Method of producing a high voltage transformer

0001The invention relates to a method for producing a high current transformer, particularly for a power source for providing a current shit of a resistance welding apparatus with at least one primary winding and at least one secondary winding with surfaces for contacting.

0002The present invention relates primarily, but not exclusively, in which particularly high DC currents in the order of several kA occur at high current transformers and its components for resistance welding devices, in particular spot welding devices. Also, high current transformers for other devices in which such a high direct currents are used, are encompassed by the subject matter of the present patent application. Examples of such devices are battery chargers, particle accelerator, means for galvanizing or the like.<patcit id="pcit0001" dnum="WO2007041729A1"><text>WO 2007/041729 A1</text></patcit> for example, describes a battery charger and a power converter for producing a sufficiently high direct current.

0003In resistance welding devices, the required high DC currents are provided by means of appropriate high-current transformers and rectifiers. Due to the high currents that occur diode rectifier are disadvantageous because of the relatively high losses, which is why mainly active rectifier with switching elements that are formed by respective transistors used. But resistance welding devices with active rectifiers, such as synchronous rectifiers, have relatively high losses and therefore relatively low efficiencies. As in the prior art by the usual separate structure, for example by high-current transformer and rectification, substantial cable lengths and thus incur line losses, a very poor efficiency due to the high currents caused.

0004For example, the <patcit id="pcit0002" dnum="DE102007042771B3"><text>DE 10 2007 042 771 B3</text></patcit> a method according to the preamble of claim 1 for operating the power supply of a resistance welding apparatus using a synchronous rectifier through which reduces the power loss and the efficiency can be improved.

0005The <patcit id="pcit0003" dnum="JP2003318045A"><text>JP 2003-318045 A</text></patcit> describes a transformer with a layered structure of the Windunge, which is unsuitable for high-current applications.

0006In the case of production lines in the automotive industry, a plurality of spot welders (often some 100 to 1000 individual units) used for the production of various compounds to the body and the chassis of the vehicle to be manufactured. After already the single spot welding devices cause high losses due to the high current transformers and power lines and switching elements, the total losses occurring in such production lines in enormous dimensions, for example, between 1MW and 50MW move. Since the losses are reflected mainly in the form of waste heat, in turn, measures must be taken to remove the heat, whereby the overall energy balance is even worse.

0007Another disadvantage arises from the fact that very high power ratings of the supply network are required by the high losses of such investments, which means very high costs for manufacturing, commissioning and operation of such a system arise.

0008To produce a single spot weld with a welding current of 20kA a connected load of the supply network of up to 150kW is according to the prior art from today's perspective, for example, needed, and when said welding current losses of up to 135kW result, whereby a very low efficiency of only about 10 % is achieved.

0009The object of the present invention is to provide a method of manufacturing a high-current transformer through which the losses can be reduced and the energy balance and the efficiency can be improved. Drawbacks of known devices and methods are to be reduced or avoided.

0010The inventive object is achieved by an above-mentioned method for producing a high-current transformer having at least one primary winding and at least one secondary winding with surfaces for making contact, wherein the first internal surfaces of the at least one secondary winding with an I-beam of electrically conductive material of the high current transformer with a first are solder connected to a first, higher melting temperature, and then at least one contact plate of electrically conductive material is soldered with outer surfaces of the at least one secondary winding with a second solder having a second, opposite the first melting temperature lower melting temperature. The advantage here is that by the production, in particular soldering, can be automated, because due to the different melting temperature for the second soldering process with the lower melting temperature, the compounds prepared in the first soldering higher melting temperature can no longer be melted. Thus, the manufacturing cost can be substantially reduced. Also is achieved, the best connection can be used, so that the lowest possible transition losses werden.Bei created a procedure in which the at least one contact plate is a board with the first solder is connected to the first, higher melting temperature, is advantageously ensures that the contact plate may be suspended at any time later further soldering.

0011After connecting the at least one contact plate with the board switching elements connected to the board and / or the contact plate, in particular with bulges on the contact board, using the first brazing material with the first, higher melting temperature. Here, the positioning and soldering of circuit elements, and other electronic components, are fully automated.

0012According to the measures, at which the switching elements, especially the connector terminals or the housing of the switching elements, with the surfaces of the at least one secondary winding are connected to the second, lower melting temperature with the second brazing material is achieved in that the connection between the contact plate and board is not more can melt. Thus, the entire unit, ie, the contact plate, the circuit board, the switching elements and other components are driven by a solder bath for cost and safe production of a soldering.

0013It is advantageous if a first solder having a first, higher melting temperature between 220 ° C and 300 ° C, in particular 260 ° C and a second solder having a second, lower melting temperature between 120 ° C and 220 ° C, in particular 180 ° C having. This ensures that the second low melting temperature soldering process, the fixed during the first soldering parts are not resolved, or the quality of the connections would be degraded.

0014The invention will be explained in more detail with reference to the accompanying drawings.

0015Therein:<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>a resistance welding apparatus of the prior art robot with a welding gun and attached thereto in a schematic representation;</dd><dt>FIG. 2</dt><dd>a schematic block circuit diagram of a resistance welding apparatus with a power source for supplying the welding current;</dd><dt>Fig. 3</dt><dd>a resistance welding device, especially a welding gun having an integrated current source for supplying the welding current in a schematic representation;</dd><dt>Fig. 4</dt><dd>a schematic block circuit diagram of the current source for supplying the welding current;</dd><dt>Fig. 5</dt><dd>one embodiment, the current source for providing a DC current;</dd><dt>Fig. 6</dt><dd>the power source in accordance with <figref idrefs="f0005">Fig. 5</figref> in exploded view;</dd><dt>Fig. 7</dt><dd>the power source in accordance with <figref idrefs="f0005">Fig. 5</figref> with plotted course of cooling channels;</dd><dt>Fig. 8</dt><dd>a view of the I-beam of the high-current transformer of the power source;</dd><dt>Fig. 9</dt><dd>the I-beam in accordance <figref idrefs="f0008">Fig. 8</figref> in a sectional view;</dd><dt>Fig. 10</dt><dd>a contact plate of the high-current transformer of the power supply, including board of the synchronous rectifier and the drive circuit; </dd><dt>Fig. 11</dt><dd>the contact plate according <figref idrefs="f0010">Fig. 10</figref> in a sectional view;</dd><dt>Fig. 12</dt><dd>a secondary winding of the high current transformer with current transformer in exploded view;</dd><dt>Fig. 13</dt><dd>the construction of a secondary winding of the high-current transformer in exploded view;</dd><dt>Fig. 14</dt><dd>a block diagram of a circuit for the supply of the synchronous rectifier and the drive circuit with electric power;</dd><dt>Fig. 15</dt><dd>a time profile of the supply voltage of the supply circuit according to <figref idrefs="f0014">Fig. 14</figref>; and</dd><dt>Fig. 16</dt><dd>Time profiles for illustrating the control of the switching elements of a synchronous rectifier in dependence of the secondary-side currents of the high-current transformer.</dd></dl>

0016In the illustrated embodiment, the <figref idrefs="f0001 f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009 f0010 f0011 f0012 f0013 f0014 f0015">Fig. 1-16</figref> there is described a configuration of a resistance welding apparatus 1 with the essential components. For the same parts the same reference numerals were given in the figures.

