Power Thermistor (= Inrush Current Limiter) Series NTC thermistors heat up when a current passes through them. The heat up then causes a dramatic decrease in resistance. This effect is used by SEMITEC s power thermistor series to suppress inrush currents. Circuits including for example electric bulbs or capacitors induce an inrush current of more than 100 times the normal current when the circuit is switched on. SEMITEC s power thermistors suppress this inrush current and thereby protect electric equipment from damage. Applications Switch circuits, adapters, LCD TVs, plasma TVs, air conditioners, DVD players, audio equipment, LCD projectors, copy machines, PCs, printers, office The temperature of a thermistor generally changes automation, slot machines and many more slowly, even if the ambient temperature is changed How to use power thermistors rapidly from T1 to T2. to an air temperature of Thethermal time constan describes the time necessary until the thermistor reaches 63.2% of the High humidity heat test temperature difference. to a humidity If a current flows through a thermistor it heats up and resistance decreases. However, the resistance is Test sample is exposed to the maximum rating current stabilized at a saturation resistance value which is at an ambient temperature of 25 for 1,000 hours. determined by the impressed electric power and the thermistor s dissipation factor. Temperature cycle Theresidual resistanc value describes the Test samples is subjected to the following temperature maximum resistance value for the maximum cycle (10 times): permissible current. If a small voltage is applied to a thermistor, then a to an air temperature of The thermistor resistance for the suppressed corresponding small current will flow and cause the current should be higher than 4.2 ohm when below thermistor to heat up. High humidity heat test 30A according to the formula below. Thedissipation facto describes the electric power to a humidity value which leads to an increase of the thermistor s temperature by 1. Test sample is exposed to the maximum rating current at an ambient temperature of 25 for 1,000 hours. t is the temperature increase of the thermistor. Temperature cycle Test samples is subjected to the following The maximum permissible current describes the Accordingly, for this example suitable thermistors are temperature cycle (10 times): current value which increases the temperature of the 6D2-22, 5D2-18 and 8D2-18. thermistor to 200 (Version 2) and 160 (Version 1) In cases where a quick response time (= small thermal respectively at an ambient temperature of 25. When time constant) is needed a small size / large effect (= the ambient temperature is higher than 25 then the large rated zero-power resistance) power thermistor maximum permissible current is reduced as per the such as the 8D2-18 is advantageous. table below. Use below circuit for power supplies of 100V and 200V. 17Safety standards UL1434 File No. E926689 (1D2-22 excluded) The rated values in thedissipation facto andthermal time constan columns are reference values. 18