Abstract:
A matrix transformer and/or inductor module has its terminations bonded rigidly to the ferrite core of which it is made. Because the ferrite core is strong and dimensionally stable, the terminations are rugged and precisely located, important criteria for assembly to printed circuit boards and the like, especially if automated assembly methods are used. In another embodiment, the module has top and bottom metal plates which are the high current output terminals. This module can be mounted sandwiched between live heat sinks. In another embodiment, deep grooves are made into the core material, and fins are bonded into the grooves. The grooves reduce core losses by reducing eddy currents and dimensional resonance effects, and the fins remove heat from within the core allowing operation at much higher flux density and frequency.

Description:
This is a continuation in part application of High Frequency Matrix Transformer and Inductor Modules Ser. No. 07/771,603 filed Oct. 4, 1991, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to power converters, and more particularly to switched-mode power converters using matrix transformers and inductors. 
     The matrix transformer is described in U.S. Pat. No. 4,665,357 issued May 12, 1987 U.S. Pat. No. 4,85,606, issue Jul. 4, 1989, U.S. Pat. No. 4,942,353 issued Jul. 17, 1990, U.S. Pat. No. 4,978,906 issued Dec. 18, 1990 and U.S. Pat. 5,093,646 issued Mar. 3, 1992, all assigned to the same assignee as the present invention, and the disclosures of which are all incorporated herein by reference. 
     This invention teaches improved matrix transformer and inductor modules having improved ruggedness, and more precise location of their terminations. 
     SUMMARY OF THE INVENTION 
     The modules of the present invention use ferrite cores which are sturdy and have well defined dimensions. The terminations of the modules are bonded to the cores to provide ruggedness and dimensional stability to the terminations. 
     The modules may have square holes for pre-wired windings. In one embodiment, the top and bottom surfaces, respectively, are the terminations of the module. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a matrix transformer and inductor module. 
     FIG. 2 shows another embodiment of a matrix transformer and inductor module. 
     FIG. 3 shows a matrix transformer and inductor module in which the top and bottom surfaces are the output terminations. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The use of matrix transformer and inductor modules is shown in U.S. Pat. No. 4,942,353. 
     FIG. 1 shows a matrix transformer and inductor module  1  of the present invention having an inductor core  2  with an insert  3  and a transformer core  4  mounted on a base plate  10 . The transformer core has a secondary winding  5  installed therein. 
     The transformer cores and the inductor cores of this invention are “solid magnetic cores”, meaning that they are of a solid material such as ferrite or sintered powdered iron, as illustrations, not limitations. If the solid magnetic core comprises more than one part, for instance, a two part E-E core, an E-I core, a U-U core, a U-I core, a pot core or any of many two part cores which would be familiar to one skilled in the art, at least the parts to which the terminals are to be bonded are fixed together immovably as by cementing or the like as an illustration, not a limitation, so that the solid core where the terminals are to be bonded is rigid and has good mechanical integrity. If the core comprises a stack of laminations, then the laminations are fixed together immovably as by bonding or welding or the like as illustrations, not limitations, so that the stack where the terminals are to be bonded is rigid and has good mechanical integrity. 
     “If the solid magnetic core is of conductive or semi-conductive material, then the “solid magnetic core” may include a thin insulating film, coating or layer on its surface to make its surface non-conductive, for example and not a limitation, electrostaticly deposited epoxy.” 
     Terminations  7 ,  8  and  9  are provided for direct installation of an industry standard rectifier. 
     As shown the secondary winding  5  is a center-tapped secondary winding, the center-tap comprising a connecting strap  6 . 
     It is understood that the several parts of the windings must be insulated from each other. If the core material is conductive, they must be insulated from the core as well. An effective method of insulating a core is by coating it with an insulating layer such as epoxy. It is also common to partially coat conductors with an insulating layer. This is well understood by one familiar with the art, but it is not a point of novelty of the invention. Some core materials, such as nickel ferrite, are good insulators, and need not be insulated. 
     FIG. 1 shows how the matrix transformer and inductor module might be constructed as a general purpose component for power converters. The transformer core  4  and its secondary winding  5  may be designed for a particular output voltage and frequency of operation. In different applications several modules are typically used and may be wired in parallel. The number and arrangement of the modules may vary for different input voltages, different primary winding configurations and different power levels, but as long as the output voltage and frequency of operation are consistent, the one part is suitable. Windings to be added to the inductor core  2  and the insert  3  may vary from application to application. 
     The inductor core  2  and the transformer core  4  are bonded securely to the base plate  10 . The terminals  7 ,  8  and  9  are also bonded to but insulated from the transformer core  4 . Terminal  8  may or may not be common to the base plate  10  as a design option. 
     An important feature of FIG. 1 is that by bonding the terminations  7 ,  8  and  9  directly to the transformer core  4 , they are securely and precisely located, and are very rugged. This makes it practical to use a matrix transformer and inductor module as an unencapsulated assembly, for economy, and for access to the inductor core  2  and its insert  3  for adding the inductor winding. 
