| 摘要 |
A heating circuit, in particular for an electric blanket or pad, comprises an elongate heating conductor and switch connected in series between input terminals for connection to an AC supply. Switch control is operative to close the switch to cause current to flow through the heating conductor. The circuit further comprises a sensor conductor coextensive with the heating conductor, and a temperature sensitive resistance coextensive with the heating and sensor conductors and having an impedance that falls with increasing temperature. A resistor is connected in series with the sensor conductor such that a current dependent on the impedance of the temperature sensitive resistance flows through the resistor, whereby the voltage across the resistor varies with said impedance. Voltage sensing structure is responsive to the voltage across the resistor reaching a predetermined value to inhibit operation of the switch control, thereby to provide normal and/or overtemperature control. Further, circuit interruption structure is responsive to excessive heating of the resistor to prevent current flow through the heating conductor, thereby to provide back-up overtemperature control. |
