Power rectifier arrangement

A power rectifier arrangement comprises at least one heat sink and at least one power rectifier. The housing floor of the power rectifier is at least partially designed as the input terminal. The secondary winding of the transformer is designed as a ribbon. The power rectifier serves as a fastening element which is screwed to the heat sink and with which the end of the ribbon is pinched between the housing floor and the heat sink. In case at least two power rectifiers are connected in parallel, the ribbon exhibits a plurality of superimposed, electrically-conductive layers corresponding to the plurality of power rectifiers and each of the electrically conductive layers is respectively connected to one power rectifier. An electrically-insulating and thermally-conductive layer is provided between two electrically-conductive layers. Advantageously, the heat sources which are formed by the transformer and the power rectifier are connected in parallel and, therefore, the heat is respectively directly dissipated to the heat sink.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a power rectifier arrangement comprising a 
transformer, at least one heat sink and at least one power rectifier which 
has a terminal at the floor of a housing. 
2. Description of the Prior Art 
As is known in the art, a power rectifier can exhibit a semiconductor 
element and structural parts such as current leads, a capsule to protect 
against mechanical and atmospheric influences, as well as a metallic 
housing floor having a contact surface and, for example, a threaded stud 
for fastening the power rectifier to a heat sink. The inputs of the power 
rectifier can be designed as terminal lugs which are secured to the upper 
side of the capsule. The threaded stud and housing floor can serve as an 
output. The threaded stud and the planar annular surface of the housing 
floor surrounding the stud can, in approximately equal parts, assume the 
dissipation of the heat arising in the power rectifier. 
In case the inputs of the power rectifier are connected to a transformer 
which produces heat, the heat is dissipated to the terminal lugs of the 
power rectifier. The heat of the transformer, therefore, is dissipated 
over the power rectifier to the heat sink. The two heat sources, 
transformer and power rectifier, are therefore connected in series. This 
can lead to undesirable overheating of the tranformer and of the power 
rectifier. 
SUMMARY OF THE INVENTION 
The object of the present invention, therefore, is to provide a power 
rectifier arrangement of the type generally set forth above which prevents 
overheating of the transformer and overheating of the power rectifier. 
The above object is achieved, according to the present invention, in that 
the terminal at the housing floor is provided as the input terminal, that 
the secondary winding of the transformer is designed as a ribbon, and that 
the power rectifier serves as a fastening element which is screwed to the 
heat sink and with which the end of the ribbon is pinched between the 
housing floor and the heat sink. 
The power rectifier advantageously comprises a threaded stud at the housing 
floor for screwing to the heat sink. In an advantageous embodiment of the 
invention, at least two power rectifiers are connected in parallel, the 
ribbon exhibits a plurality of superimposed, electrically-conductive first 
layers corresponding to the plurality of power rectifiers, each of the 
first layers respectively connected to one of the power rectifiers, and an 
electrically-insulating, thermally-conductive second layer is provided 
between two first layers. A power rectifier constructed in accordance with 
the invention has the advantage that the heat of the transformer which can 
arise from core and copper losses, is directly conducted to the heat sink. 
The electrical connection to the power rectifier is thereby simultaneously 
produced. Given a full load of the power rectifier, its heat loss is no 
longer emitted to the secondary winding of the transformer but, rather, is 
emitted to the heat sink. The heat sources, transformer and power 
rectifier, therefore, are connected in parallel. It is further 
advantageous that a skin effect is avoided, whereby an additional heat 
generation due to too high a current density in the transformer, is 
prevented. By dividing the ribbon into different layers and by connecting 
a respective electrically-conductive layer to a power rectifier, each 
individual ribbon is separately rectified and a current balance is thereby 
achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The power rectifier arrangement illustrated in FIG. 1 comprises a 
transformer 7, four power rectifiers 1, 2, 3 and 4, and inductive load 5 
and a capacitive load 6. The power rectifiers 1, 2, 3, 4 are connected as 
a full-wave rectifier circuit to the secondary winding of the transformer 
7, whereby respectively two power rectifiers 1, 2 and 3, 4 are connected 
in parallel to one another. The cathodes of the power rectifiers 1, 2, 3, 
4 are connected to the transformer 7. The anodes of all power rectifiers 
1, 2, 3, 4 are connected to the inductance 5. The capacitance 6 is 
disposed in parallel to the output of the circuit. The junction of the 
inductance 5 and of the capacitance 6 lies at zero volts. 
