Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
2000-11-09
2001-11-13
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S021040
Reexamination Certificate
active
06317341
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power conversion and, more specifically, to a switching circuit, a method of operation thereof, and a single stage power factor corrector employing the switching circuit or the method.
BACKGROUND OF THE INVENTION
A power converter is a power processing circuit that converts an input voltage or current source waveform into a specified output voltage or current waveform. A switched-mode power converter is a frequently employed power converter that converts an input voltage waveform into a specified output voltage waveform. A power factor corrector is one example of a switched-mode power converter that is typically employed in off-line applications wherein power factor correction at the input and a stable, regulated voltage at the output are desired.
Power factor correctors generally employ a two stage topology, including a boost converter and a DC-DC converter. The boost converter generally includes a boost inductor and a power switch coupled thereto. The boost converter further includes a rectifying diode coupled to a node between the boost inductor and the power switch. The boost converter still further includes an output capacitor coupled across an output of the boost converter. The output capacitor is usually large to ensure a constant output voltage. The boost converter generally provides adequate power factor correction. Power factor is defined as a ratio of the actual power delivered to the load to a product of the voltage and current at the input of the boost converter.
An output voltage of the boost converter is always greater than the input voltage (e.g., a voltage of the AC source). The DC-DC converter, therefore, is employed to scale the output voltage of the boost converter down to a voltage required by a load. The DC-DC converter may employ any of the commonly known topologies, depending on such factors as the amount of power to be processed and the required efficiency.
The use of the boost converter in combination with the DC-DC converter generally results in lower efficiencies due, in part, to losses experienced in both the boost converter and in the DC-DC converter. A single stage power converter was developed to reduce the number of stages required to perform power factor correction and to provide a DC output voltage of a level employable by the load. Available single stage power converter topologies, however, require the use of a post regulator to maintain output voltage regulation. The post regulator stage, however, is also subject to losses and may reduce the overall efficiency of the single stage power converter employing the post regulator.
Accordingly, what is needed in the art is a switching circuit and method of processing power for a power converter that overcomes the deficiencies of the prior art.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a switching circuit, a method of processing power, and a single stage power factor corrector employing the switching circuit or the method. In one embodiment, the switching circuit includes: (1) a power switch coupled to a primary winding of a transformer; and (2) an active clamp coupled to the power switch. The active clamp includes: (2a) series-coupled first and second capacitors, coupled across the power switch and the primary winding, having opposing polarities thereacross, and (2b) a clamping switch coupled to a node between the series-coupled first and second capacitors. The clamping switch opens to allow energy stored in the first capacitor to be transferred to an output of the power converter via the second capacitor. The clamping switch closes to allow energy stored in the second capacitor to be transferred to the output.
The present invention introduces, in one aspect, the concept of coupling first and second capacitors across a power switch and primary winding of a power converter. The first and second capacitors are oriented such that their polarities are opposing. Energy stored in the first capacitor may be transferred to an output of the power converter via the second capacitor when a clamping switched coupled to the first and second capacitors is open. Energy stored in the second capacitor may then be transferred to the output when the clamping switch is closed.
In one embodiment of the present invention, the switching circuit may be employed as a part of an AC-DC single stage power factor corrector, and the first capacitor is substantially larger than the second capacitor. The first capacitor may store the energy required to maintain output regulation during a trough in the AC input power. In an alternative embodiment, the switching circuit may be employed as a part of a DC-DC power converter, and the first and second capacitors may be about the same size.
In one embodiment of the present invention, the active clamp includes an input inductor. The second capacitor and the input inductor may thus form a resonant circuit to regulate an input current of the power converter. In a related embodiment, the input inductor and the first and second capacitors cooperate to deliver an adequate amount of energy to the primary winding to maintain output regulation of the power converter. In another related embodiment, the input inductor and the first and second capacitors cooperate to allow the input inductor to operate with continuous current therethrough.
In one embodiment of the present invention, the active clamp further includes a zero voltage switching circuit, coupled across the clamping switch, that enables zero voltage switching of the clamping switch. The zero voltage switching circuit may include: (1) series-coupled first and second diodes; (2) an auxiliary winding of the transformer coupled to a node between the series-coupled first and second diodes; and (3) an auxiliary inductor and an auxiliary capacitor coupled in series with the auxiliary winding. In an alternative embodiment, the zero voltage switching circuit may include: (1) a first diode; (2) an auxiliary winding of the transformer coupled in series to the first diode; (3) a second :L diode coupled between the auxiliary winding and a node between the clamping switch and the first capacitor; and (4) a series-coupled auxiliary inductor and auxiliary capacitor coupled across the second diode.
In one embodiment of the present invention, the power switch and the clamping switch are complementarily switched. The power switch may be conducting during a D portion of a duty cycle, while the clamping switch may be conducting during a (1-D) portion of the duty cycle.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features 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 can readily use the disclosed conception and specific embodiment as a basis for designing or modifying 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: 5303138 (1994-04-01), Rozman
patent: 5883795 (1999-03-01), Farrington
patent: 6061254 (2000-05-01), Takegami
patent: 6069803 (2000-05-01), Cross
Fraidlin Simon
Polikarpov Anatoliy
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