0017In <figref idrefs="f0001">Fig. 1</figref> is shown in perspective a resistance welding apparatus 1 for resistance welding of at least two workpieces 2, 3 with a robot for manipulation. The resistance welding device 1 comprises a fixed to the robot welding gun 4 with two tong arms 5, which are connected to receptacles 6 arranged to receive a respective electrode. 7 Around the electrodes 7 are respectively a band 8, which reduces the contact resistance at the resistance welding and the electrodes 7 protects extends. Moreover, the resulting band at 8 illustration of spot weld produced analyzed and used to evaluate the welding quality. The band 8 for protecting the electrodes 7 is unwound from a winding device 9, which may be disposed on the welding gun 4 and the gripper arms 5 and along the gripper arms 5, the electrode holders 6 and the electrode 7 back to the winding device 9, where the belt 8 rolled back out. To carry out the spot welding, the welding current, which is supplied by a corresponding power unit 19, passed through the electrodes. 7 Thereby, the workpieces 2, 3 are interconnected by a generated during spot welding the welding point. Usually, there is the power unit 19 for supplying the welding current outside of the resistance welding apparatus 1, as shown schematically in<figref idrefs="f0001">Fig. 1</figref> shown. The welding current is conducted via appropriate lines 11 to the electrodes 7 and the electrically conducting gun arms formed 5th Due to the amplitude of the welding current in the range of several kA large cross-sections for the lines 11 are correspondingly required, thereby correspondingly high ohmic losses result.

0018In addition, long primary supply lines lead to increased inductance of the lines 11, so the switching frequency at which a high-current transformer 12 is operated to a power source 10, are limited, resulting in very large high-current transformers 12. In the prior art, the power unit 19 in a cabinet next to the welding robot, so very long supply lines, for example, up to 30m, the high-current transformer 12 are required for the welding tongs 4 on the robot.

0019When solving a considerable weight and size reduction is achieved, so that a position of the power unit 19 is directly on the robot, particularly in the area of ​​the chuck holder, allows. In addition, the power unit 19 is preferably designed to be water-cooled.

0020<figref idrefs="f0002">FIG. 2</figref> shows a schematic block diagram of a resistance welding apparatus 1 to a power source 10 for supplying the welding current. Although the power source 10 is used in the illustrated embodiment to provide the welding current for the resistance welding device 1, the current source 10, in particular, the entire structure of the power supply, also to provide a DC current for other applications can be used. The current source 10 includes a high-current transformer 12 with at least a primary winding 13, at least a secondary winding 14 with center tap and a ring core 15. The transformed by means of the high current transformer 12 power is rectified in a synchronous rectifier 16 and the gripper arms 5 and

0021Electrodes 7, the resistance welding apparatus 1 is supplied. In order to control the synchronous rectifier 16, a drive circuit 17 is provided. The drive circuit 17 sends corresponding control pulses to the switching elements 24 of the synchronous rectifier 16 based on the measured, for example, via current transformer 18 secondary-side currents of the high-current transformer 12th

0022As is well known, occur due to the high welding currents by the sum of the required cable length both significant ohmic and / or inductive losses and conduction and switching losses in the switching elements 24 of the synchronous rectifier 16. In addition, also occur in the rectifier, the supply for the synchronous rectifier 16 and the drive circuit to 17 losses. Accordingly low, the resulting efficiency of such resistance welding devices. 1

0023In order to generate the primary-side current of the high current transformer 12, a power unit 19 is provided, which is arranged between a power supply and the current source 10th The power section 19 provides the primary-side current for the high-current transformer 12 and the current source 10 with the desired amplitude and desired frequency.

0024<figref idrefs="f0003">Fig. 3</figref> shows a resistance welding device 1 with integrated power source 10 in a schematic representation. The current source 10 is directly, in particular as a supporting element, on the welding gun 4 and the gripper arms 5 of resistance welder 1 are arranged so that at least part of the lines 11 can be omitted for guiding the welding current to the electrode 7 and thus considerably shortens the line length , since only the connection to a gun arm 5 is required. The current source 10 has to form an Mehrpunktkontaktierung at least four contacts 20, 21, 22, 23, wherein two first contacts 20, 21 of one polarity a gun arm 5, and two further contacts 22, 23 of an opposite polarity to the other gun arm 5 connected to the are. Advantageously, the two first contacts 20, 21, 23 are arranged with the one polarity and the other two contacts 22, with the other polarity in each case opposite, wherein the two other contacts 22, 23 relative to the two first contacts 20, 21 substantially by 90 ° are arranged offset to one another. By Mehrpunktkontaktierung lines 6 of the resistance welder 1 are usually for connecting the secondary side 14 of the high-current transformer 12 with the gripper arms 5 and the electrodes required can be avoided or their length can be reduced and thus the ohmic losses as well as contact losses are significantly reduced , Thus short cables can be used with the widest possible cross-section, wherein the flexibility of the welding gun remains 4 obtained. A further advantage is that due to such contact, the losses, in particular contact resistances can be reduced. Due to the at least four contacts 20, 21, 22, 23 of the welding current to be transmitted can be halved, thereby also a reduction of transition loss is caused because the contact resistance can be reduced by the substantial increase in the active contact surfaces. For example, each of the four contacts 20, 21, 22, 23 in the dimensioning of a high-current transformer 12 and a current source 10 for providing a DC current of 20kA an area between 15cm x 15cm to 25cm x 25cm, preferably 20cm x 20cm on.

0025In the illustrated example, the current source 10 is formed substantially cube shaped, with the side surface of the cube form the contacts 20, 21, 22, 23rd The first two contacts 20, 21 are an electrode 7 and the two other contacts 22, 23 with the other electrode 7 of the resistance welding apparatus 1 via the gripper arms 5 is connected to the. As shown in the partially exploded view, is at least one gun arm 5, in particular the lower arm of the tongs 5, connected via a supporting member 23a of the lower tong arm 5, whereas the other, in particular the upper tong arm 5 via a flexible connector clip 23b with the additional contacts 22, 23 is connected. At least one gun arm 5 is thus directly connected to the high-current transformer 12 and the other gun arm 5 for a very short line, for example, shorter than 50cm, connected thereto. The fact that the lines 11 eliminated between the power source 10 and the electrodes 7 and the gripper arms 5 of the resistance welding device 1 or be particularly short, the resistive and inductive losses can be significantly reduced.

