Defrosting Control Circuit for Electric Refrigerator

摘要

1,198,380. Defrosting circuits. MATSUSHITA ELECTRONICS CORP. 20 Dec., 1968 [23 Dec., 1967], No. 60721/68. Heading H2H. [Also in Division F4] A defrosting control circuit for an electric refrigerator has a first transistor 1 for triggering a solid state switching element e.g. a thyristor 3, and a second transistor 2 for resetting the circuit on completion of a defrosting operation, the second transistor base being supplied with a determined potential while the element is conductive and a temperature detecting element e.g. a thermistor 10, sensitive to the temperature inside the freezer, arranged to supply a base bias to one of the transistors during the defrosting operation. Momentary closure of a pair of manually or time-switch operated contacts 8 renders transistors 1, 2 conductive which fires a thyristor 3 energizing a defrosting heater 6, the voltage across which maintains the transistors conductive on release of the switch 8. A rise of temperature of the freezer decreases the resistance of thermistor 10 which at a given point resets the circuit into a non-conductive condition. In another arrangement. Fig. 2 (not shown), the contacts 8 and thermistor are connected to the base of transistor 2. The heater 6 may be replaced by a valve through which a hot gas may be supplied to the freezer. The arrangement is stated to completely defrost a freezer irrespective of the amount of frost accumulated.