GB1423076A - Temperature regulating devices - Google Patents

Abstract

1423076 Automatic control of temperature K ARITA 4 Feb 1974 [5 Feb 1973] 05106/74 Heading G3R [Also in Division H5] A temperature regulating device for a heating element 12, connected in series with a thyristor 11 to an A.C. supply 9, 10, comprises an electrically-conducting layer 21 which has a steep N.T.C. characteristic and is interposed between the element 12 and a further electrical conductor 18 which extends along element 12. The variation of the resistance between element 12 and conductor 18 is used to determine the period of conductivity of a gate controlled element, e.g. transistor 14, and hence that of thyristor 11 during the times that positive half-cycles are applied thereto. The device may be used in an electric blanket. When terminal 10 is positive capacitors 19 and 16 charge up. Immediately after switching on the supply element 12 is cold so that the resistance of layer 21 is high and when terminal 9 is positive capacitor 16 can discharge only slowly through layer 21 and the base-emitter circuit of transistor 14. Accordingly at such times capacitor 19 biases the base electrode of transistor 14 negative so that it does not conduct and so thyristor 11 does conduct. When element 12 has heated up, the resistance of layer 21 is low, capacitor 16 can discharge relatively quickly thus rendering transistor 14 conductive and thyristor 11 non-conductive. The operating temperature is set by varying the value of a resistor 20. Transistor 14 may be replaced by a small capacity thyristor.