Transformer design for fast pulse circuits

The objective of this study was to develop the design requirements for pulse transformers having rise times as short as one nanosecond. Using operational methods and equivalent circuits, a theoretical analysis of a high-speed pulse transformer was performed. The results of the theoretical analysis were applied to the design of nanosecond pulse transformers. The value of primary inductance necessary for the required low-frequency response may be calculated from the results of the theoretical analysis. For a given core material, core size, and number of primary turns, an approximate value of primary inductance may be calculated from the specifications of the core material. The actual value of inductance is generally within 20% of the calculated value. The relationship between the core size, core material, and number of primary turns which optimizes the rise-time response of the transformer must be determined by trial and error. An example illustrating the method of designing nanosecond pulse transformers is included. Pulse transformers having rise times between 0.2 and 2.1 nanoseconds were constructed. The input pulse widths at which the output voltages of these transformers decayed to 36.8% of their 100% value ranged from 59 to 1950 nanoseconds.