14.1 Introduction

In all previous chapters, voltage and current waveforms have been shown at critical points for the various topologies (e.g., Figs. 2.1, 2.10, 3.1, 4.1 for the major topologies).

These are idealized waveforms, and newcomers to switching power supply design may wonder how idealized these waveforms really are. They may wonder how closely actual waveforms resemble the theoretical ones on which much of the circuit design is based.

Newcomers may question how these waveshapes vary with line voltage and load current variations; whether there are noise spikes on ground buses; whether there is decaying, oscillatory, ringing waveform at sharp transitions in voltage and current; and whether there is time jitter at the leading or trailing edges of the waveforms. Other questions may be as follows: How closely does the on volt-second product equal the reset volt-second product in a transformer or an inductor? What does a leakage inductance spike really look like? Since output inductors and flyback transformers are designed to yield certain current waveshapes, how close are these actual waveshapes to the theoretical ones? Since much of the power transistor dissipation at high frequencies comes from simultaneous high voltage and current at turnoff and turnon, can this be observed on a fast time base? What sort of waveform oddities may be expected?

It is thus felt that it would be very instructive and provide a feeling of confidence, especially to designers seeing high-frequency switching waveforms for the first time, if some actual oscilloscope waveforms at...