Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-06-06
2001-08-21
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S016000, C363S020000
Reexamination Certificate
active
06278621
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to DC-to-DC converters, more particularly to single ended forward DC-to-DC converters having circuitry for resetting a transformer core.
BACKGROUND OF THE INVENTION
DC-to-DC converters are used to convert an input DC voltage to a different output DC voltage for delivery to a loads Such converters typically comprise a transformer that is electrically coupled via a switching circuit between the voltage source and the load Converters known as single-ended forward converters are a class of converters that rely on a single switch connected between the voltage source and the primary winding of the transformer to provide forward power transfer to the secondary winding of the transformer when the switch is on and conducting.
To discharge the leakage inductance at the transformer, the transformer core is “reset” during the off period of the switch. Resetting is typically accomplished with the use of additional circuitry, such as a third transformer winding in parallel with the primary transformer winding, or a LC resonant circuit electrically coupled to the secondary winding. The driving waveforms of such circuitry, however, exhibit a “dead time”, a period during which the switch remains open, the voltage across the switch equals the source voltage, and the current vanishes. Dead time decreases the overall efficiency of the converter and places voltage stresses on the switch.
It is an object of the present invention to provide a single-ended forward DC-to-DC converter that effectively resets the transformer core while exhibiting substantially no dead time and minimizing voltage stress on the components thereof.
SUMMARY OF THE INVENTION
The invention relates to a single ended forward DC-to-DC converter that effectively resets the transformer core, thereby enhancing its ability to carry out self-driven synchronous rectification. In one embodiment, the converter comprises a transformer having a primary winding electrically connected to a primary switch, and a secondary winding electrically connected to a secondary switch and a clamping capacitor. The secondary winding is in electrical communication with a pair of rectifiers and an LC filter circuit that provides rectification and smoothing of the power signal that reaches the load. When the primary switch is on, the primary winding is conductive and an input voltage exists across the secondary winding. When the primary switch is turned off, the secondary switch is turned on, a magnetizing current existing in the secondary winding is transferred to the clamping capacitor, and the clamping capacitor is charged to substantially the input voltage. During the period that the primary switch is off, the voltage across the secondary winding is maintained constant, and the transformer core is reset.
In other embodiments of the invention, the primary and secondary switches include MOSFET switches. In such embodiment, when the primary MOSFET switch is open, a voltage appearing at the secondary winding causes the secondary MOSFET switch to become conductive. In still other embodiments, the primary switch comprises an n-channel MOSFET and the secondary switch comprises a p-channel MOSFET. In yet another embodiment, the secondary switch comprises an n-channel MOSFET and the secondary winding is electrically coupled with a third winding. The third winding provides a positive voltage necessary to activate the n-channel MOSFET.
Other embodiments of the invention relate to a method for resetting the core of the transformer by activating and deactivating a primary MOSFET coupled to a primary winding of a transformer, such that upon deactivation, the secondary MOSFET is activated, a clamping capacitor is charged, and the secondary winding is clamped to the voltage of a clamping capacitor.
The present invention provides synchronous rectification and zero voltage switching, techniques that are useful in providing lower output voltages and higher power densities at the load. Moreover, the use of a clamping capacitor and MOSFET switches increases the simplicity of the DC-to-DC converter while eliminating undesirable characteristics such as dead time and voltage stresses on the switches.
These and other features of the invention will be made apparent from the description below and the claims.
REFERENCES:
patent: Re. 36571 (2000-02-01), Rozman
patent: 4444146 (1984-04-01), Vinciarelli
patent: 4688160 (1987-08-01), Fraidlin
patent: 4809148 (1989-02-01), Barn
patent: 4975821 (1990-12-01), Lethellier
patent: 5111372 (1992-05-01), Kameyama et al.
patent: 5126931 (1992-06-01), Jitaru
patent: 5291382 (1994-03-01), Cohen
patent: 5353212 (1994-10-01), Loftus, Jr.
patent: 5434767 (1995-07-01), Batarseh et al.
patent: 5434768 (1995-07-01), Jitaru et al.
patent: 5457620 (1995-10-01), Dromgoole
patent: 5521807 (1996-05-01), Chen et al.
patent: 5528482 (1996-06-01), Rozman
patent: 5610508 (1997-03-01), Kammiller
patent: 5625541 (1997-04-01), Rozman
patent: 5636106 (1997-06-01), Batarseh et al.
patent: 5636107 (1997-06-01), Lu et al.
patent: 5726869 (1998-03-01), Yamashita et al.
patent: 5734563 (1998-03-01), Shinada
patent: 5781420 (1998-07-01), Xia et al.
patent: 5805432 (1998-09-01), Zaitsu et al.
patent: 5862043 (1999-01-01), Youn et al.
patent: 5872705 (1999-02-01), Loftus et al.
patent: 5886881 (1999-03-01), Xia et al.
patent: 5991171 (1999-11-01), Cheng
patent: 5999419 (1999-12-01), Marrero
patent: 6021051 (2000-02-01), Laskai et al.
patent: 6141233 (2000-10-01), Nakamura
patent: 0 515 988 A1 (1992-05-01), None
patent: 89614 (1980-04-01), None
patent: WO 83/02858 (1983-08-01), None
Carsten, Bruce, “High Power SMPS Require Intrinsic Reliability”, Telecom Power Corporation, Vancouver, Canada, PCI '82 Proceedings, Intertec Communications, Inc. (Dec. 1982).
Carsten, Bruce, “Design Tricks, Techniques and Tribulations at High Conversion Frequencies”,HFPC, pp. 139-152 (Apr. 1987).
Carsten, Bruce, “Design Techniques for Transformer Active Reset Circuits at High Frequencies and Power Levels”,HFPC, pp. 235-246 (May 1990).
Javonoic et al., “Evaluation of Synchronous-Rectification Efficiency Improvement Limits in Forward Converters”, vol. 42, No. 4,IEEE Transactions on Industrial Electronics, pp. 387-395 (Aug., 1995).
Ma Fei
Xia Gang
International Power Devices, Inc.
Nguyen Matthew
Testa Hurwitz & Thibeault LLP
LandOfFree
Single ended forward DC-to-DC converter providing enhanced... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Single ended forward DC-to-DC converter providing enhanced..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Single ended forward DC-to-DC converter providing enhanced... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2455043