Parallel operation of Darlington transistors in a large 480 V, 700 HP induction motor drive

Bipolar transistors have been used successfully in variable-frequency induction motor drive equipment. A practical approach to paralleling bipolar Darlington 600 A transistor modules in order to produce 700 HP, 480 V equipment, is described. Emphasis is placed on the base drive circuitry, the methods of controlling parasitic inductance in the power circuit, and the mechanical arrangement of the equipment. Darlington transistors could be applied straightforwardly in parallel conjunctions as long as simple precautions were followed. The resulting equipment contained liberal safety margins in current and in operating temperature. This provided conditions conducive to long life and reliability.<>