Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By presence or absence pulse detection
Reexamination Certificate
1998-07-16
2001-07-03
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By presence or absence pulse detection
C327S021000, C327S037000, C327S074000, C340S648000
Reexamination Certificate
active
06255860
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power conversion and, more specifically, to a pulse detection circuit, a method of operation thereof and a fan assembly test circuit employing the same.
BACKGROUND OF THE INVENTION
Single or multiple brushless DC cooling fans are widely employed in AC-DC, DC-DC and DC-AC power conversion systems to remove the heat generated by semiconductor switching devices, various magnetic components and other circuit components that are part of the power conversion equipment. Typically, the cooling fan allows the power conversion equipment to be operated at higher temperatures. As a result, the proper operation of the cooling fan plays an important role in overall power system reliability and lifetime.
In most applications, a speed feedback signal from the fan is employed to govern a fan alarm or a system-wide safety interlock. Whenever the speed feedback signal is not detected, the alarm is tripped or the power conversion system is shut down to protect “on-board” circuit components of the power conversion system from excessive heating. In the normal course of assembly and operation, a fan alarm and possible shutdown may be caused by one or all of the following: a broken fan power cable(s), a shorted fan power cable, a loose fan cable connection, an incorrect wiring of the fan power cable, a malfunction of the fan's internal speed sensor, a problem with the fan's power supply and a malfunction of the fan's speed detection circuit.
Generally, after the fan has been assembled into the power conversion system, it becomes difficult (and sometimes impossible) to inspect the fan visually to determine whether it is operating properly or to identify the nature of a malfunction. Alternative, non-visual inspection methods typically require complex inspection/detection circuitry that increase the fan's material and manufacturing costs. The primary reason for the complexity of the inspection/detection circuitry is that the fan speed feedback signal can either be a variable frequency alternating signal, e.g., a 60 Hz to 120 Hz pulse train, or a constant voltage signal, e.g., a 0V or 5V signal.
The form of the fan feedback signal depends on the status of the fan. In the case of a brushless DC fan, the fan feedback signal assumes a constant voltage when the fan is stalled or not running. During normal operation, a pulse train with a peak amplitude of e.g., 5V, is provided at the fan's feedback signal terminal.
The different forms and signal levels that might be encountered results in existing on-board fan detection circuits that are quite cumbersome and complex. Accordingly, what is needed in the art is an improved fan operation detection circuit that overcomes the above-described limitations.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a pulse detection circuit, a method of operation and a fan assembly test circuit employing the same. In one embodiment, the pulse detection circuit includes a charge pump that receives an input signal and varies a charge in a charge storage device based on the input signal. A level detector, coupled to the charge pump, makes a comparison among a voltage across the charge storage device and first and second reference voltages. Finally, a signaling circuit, coupled to the level detector, generates an output signal based on the comparison and indicating an existence of the pulse. The pulse detection circuit may be part of an overall fan assembly test circuit that further includes a socket adapted to receive an input signal from a cooling fan under test.
In one embodiment of the present invention, the input signal is a fan speed feedback signal. Under normal operating conditions (fan operating normally), the feedback signal is a variable frequency alternating signal. It should also be noted that the present invention is not limited to determining the operational status of a fan and may also be advantageously employed where detection of a variable frequency alternating signal is required.
In one embodiment of the present invention, the signaling circuit further includes a current indicator that indicates a state of the level detector. In yet another embodiment, the current indicator is a light emitting diode (LED). Alternatively, audible devices, such as buzzers, may also be advantageously employed. Those skilled in the art should readily appreciate that any device capable of detecting current flow and generating a signal in response thereto is well within the broad scope of the present invention.
In one embodiment of the present invention, the level detector includes first and second operational amplifiers (op-amps) configured as open-collector comparators. In an embodiment to be illustrated and described, the first and second reference voltages, which are derived from taps of a voltage divider network, are coupled to the inverting nodes of the second comparator and the non-inverting node of the first comparator, respectively.
In one embodiment of the present invention, the charge storage device is a capacitor. However, it should also be readily apparent to those skilled in the art that the charge storage device is not only limited to capacitors, other energy storage devices may also be advantageously employed and are within the broad scope of the present invention.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the concepts and the specific embodiments disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 3653018 (1972-03-01), Budrys
patent: 4581544 (1986-04-01), Feldman
patent: 4845379 (1989-07-01), Carlsten
Chavez Frank H.
He Jin
Jorgenson Greg P.
Callahan Timothy P.
Lucent Technologies - Inc.
Nguyen Minh
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