0026Particular advantages result if at least two contacts 20, 21 are directly or cable required and thus connected without contact resistances with a tong. 5 This can be achieved that in the current source 10 these two contacts 20, 21 are virtually integrated, which with the corresponding parts of the resistance welding apparatus 1, in particular the gripper arms 5, are directly, without routing cables connected. a leadless interconnection is achieved by directly connecting a gun arm 5 with the contacts 20, 21 of the high-power transformer 12. Thus, whereas the second gun arm 5 must be combined with very short leads with the contacts 22, 23rd This can be a very high reduction of line losses can be achieved, since the cable length can be reduced to the minimum. In the prior art is positioned in the optimal case, the high current transformer as close to the welding tongs 4, so that then the welding tongs 4, the cables must be laid from the high-current transformer 12, whereas in the high-current transformer 12 is integrated in the welding tongs 4 and simultaneously a tong 5 directly on secured high-current transformer 12, so that only the second gun arm 5 must be connected with one or two short lines. Of course, for example, sliding contacts or other fasteners can be used instead of lines. The losses within the power source 10 can be significantly reduced due to the compact design and direct, so leadless, connecting the components of the power source tenth

0027Advantageously, all components of the current source 10, so the synchronous rectifier 16, the driving circuit 17, the current transformer 18 and all the supply circuits for the synchronous rectifier 16 and the drive circuit 17 in the cube or cuboid unit are included. That is, a structural unit is provided in the form of a cube by the integration of the electronic components / circuits to the user on the primary side only has to provide power in the form of corresponding AC voltage or corresponding AC current to the secondary side according to a correspondingly dimensioned direct current or a to obtain dimensioned DC voltage with high power. The control and regulation is independently carried out in the cube or the power source tenth In order for the dice or the power source 10 to supply versatile components with large DC applicable. In particular, the current source 10 serves to supply low voltage, high current, as is customary in resistance welding processes.

0028When used in a resistance welding process, parts of Cube-shaped can formed by current source 10 components of the resistance welding apparatus 1, for example, parts of the gun arms 5 or the like, to be formed, as illustrated. Here, the cube and the current source 10 assumes a supporting function by a gun arm 5 is fixed directly on the cube. The other tong arm 5 is contacted via connection lines (not shown). By this construction, long leads can be prevented, so that a substantial reduction of the losses is obtained. Thus, the cube can be integrated into such a welding gun 4, however, it is necessary that its size is minimized. For example, the cube and the current source 10 at a dimensioning of the hbereitzustellenden DC current of up to 20kA a side length of between 10cm and 20cm, 15cm in particular, on. This compact configuration of the cube-shaped power source 10, it is easy to integrate this example, in the main body of the welding gun. 4

0029<figref idrefs="f0004">Fig. 4</figref> shows a schematic block diagram of the current source 10 to provide a direct current, in particular a welding current. In this preferred embodiment the current source 10 ten primary windings 13 of the high-current transformer 12 are connected in series and ten secondary windings 14 of the high-current transformer 12 in parallel with center tap. By such a design of the high-current transformer 12, the correspondingly high ratio 13 and low numbers of turns of the secondary windings 14 can be achieved in order to achieve a correspondingly high secondary-side current even at low numbers of turns of the primary windings. For example, can be achieved with ten primary windings 13 and also ten secondary windings 14 a gear ratio of one hundredth The primary current flows through the series-connected primary windings 13 of the high-current transformer 12, whereas the relatively high secondary-side current is distributed to the ten parallel-connected secondary windings fourteenth The secondary side partial flows are the respective switching elements 24 of the synchronous rectifier 16 is supplied. By such division results despite lower primary and secondary-side turns a correspondingly high ratio (here 100). By this construction, the primary side lower number of turns, in contrast to conventional high power transformers required, whereby the length of the primary winding 13 can be reduced and thereby the Ohm'-'s losses can be reduced. Due to the reduced number of turns of the primary winding 13 and thus a resulting reduction of the cable length, the typical system leakage inductance of the high-current transformer is in turn 12 is reduced, whereby the high-current transformer 12 may be at higher switching frequencies, such as 10kHz operated. The comparison with conventional high current transformers higher switching frequencies in turn cause a reduction in size and weight of the high-current transformer 12 and thus advantageous mounting options. Thus, the high-current transformer 12, for example, be positioned very close to the electrodes 7 of a resistance welding machine in the first Thus, the load of the welding robot due to the low weight of the high-current transformer 12 can be reduced, so a little cheaper welding robot the Auslangen can be found.

0030Conventional transformers in which no serial / parallel connection of the primary and secondary winding is carried out would require correspondingly more primary turns, which considerably longer primary-side wire length would result. Because of the greater length of wire to rise on the one hand the ohmic losses and results on the other hand a higher leakage inductance, and therefore the frequencies at which the transformer of the prior art can be operated, are limited to a few kHz.

0031In contrast, the ohmic losses and the system-inherent leakage inductance of the primary windings 13 and secondary windings 14 are low in the presently described construction of the high-current transformer 12, which is why frequencies are used in the range of about 10kHz and can. This, in turn, a much smaller size of the high-current transformer 12 are achieved. The smaller size of the high-current transformer 12 and the current source 10 in turn allows this or them closer to the place where the electricity generated will be required to arrange, for example, the gripper arms 5 of a resistance welding device. 1

0032The resulting high secondary-side current to a plurality of substreams is divided by the parallel connection of the secondary windings 14 of the high-current transformer 12th These sub-streams are forwarded to the switching elements 24 of the synchronous rectifier 16, as shown schematically. For activating the switching elements 24 is a driving circuit 17, which is located in the area of ​​the primary winding 13 and secondary winding 14, is provided, wherein both the synchronous rectifier 16, and the drive circuit 17 with associated sensors, disposed inside the cube, ie, within the high-power transformer 12. , The synchronous rectifier 16 and the drive circuit 17 are configured and dimensioned such that they perform autonomously, without influence from the outside, the regulation and control of the power source tenth Therefore, the dice preferably has no control lines for engagement from the outside in, but only terminals or contacts for the primary-side supply and connectors or contacts for the supply of the secondary energy produced, in particular to the high secondary direct current.

0033It is however possible that a corresponding connection of the drive circuit 17 is led out to the drive circuit 17 specify setpoints. Through external adjustments, the current source 10 can be optimally matched to the application. As known from the prior art, however, systems for changing or transferring data can be used, which, preferably inductively, magnetically or via Bluetooth are wireless, so no control terminal has to be taken out.

0034The control and / or regulation of the current source 10 takes place via the integrated sensors. By measuring the secondary currents of a secondary winding 14 by means of respective current transformers 18, the drive circuit 17 receives the information, the times at which the switching elements 24 of the synchronous rectifier to appear 16th Because the current transformer 18 measure only a fraction, here one-tenth, the secondary-side current of the high-current transformer 12, it can be made smaller, which again has a positive effect on the size of the power source tenth

0035To reduce the conduction losses and switching losses, the switching elements 24 of the synchronous rectifier 16 are connected as possible at the zero crossing of the secondary currents through the secondary windings 14 of the high-current transformer 12th As it comes from the detection of the zero crossing of the secondary-side current through the current transformer 18 to the activation of the switching elements 24 of the synchronous rectifier 16 to some delay, the drive circuit 17 is adapted to control the switching elements 24 of the synchronous rectifier 16 at a preset time prior to reaching the zero-crossing the current to turn in the secondary winding fourteenth The drive circuit 17 thus causes the switching of the switching elements 24 of the synchronous rectifier 16 to a point in time at which the currents measured by the current transformer 18 in the secondary winding 14 of the high-current transformer 12 a certain switch-on and switch-off threshold exceeded or not reached. By this measure it can be achieved that the switching elements 24 of the synchronous rectifier 16 substantially during the zero crossing of the currents are switched by the secondary winding 14 of the high-current transformer 12, whereby the on-state losses and switching losses can be minimized (see also<figref idrefs="f0015">Fig. 16</figref>).

