Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1994-03-15
1996-07-16
Wong, Peter S.
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
340661, H01M 1048, G01N 27416, G08B 2100
Patent
active
055370241
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a circuit arrangement to detect a voltage, including a voltage divider having applied to its divider node the input of a voltage detector which comprises a Schmitt-Trigger with reference voltage and an output driver, with the output of the voltage detector being connected to the positive potential of the voltage.
Voltage detectors comprising internally a Schmitt-Trigger with reference voltage and an output driver are commercially available devices. FIG. 4 illustrates the wiring of such a voltage detector VD when a specified voltage, for example, the voltage of two serially connected battery cells or accumulator cells (B), is to be detected which is greater than the internal reference voltage of the voltage detector VD. In this event, a voltage divider comprised of resistors R1 and R4 is connected in parallel with the battery B, and the junction of the two resistors R1 and R4 is connected to the IN input of the voltage detector VD. The OUT output of the voltage detector VD is applied to the positive potential of the battery B through a resistor R2. The voltage divider R1/R4 is so dimensioned that the internal reference voltage (2.1 volts, for example) will be present at the IN input of the voltage detector VD when the voltage to be detected (2.3 volts, for example) is present at the battery B. When the battery voltage drops below-this value, the output of the voltage comparator VD will go from "high" to "low".
However, such commercially available voltage detectors have the disadvantage of having a hysteresis of, for example, 0.1 volts. This means that with the battery voltage falling the output of the voltage detector VD will go from "high" to "low" when the voltage at the input reaches 2.1 volts (correspondingly 2.3 volts at the battery), however, with the battery voltage rising (for example, when the battery is being recharged), the output of the voltage detector VD will not reverse its state until the voltage at the input reaches 2.2 volts (2.1 volts+0.1 volts). This is not satisfactory for some applications requiring an accurate voltage detection as, for example, when it is desired to detect a specified voltage accurately on a battery during both discharging and charging of the battery.
It is therefore an object of the present invention to configure a circuit arrangement of the type initially referred to in such a manner as to permit a hysteresis-free detection of a specified voltage.
According to the present invention, this object is accomplished in that the output signal of the voltage detector is applied to the base of a first transistor, that the collector-emitter circuit, together with a series-connected capacitor, is connected in parallel with the voltage to be detected, that the junction of the capacitor and the first transistor is connected to the input of the voltage detector through a first resistor, and that the output of the voltage detector is further applied to the input of a component delivering different output signals in dependence upon whether its input receives a constant signal level or a varying signal level.
When it is desired to detect several specified voltages using the same voltage detector or to be able to vary the value of the voltage to be detected, the resistor of the first voltage divider connected to reference potential is comprised of a second voltage divider to which an integrating capacitor is connected in parallel and whose divider node receives a square-wave voltage whose pulse duty factor is variable.
Further advantageous embodiments of the present invention will become apparent from the other subclaims and the subsequent description.
Embodiments of the present invention will now be described in more detail in the following with reference to the accompanying drawings, in which:
FIG. 1 is a schematic diagram showing a circuit arrangement for detecting a specified voltage value on a battery;
FIGS. 2 and 3 are schematic diagrams showing circuit arrangements for detecting several voltage values using a single voltage detector; and FIG. 4 is a s
REFERENCES:
patent: 3670246 (1972-06-01), Gately
patent: 4429236 (1984-01-01), Nitschke
patent: 4445090 (1984-04-01), Melocik et al.
patent: 4758772 (1988-07-01), Lang
patent: 4829290 (1989-05-01), Ford
patent: 4906055 (1990-03-01), Horiuchi
Braun Aktiengesellschaft
Law Patrick B.
Wong Peter S.
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