Medium frequency resistance welding DC transformer
Isomatic Lab.

ISOMATIC Lab successfully developed and brought to market the MIT Line of Medium Frequency Integrated DC Transformers designed for integration in welding robots and machines. Medium-frequency DC transformers are a result of recent advances in resistance welding technology. They are powered by a transistor inverter, supplying usually square wave AC 500 V @ 1000 Hz which is converted by the MF transformer to a low alternating voltage at high current. This low voltage AC current is rectified to DC by a diode block built into the transformer and is then used for welding. The higher operating frequency of such a MFDC system allows efficient energy conversion using a smaller and lighter transformer. Other benefits with MFDC transformers used in portable and robotic welding guns are:

* When welding with DC the reactance of the welding loop only limits the upslope and downslope of the welding current, whilst the peak welding current in limited only by the welding loop's resistance. The net result is smaller transformer, especially when welding with large throat, high-impedance guns.
* MFDC welding is less demanding on the plant power system too. The MF inverter draws balanced line current from all 3 phases and operates at high power factor (cos φ> 0,9).
* With MFDC transformers the peak welding current almost equals its RMS value, which helps to obtain quality welds with no splash and constant strength even at lower pressure.
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The high frequency permits much faster - 1000 times per second - process control, which again results in better weld quality.