0036For a primary winding 13 and secondary winding 14 is in <figref idrefs="f0004">Fig. 4</figref> the supply circuit 48 to supply the synchronous rectifier 16 and the drive circuit 17 with electrical power drawn. Also this supply circuit 48 is preferably integrated into the current source 10, so in the cube. Since the supply of the synchronous rectifier 16 and the driving circuit must be 17 of the current source 10 with sufficient electrical energy to the desired time of delivery of the DC current, for example of the welding current ensures a sufficiently rapid activation of the supply circuit 48 is required (see<figref idrefs="f0014">Fig. 15</figref>) And this is designed such that upon activation of the current source 10 is available as soon as possible a sufficiently high supply voltage is available, then the required power or the required current is delivered.

0037<figref idrefs="f0005">Fig. 5</figref> shows the embodiment of the power source 10 in accordance with <figref idrefs="f0003">figure 3</figref> in an enlarged view. The current source 10 for providing a DC current, for example, welding current, has substantially the shape of a cube or cuboid, with the faces of the cube or cuboid represent the contacts 20, 21, 22, 23, via which the DC power generated at the respective consumer , for example, the gripper arms 5 or 7 electrodes of a resistance welding apparatus 1, can be passed. All components of the power source 10, that the high-current transformer 12, the synchronous rectifier 16, the driving circuit 17, the current transformer 18, the power supply circuit 48, etc. are included or integrated in this cube or cuboid-shaped element of the current source 10th This compact design, the loss of the power source 10 can be kept particularly low and hence their efficiency can be significantly increased, as an optimal shortening of the lines, and thus the switching times with the integration of electronic components, particularly the boards with the synchronous rectifier 16, the drive circuit 17 and the power supply circuit 48, is achieved in the cube. Through the integration of the synchronous rectifier 16 and the drive circuit 17 and the supply circuits 48 of the current source 10 in the high-power transformer 12 and parallel connection of several switching elements 24 of the synchronous rectifier 16 and leadless connection of the switching elements 24 to the secondary windings 14 of the high-current transformer 12 are no lines between the synchronous rectifier 16 and the secondary side 14 of the high-current transformer 12 required, thereby avoiding the need any ohmic losses and other losses through such lines. The power unit 19 for the supply of high-current transformer 12 is positioned as close to this, so as to achieve the shortest possible connecting lines and line losses and line inductances. By integrating all components an autonomous unit is formed, which on the input side only with the power unit 19 and the output side - must be connected to the gripper arms 5 and electrodes 7 - in the case of resistance welding machine. 1 Conventional lines between the individual circuits of the power source 10 can be at least significantly reduced in their length or omitted.

0038The base of the high current transformer 12 of the power source 10 forms a transformer element in the form of an I-beam 25 of electrically conductive material, in particular copper or a copper alloy, possibly with a coating, for example made of silver. In the recesses 25a of the I-beam 25 on both sides of the ring cores 15 are arranged to the secondary windings 14 of the high-current transformer 12th It is spatially advantageous if the ring cores 15 have non-circular, but oval or flat cross-section. In the illustrated embodiment, five ring cores 15 are arranged in parallel with the respective secondary windings 14 in each recess 25a of the I-beam 25th The primary winding 13 and the combined series-connected primary windings 13 (dash-dotted line) passing through the arranged in the recesses 25a of the I-beam 25 ring cores 15 and around the central web of the I-beam 25. Through this the course of the primary winding 13 by the particular symmetrically in the two recesses 25a of I-beam 25 arranged annular cores 15, an optimum magnetic coupling can be achieved at the secondary windings fourteenth The terminals 26 of the primary coil 13 be about at least one opening 27 guided out to an outside surface 28 of the I-beam 25th These ports 26, the primary winding 13 of the high-current transformer 12 can be connected to the corresponding power section 19th The outer surfaces 28 of the I-beam 25 forming the first two contacts 20, 21 the current source 10, which are for example connected to the one electrode 7 of the resistance welding machine in the first

0039About the recesses 25a of I-beam 25 are contact plates 29, the outer surfaces of the two other contacts 22, 23 of the current source 10 form and are isolated from the I-beam 25th The contact plates 29 are also formed of electrically conductive material, such as copper or a copper alloy, possibly with a coating, for example of silver. Copper or copper alloys have optimal electrical properties and exhibit good thermal conductivity whereby heat losses occurring more rapidly can be dissipated. The silver coating prevents oxidation of the copper or the copper alloy. Instead of copper or copper alloys, aluminum or aluminum alloys come into consideration, which is opposed to copper having a weight advantage, although the corrosion resistance is not so high. Instead of a silver coating and a coating of tin and other materials or compounds or layers is possible. the sinkers 35 of the synchronous rectifier 16 and the drive circuit 17 are arranged between the contact plates 29 and the corresponding terminals of the secondary windings 14 of the high-current transformer 12th These boards 35 or printed circuit boards are soldered directly to the contact plates 29 and are then attached isolated on I-Beams 25th Due to this design, the secondary-side terminals of the high-current transformer 12 can be connected or contacted directly with the switching elements 24 of the synchronous rectifier 16 without cables must be laid. The outputs of the synchronous rectifier 16 are also preferably directly connected to the contact plates 29, whereby no cables are required. The contact plates 29 are connected to the I-beam 25, preferably screwed (not shown). On the outer faces 28 of the I-beam 25 and the outer surfaces of the contact plates 29 may connecting means 30, for instance holes with corresponding threads for receiving screws, may be arranged. About this connection means 30, for example, the lines to the gripper arms 5 of a resistance welding apparatus 1, or other to be supplied to the DC devices can be attached or may be a tong are 5 attached directly to the I-beam 25 or on the contact plates 29th

0040At the top and the bottom of the cube or cuboid-shaped current source 10 can be arranged cover plates 31 and with the I-beam 25 and the contact plates 29 are connected, for example screwed, (see <figref idrefs="f0006">Fig. 6</figref>). Preferably, the cover plates 31 is also formed of electrically conductive material and is screwed to the contact plates 29, whereby a stable unit of the high current transformer 12 and results produced over the cover plates 31 also provide electrical connection between the contact plates 29th This ensures that on the cover plate 31 held a charge balance and it can therefore be no unbalanced loads of high power transformer 12th This allows a separate electric line which would 29 connect the two contact plates are electrically connected together, omitted to make the voltage or potential equalization and to avoid asymmetries. Over the cover plates 31 so the electric connection between the two contact plates 29 is made of the symmetrical arrangement of the high-power transformer 12 and the current source 10 for supplying the welding current. Of course, in this case an appropriate insulation for I-beam must be 25 ensured. The cover plates 31 are such as the I-beam 25 and the contact plates 29 are preferably formed of copper or a copper alloy, preferably with a silver coating.

