Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Patent
1995-06-06
1997-05-27
O'Shea, Sandra L.
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
320 48, 340636, 324426, G01R 3136, G01R 1340
Patent
active
056335920
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a circuit arrangement for a charge status indicator of a primary battery or a secondary battery (rechargeable accumulator) in an electrical appliance as, for example, a battery-powered shaving apparatus.
Voltage-dependent battery monitoring devices are known in the art which detect the charge status of the battery during operation of the appliance in one or several stages, indicating the charge status permanently or intermittently and/or providing an information of a specified charge status after the appliance is turned off.
Indicating devices which indicate the charge status permanently in several stages after the appliance is turned off require high technical complexity (microcontroller) and are accordingly expensive. On the other hand, inexpensive indicators draw such a high current that a permanent indication after the appliance is turned off is possible for only a short period because its drain on the battery.
Further, from the journal EDN--Electrical Design News, Vol. 35 (1990), Aug. 20, No. 17, Newton, Mass., US, page 151, an indicating device is known in which the battery voltage is applied to a voltage divider, and a voltage tapped in this voltage divider is fed to a microcontroller input. This microcontroller receives further voltage values to provide a comparator with a hysteresis, as well as an external oscillation frequency intended to operate, where applicable, a light-emitting diode serving as an indicating device. This indicating device is rendered active when the battery voltage has dropped to a critical value. In this prior art, the power consumption of the indicating device is lowered by operating the indicating device intermittently with the external oscillation frequency.
It is an object of the present invention to provide a circuit arrangement for a charge status indicator which is of a straightforward and inexpensive construction and draws such a low current that its connection to the battery can be always maintained also after the appliance is turned off.
SUMMARY OF THE INVENTION
This object is accomplished by a circuit arrangement for indicating the charge status of a battery in an electrical appliance, in which the circuit arrangement includes a voltage comparator with hysteresis for detecting the battery voltage, as well as an oscillator driven by the voltage comparator, and an indicating device. The oscillator oscillates when the voltage is above a first threshold voltage and switches the indicating device to an active condition. The oscillator is blocked when the voltage is below a second threshold voltage and switches the indicating device to the passive condition, with the absolute value of the first threshold voltage being greater than the absolute value of the second threshold voltage.
Particularly advantageously, such an arrangement can be used in a liquid crystal display (LCD) serving as indicating device on which a symbol is printed which is visible in the passive condition of the indicating device, signaling to the user that the accumulator (secondary battery) need to be recharged or that the battery (primary battery) need to be replaced.
Further advantageous embodiments are indicated in the subclaims and the description.
An embodiment of the present invention will be described in more detail in the following with reference to the accompanying drawings. In the drawings ,
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an embodiment of the present invention;
FIG. 2 shows, by way of example, an imprint on a liquid crystal display which is visible in the passive condition; and
FIG. 3 shows signal waveforms in the circuit arrangement of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, the input of a voltage comparator K is applied to the junction of a voltage divider comprised of two resistors R1/R2 connected in parallel to a battery B. This battery B is, for example, a two-cell accumulator of an electric shaving apparatus. The comparator K is a commercially available component (voltage detector), comp
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Braun Aktiengesellschaft
Mah Raymond Y.
O'Shea Sandra L.
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