Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-09-30
2001-03-27
Lieu, Julie (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S661000, C340S635000, C340S663000, C361S086000, C323S284000, C363S017000, C363S019000
Reexamination Certificate
active
06208258
ABSTRACT:
TECHNICAL FIELD OF INVENTION
This invention relates to power supply circuitry operating from AC mains, and to a circuit which determines whether the AC mains voltage is below or above a predetermined set point.
BACKGROUND OF THE INVENTION
Electrical power from AC mains is used to provide a source of energy for numerous devices. Unfortunately, the electrical power provided by AC mains may be interrupted either partially (e.g., brown out) or wholly (e.g., power failure). Recognizing this problem, prior art power supply circuits have included voltage level detection and time period detection so as to determine when power is lost and whether the duration is temporary or more permanent. These prior art circuits either required a separate Vcc power supply or used excessive amounts of power from the AC mains. Accordingly, there is a strong need in the art for a simple, inexpensive and energy efficient manner for detecting the loss of the AC mains in a power supply circuit.
SUMMARY OF THE INVENTION
The present invention provides a novel circuit and method for determining whether an AC mains voltage is below or above a predetermined set point. Initially the circuit rectifies the voltage of the AC mains and reduces the voltage with a voltage divider. The rectification of the AC voltage of the AC mains allows the circuit of the present invention to detect both the positive half and the negative half of the AC mains voltage signal. A level sensitive trigger circuit receives the reduced voltage. When the level sensitive trigger circuit senses that the voltage is above the predetermined set point, the level sensitive trigger circuit fires by generating a pulse which is conveyed to a comparator circuit by an isolator such as a photo coupler. The comparator circuit determines a duration since a pulse has been generated and indicates a power failure when the duration exceeds certain period of time.
The method and circuit of the present invention eliminates the need to have either a separate Vcc power supply for the circuit in relation to the AC mains, or the need to draw excessive amounts of power from the AC mains. Additionally, since the signal indicating whether the AC mains has been interrupted is separated from the AC mains by an isolator, the need to separately isolate this signal from the AC mains is eliminated. Accordingly an improved circuit for detecting failure of an AC mains is provided by the present invention.
To accomplish the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
The present invention will now be described more fully with reference to the accompanying drawings in which several embodiments of the invention are shown. The present invention, however, may be embodied in many different forms and should not be construed as limited to the embodiment shown. The several embodiments described are provided.
REFERENCES:
patent: 3947752 (1976-03-01), Morgan
patent: 4524411 (1985-06-01), Willis
patent: 5555483 (1996-09-01), Pressman et al.
patent: 5579197 (1996-11-01), Mengelt
patent: 6108219 (2000-08-01), French
Core Technology Inc.
Lieu Julie
Renner , Otto, Boisselle & Sklar, LLP
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