0041On an outer surface 28 of the I-beam 25, in particular the first contact 20, two inlets 32 are arranged for supplying a cooling fluid and an outlet 33 for discharging the cooling fluid to facilitate cooling of the components of the power source 10th The cross section of the outlet 33 for discharging the cooling fluid comprises the sum of the cross sections of all inlets 32 for supplying the cooling fluid. For an optimum course of cooling fluid, the cooling channels 39 are arranged accordingly (see<figref idrefs="f0009">figure 9</figref> and <figref idrefs="f0011">11</figref>). As a cooling fluid may be water or another liquid, but also a gaseous coolant can be used.

0042As the exploded view of the power source 10 in accordance with <figref idrefs="f0006">Fig. 6</figref> can be removed, the current transformer 18 for measuring the secondary-side currents of the high-current transformer 12 are placed directly on the top of which is arranged the secondary windings 14, ie, a current transformer is in each case at the first or uppermost secondary winding 14 on both sides of I-beam 25 18 arranged so that the current can be determined by this secondary winding 14 due to the induced current. To avoid influencing the temperature measured by the current transformer 18 flows through external magnetic fields is preferably a housing 34 of magnetically conductive material, such as ferrite, arranged to shield over the current transformers 18th

0043The current transformers 18 are on both sides of I-beam 25 arranged on the respective first and second secondary winding fourteenth Due to the current flow through the primary windings 13 of current occurs on one side of I-beam 25, whereby the uppermost secondary winding 14. Thus, the first secondary winding forms 14, whereas now the stream enters on the opposite side to the uppermost secondary winding 14 and thus the second secondary winding forms. By using a full-bridge, it is necessary that the current flow is always detected by the first and second secondary winding 14 independently of one another, so that depending on the function of the current, the corresponding switching elements 24 of the synchronous converter 16 can be driven. Thus, it is possible that the switching elements 24 of the two sides of the I-beam 25 are almost in synchronism driven by a caused by the current transformer 18 driving signal.

0044Between the contact plates 29 and the I-beam 25, the boards 35 of the synchronous rectifier 16 and the drive circuit 17 are arranged. The boards 35 simultaneously provide the necessary isolation between the I-beam and the contact plates 29. The respective switching elements 24 of the synchronous rectifier 16 can be contacted directly with the secondary windings 14 of the high-current transformer 12th Via appropriate protrusions 36, in particular crenellated projections on the inner surface of the contact plate 29 and corresponding openings 37 on the board 35 below the switching elements 24 can be made a direct contacting of the switching elements 24 with the contact plates 29th The switching elements 24 are preferably formed by suitable field effect transistors whose drain terminals are formed by the housing. The housing of the field effect transistors are connected directly or cable required with the at least one secondary winding 14 of the high-current transformer 12, so that no lines between these units are required. For example, field-effect transistors are used silicon or gallium nitride. The current transformers 18 are directly connected to the juxtaposed board 35 of the synchronous rectifier 16 and the drive circuit 17 and via a suitable conduit 38 with the opposite board 35 of the synchronous rectifier 16 and the drive circuit 17th

0045The assembly of the current source 10 in accordance with the <figref idrefs="f0005">Fig. 5</figref> and <figref idrefs="f0006">6</figref> is inventively with a soldering using two different soldering temperatures. First, the secondary windings 14 with the recesses 25a of the I-beam 25 using a brazing material, in particular a solder, which at a first, higher temperature T_S1, For example, 260 ° C, melts, respectively. Also, the contact plates 29 are, using a brazing material, which at the first, higher melting temperature T_S1, For example, 260 ° C melt, contact with the boards 35th Thereafter, again using a brazing material, which at the first melting temperature T_S1, For example 260 ° C, melts, the components of the synchronous rectifier 16 and the drive circuit 17 mounted on the board 35th By the capillary action of the circuit board 35 on the contact plate 29 is no danger of a solution of the board 35 is given by the contact plate 29th After these steps, the outside contacts of the secondary windings 14 and the contacts on the boards 35 with solder having a second, opposite the first melting temperature T are_S1 lower melting temperature T_S2, For example, 180 ° C, besiebt, the contact plates 29 connected to the circuit boards 35 with the I-beam 25, preferably screwed, and then over the second melting temperature T_S2 the solder material, for example, heated to 180 ° C, so that the connection of the secondary windings 14 to the switching elements 24 of the synchronous rectifier 16 made. By using a brazing material of this second, lower melting temperature T_S2 it can be ensured that the T with the brazing material with a higher melting temperature_S1 Solder joints produced are not melted or highly resistive by crystallization processes. Finally, the primary winding 13 is threaded through the ring cores 15, and then the current transformer 18 are mounted and contacted, and the conductor run 38th By attaching the cover plates 31, the current source 10 is completed. In order to reduce tension and bending forces to the components of the current source 10 all the cavities can be cast prior to assembly of the cover plates 31st Via openings provided (not shown), for example in the cover plates 31 can be a casting, even after the mounting of the cover plates 31 take place.

0046<figref idrefs="f0007">Fig. 7</figref> shows the current source 10 in accordance with the <figref idrefs="f0005">Fig. 5</figref> and <figref idrefs="f0006">6</figref> (drawn with dashed lines) with indicated the course of the cooling channels. 39 Accordingly, the cooling channels 39 symmetrically disposed on the two inlets 32 is first run into the contact plates 29, where the most heat sources (the switching elements 24 of the synchronous rectifier 16 and the components of the drive circuit 17) and the sensitive elements with the cool cooling fluid cooled are. Thereafter, the cooling channels 39 extend into the outer elements of the I-beam 25 and in the central web of the I-beam 25, where the windings of the high-current transformer 12 can be cooled, wherein the two laterally flowing cooling channels collect 39 in the central web to form a single cooling passage. 39 Thereafter, the cooling channels open 39 in the common outlet 33 for the cooling fluid. The cooling channels in the contact plates 29 and the I-beam 25 are preferably made ​​through corresponding holes 40 to be completed in the appropriate places by finishing elements 41st Are between the I-beam 25 and the contact plates 29 to seal off the cooling channels corresponding sealing elements 39 42, for example O-rings, arranged (see<figref idrefs="f0008">Fig. 8</figref>).

