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with Jim Williams, Staff Scientist
Most circuit designers are familiar with diode dynamic characteristics such as charge storage, voltage dependent capacitance and reverse recovery time. Less commonly acknowledged and manufacturer specified is diode forward turn-on time. This parameter describes the time required for a diode to turn on and clamp at its forward voltage drop.
Historically, this extremely short time, units of nanoseconds, has been so small that user and vendor alike have essentially ignored it. It is rarely discussed and almost never specified.
Recently, switching regulator clock rate and transition time have become faster, making diode turn-on time a critical issue. A potential difficulty due to diode turn-on time is that the resultant transitory “overshoot” voltage across the diode, even when restricted to nanoseconds, can induce overvoltage stress, causing switching regulator IC failure. This video provides a testing methology enabling proper diode selection for switching regulators.