Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-09-28
2001-01-23
Lefkowitz, Edward (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C324S522000, C361S018000
Reexamination Certificate
active
06177875
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
MICROFICHE APPENDIX
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to voltage sensing circuitry, and more particularly to threshold window circuits which determine whether a measured voltage lies within a given voltage range.
Window comparator circuits have long been used in various electronic industries to determine whether a measured parameter is within a window bound by upper or lower limits. One particularly useful application for window sensing is in voltage sensing circuits which determine if a voltage between two nodes is within a window. Typical circuits of this type generate a signal when a measured voltage is within the window.
One well-known voltage window sensing circuit includes, among other circuitry, two comparators, two voltage dividers (e.g., four resistors) and an output pull-up resistor. Unfortunately, while being sufficiently accurate, a large parts count renders these types of comparators relatively expensive and requires significant printed circuit board space. For these reasons, when costs and circuit board space need to be minimized, comparators of this well-known type are unsatisfactory.
As is evident from the foregoing, a need exists for a cost-effective, space-minimizing voltage-window sensing circuit capable of preserving the functionality of the common window comparator circuit at a relatively low cost and which requires minimal circuit board space.
BRIEF SUMMARY OF THE INVENTION
It has been recognized that a simple arrangement including two Zener diodes, two “digital” transistors (two bipolar junction transistors, each transistor having resistors situated across its base-emitter junction and in series with its base) and a current sensor can be constructed which has a small parts count, is extremely inexpensive, is extremely reliable, and requires relatively little circuit board space. To this end, one inventive embodiment comprises first and second Zener diodes which are chosen such that their first and second breakdown voltages, respectively, essentially define the lower and upper limits of a voltage window needed in a given application.
The Zener diode cathodes are linked to a first node and the first and second Zener diode anodes are linked to first and second bases of the first and second transistors, respectively. Negligible amounts of current flow into these bases until the respective Zener diode voltages are exceeded. The collector of the second transistor is linked to the first node and its emitter is linked to the second node. The indicator is linked in series with the first transistor between the first and second nodes. When either transistor conducts, current passes from the first node to the second node. The current sensor may be any sensing element, such as a light emitting diode, an opto-coupled or magnetically-coupled circuit, an LED, etc.
When so constructed the circuit defines three voltage ranges between the first and second nodes, a first range below the lower voltage window limit, a second range within the window and a third range above the upper voltage window limit. To this end, when voltage between the first and second nodes is below the lower window limit (i.e., in the first range), neither Zener diode conducts, corresponding transistors are off and hence no current is sensed by the current sensor.
When the voltage between the first and second nodes exceeds the lower window limit but not the upper window limit, the first Zener diode breaks down causing the first transistor to conduct. Current passing through the first transistor is sensed by the sensor which indicates a voltage within the voltage window.
When the voltage between the first and second nodes exceeds the upper window limit both the first and second Zener diodes break down and corresponding transistors conduct. Assuming the current sensor has some resistance, all current passes through the second transistor and not the first such that the current sensor will not sense a current and will not indicate a voltage within the window.
Thus, one object is to determine if a voltage between the two nodes is within a voltage window. Another object is to achieve the aforementioned object inexpensively. This is accomplished by configuring a circuit with a reduced parts count.
Yet another object is to achieve the aforementioned objects while requiring only minimal circuit board space. This object also is accomplished by configuring a circuit with a reduced parts count.
In a preferred embodiment of the invention a resistor can be linked in series with the first transistor between the first and second nodes to ensure that no current passes through the first transistor when the voltage between the first and second nodes is above the upper voltage window limit.
In yet another embodiment of the present invention, a second resistor can be linked between the second collector and the first node such that the node between the second collector and second resistor becomes a voltage dividing node and wherein the first resistor is then linked between this dividing node and the first collector. Preferably the second resistor resistance is much greater than the first resistor's resistance (e.g., 10 to 1000 times the first resistor resistance). In fact, in at least one embodiment, the second resistor may be altogether removed.
The foregoing and other objects, advantages, and aspects of the present invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown, by way of illustration, a preferred embodiment of the present invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must also be made to the claims herein for properly interpreting the scope of this invention.
REFERENCES:
patent: 4819116 (1989-04-01), Piteo
patent: 4999730 (1991-03-01), Pickard
patent: 5418834 (1995-05-01), Byatt et al.
patent: 5440234 (1995-08-01), Kondo
patent: 5604785 (1997-02-01), Pryor et al.
patent: 5903140 (1999-05-01), Acatrinei
patent: 5978235 (1999-11-01), Lampinen
Horn John J.
Jaskolski Michael A.
Lefkowitz Edward
Rockwell Technologies LLC
Walbrun William R.
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