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## N_06L00681 Datasheet(PDF) 5 Page - AVX Corporation

 Part No. N_06L00681 Description NTC Thermistors Download 38 Pages Scroll/Zoom 100% Maker AVX [AVX Corporation] Homepage http://www.avx.com Logo

 5 page 42.1.9. Shaping of the R (T) characteristicBy the use of a resistor network, it is possible to modify theR (T) characteristic of a thermistor so that it matches therequired form, for example a linear response over a restrict-ed temperature range.A single fixed resistor Rp placed in parallel with a thermistorgives a S–shape resistance–temperature curve (see Figure 2)which is substantially more linear at the temperature rangearound the inflexion point (Ro, To).Figure 2 – Linearization of a thermistorIt can be calculated that better linearization is obtained whenthe fixed resistor value and the mid-range temperature arerelated by the formula:Rp = RToxB – ToB+ 2ToFor example, with a thermistor ND03N00103J —R25°C = 10kΩ, B = 4080 Kgood linearization is obtained with a resistor in parallel wherethe value is:Rp = 10,000 Ω x4080 - 298= 8088 Ω4080 + (2 x 298)2.1.10. Demonstration of the R (T) parameterscalculationTo help our customers when designing thermistors fortemperature measurement or temperature compensation,software developed by our engineering department is avail-able upon request.2.2 CHARACTERISTICS WITH ENERGYDISSIPATIONWhen a current is flowing through an NTC thermistor, thepower due to the Joule effect raises the temperature of theNTC above ambient.The thermistor reaches a state of equilibrium when thepower supplied becomes equal to the power dissipated inthe environment.The thermal behavior of the thermistor is mainly dependenton the size, shape and mounting conditions.Several parameters have been defined to characterize theseproperties:2.2.1. Heat capacity (H)The heat capacity is the amount of heat required to changethe temperature of the thermistor by 1°C and is expressed inJ/°C.2.2.2. Dissipation factor ( )This is the ratio between the variation in dissipated powerand the variation of temperature of the NTC. It is expressedin mW/°C and may be measured as:=U.I85 – 25where U.I is the power necessary to raise to 85°C the tem-perature of a thermistor maintained in still air at 25°C.2.2.3. Maximum permissible temperature (T max)This is the maximum ambient temperature at which the ther-mistor may be operated with zero dissipation. Above thistemperature, the stability of the resistance and the leadsattachment can no longer be guaranteed.2.2.4. Maximum permissible power at 25°C (Pmax)This is the power required by a thermistor maintained in stillair at 25°C to reach the maximum temperature for which it isspecified.For higher ambient temperatures, the maximum permissiblepower is generally derated according to the Figure 3 here-after and TL = Tmax – 10°C.Figure 3 – Derating of maximum powerR(kΩ)T (°C)RTORpROTORpPmax25°TLTmaxT°CNTC ThermistorsGeneral Characteristics