Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2003-05-30
2004-07-13
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06762589
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a charging circuit for charging a rechargeable battery unit, with the rechargeable battery unit supplying an electrical appliance with voltage, and to a method for charging a rechargeable battery unit by an external charging voltage.
The present commercial requirements result in the manufacturers of electrical and electronic appliances having to produce ever smaller appliances. In this case, the progress in the miniturization of electronic assemblies allows the production of convenient appliances, which can be used in a mobile form. A pronounced trend in this direction can be observed in particular in the field of telecommunications. This relates primarily to appliances such as mobile telephones, cordless telephones, pagers, palmtops, etc. Since these appliances are not connected to any mains supply, they must be operated via rechargeable batteries. In this case, it must be possible to charge the rechargeable batteries in the appliance itself. For example, the rechargeable battery that is located in the portable handset of a cordless telephone must be capable of being recharged via the associated base station. It would not be acceptable for the rechargeable battery to have to be removed from the appliance in advance for charging.
This requirement results in that not only the rechargeable battery but also the appliance which is operated by the rechargeable battery remains in contact with a charging voltage via the charging circuit throughout the charging process, with the charging voltage generally being obtained from the mains voltage. There is a risk of an incorrect (excessively high) charging voltage being applied to the appliance. In some circumstances, the mains voltage may also be subject to considerable short-term fluctuations. The electrical appliance must therefore be protected against being destroyed by excessively high voltages, by over-voltage protection circuits.
Discrete components are generally used for this purpose. Zener diodes are frequently used in this case. These diodes are characterized by a precisely defined breakdown voltage, at which the reverse current rises steeply. If the applied voltage exceeds the breakdown voltage, then the impedance of the zener diode in consequence becomes low. The voltage that is applied to the zener diode is thus always limited to the breakdown voltage.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a circuit for charging rechargeable batteries that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which the complexity resulting from discrete components is reduced.
With the foregoing and other objects in view there is provided, in accordance with the invention, a charging circuit for charging a rechargeable battery unit with an external charging voltage, with the rechargeable battery unit supplying an electrical appliance with a voltage. The charging circuit contains a charging contact for connecting to the external charging voltage, and a charge regulator for controlling a current and/or a voltage profile of a charging process. The charge regulator has a control transistor through which a charging current flows, and a series transistor with a collector-emitter path connected to the control transistor and through the collector-emitter path a control current of the control transistor flows. The series transistor has a base connection electrically coupled to the charging contact. A monitoring unit is provided for comparing a signal representing a given voltage applied to the rechargeable battery unit, with a predetermined maximum value, and, if the predetermined maximum value is exceeded, the monitoring unit causes the charge regulator to switch off or reduce the given voltage applied to the rechargeable battery unit.
The present invention relates to a charging circuit for charging a rechargeable battery unit by an external charging voltage, with the rechargeable battery unit supplying an electrical appliance with voltage. The charging circuit has a charging regulator, which controls the current and/or voltage profile of the charging process. Furthermore, the charging circuit has a monitoring unit, which compares a signal, which represents the voltage that is applied to the rechargeable battery unit, with a predetermined maximum value and, if this maximum value is exceeded, causes the charging regulator to switch off or to reduce the voltage that is applied to the rechargeable battery unit.
Electrical appliances which are powered by a rechargeable battery unit have until now been equipped with a charging regulator for controlling the charging process, and with additional components in order to protect the rechargeable battery unit and the electrical appliance against over-voltages. With the present invention, the charging regulator carries out both functions, that is to say it controls the process of charging the rechargeable battery unit while at the same time being used for protection against over-voltages when the monitoring unit indicates to it that an excessive voltage has occurred. This makes it possible to save additional, discrete components, such as zener diodes, which were used for over-voltage protection. In consequence, owing to the saving of discrete components, the charging circuit according to the invention allows the electrical appliance to be produced at a lower cost and to be more compact. The rechargeable battery unit can remain in the electrical appliance during the charging process.
If the predetermined maximum voltage is exceeded, the voltage that is applied to the rechargeable battery unit can either be switched off or reduced. The simplest solution is to completely switch off the voltage that is applied to the rechargeable battery unit when a predetermined maximum value is exceeded. This embodiment can be implemented by a simple comparison circuit.
A solution in which the voltage is only limited and is not switched off completely has the advantage that the electrical appliance is still supplied with a voltage, despite the excess voltage. This may be a critical factor for many applications, for example in the case of appliances with volatile electronic memories. The data stored there would be lost if the supply voltage were switched off completely.
One preferred embodiment of the charging circuit according to the invention provides for the charging regulator to have a control transistor through which the charging current flows. In this embodiment, the control transistor is the central component for controlling the charging of the rechargeable battery unit. The desired charging current can be set by the control transistor.
According to a further advantageous embodiment of the invention, the monitoring unit as well as parts of the charging regulator are implemented on a common silicon substrate, while the control transistor is in the form of a discrete component. All the control electronics for controlling the sequence of the charging process as well as the voltage monitoring for detection of over-voltages can be accommodated in an integrated circuit. The control transistor is a discrete component, in the form of the only power component. The control electronics are supplied with a signal that represents the voltage that is applied to the rechargeable battery unit. The control connection of the control transistor (the gate connection when using an FET, and the base connection when using a bipolar transistor) is connected to the integrated circuit in order to make it possible to use the control transistor to check the charging current by the integrated control electronics. One control transistor, which is connected to the integrated control electronics via two signal lines, is thus sufficient for providing combined charging regulation with over-voltage protection.
It is advantageous for the control transistor to be a field-effect transistor, via whose source-drain path the charging current flows. The charging current and/or the voltage that is applied to th
Beerwerth Rolf
Kirchhoff Hans-Gerd
Kranz Christian
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Stemer Werner H.
Tso Edward H.
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