# Chip NTC Thermistor FAQs

A thermistor is a temperature dependent resistor - the term itself is a combination of the words “thermal” and “resistor”. There are two major types of thermistors:

Type Description
PTC Positive Temperature Coefficient - when temperature increases, resistance increases
NTC Negative Temperature Coefficient - when temperature increases, resistance decreases

Current stock we carry for chip NTC thermistors can be found here.

This post serves provides answers to some of the more commonly asked questions about our chip NTC thermistors:

What Is Temperature Compensation?

NTC thermistors are often used for temperature compensation of oscillating frequency of a quartz crystal oscillator. Temperature compensation is a process which aims to reduce the effect of temperature fluctuations on components that are sensitive to changes of temperature.

What Is the Thermal Time Constant?

The period in which a Thermistor’s temperature will change 63.2% of its temperature difference from ambient temperature T0 (°C) to T1 (°C).

This shows that the constant τ (sec.) is defined as a time for the thermistor to reach 63.2% of the total difference between its initial and final body temperatures.

What Is Withstand Voltage?

This is an indicator of the amount of voltage that can be resisted when applied for three minutes in still air at 25°C. Withstand voltage is measured using a method that starts at 0V and then gradually increases the amount of voltage applied.

What Is the B Constant?
The B constant expresses how sensitive a thermistor is (in change rate of its resistance) to temperature changes.The change rate can also be expressed by the gradient of a line. The larger the gradient, the higher the sensitivity.

This constant is calculated using the resistance value at two specified ambient temperatures according to the following formula.

B=ln (R/R0) / (1/T-1/T0)

R: Resistance value at time when ambient temperature is T (K) R0: Resistance value at time when ambient temperature is T0 (K)

Content and images provided courtesy of TDK’s FAQs:

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