| 摘要 |
A circuit for an electric blanket or other heater comprises a heating conductor (2) connected between input terminals (5, 6), and a sensor conductor (3) and temperature sensitive medium (4) substantially co- extensive with the heating conductor. In the event of overheating, the impedance (Z) of the medium (4) drops from a relatively high to a relatively low value and/or it melts to permit contact of the conductors (2, 3) whereby the impedance (Z) will drop to substantially zero. A self-regulating PTC resistive element (7) is connected in series with the heating conductor (2) but disposed remotely therefrom. The element (7) is thermally coupled to resistors (9, 11), such that in the event of the medium (4) being overheated anywhere along its length the resultant current through the resistors (9, 11) will heat the element (7) so that it adopts and stays in a high resistance state, terminating the flow of heating current to the conductor (2). <IMAGE> |
