Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-11-13
2004-10-19
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021040, C363S021060, C363S024000
Reexamination Certificate
active
06807069
ABSTRACT:
The present invention relates to direct-current current converters. In particular, the invention concerns a chopper-type direct-current converter, a chopper-type per-type regulator and methods for forming these.
BACKGROUND OF THE INVENTION
Today, power source constructions aim at a minimum size and a maximum power density, in other words, the aim is to maximize the power to volume ratio of the power source. An obstacle to the reduction of the size of power sources is the physical size of the components and the problem of heat production. The physical size of electronic components, especially semiconductors, is continuously diminishing. The largest components in a power source are magnetic components, such as transformers and filter coils. The size of the magnetic components can be reduced to a certain limit by increasing the switching frequency of the semiconductors. However, an obstacle to increasing the frequency are the losses occurring in the core material of magnetic components and in semiconductors as well as the generation of heat in power sources. If the size of the power source is reduced while the power dissipation remains the same, the surface area emitting heat to the environment is usually also reduced, resulting in a rise in the temperature of the power source. The heat produced is detrimental to other components as well when the power source is placed close to other electronics.
By increasing the switching frequency, it is possible to reduce the size of the magnetic components, but a high frequency results in further losses. It is not sensible to increase the frequency beyond a few hundred kilohertz. A space saving has also been achieved by replacing traditional tall wire-wound magnetic components with low planar structures.
Increasing the switching frequency from the present level to a level sufficient to allow a reduction of the size of magnetic components is not a viable solution in view of the overall effects. The effects produced in the windings by parasitic elements, such as e.g. the losses due to hysteresis of the core material and switching losses, are increased. The work performed by magnetic hysteresis cannot be restored into electric energy; instead, it is converted in the core material into losses, which again increase the temperature of the core material.
Hysteresis losses are increased as the frequency and the alternating component of the magnetic flux are increased. Hysteresis losses account for a substantial portion of the total power dissipation occurring in a magnetic component, such as a transformer or coil. Coil structures get saturated above a certain load current. The advantage achieved by reducing the size of magnetic components is not in proportion to the additional costs arising from the increased power losses.
One method for reducing the size of magnetic components is to integrate several magnetic components around the same magnetic core. Specification U.S. Pat. No. 5,555,494 presents a structure in which several magnetic components have been integrated around the same magnetic core. In the construction, an E-type magnetic core is utilized in which each side leg has an air gap while the center leg is of a continuous structure. Integrated around the magnetic core are the transformer windings and filter coils used for filtering the output voltage of the converter. In this solution, the filter coils are placed around the side legs of the magnetic core.
The object of the present invention is to eliminate the problems referred to above. A specific object of the invention is to disclose a new type of direct-current converter and a chopper-type regulator in which the transformer windings and the output voltage filtering coils are integrated on the same magnetic core. A further object of the invention is to disclose methods for forming a converter and a regulator as specified above.
BRIEF DESCRIPTION OF THE INVENTION
The invention concerns a method for forming a chopper-type direct-current converter. In this case, the direct-current converter is transformer coupled, so the current supply to the converter is isolated. In other words, there is no galvanic connection between the primary and secondary sides of the converter. The magnetic core of the converter comprises a first and a second side leg, the ends of which are connected to each other by end pieces, and a center leg provided with an air gap and connected to the end pieces between the first and the second side legs. The magnetic core is preferably an E-type structure. Disposed around the magnetic core are a primary winding, a secondary winding and a filter coil for the secondary side. In the method of the invention, the filter coil is placed around the center leg. The primary and secondary windings are so arranged around the side legs that the magnetic flux produced by them flows in the same direction with the magnetic flux of the filter coil.
In a preferred embodiment of the invention, four windings are provided on the primary side of the converter, connecting two windings in series around the first and second side legs. The windings are so arranged around the side legs that the magnetic flux generated by the windings flows in the same direction on each side leg. Further, on the secondary side of the converter, two windings are arranged around the first and second side legs so that the magnetic flux produced by the windings flows in the opposite direction relative to the primary winding placed on the same side leg. The direction of the magnetic flux is the same on each side leg when the magnetic flux can be thought of as circulating around the magnetic core, the path of the flux consisting of the side legs and the end pieces. Thus, the magnetic flux in the first side leg intensifies the magnetic flux in the second side leg.
In an embodiment, the primary windings are controlled by means of a first and a second switching element. Moreover, two capacitors are provided on the primary side, the first capacitor being connected between the switching elements and the second capacitor in parallel with the supply voltage.
In another embodiment, two switching elements and two capacitors are provided on the primary side of the converter, the first switching element being connected between two primary windings and the second switching element correspondingly in series between the other two primary windings. In addition, the first capacitor is connected from the first side of the first switching element to the second side of the second switching element, and the second capacitor is connected from the second side of the first switching element to the first side of the second switching element. The two sides of the switching element may be understood in different ways depending on the switching element; for example, in a MOSFET transistor, the drain is the first side and the source is the second side; similarly, e.g. in a bipolar transistor, the emitter may be the first side and the collector the second side. This definition may be made in accordance with the switching element in question, in a manner known to the person skilled in the art.
In an embodiment, four windings are provided on the primary side of the converter, two windings being connected in series around the first and the second side legs in such manner that the magnetic flux produced by the windings flows in the same direction on each side leg, the other two windings being so connected that the direction of the magnetic flux produced by them on the same side leg is opposite to the flux of the first two windings. Further, two switching elements and a capacitor are provided on the primary side, the first switching element being connected by one end in series with two primary windings and by the other end to the second pole of the supply voltage. The second switching element is connected in a corresponding manner with the other two primary windings. The capacitor is connected in parallel with the supply voltage.
In an embodiment, two switching elements, two capacitors and two windings are provided on the primary side in such manner that the s
Laitinen Marko
Nieminen Pentti
Nokia Corporation
Squire Sanders & Dempsey LLP
Sterrett Jeffrey
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