Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-11-21
2002-06-04
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021100, C363S097000, C363S131000
Reexamination Certificate
active
06400582
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to power conversion and, in particular, to DC/DC power converters having improved topologies that provide high efficiency with low output impedance. More particularly, the present invention relates to a dual forward power converter and a method of operation thereof.
2. Description of the Related Art
Regulated DC power supplies are typically needed for most analog and digital electronic systems. Two major categories of regulated DC power supplies are linear power supplies and switching power supplies. Generally, in linear power supplies, a transistor (operating in its active region) is connected in series with an input voltage source and the voltage drop across the transistor is automatically adjusted to maintain an output voltage at a desired level.
In switching power supplies, transformation of DC voltage from one level to another is accomplished typically by means of DC/DC converter circuits, such as step-down (buck) or step-up (boost) converter circuits. Solid-state devices, such as transistors, are operated as switches (either completely ON or completely OFF) within these switching converters. Since the power devices are not required to operate in their active region, this mode of operation results in lower power dissipation. Furthermore, increasing switching speeds, higher voltage and current ratings of these power devices are some of the advantages that have increased the popularity of switching power supplies.
It is not uncommon for switching power supplies to have a switching frequencies of 100 kHz or higher. The high switching frequencies permit the components utilized in construction of the power converter, such as capacitors, inductors and transformers, to be physically small. The reduction in the overall volume (size) of the converter that results is desirable to the users of such supplies. Another important attribute of a power supply is its thermal efficiency. The higher the efficiency, the less heat that is dissipated within the supply, and the less design effort, volume, weight, and cost that must be devoted to remove this heat.
Distributed power systems are increasingly being utilized in modern systems, for example, due to different power levels requirements in a power consuming system. Furthermore, with the increasing popularity and utilization of complementary metal oxide semiconductor (CMOS) technologies in present and future projected electronic systems, highly dynamic loading conditions is a common problem encountered by power systems. This highly dynamic loading conditions necessitates a low impedance power distribution network driven by low impedance power supplies.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved low output impedance DC/DC power converter.
It is another object of the invention to provide a high efficiency dual forward power converter.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a dual forward power converter is disclosed. The dual forward power converter includes first and second power transformers, where each of the power transformers has first and second primary windings of opposite polarity and a secondary winding. The dual forward power converter also includes first and second switches that alternatively couple the first primary windings of the first and second power transformers, respectively, to a source of input power. The first and second switches, in an advantageous embodiment, are Field Effect Transistors (FETs) and are driven in a complementary manner with substantially 50% duty cycles. The dual forward power converter further includes first and second coupling capacitors that couple the second primary windings of the first and second power transformers to the second and first switches, respectively, and are utilized to reset the first and second power transformers with minimum losses. In a related embodiment, the dual forward power converter includes third and fourth switches that are coupled to the secondary windings of the second and first power transformers, respectively, and are driven in a substantially identical manner as the second and first switches, respectively.
The present invention discloses a novel low output impedance power converter. The present invention recognizes that the utilization of the coupling capacitors, in contrast to prior art power converters employing devices, such as diodes, improves the overall efficiency of the power converter due to their “lossless” nature. The improved efficiency is due to the substantial elimination of energy losses, i.e., thermal energy, that are a consequence when devices such as diodes are utilized. Additionally, unlike diodes, the current can flow from both directions into the coupling capacitors during their charging and discharging cycles, resulting in zero-voltage-switching (ZVS) during the turn ON of the first and second switches. Furthermore, since the coupling capacitors can charge and discharge in both directions, the currents through the first and second switches are the combination of a primary winding current and the current through a coupling capacitor. Consequently, since the coupling capacitors are also contributing to the current flow through the switches, a smaller input capacitor is required.
The foregoing description 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 matter 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.
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“Low Output Impedance DC/DC Converter”;IBM Technical Disclosure Bulletin, Sep. 1994, vol. 37, No. 09.
Hemena William
Ngo Thai Quoc
Strand Scott Douglas
Bracewell & Patterson LLP
International Business Machines - Corporation
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