Circuit arrangement for automatically stabilizing the temperature of an electrical heating appliance

Claim 1

A CIRCUIT ARRANGEMENT FOR AUTOMATICALLY STABILIZING THE TEMPERATURE OF AN ELECTRICALLY HEATED APPLIANCE INCLUDING A HEATING CIRCUIT, COMPRISING A TEMPERATURE DEPENDENT RESISTOR MADE FROM CERAMIC MATERIAL, AND HAVING A POSITIVE TEMPERATURE COEFFICIENT OF RESISTANCE, AT LEAST WITHIN THE UPPER PART OF ITS OPERATING TEMPERATURE RANGE; SAID RESISTOR CONSISTING OF FERROELECTRIC MATERIAL HAVING A CURIE TEMPERATURE, ABOVE WHICH THE MATERIAL LOSES ITS PERMANENT POLARIZATION, LYING AT LEAST BELOW THE UPPER LIMIT OF THE OPERATING TEMPERATURE RANGE, SAID MATERIAL BEING CONDUCTIVE AS A RESULT OF IMPURITY CENTERS, WHEREBY THE SPACING OF THE DONORS FROM THE LINE BAND AND OF THE ACCEPTORS FROM THE VALENCE BAND IS SMALLER, ESPECIALLY CONSIDERABLY SMALLER THAN HALF THE WIDTH OF THE PROHIBITED ZONE BETWEEN THE VALENCE BAND AND LINE BAND, WITH THE CONDUCTIVITY OF THE MATERIAL BEING LOW AS COMPARED WITH IMPURITY CENTER CONDUCTIVITY, AT LEAST IN A PART OF THE OPERATING TEMPERATURE RANGE IN WHICH THE RESISTOR HAS A POSITIVE TEMPERATURE COEFFICIENT, SAID RESISTOR BEING OPERATIVELY CONNECTED IN SERIES IN A HEATING CIRCUIT, THE RESISTANCE VALUE OF SAID RESISTOR INCREASING STRONGLY WITH RISING TEMPERATURE AT THE TEMPERATURE TO BE STABILIZED, SUCH INCREASE BEING APPROXIMATELY 10**1 POWER AT ABOUT 20* TEMPERATURE RISE.