0047In <figref idrefs="f0008">Fig. 8</figref> is the I-beam 25 of the high-current transformer 12 isolated from the other components of the high-current transformer 12 and the current source shown 10th At the opening points of the cooling channels 39 are the above-mentioned sealing 42, for example in the form of O-rings, arranged. The recesses 25a in the I-beams 25 are accurately formed to hold the ring core 15, thereby a very compact construction is achieved. Simultaneously, the central web of the I-beam 25 forms the contact surface for the center tap of the secondary windings 14 of the transformer 12 from high current. The center taps of the secondary windings 14 are connected to cable required the central web of the I-beam 25, which in turn may be omitted corresponding lines. The direct connection of the secondary windings 14 to the I-beam 25, a significant increase in the terminal area is achieved and can thus again transition losses and line losses.

0048The I-beam 25 forms the base of the high current transformer 12, by which the secondary windings 14 are arranged such that no connecting lines are required. The outer surfaces of the I-beam 25 are the two first contacts 20, 21 of the current source 10, which are directly, ie cable required, connected to the gripper arms 5 of the resistance welding machine. 1 A space-saving arrangement is achieved in that the toroidal cores 15 are not designed to be circular, but oval or flat. closed ring cores 15 are preferably used. By this design, the serial / parallel connection of the primary windings 13 and secondary windings can be realized 14 through which the required transmission ratio of the high-current transformer 12 for the high bereitszustellenden DC with reduced numbers of turns of the primary windings 13 and secondary windings 14 is achieved. Such a construction pays off in particular when at least three parallel-connected secondary windings 14 are arranged on each side of I-beam 25th

0049<figref idrefs="f0009">Fig. 9</figref> shows the section through the I-beam 25 from <figref idrefs="f0008">Fig. 8</figref> along the section line IX-IX. From this, the course of the cooling channels 39 to the common outlet 33 is clearly visible for the cooling fluid.

0050<figref idrefs="f0010">Fig. 10</figref> shows a contact plate 29 of the high-current transformer 12 and the current source 10 and arranged above board 35 for the synchronous rectifier 16 and the drive circuit 17 in an enlarged view. As already mentioned above, the switching elements 24 of the synchronous rectifier 16 can be contacted on one side directly to the corresponding secondary windings 14 of the high-current transformer 12 and connected on the other side directly to the contact plate 29th For this purpose, on the inner surface of the contact plate 29 bulges 36, in particular crenellated protrusions arranged projecting into corresponding holes 37 on the board 35, where the source terminals of which is arranged over the openings 37 switching elements 24 directly, or cable required contact , By the bulges 36 may be on interconnections between the switching elements 24 of the synchronous rectifier 16 and the contact plates 29 are dispensed with, on the one hand the Ohm'-'s losses can be reduced and on the other hand, the thermal transition between the switching elements 24 and the contact plates 29 can be improved. Finally, the production cost is reduced because must be laid and connected no connecting lines, but the switching elements 24 directly connected to the protrusions 36, preferably are soldered. Even so, a simple positioning of the board 35 allows, and thus the production will be significantly simplified.

0051By arranging the drive circuit 17 and the synchronous rectifier 16 on the board 35, which is arranged on the inside of the contact plate 29, may be the direct or leadless contact with the terminals of the secondary windings 14 to the switching elements 24 of the synchronous rectifier 16 and also a direct or leadless contact the outputs of the synchronous rectifier 16 reaches the contact plate 29th Preferably, the high-current transformer 12 and the current source 10 is constructed for providing the DC current symmetrical, with both sides of the symmetrically arranged secondary windings 14 are each a printed circuit board 35 is disposed with a part of the synchronous rectifier 16 and the drive circuit 17 below a respective contact plate 29th

0052When synchronous rectifier 16 in accordance <figref idrefs="f0010">Fig. 10</figref> ten switching elements 24 are arranged in a row. To ensure that all parallel-connected switching elements 24 are substantially simultaneously driven and run-time losses affect only slightly, there is a symmetric control of the switching elements 25 of both sides, that is, on both sides arranged gate drivers are each preferably five shift elements 24 of the right and left driven. It can also be arranged other control options such as an additional centrally extending gate driver, whereby the cable lengths and the inductors are divided into thirds. By such parallel the gates driving the switching elements 24 of the synchronous rectifier 16 short control paths and thus nearly synchronous switching times of the switching elements 24 to ensure there is no or hardly runtime losses.

0053When mounting the circuit board 35 on the contact plate 29, the projections protrude 36 of the contact plate 29 through the openings 37 in the board 35 therethrough, thereby simultaneously forming the back of the board 35 with the contact plate 29 can be securely soldered and additionally arranged on the opposite side switching elements 24 can also be soldered to the contact plate 29th This may account for the high standard wiring. Even so is an easy positioning of the board 35 on the contact plate 29 possible and this can no longer slip during soldering. If 48 are arranged on the circuit board 35 of the synchronous rectifier 16, the driving circuit 17 and the power supply circuit, a self-sufficient structure for the integration of the circuit board 35 in the high current transformer 12 can be achieved. Is also of advantage when the drive circuit 17 is arranged on both sides of which is arranged parallel and in series with the switching elements 24, since a reduction in the conduction paths to the individual switching elements 24 is achieved. Thus, it can be ensured that within a very short period of time all the parallel-connected switching elements 24 are turned on. Through the two-sided arrangement of the drive circuit 17 is a halving of the cable length and, consequently, achieve a reduction of lead inductance and thus a substantial shortening of the response times 24th On one side of the board 35 a solderable surface for soldering is preferably the entire surface provided with the contact plate 29, whereby a reliable connection to the contact plate 29 can be achieved. Thus, the contact resistance can be significantly reduced, as a full-surface connection of the circuit board 35 having a lower contact resistance. Instead of the preferred direct bonding by soldering can also short connecting wires, so-called bonding wires, are provided.

0054The supply circuit 48 is preferably to form a correspondingly high switching currents, for example, between 800A and 1500A, 1000A in particular, and adapted to supply the devices of adequate supply voltage. Due to the very high switching current can be a very short switching time, especially in the ns range are achieved. This ensures that there is always the zero crossing or directly shortly before the zero crossing at low output current, the switching elements are connected in 24, so that no or hardly any switching losses occur. If a data communication circuit for wireless transmission of data, preferably inductively, magnetically, or via Bluetooth, is provided, data may be wirelessly transmitted from and to the circuit board 35 (not shown). Thus, an adjustment of the switching time points are made to different fields of use of the high current transformer 12th Also, from an arranged on the board 35 memory (not shown) data for further processing or control or for quality monitoring are read.

0055Establishing a protection of the switching elements 24 of the synchronous rectifier 16 from overvoltages, it is advantageous, the switching elements 24 turned on, if they are not needed. In case of application in a resistance welding apparatus 1 is thus enabled in the welding breaks the active synchronous rectifier 16 in order to prevent destruction of the switching elements 24th It is monitored whether a primary current or secondary current flows through the high-current transformer 12, and in the case of no current flow, while the welding gun 4 is appropriately positioned for a new welding point, the drive circuit 17 activates all the switching elements 24 by corresponding actuation of the gates. If the power source 10 is activated after positioning of the welding gun 4, thus starting a manual or automatic welding operation, an AC voltage is applied to the primary winding 13 of the high-current transformer 12 is applied, which in turn is recognized by the drive circuit 17 due to a current flow, and thus the protection mode of the switching elements 24 is deactivated. Of course, the activation and deactivation of the switching elements 24 of the synchronous rectifier 16 via control signals transmitted inductively or magnetically or by radio to the drive circuit 17, take place. At the switched-on switching elements 24 any surges can cause any damage. Also a certain minimum protection of the switching elements 24 by means of zener diodes may be provided.

