Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Reexamination Certificate
2001-09-13
2004-03-02
Berhane, Adolf D. (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
Reexamination Certificate
active
06700766
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic device protection circuit for inhibiting an overvoltage exceeding the rated voltage of an electronic device such as a lithium-ion secondary battery and a semiconductor device from being applied thereto so as to protect the electronic device from performance degradation, damage and so on.
Further, the present invention relates to an electronic device protection circuit for protecting an electronic device such as a semiconductor integrated circuit included in, for example, a lithium-ion secondary battery or a cellular phone apparatus from damage resulting from overvoltage or overcurrent.
2. Description of the Related Art
When an overvoltage greater than the rated voltage of an electronic device is applied thereto, it may result in performance degradation in or damage to the electronic device. In order to protect the electronic device from the application of such overvoltage, various protection circuits have been proposed.
Conventionally, as an electronic device protection circuit of this kind, a protection circuit in which, for example, the power source terminals of a semiconductor integrated circuit or input/output terminals (cathode and anode) of a secondary battery are connected in parallel to a zener diode, and a fixed resistor device is provided between the semiconductor integrated circuit or the secondary battery, and external connection terminals where a voltage is externally supplied is typically used.
In recent years, as mobile electronic apparatuses and cellular phones have been developed, lithium-ion secondary batteries have been used as thin secondary batteries which are compact and capable of long-duration discharge. In general, the lithium-ion secondary battery is charged with a voltage slightly greater than its rated discharge voltage. When an excessive charge voltage greater than the rated voltage is applied to the lithium-ion secondary battery, for example, because an abnormal condition in a charger is encountered or a user accidentally connects the battery to an out-of-specification charger, a battery/cell in the battery may generate heat, which may lead degradation or damage therein due to a rise in gas pressure. In order to protect the lithium-ion secondary battery from such degradation and damage, a protection circuit for preventing an overvoltage from being applied to the lithium-ion secondary battery is required.
In accordance with such conventional electronic device protection circuit, when an overvoltage exceeding the breakdown voltage of the zener diode is applied to the external connection terminals of the semiconductor integrated circuit or the secondary battery, the zener diode enters in a state that a current flows therethrough, so that an larger amount of the overcurrent resulting from the overvoltage can flow through the zener diode than through the semiconductor integrated circuit or the secondary battery, and due to the breakdown voltage characteristics of the zener diode, a voltage between terminals of the semiconductor integrated circuit or the secondary battery can be set not to exceed the rated voltage. At this time, as the passage of a large current through a fixed resistor results in a voltage drop, the voltage applied to the semiconductor integrated circuit or the secondary battery can be reduced to the amount determined by the subtraction of the voltage drop by the fixed resistor from the voltage applied to the external connection terminals.
As a technology of the protection circuit for the lithium-ion secondary battery, there is a protection circuit proposed in, for example, Japanese patent laid-open publication Hei 2-87935 (Japanese Patent No. 2720988). In this technology, a zener diode is connected in parallel to a battery/cell in the secondary battery, and a thermal fuse is connected in series to the battery/cell, so that when an overvoltage is applied to the secondary battery, a current flows through the zener diode, which thereby generates heat. As the heat and heat generated in the thermal fuse result in a fusion of the thermal fuse, the overvoltage is prevented from being applied to the battery/cell.
Further, in Japanese utility model publication Hei 6-31345, a technology that in a case where a voltage between a positive terminal and a negative terminal of a secondary battery is detected by a voltage detection circuit, when the voltage detection circuit detects that the voltage rises to become an overvoltage greater than the rated voltage, a heat generation switching device turns on to generate heat, which is applied to a thermal sensitive interrupting device to be brought into an interrupting state, so that the overvoltage is prevented from being applied to the secondary battery has been proposed.
Further, other various technologies such that a charge voltage is applied to a secondary battery through a protection circuit with a complicated circuit configuration using a thermistor or a digital circuit device, and that a bimetal is used instead of a fuse have been proposed.
However, the foregoing technologies which have conventionally proposed have some problems such that when a further overvoltage is applied, the protection circuit itself may be damaged so as to become inoperable, or may generate heat which thereby causes degradation or damage in the battery/cell.
Further, there is a problem that in the foregoing conventional electronic device protection circuit. When an overvoltage is continuously applied to the external connection terminals, or when an overvoltage which may result in an increase in current to greater than the maximum allowable current of the zener diode is applied, the zener diode abnormally generates heat, which may damage circuit devices or semiconductor integrated circuits on its periphery, or the zener diode itself due to overheating.
In the technology proposed in Japanese patent laid-open publication Hei 2-87935, for example, when a user accidentally connects the secondary battery to the out-of-specification charger, and an excessive charge voltage which is much greater than the rated voltage is applied to the secondary battery, the thermal fuse generates heat, resulting in the fusion of the thermal fuse, so that the overvoltage can be prevented from being applied to the secondary battery. However, when an overcurrent much higher than the rated current due to the overvoltage continuously flows through the zener diode, the zener diode itself will be overheated, which may result in the degradation in or damage to the battery/cell.
Moreover, before the fusion of the thermal fuse, when the zener diode is damaged and fixedly bypasses a current, so that the battery/cell may be useless as a secondary battery because the battery/cell may not be charged permanently, or the positive and negative terminals of the battery/cell may be always short-circuited. Alternatively, when the zener diode is damaged so as to become an electrical resistor, the current continuously flows through the damaged zener diode. As a result, the zener diode itself is overheated, which thereby may result in degradation in or damage to the battery/cell.
In the technology proposed in Japanese utility model publication No. Hei 6-31345, for example, in a case where the excessive charge voltage which is much greater than the rated voltage is accidentally applied to the secondary battery, at the moment when the excessive charge voltage is applied, a returnable type thermal sensitive device has not been brought into an interrupting state yet, so an overcurrent flows through at the moment, resulting in damage to a heat generation switching device. Thereby, even if the excessive charge voltage is applied, the excessive charge voltage cannot be detected and the thermal sensitive device does not function. Accordingly, as the excessive charge voltage is continuously applied to the secondary battery, the secondary battery generates heat, which thereby may result in degradation in or damage to the secondary battery. Alternatively, when the heat generation
Berhane Adolf D.
Maioli Jay H.
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