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Part Name  Description 
N_09U00154 Datasheet(PDF) 5 Page  AVX Corporation 

5 page 4 2.1.9. Shaping of the R (T) characteristic By the use of a resistor network, it is possible to modify the R (T) characteristic of a thermistor so that it matches the required form, for example a linear response over a restrict ed temperature range. A single fixed resistor Rp placed in parallel with a thermistor gives a S–shape resistance–temperature curve (see Figure 2) which is substantially more linear at the temperature range around the inflexion point (Ro, To). Figure 2 – Linearization of a thermistor It can be calculated that better linearization is obtained when the fixed resistor value and the midrange temperature are related by the formula: Rp = R To x B – To B+ 2To For example, with a thermistor ND03N00103J — R25°C = 10kΩ, B = 4080 K good linearization is obtained with a resistor in parallel where the value is: Rp = 10,000 Ω x 4080  298 = 8088 Ω 4080 + (2 x 298) 2.1.10. Demonstration of the R (T) parameters calculation To help our customers when designing thermistors for temperature measurement or temperature compensation, software developed by our engineering department is avail able upon request. 2.2 CHARACTERISTICS WITH ENERGY DISSIPATION When a current is flowing through an NTC thermistor, the power due to the Joule effect raises the temperature of the NTC above ambient. The thermistor reaches a state of equilibrium when the power supplied becomes equal to the power dissipated in the environment. The thermal behavior of the thermistor is mainly dependent on the size, shape and mounting conditions. Several parameters have been defined to characterize these properties: 2.2.1. Heat capacity (H) The heat capacity is the amount of heat required to change the temperature of the thermistor by 1°C and is expressed in J/°C. 2.2.2. Dissipation factor ( ) This is the ratio between the variation in dissipated power and the variation of temperature of the NTC. It is expressed in mW/°C and may be measured as: = U.I 85 – 25 where 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 this temperature, the stability of the resistance and the leads attachment 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 still air at 25°C to reach the maximum temperature for which it is specified. For higher ambient temperatures, the maximum permissible power is generally derated according to the Figure 3 here after and TL = Tmax – 10°C. Figure 3 – Derating of maximum power R (k Ω) T ( °C) RT O Rp RO TO Rp P max 25 ° TL Tmax T °C NTC Thermistors General Characteristics 
