A four layer protective device for communication system applications

Solid state electronic equipment used in communication systems is particularly vulnerable to damage from voltage and current surges when connected to outside lines. At the present time there is a dearth of compatible devices useable to protect this equipment by grounding such surges. Ideal surge protectors should incorporate the following features: • A high impedance and a high conductance state. • Fast response to surges at well defined voltage limits. • Rapid and complete recovery in the presence of normal line operating voltages. • High peak current handling capability. • Useful life of many surges. • Safe failure mode. • Low cost. With the increasing trend towards connection of customer terminal equipment to public communication system there is also need for interface devices to protect both the system and the customer. PNPN diodes are potentially capable of meeting the above requirements but must incorporate special design features in order to optimize them to surge protection applications.