Protection of electrical systems using PTC devices.

摘要

An electrical systems is described in which a PTC device (20) is used to protect a circuit against a thermal or electrical fault. The systems comprise two circuits (17, 18) one containing a PTC device (20) and the other containing a resistor (23, 23a) which is thermally coupled to the PTC device and which is heated when a fault condition occurs; this heating of the resistor (23, 23a) converts the PTC device (20) to the high resistance state and thus causes a desired change in the electrical condition of one or both circuits. The circuit can be used for the electrical circuitry of an electric blanket.