable phone typically has spring-loaded contacts for mating engagement with flush contacts of an external battery pack when releasably secured to the phone. Various types of releasable fastening devices are used to secure such battery packs to portable phones. The battery pack fits into a charging unit with similar spring-loaded contacts when re-charging is required.
One problem with such external battery packs is that they may be accidentally short circuited by the user when not connected to the phone or charging unit. Most such battery packs, such as Li-ion battery packs, for example, have built in self protection circuitry for preventing overcharge or over discharge of the battery pack. However, when spare battery packs are carried loose in a user's bag, pocket, or purse, an accidental short circuit may occur where loose coins or keys connect the positive and negative exposed contacts. Such a situation may not activate the built in self protection circuit, since the thresholds for such short circuits must be higher than the operating discharge current under normal conditions, i.e. if the device draws peak currents at 1 amp, then the self-protection circuit of the battery pack must trip at currents above 1 amp. This will not activate the current self protection circuit provided in such battery packs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new and improved protection circuit for an external battery pack, particularly a portable phone battery pack.
According to the present invention, a battery protection circuit is provided, which comprises a switch assembly having an input for receiving a control signal, the switch assembly controlling connection of a battery output to a load, a detector for detecting a resistance at a load terminal, and a control assembly for determining whether the resistance has a value between a predetermined maximum value and a predetermined minimum value, and for generating the control signal in response to the determination, the control signal causing the switch to close if the determination is positive, and causing the switch to open otherwise, so that the battery output is connected to the load only when the detected resistance has a value between the predetermined minimum and maximum values.
Preferably, the control assembly comprises a first comparator for comparing the resistance to the predetermined maximum value and producing a first output signal if the resistance is above the predetermined maximum value and a second output signal if the resistance is below the predetermined maximum value, a second comparator for comparing the resistance to the predetermined minimum value and for producing a third output signal if the resistance is below the predetermined minimum value and a fourth output signal if the resistance is above the predetermined minimum value, and a second detector connected to the outputs of the first and second comparators for producing the control signal to close the switch if the resistance is between the minimum and maximum values.
Preferably, the load to be powered by the battery has positive and negative input contacts for connection to battery positive and negative outputs, respectively, and an ID output to which a predetermined load identifying resistance is applied. When the battery is connected through the battery protection circuit to the proper load, the ID output is connected to the first and second comparators which compare its resistance to the predetermined minimum and maximum values, and only permit power to be supplied from the battery to the load when the detected resistance is between the minimum and maximum values.
In a preferred embodiment of the invention, the circuit also includes a self-protection control unit for controlling discharge of the battery, the control unit having an input, an overdischarge output, and the switch assembly includes a first switch controlling series connection of the battery to a load in a discharge mode, the first switch having a control input connected to the overdischarge output of the control unit, and a second switch for disabling the first switch if the load ID resistance is detected to be outside the predetermined range between the minimum and maximum values. The second switch may be arranged to control the power input to the control unit, so as to disable the control unit itself when the detected resistance is outside the predetermined range, or may be connected between the overdischarge output of the control unit and the first switch to disable the control input to the switch in the event that the detected resistance is outside the predetermined range.
The control unit may also have an overcharge output, and a third switch for controlling charging of the battery is series connected between a charge input and a battery input, the third switch having a control input connected to the overcharge output. The control unit is arranged to open the third switch when the battery has been charged to a predetermined value. A fourth switch, also controlled by the output from the second detector, may be connected between the overcharge output and the third switch, so that the battery cannot be charged or discharged where the detected ID resistance is outside the predetermined range.
The battery protection circuit will prevent the battery from being accidentally shorted out by metallic objects such as keys, coins or the like when not in use. Discharge is only possible when the circuit detects connection to a load having the proper ID resistance.
REFERENCES:
patent: 5206782 (1993-04-01), Landmeier et al.
Brown Charles D.
Tso Edward H.
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