The power rectifiers 1, 2, 3, 4 in FIGS. 2 and 3 exhibit a housing 
protecting against mechanical and atmospheric influences and having a 
housing floor which is provided with an annular contact surface and a 
threaded stud. Two respective power rectifiers 1, 2, 3, 4 are screwed into 
two heat sinks 11. The contact surface at the housing floor and the 
threaded stud serve as a cathode. Terminal lugs 10 are attached to the 
upper side of the housing as anodes. The heat sink 11 and the transformer 
7 are disposed on a cooled bottom plate 18. The secondary winding of the 
transformer 7 leads out of the transformer. The winding comprises a ribbon 
8, 8', 9 which consists of two first layers 8, 8' which are electrically 
conductive and a second layer 9 which is electrically insulating and 
thermally conductive. Such a ribbon is known, for example, under the 
tradename Kapton ribbon. 
The ribbons 8, 8' are respectively pinched between the housing floor of the 
power rectifiers 1, 2, 3, 4 and the two heat sinks 11. The power 
rectifiers 1, 2, 3, 4 thereby serve as fastening elements in the manner of 
a screw. The inputs of all power rectifiers 1, 2, 3, 4 are thus directly 
connected to the secondary winding of the transformer 7. The connection of 
the terminal lugs 10 to the inductance 5 occurs over a first conductor 13. 
The electrically-conductive connection from the threaded studs to the 
output of the circuit arrangement occurs by way of the heat sink 11 and a 
further conductor 12 which is electrically connected to the heat sink in 
which the power rectifiers 3, 4 are screwed. 
The thickness of the electrically-conductive layers 8, 8' depends on the 
penetration depth of the current. It is dimensioned such that a skin 
effect is prevented. Each electrically conductive layer 8, 8' is connected 
to a respective power rectifier 1, 2, 3, 4. This occurs in that the ribbon 
8, 8', 9 is pinched at the power rectifiers 1, 3 which are closest to the 
transformer 7, together with all layers 8, 8', 9. By so doing, an 
electrically conductive connection is provided exclusively over the 
uppermost layer 8 between the transformer 7 and the power rectifiers 1, 3. 
The dissipation of the heat of the power rectifiers 1, 3, however, occurs 
over all layers of the ribbon 8, 8', 9 to the heat sink 11. A large 
portion of the heat of the transformer 7 is likewise dissipated over all 
layers of the ribbon 8, 8', 9 to the heat sink. For the purpose of 
connecting the further power rectifiers 2, 4, the upper 
electrically-conductive layer 8 and the second layer 9 are removed. 
Therewith, an electrically-conductive connection exists between the 
transformer 7 and the power rectifiers 2, 4 only over the lower 
electrically conductive layer 8'. The dissipation of the heat likewise 
occurs over the layer 8'. 
FIG. 4 illustrates a further exemplary view of a circuit arrangement having 
a power rectifier 1'. The housing of the power rectifier 1' comprises a 
synthetic material which is cast around the semiconductor elements. The 
housing floor of the power rectifier 1' comprises, partly, a metal plate 
21 which serves as the input terminal. The power rectifier 1' is screwed 
to the heat sink 11 by a screw 20 which is conducted through an opening in 
the metal plate 21. The ribbon 8 is pinched between the housing floor and 
the heat sink 11. The terminal lugs 10' are conducted laterally out of the 
housing of the power rectifier 1'. 
FIG. 5 illustrates a heat source 16 which is formed by the transformer 7. 
The source 16 is connected to a heat sink 19 by way of a thermal resistor 
14. A heat source 17, which is formed by the power rectifiers 1, 2, 3, 4 
is connected to the heat sink 19 over a further thermal resistor 15. The 
thermal resistors 14, 15 are thus connected in parallel. They are 
respectively loaded only with the heat flows from the allocated heat 
sources 16 or, respectively, 17, to the heat sink 19. The amounts of heat 
arising in the thermal resistors 14 and 15 correspond to the heat loss of 
the transformer 7 or, respectively, of the power rectifiers 1, 2, 3, 4. 
FIG. 4 represents an electrical equivalent diagram illustrating the heat 
flow. 
Although we have described our invention by reference to particular 
illustrative embodiments thereof, many changes and modifications of the 
invention may become apparent to those skilled in the art without 
departing from the spirit and scope thereof. We therefore intend to 
include within the patent warranted hereon all such changes and 
modifications as may reasonably and properly be included within the scope 
of out contribution to the art.