0056<figref idrefs="f0011">Fig. 11</figref> shows a section through the contact plate 29 in accordance with <figref idrefs="f0010">Fig. 10</figref> along the section line XI-XI. From the course of the cooling channels 39 can be clearly seen. The production-related openings in the holes 40 to form the cooling channels 39 are sealed by respective end elements 41st The end elements 41 can be screwed into corresponding threads in the holes 40 by appropriate screws, be realized.

0057<figref idrefs="f0012">Fig. 12</figref> shows a ring core 15 arranged thereon with two secondary windings 14 of the high-current transformer 12 together arranged above the current transformer 18, which was shown in an exploded view. The current transformer 18 is protected by the shielding housing 34 and a shield 43 from unwanted magnetic fields, so that the secondary-side current can be measured as accurately as possible through the secondary winding 14 and the drive circuit 17 can be supplied to control the switching elements 24 of the synchronous rectifier 16th To shield magnetic fields ferrites are suitable as materials especially. The current transformer 18 is thereby positioned and secured over a portion of one of the two secondary windings arranged fourteenth As known from the prior art, the current converter 18 is formed of a magnetic core disposed above winding, the terminals of the winding are connected to the drive circuit 17th Furthermore, between the ring core 15 and the secondary winding 14, the shield 43 and a core sheet for the current transformer 18 is arranged, wherein the core of the current transformer 18 on this core sheet is placed.

0058In this structure, the high-current transformer 12 has two secondary windings 14 constructed in this manner are arranged on both sides of I-beam 25, so that the drive circuit 17 measures the current flow through one of the parallel-connected on both sides and positioned secondary windings fourteenth If the drive circuit 17 is connected to this current transformer 18, a precise control or regulation is possible, since through the current converter 18, the states in the high current transformer 12 can be detected.

0059Due to the above-described parallel connection of the secondary windings 14 the same current flows in each secondary winding 14th Thus, the current only a secondary winding 14 must be tapped in order to return close to the total current flow can. In a parallel connection of ten secondary windings 14 only one-tenth of the total current flow is measured from the current transformers 18, which is why they can be dimensioned much smaller. This, in turn reducing the overall size of the high-current transformer 12 and the current source 10 is achieved. It is advantageous when the power converter 18 substantially are arranged oriented 90 ° to the direction of the DC current, in particular the welding current, as characterized by the disturbances caused by the direct current magnetic field and hence measurement errors can be reduced. Thus, a very accurate measurement can be performed.

0060As the exploded view in <figref idrefs="f0013">Fig. 13</figref> can be seen from the secondary windings 14 of the high-current transformer 12 is preferably by two by an insulating layer 46, for example a paper layer, insulated from one another metal sheets 44, 45, 15 and formed with a substantially S-shaped from the same course of the cross section of a toroidal core through the annular core 15 are which are arranged one inside. On a ring core 15 so two secondary windings 14 and the parts of the secondary winding 14 are arranged with center. The outer surfaces 47 of the sheets 44, 45 of the secondary windings 14 constitute at the same time the contact surfaces for making contact with the switching elements 24 of the synchronous rectifier 16 and the I-beam 25, which acts as the center of rectification. Thus, no lines for connection of the secondary windings 14 of the high-current transformer 12 to the switching elements 24 of the synchronous rectifier 16 are required. The secondary windings 14, in particular the secondary windings 14 forming plates 44, 45 are connected directly or cable required to the switching elements 24 of the synchronous rectifier 16 and the central web of the I-beam 25 and the focus of rectification. Thus, a very space-saving and compact design is achieved with low weight and low losses. Simultaneously represent a contacting available in order to ensure 16 relatively large surfaces 47 with the least possible loss of excess current flow for the connection of the secondary winding 14 with the central web of the I-beam 25 and the switching elements 24 of the synchronous rectifier. By this arrangement, a midpoint rectifier is realized on the secondary side, wherein the I-beams 14 form 25 with the associated one end of the secondary windings of the center.

0061The toroidal core 15 may be formed of ferrites, amorphous materials or nanocrystalline materials. The better the materials used in terms of the magnetic properties, the smaller the ring core can be carried out 15th However, this of course also increases the price of the ring core 15. It is essential in the formation of the sheets 44, 45, that they are so folded or bent to be at least once through the toroidal 15th The two arranged on a toroidal core 15 sheets 44, 45 and secondary windings 14 are diametrically opposed formed and isolated from each other.

0062<figref idrefs="f0014">Fig. 14</figref> shows a block diagram of a supply circuit 48, in particular of a power supply for supplying the synchronous rectifier 16 and the drive circuit 17 with electrical power. The supply circuit 48 is connected to the secondary side and the terminals of the secondary winding 14 of the high-current transformer 12 and includes a peak detector 49, a voltage booster 50, a series regulator 51 and a voltage divider 52. The voltage booster 50 or booster ensures that the supply of components the current source 10 is as soon as possible available. Simultaneously, the internal supply voltage of the active synchronous rectifier 16 is as fast as possible is generated. By using the voltage booster 50 activation is ensured in the initial stage, that at the earliest possible time, the required amplitude of the supply voltage is generated first in order to ensure safe operation of the integrated in the high-current transformer 12 synchronous rectifier 16 at the earliest possible time.

0063<figref idrefs="f0014">Fig. 15</figref> shows the time course of the supply voltage V of the supply circuit 48 according to <figref idrefs="f0014">Fig. 14</figref>, The ramp of the voltage increase .DELTA.V / .DELTA.t is chosen sufficiently steep so that it is ensured that the required voltage VCC with a maximum time delay T_d applied to the synchronous rectifier 16 and the drive circuit 17th For example, should the time delay T_d &lt;200μs respectively. By appropriate design of the circuits of the peak value rectifier 49 and voltage booster 50 and correspondingly low capacity, a sufficient rate of rise of the voltage can be achieved. One can therefore say that first the minimum height of Vorsorgungsspannung ensures with a steep rise and then only the correct supply is built.

