Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Reexamination Certificate
2000-03-13
2002-10-22
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
C307S129000
Reexamination Certificate
active
06469883
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to power failure detection, and more particularly to early AC power detection.
BACKGROUND OF THE INVENTION
The use of alternating current (AC) to power electronic devices is very well known in the art. When AC power fails, the voltage drops to zero volts within a few milliseconds. The devices may use the time between the detection of the AC power failure and the drop to zero volts to perform power down operations, such as saving important system information.
FIG. 1
illustrates a conventional method of detecting an AC power failure.
FIG. 1
illustrates a sample AC power waveform
102
with a periodicity of t
2
. Within one period, the waveform
102
has two zero-crossings, at t
1
, and t
2
. Knowing the periodicity of the waveform
102
, its zero-crossings may be anticipated. Thus, at times t
1
, t
2
and t
4
, the waveform
102
will cross zero volts if the AC power has not failed. The conventional method thus uses a zero-crossing detection circuit to detect whether or not the waveform
102
crosses zero at the anticipated times, t
1, t
2
, and t
4
.
For example, assume that the AC power waveform
102
fails at t
3
. At t
4
, the zero-crossing detection circuit detects if the waveform
102
crosses zero volts. Since the AC power waveform
102
has failed, it does not. Thus, the AC power failure is detected at t
4
. A signal indicating the failure may then be sent to initiate the power down operations for the device.
However, under the conventional method, the AC power failure is not detected until time t
4
, although the AC power failed at the earlier time, t
3
. Thus, there is a lag time between the actual AC power failure and its detection. The device is thus not able to use this time period to perform more extensive power down operations.
Accordingly, there exists a need for an improved method and apparatus for AC power failure detection. The method and apparatus should be easy to implement and able to detect an AC power failure earlier than conventional methods. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for alternating current (AC) power failure detection. The method includes amplifying an AC power waveform, where the amplified waveform is asserted when the AC power waveform is in a vicinity of a zerocrossing and negated at all other times; initiating a counter when the amplified waveform is asserted; and determining if the counter equals or exceeds a reference number, where the counter being equal or exceeding the reference number indicates an AC power failure. The present invention converts an AC power signal to a near digital signal, where the near digital signal is asserted when the AC power signal is in the vicinity of a zero-crossing and negated at all other times. When the near digital signal is asserted, a counter in a controller begins counting, and ends the counting when the near digital signal is negated. If the counter equals or exceeds a reference number before the near digital signal is negated, then a failure of the AC power signal is detected. A signal indicating the AC power failure is then output by the controller to initiate power down operations. By measuring the length of time the AC power signal remains in the vicinity of a zero-crossing, a failure of the AC power can be detected earlier than with conventional methods. This allows more time to perform power down operations.
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patent: 4642616 (1987-02-01), Goodwin
patent: 4855722 (1989-08-01), Mostyn et al.
patent: 5285452 (1994-02-01), Wee et al.
patent: 5568398 (1996-10-01), Trainor
Coactive Networks, Inc.
Leja Ronald W.
Sawyer Law Group LLP
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