     FIG. 2 shows a matrix transformer and inductor module  20  which in many respects is similar to the matrix transformer and inductor module  1  of FIG.  1 . An inductor  21  comprising two ferrite cores  22  and  23  with an insert  24 , and a transformer  31  comprising two ferrite cores  32  and  33  are mounted on a base plate  30 . 
     The base plate  30  may optionally be a two layer assembly the top layer  44  of which is common to the terminal  8  and the bottom layer  42  of which is an insulated heat sink mounting surface. An insulation layer  43  separates the top layer  44  from the bottom layer  42 . 
     The inductor  27  has a winding  25  with a first termination  23  and a second termination  26 . One inductor winding  25  may be suitable for a wide range of applications, as the current through it is largely determined by the rating of the rectifier with which it is used and its value is largely determined by the tolerable ripple voltage and the filter capacitor with which it is to be used. These may be consistent for many applications. 
     The inductor  21  is terminated at an output terminal  28  and at a center-tap terminal  41  of the transformer  31 . The center-tap terminal  41  is part of a center-tap connection  39 . 
     Terminals  35 ,  36  and  37  are provided for direct connection to an industry standard rectifier. Additional terminals  38 ,  39  and  40  may be provided for ancillary components such as snubbers, if used. As shown, terminal  36  is common with the base plate  30  and an output terminal  29 . Alternatively terminals  29  and  36  may be connected to each other but insulated from the base plate  30 . 
     FIG. 3 shows a matrix transformer and inductor module  50  which has many features which are common with the matrix transformer and inductor module  20  of FIG.  2 . These common features are not identified and discussed again unless further aspects of the invention would be shown. 
     An inductor  51  and a transformer  52  are mounted between a base plate  53  and a top plate  54 . The base plate  53  may be common to a terminal  56 , and may be the positive output termination for the matrix transformer and inductor module  50 . The inductor  51  may be connected to the top plate  54  through a connection  57 , and the top plate  54  may be the negative output termination for the matrix transformer and inductor module  50 . A capacitor  58  may also be connected to the top plate  54  at the connection  57  and to the bottom plate  53  through a connection  59 , and may serve as an output filter capacitor. 
     FIG. 3 shows that the top plate  54  covers the top of the inductor  51  and the transformer  52 , and the bottom plate  53  covers the bottom of the inductor  51  and the transformer  52 . For the purpose of this specification and the claims, a top or a bottom plate “covers” a top or a bottom surface of a core or cores if the top or the bottom plate is proximate to the top or the bottom surface of the core or cores and extends over at least most of the top or the bottom surface of the core or cores. 
     FIG. 3 shows a rectifier  83  connected to terminals  56 ,  60  and  61  of the module  50 . The rectifier has a first anode  81  and a second anode  82 , and a common cathode which is its bottom surface and center terminal, which may be connected to the base plate  53  using terminal  56 . 
     One intended use of the matrix transformer and inductor module  50  is in a power converter comprising a number of similar matrix transformer and inductor modules which are mounted sandwiched between live heat sinks. A “live heat sink” is one which both conducts heat and electrical current, so it must be in good thermal and electrical contact with the matrix transformer and inductor module  50  and the other matrix transformer and inductor modules with which it is used, but must be insulated from other components to which there must not be an electrical contact. Heat sinks are normally robust, and are often of materials having good electrical conductivity. It provides significant savings in weight and volume as well as cost if the functions can be combined, eliminating bus bars and the like. 
     The transformer core  4  is preferably made of ferrite, though it would be functionally equivalent to construct it of another magnetic material having suitable properties. If it is made of multiple parts, for instance a stack of laminations, they must be bonded rigidly together so the core as a whole becomes a solid piece having structural integrity and reasonably good dimensional stability. If the magnetic core  4  is made of a conductive material, such as a manganese zinc ferrite or steel laminations, then it must be insulated at least over the portions of its surface which would contact the winding  5  or the terminals  6 ,  7  and  9 . The insulation may be a thin coating such as epoxy. Coating magnetic cores is a usual process in the art. If the core  101  is of a non-conductive material such as nickel ferrite, it need not be insulated. 
     There are some advantages to using two cores  32  and  33  for the magnetic structure which offset the inconvenience of handling two parts (in contrast to using a core such as the core  4  of FIG.  1 ). One is that eddy current losses will be less. It is often assumed that eddy current losses in ferrites are negligible, but that is not necessarily the case at high frequencies. Another is the simplicity of tooling. The two pieces may net out to a lower cost than the one part core. Another is that the tolerance between the holes of a dual core  4 , with reference to FIG. 1, may be hard to hold due to variations in shrinkage during cure. Any variation can be eliminated when two core parts  32  and  33  with reference to FIG. 2 are bonded together by varying the amount and thickness of the bonding material.