FUNDAMENTALS OF RESETTABLE FUNCTIONALITY IN PPTC DEVICES

摘要

In many of today's applications resettable devices such as polymeric positive temperature coefficient (PPTC) devices, ceramic PTC devices, and bimetal breakers, provide circuit protection. These devices do not require replacement after a fault event, and allow the circuit to return to the normal operating condition after the power has been removed and/or the overcurrent condition is eliminated. Although 'resettable fuss' is a common term used in describing PPTC devices, they are in fact, non-linear thermistors and are not fuses. A PPTC device is a non-linear thermistor that limits current. Because under a fault condition all PPTC devices go into a high resistance state, normal operation can still result in hazardous voltage being present in parts of the circuit. It is important that the circuit designer recognize critical differences between the two devices.