Approximate analytical formulas are obtained to evaluate the main characteristics of diffused step recovery diodes (SRD) operating as current interrupters in high-power generators of nanosecond pulses with an inductive energy storage: the unwanted pre-pulse voltage, characterizing resistive losses in SRD, amplitude, duration of front and duration of voltage pulse formed on the resistive load. For comparison, similar formulas for epitaxial SRD, partially obtained for the first time, and partially clarifying the early results, are given.