Electricity: power supply or regulation systems – Input level responsive – Using a linearly acting final control device
Reexamination Certificate
2000-02-23
2001-07-10
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Input level responsive
Using a linearly acting final control device
Reexamination Certificate
active
06259239
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power electronics and, more specifically, to a circuit for conditioning an average AC signal for use with a controller adapted to receive peak input signals, a method of operation thereof and a power supply employing the circuit or the method.
BACKGROUND OF THE INVENTION
Power supplies and especially power converters are an important and rapidly expanding technology that impacts a broad range of applications including computer systems and telecommunication environments. A power converter is a power processing circuit that converts an input voltage waveform into a specified output voltage waveform. In many applications requiring a stable and well-regulated output, switched-mode power converters are frequently employed to advantage. A typical power converter operating in a switched-mode fashion may include an EMI filter, an inverter, a transformer having a primary winding coupled to the inverter, an output circuit coupled to a secondary winding of the transformer, an output filter and a controller. The inverter generally includes a power switch, such as a field-effect transistor (FET), that converts an input voltage to a switched voltage that is applied across the transformer. The transformer generally transforms the voltage to another value. The output circuit generates a desired voltage at the output of the converter and typically includes an output capacitor that smooths and filters the output voltage for delivery to a load.
Power converters must sometimes accommodate severe transient conditions and operate within a specific range of input voltages. During a start-up mode, a transient condition of particular interest occurs at the time that an input voltage is first applied to a power converter. If an AC power source is applied at a time near its peak voltage, a large inrush current transient may cause damage to components of the power converter. This condition may be avoided by the use of an inrush limiting resistance that limits the maximum value of the inrush current transient to an acceptable level. The inrush resistance, however, must be removed from the circuit during normal operation to preserve the overall efficiency of the power converter. Ideally, the inrush resistance should be placed on the input voltage side of the power converter between the EMI filter and the inverter to protect the power converter from the transient condition and to prevent EMI noise from emitting out into the source of input voltage by bypassing the EMI filter.
The power supply controller typically monitors the input voltage to determine if and when the input voltage has reached a required value both to start and to sustain the operation of the power converter. The ideal position for monitoring the input voltage is between the EMI filter and the inrush resistor. The controller typically monitors the peak value of the AC input voltage to determine when the required value is reached. If the inrush resistance is placed at the input of the power converter, (i.e., before the EMI filter) to maximize component protection, the peak of the AC input voltage waveform may be sufficiently distorted or reduced on the output side of the inrush resistance to cause the controller to misinterpret the magnitude of the AC input voltage. Such a misinterpretation may cause the power converter either not to start or to sustain its operation.
Accordingly, what is needed in the art is a system and method employable with a peak-mode controller to accommodate average signals thereby overcoming the deficiencies of the prior art, such as those described above.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides, for use with a controller adapted to receive a signal representing a peak input signal a conditioning circuit, a method of operation thereof and a power supply employing the circuit or the method. In one embodiment, the conditioning circuit includes: (1) a comparator circuit that compares an average input signal to a reference signal and develops therefrom a comparison signal representing the average input signal, and (2) a switching circuit, coupled to the comparator circuit, that transforms the comparison signal into a format employable by the controller.
The present invention, in one aspect, introduces the broad concept of conditioning and transforming a signal format dictated by one type of circuit with system constraints into a signal format adapted for the operation of another type of circuit, such as a controller. This transformation allows the controller to remain largely unchanged, which is highly advantageous. Often, a controller that is microprocessor-based finds extensive use in a variety of applications. Over time, the extensive use of the controller generates a high level of confidence that the controller is reliable and therefore creates a reluctance toward making modifications to the controller. Additionally, such modifications may be costly, especially in the area of testing wherein some level of reliability must again be at least initially established. The present invention recognizes the advantages associated with such controllers and provides a circuit that allows the controller to be applied for other purposes or in different environments.
In one embodiment of the present invention, the comparison signal assumes a first level when the average input signal is below the reference signal. Additionally, the comparison signal assumes a second level when the average input signal is above the reference signal. The first level may represent a logical “zero” or false response for the comparison of the two inputs to the comparator circuit. The second level may then represent a logical “one” or true response. The average input signal being below or above the reference signal could be representative of a condition wherein the amplitude of the AC power signal is below or above a threshold value that determines whether the power supply should be operational. Of course, the meaning of these two levels may be reversed as an application dictates.
In one embodiment of the present invention, the comparison signal switches between the first and second levels as a function of the comparison signal and the switching circuit. This characteristic allows the comparison signal to be synchronized to the timing and polarity needs of the controller.
In one embodiment of the present invention, the switching circuit transforms the comparison signal by intermittently grounding the average input signal. By grounding the average input signal, the switching circuit may thus develop a signal employable by the controller.
In one embodiment of the present invention, the switching circuit employs a zero crossing signal. A zero crossing signal may be used for timing purposes to synchronize the comparison signal. Often the zero crossing signal is correlated with the zero crossings of an AC power waveform. However, another waveform having periodic or aperiodic intervals may also be used as an application may dictate.
In one embodiment of the present invention, the switching circuit comprises an error amplifier and a switch. The error amplifier and the switch work in concert to establish the timing with respect to the needs of a particular controller. The error amplifier allows a timing signal to be referenced to another signal to more precisely control the operation of the switch. Of course, other types of circuits may be employed in the switching circuit and still well within the broad scope of the present invention.
In one embodiment of the present invention, the switching circuit comprises at least one semiconductor device. The semiconductor device may be a transistor, such as a metal oxide semiconductor (MOS) field effect transistor. In an alternate embodiment, the semiconductor device may be a bipolar transistor or a diode. Of course, the switching circuit is not limited to any particular device.
The foregoing has outlined, rather broadly, preferred and alternative features of the
Nguyen Matthew
Tyco Electronics Logistics AG
LandOfFree
Circuit and method for conditioning an average AC signal for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit and method for conditioning an average AC signal for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit and method for conditioning an average AC signal for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2488204