Overview

The replacement of receiving tubes by transistors and integrated circuits created new requirements for electronic circuit protection. Tube circuits could operate reliably in elevated temperature environments while simultaneously emitting considerable amounts of heat without much concern for their failure, but all semiconductor devices are vulnerable to excess heat. Moreover, tube circuits operated from high-voltage sources, typically the AC line, and they were tolerant of variations in power supply output, while semiconductor devices can easily be destroyed by overvoltages. In addition, electrostatic discharge (ESD) was not viewed as a threat during the tube-circuit era.

These facts focused more attention on circuit protection beyond the installation of simple fuses and perhaps fans. Semiconductor device vulnerability created new industries for the manufacture of protective devices, tools, and workstation products. And the vulnerability of solid-state circuits became a more critical issue as the component density on circuit boards increased and integrated circuits become more complex and expensive. Some MOS ICs were found to be particularly susceptible to damage or destruction by ESD and over-voltage.

The circuit breakers and fuses installed in the AC service panels of homes, offices, and factories respond too slowly and imprecisely to guard sensitive devices or circuits against overcurrent, and they are incapable of screening out transient voltage spikes. This means that circuit and system designers have had to bring circuit protection down to the circuit level or at least in close proximity to the circuits. Consequently, electronics manufacturers now include a variety of protective devices such as fuses,...