Electricity: battery or capacitor charging or discharging – Battery or cell charging – With thermal condition detection
Reexamination Certificate
2000-05-02
2001-05-01
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With thermal condition detection
Reexamination Certificate
active
06225787
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to analog integrated circuits, and more particularly to current sources implemented in analog integrated circuits.
Constant current sources and constant voltage sources are used for a variety of purposes in analog integrated circuits. As used herein, “constant” means that the output of the source remains at a relatively constant direct current (d.c.) level, although the output levels of such sources can typically be adjusted (“set”) with a control signal. Once set, the output of a constant current or voltage source may change with temperature (i.e. be “temperature dependent”) or may be stable with temperature. In many applications, it is desirable to have a constant current or voltage source that does not vary in output as the temperature changes. Such applications include power supplies that are suitable for charging batteries and the like. Unfortunately, however, conventional battery chargers are not capable of charging batteries that have been discharged below approximately 2.5 to 3.0 volts.
If the output of a constant, temperature stable, current source is coupled from an output resistor that is temperature stable, the result is a constant, temperature stable voltage source, as will be appreciated by those skilled in the art. These constant, temperature stable voltage sources are useful for many purposes, such as providing a reference voltage, for adjusting the threshold of a comparator, etc. that are useful power supplies for charging a battery
Therefore, what is desired is a temperature stabilized, adjustable, yet constant current source suitably arranged to charge a battery that has been discharged to as low as 1.0 volts.
SUMMARY OF THE INVENTION
The invention is an electrical circuit that provides a temperature stabilized current source with a stable control voltage capable of charging a battery having been discharged to as low as approximately 1 volt. As used herein, “stable” means that the voltage remains essentially unchanged with changes in temperature, i.e. it is not temperature dependent. The circuit solves the problem of providing an adjustable temperature stabilized current source suitable for charging deeply discharged (i.e. in the range of 1.0 V) batteries.
A temperature stabilized, constant current source of the present invention includes a feedback control stage arranged to provide feedback control so as to maintain a battery charging current to within a predetermined range of current values. The current source also includes a temperature stabilized current source stage operative to produce an output current that is constant over a wide range of ambient temperatures. The current source stage includes a temperature-dependent input stage with positive temperature coefficient and a negative temperature coefficient controlled constant current source providing a countervailing control current such that the current through a sensing resistor is constant over a large temperature range. The temperature dependencies of the positive temperature coefficient voltage source and a negative temperature coefficient current source are combined so as to provide a control voltage that is independent of any resistor temperature dependency.
As a method for providing a temperature independent current suitable for charging a highly discharged battery, a battery charging current is maintained to the battery within a specified range of battery charging currents using a feedback control circuit. The feedback controlled battery charging current is further temperature stabilized over a range of operating temperatures by a temperature stabilized current source having positive temperature coefficient current source and a countervailing negative temperature coefficient current source that maintains a temperature stabilized current through a sensing resistor.
The method and apparatus of the present invention therefore solves the problem of providing a temperature independent (i.e., zero temperature coefficient, or tempco) current source whose output is a stable fraction of total current available, regardless of any changes in the total current due to changes in temperature.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawing.
REFERENCES:
patent: 3887858 (1975-06-01), Burkett et al.
patent: 4061956 (1977-12-01), Brown et al.
patent: 5633574 (1997-05-01), Sage
Chen Sean S.
Pease Robert
Beyer Weaver & Thomas LLP
National Semiconductor Corporation
Tibbits Pia
Wong Peter S.
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