0064<figref idrefs="f0015">Fig. 16</figref> is a timing chart of the secondary-side current I_S the high-current transformer 12 and the control signals G₁ and G₂ for the switching elements 24 of the synchronous rectifier 16 for illustrating the lossless control. By measuring the secondary-side currents I_S a secondary winding 14 by means of respective current transformers 18 is replaced by the drive circuit 17 the information when the switching elements 24 of the synchronous rectifier to appear 16th To reduce the conduction losses and switching losses, the switching elements 24 of the synchronous rectifier 16 are connected as possible at the zero crossing of the secondary currents through the secondary windings 14 of the high-current transformer 12th I Since it from the detection of the zero crossing of the secondary-side current_S some delay T through the current transformer 18 to the activation of the switching elements 24 of the synchronous rectifier 16_Pre comes, the control circuit 17 is adapted to control the switching elements 24 of the synchronous rectifier 16 at a preset time prior to reaching the zero crossing of the current in the secondary winding fourteenth The drive circuit 17 thus causes the switching of the switching elements 24 of the synchronous rectifier 16 at instants at which the currents I measured by the current transformer 18_S in the secondary winding 14 of the high-current transformer 12 a certain switch-I_SE and switch-off I_SA below or exceed. By this measure it can be achieved that the switching elements 24 of the synchronous rectifier 16 substantially during the zero crossing of the currents I_S are connected through the secondary winding 14 of the high-current transformer 12, whereby the conduction losses and switching losses of the switching elements 24 of the synchronous rectifier 16 can be minimized. The connection and disconnection of the switching elements 24 of the synchronous rectifier 16 is therefore not with the zero crossing of the secondary-side current but on reaching the defined switch-I_SE and switch-off I_SA set. The switch I_SE and switch-off I_SA is defined according to the expected switching delays. At most, where the switch-I_SE and switch-off I_SA be designed to be adjustable to the losses reduce even more can. In a 20kA high current transformer 12, for example, the switching time can be set to 100 ns before the zero crossing, so that the switching elements 24 of the synchronous rectifier 16 must be activated within this time period.

0065A conventional high-current transformer of the prior art for a resistance welding apparatus for supplying a welding current of 20 kA for example comprises about 40-50 kW losses. Overall, a connected load of up to 150kW is for supplying a welding current of 20kA according to the prior art requires, the total losses amount to about 135kW, resulting in an efficiency of about 10%. In contrast, a high-current transformer 12 shows the present type just 5-6kW losses. The conduction losses can be reduced from typically 30kW to 20kW. Thus, in a resistance welding device 1 for generating a welding current of 20kA, the connected load to 75kW are reduced because the total losses amount to only about 60kW. The resulting efficiency is thus about twice as high as in the prior art with about 20%. This comparison clearly shows the potential savings potential, particularly in production lines in the automotive industry with a variety of resistance welding equipment.

0066Basically, the power source described 10 or the high-current transformer 12 is formed in the form of a cube or cuboid, with two side faces are formed by an I-beam 25, to which side surfaces electrically insulated contact plates 29 are arranged for forming the third and fourth side face. The face side is to the four side surfaces in each case a cover plate 31, which is opposite to the I-beam 25 is electrically isolated, is arranged to form the fifth and sixth side surface of the cube or cuboid. Inside the cube, in particular the side surfaces, the synchronous rectifier 16 and the drive circuit 17 is disposed on at least one printed circuit board 35 or circuit board. Thus, the dice has only connectors 26 for the primary windings 13 of the high-current transformer 12 and the side surfaces as contact surfaces to the decrease of the DC current or DC voltage. In addition, in particular, the inlets 32 and the outlet 33 are still cooling ports, provided for a cooling fluid. Control lines for the integrated in the cube synchronous rectifier 16 and the drive circuit 17 are preferably not provided, since this system operates autonomously and thus no connections to power unit 19 and to a control device of the system are necessary. With such a structure preferably no control cables are needed, but the power source 10 only on the primary side connected to a power unit 19, after which stands on the secondary side of the appropriately sized DC, for example, 15kA to 40kA available. The user need therefore to make any settings, but only to connect the power source tenth The Association of actually independent stand-alone components to such a common unit causes the size and thus the weight of the power source 10 can be substantially reduced. At the same time, the unit also as a structural element directly in an application, in particular a welding tongs 4, are used. The ease of use is significantly increased.

0067An essential feature of the structure is further that the switching elements 24 cable required connected to the respective components, ie the welding current conductive source terminals of the switching elements formed by field effect transistors 24 are connected or soldered directly to the bulges 36 of the contact plate 29, which also the gate terminals of the switching elements 24 on the circuit board 35 and the drive circuit are constructed thereon 17 (gate driver) arranged or soldered. Thus, the inductances of lines can be reduced by completely saving the lines so that high switching speeds and very low conduction losses can be achieved.

0068In the illustrated and described embodiment, the high-current transformer 12 has been dimensioned for a current of 20kA at an output voltage between 5V and 10V. Here, the I-beam 25 has a height of 15 cm on both sides so that five secondary windings 14 can be arranged with the ring cores 15th To arrive at an appropriate ratio of 100, ten primary windings 13 are necessary in the illustrated embodiment.

0069Will you now the high-current transformer 12 dimensioned for a higher current of 30kA, for example, as the number of secondary windings 14 used to be simply increased. For example, both sides in the recesses 25a of I-beam 25 seven secondary windings 14 are arranged, wherein the I-beam 25 is correspondingly increased in height, for example, is carried out only 5cm higher and a correspondingly larger base is used. Thus, the I-beam 25 of the high-current transformer 12 merely adds to both sides by two secondary windings 14, in order to provide a higher current. By increasing the contact cooling surfaces can be increased. Further more switching elements 24 are arranged in parallel accordingly. The primary winding 13 can be reduced to a smaller number of turns, for example, seven turns, so that a translation of, for example, 98 is achieved. Higher primary winding losses are compensated by the higher primary current due to the possible increase of the cross section and the reduction of cable length.

0070An increase of the secondary welding current of 20kA to 30kA therefore merely an extension of the cube or high-current transformer 12 for example, 5cm result.

0071Since the high-power transformer 12 preferably operates independently and has no control lines, a communication to the outside should be with external components, in particular a control device, allows for any error messages. For this purpose, the secondary circuit comprising the secondary windings 14 and the synchronous rectifier 16 and the drive circuit can be used 17th Here, in certain conditions, especially during idling of the high-current transformer 12, these are deliberately short-circuited by means of the synchronous rectifier 16, so that an idle current flow is detected in the primary lines of an external monitoring unit or a control device, and thus the basis of the current communication or an error message can take place.

0072For example, by integration of a temperature sensor in the high-current transformer 12, in particular at the synchronous rectifier 16, the temperature detected and evaluated. If the temperature rises, for example, over a defined threshold value, then the control circuit 17 of the synchronous rectifier 16 idle, defined so during breaks in welding shorted. Since the external control device to idle while desm is being performed no welding, knows, this is detected or recognized by the increased current flow in the primary lines of the high-current transformer 12th Now can be checked by the external control device, if the cooling circuit is activated, or it has an error or the cooling power is increased to increase the cooling takes place.

0073Of course, different error messages are communicated to the outside at idle via corresponding switching or pulse pattern, so defined opening and closing of the switching elements 24 of the synchronous rectifier 16th For example, different temperature values, secondary voltages, currents, error messages, etc. can be sent to the outside.

0074However, it is also possible that such communication is performed during a weld, although such detection is much more difficult. In this case, for example, signals corresponding to the primary-side current, in particular through the primary windings modulate thirteenth