Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-01-18
2001-02-27
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S134000
Reexamination Certificate
active
06194868
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a voltage indicator for supplying an indication signal to indicate that a voltage of a battery passes a given value, comprising: a battery terminal for connection to the battery, a reference voltage source for supplying a reference voltage, and a comparator for comparing the reference voltage with a voltage on the battery terminal, which comparator has a first input terminal coupled to the reference voltage source, a second input terminal coupled to the battery terminal, and an output for supplying the indication signal in response to the comparison.
SUMMARY OF THE INVENTION
Such a voltage indicator is known from U.S. Pat. No. 5,705,913, particularly
FIG. 2
, and is used for indicating whether a rechargeable battery is nearly empty. For this purpose, the comparator of the known voltage indicator compares a fraction of the battery voltage with a reference voltage and, when the battery voltage passes the reference voltage, the output voltage of the comparator changes to another extreme value. In the development of electrical and electronic apparatuses having rechargeable batteries, the type of rechargeable battery as well as the number of cells of the rechargeable battery is not a predetermined fact. The voltage levels at which the cells are nearly empty are not the same for various cells, such as NiCd (Nickel-Cadmium), NiMH (Nickel-Metal Hydride) and the like. Moreover, the level of this voltage changes as a result of the developments in the cell formulation. Furthermore, there are apparatuses using one, two or more rechargeable cells in series.
It is an object of the invention to provide a voltage indicator by means of which the voltage level which is indicative of a nearly-empty state of a battery having one cell or more cells in series can be adjusted with the aid of two resistors. To achieve this object, the voltage indicator of the type defined in the opening paragraph is characterized in that the voltage indicator further comprises:
a further reference voltage source for supplying a further reference voltage;
a first resistor;
a second resistor connected between the battery terminal and the second input terminal of the comparator;
a voltage-to-current converter having a first current output and a second current output for supplying a first current and a second current, respectively, which currents have current intensities which are proportional to the further reference voltage and inversely proportional to the value of the first resistor, the second current output being coupled to the second input terminal of the comparator;
means coupled to the first current output, for supplying a switching signal in response to the first current; and
means for switching the reference voltage from the first-mentioned reference voltage source between at least two different values in response to the switching signal.
The first resistor defines the number of cells in series, for example, one or two. For this purpose, the first current of the voltage-to-current converter is compared with a threshold value. Upon passage of the threshold value the reference voltage with which the battery voltage is compared is changed to a value which is a multiple of said reference voltage, the multiple corresponding to the number of cells of the battery. The second current of the voltage-to-current converter flows through the second resistor which is arranged in series with the second input terminal of the comparator and which is connected to the battery. Thus, a correction voltage is added to the battery voltage so as to enable the nearly-empty indication to be adapted to the cell type, which correction voltage is adjustable by the appropriate choice of the value of the second resistor. When it is assumed that the voltage indicator, particularly the reference voltage sources of this indicator, is constructed as an integrated circuit, the voltage indicator in accordance with the invention offers the possibility of defining the nearly-empty indication voltage by means of two external resistors.
If the choice is only between a battery having one cell or two cells in series the voltage indicator can be implemented by using a further comparator having first and second inputs coupled respectively to the first current output and to bias voltage, and an output for supplying the switching signal. Depending on the value of the first resistor the output signal of the further comparator assumes either of two values. For the one value the reference voltage is switched to a reference value corresponding to a single cell. For the other value the reference voltage is switched to the double reference value corresponding to two cells in series. It is alternatively possible to switch from the full reference voltage to half the reference voltage.
If a distinction is to be made between three or more cells in series, the first current of the voltage-to-current converter is compared with a plurality of threshold values and the reference voltage is switched between three or more values which are multiples of each other.
Switching over of the reference voltage can be effected by choosing from a plurality of reference voltages by means of a selector in response to the switching signal. Alternatively, the reference voltage can be switched over by attenuating a reference voltage by a factor of two, three or more by means of a voltage divider having a switchable voltage dividing factor.
The second resistor, which defines the correction voltage, further has the advantage that in combination with a capacitor it can serve as a smoothing filter for possible ripple voltages on the battery voltage to be measured.
The invention can be used in apparatuses having rechargeable batteries or having non-rechargeable (primary) batteries, in which it is desired to have an indication or to show that the batteries are nearly empty. The voltage indicator may activate a visual or acoustic signal which warns the user that the battery is nearly empty. The voltage indicator may also form part of a complex battery management system which controls and monitors the charging and discharging process and which, for example, inhibits further discharging of the battery when the battery is nearly empty. Examples of apparatuses of this kind are in the fields of personal care such as shavers and toothbrushes, of telecommunication such as portable phones, of computers such as laptops and organizers, and of portable audio and video equipment.
REFERENCES:
patent: 5705913 (1998-01-01), Takeuchi et al.
patent: 5814995 (1998-09-01), Tasdighi
patent: 0653826 (1995-05-01), None
patent: 7-318621 (1995-12-01), None
Patent Abstracts of Japan, vol. 1996, No. 4, Apr. 30, 1996.
Bartlett Ernestine C.
Tso Edward H.
U.S. Philips Corporation
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