Thermally Coupled NTC Disk Thermistors for Power Applications

A pair of small disk negative thermal coefficient (NTC) thermistors were joined together laterally using a thin layer of silicon resin between them to form a novel thermally coupled device (TCT). The epoxy coating on disk thermistors enables concurrent galvanic isolation and thermal coupling. Input thermistor Th1 in the coupled pair was self-heated at constant voltages and acts as heat transmitter while the output thermistor Th-2 acted as a heat receiver through the epoxy layer and silicon resin. Small NTC disk thermistors with different nominal resistances were produced out of nickel manganese and modified nickel manganese powder. The disk thermistor resistances and the thermistor exponential temperature factor B were measured in the climatic test chamber. The input power, resistance, and temperature of both disk thermistors were measured at different ambient temperatures as a function of input voltage and time. The temperature of thermistors Th1 and Th-2 (input and output) was determined using the Steinhart-Hart equation. The TCT device sensitivity, stability, and inaccuracy were also analyzed. The applications of disk TCT devices are based on the measuring of output temperature versus input power in automotive electronics, home appliances, and power convertors.