Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-06-21
2001-06-12
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S097000
Reexamination Certificate
active
06246592
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
The invention relates generally to power supplies, and more particularly to cascaded power converters.
Cascaded power converter arrangements including two or more power converters are well known. The cascaded arrangement of conventional converter topologies is dependent upon the requirements of a particular application. Cascaded converters are most commonly used to provide large input to output voltage conversion ratios (step-up or step-down) or for providing multiple functions that are not feasibly implemented in a single converter.
In one conventional cascaded arrangement, a first buck converter is followed by a second buck converter. A buck converter is characterized by its voltage step-down ratio wherein the output voltage is lower than the input voltage to thereby produce a higher average output current. The cascaded buck converters produce an even larger voltage step-down ratio and a correspondingly greater average output current.
Another known arrangement utilizes cascaded boost PFC converters. A boost converter is characterized by its voltage step-up ratio wherein the output voltage is higher than the input voltage but produces a lower average output current. The cascaded boost converters produce an even larger voltage step-up ratio and a correspondingly smaller average output current.
In yet another known arrangement, a non-isolated boost converter is followed by one of several possible post regulator circuits, such as a buck or isolated buck derived converter, to provide for independently regulated auxiliary output voltages in single or multiple output converters.
With the proliferation of new semiconductor device families, the number of different supply voltages needed to power data communication and telecommunication systems has increased significantly. These supply voltages must also be generated at ever increasing current ratings, stringent output voltage tolerances, and fast transient responses. Conventional cascaded converters can be inadequate for systems with these requirements. Therefore, a new approach in power conversion and distribution is needed.
BRIEF SUMMARY OF THE INVENTION
A power supply for high-current, low-voltage applications comprises a transformer-coupled input power converter cascaded with a buck output power converter. The transformer-coupled input power converter steps down an input voltage to an unregulated intermediate voltage that is inversely proportional to the turns ratio, N:1, of a transformer. The transformer-coupled input power converter is preferably capable of producing a nearly 100% maximum duty cycle output waveform to eliminate the need for an output filter on the secondary side of the transformer, and it is preferably operated in a free-running mode to avoid the need to feed back a switching pulse width control signal and to eliminate the need for a start-up circuit. Furthermore, the nearly 100% maximum duty cycle is preferably adjusted so that a pair of primary-side power switches operate with zero voltage transition to essentially eliminate primary-side switching losses. A minimum freewheeling time interval can allow for the use of self-driven, synchronous rectifiers on the secondary side that do not require the complicated timing circuits usually associated with synchronous rectifiers. The cascaded buck output power converter, which may employ either a conventional diode rectifier or synchronous rectifiers, converts the unregulated intermediate voltage into a regulated output voltage.
Other aspects, features, and advantages of the present invention are disclosed in the detailed description that follows.
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Andreycak William M.
Balogh Laszlo
Bridge Christopher D.
Nguyen Matthew
Texas Instruments Incorporated
Weingarten, Schurgin Gagnebin & Hayes LLP
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