Fast Rise-Time Pulse Transformers Based on Transmission Line Transformer Like Structures

A new set of fast rise-time transformers based on transmission line transformer techniques (TLT´s)1 are described. The transformers are wound using loosely coupled wire pairs rather than transmission lines in order to avoid high voltage cable failure problems experienced with commercial coaxial transmission lines commonly used in TLT´s. Although the high frequency response, associated with conventional TLT´s, is not quite as good, when using wire pairs, it is still quite possible to design high turns ratio transformers with rise-times below 100 ns. The frequency response of these transformers can be predicted by relatively simple transformer models which can also be used to predict rise-time performance into a variety of loads. These models can further be used to determine how much inductance is required at each stage of the transformer to achieve a specified low frequency performance. They also show that mutual coupling of windings within the transformers can significantly improve their low frequency response and pulse droop. Results will be presented on both low voltage test transformers and on a medium scale high voltage pulse transformer.