Transient voltages generated by inductive switching in control circuits

In certain control applications a common d.c. supply is used for both electronic and electromechanical equipment. In this situation semiconductor devices may be subjected to transient voltages generated by the operation of mechanical switches in inductive circuits. This paper describes the factors involved in the generation of such transients and methods for predicting their time duration are proposed. The circuit interruption process is described in terms of either stable or unstable arc switching and the limiting factors for these two conditions are discussed. It is shown that when unstable arc switching occurs short-duration voltage spikes appear across the common power supply and, by implication, across all parallel-connected equipment. Reasonable correlation is shown to exist between predicted and measured transient-voltage time durations and the analytical models proposed could be used as a theoretical basis for transient-voltage specifications.