# PTC Thermistor

Switching type positive temperature coefficient (PTC) thermistor

**Library:**Simscape / Electrical / Sensors & Transducers

## Description

The PTC Thermistor block represents a switching type Positive Temperature Coefficient (PTC) thermistor. This type of thermistor has a decreasing resistance with temperature increasing up to the Curie temperature. Above the Curie temperature the resistance increases very rapidly with increasing temperature, as shown in the following plot. The region to the right of the Curie temperature is called the PTC regime. To represent a non-switching linear PTC thermistor, use the Thermal Resistor block.

For a switching type PTC thermistor, the resistance *R* at
temperature *T* is given by

$$R=\{\begin{array}{ll}{R}_{0}{e}^{{\alpha}_{0}\left(T-{T}_{0}\right)}\hfill & \text{for}T\text{}{T}_{\text{c}}\hfill \\ {R}_{1}{e}^{{\alpha}_{1}\left(T-{T}_{1}\right)}\hfill & \text{for}T\text{}\ge \text{}{T}_{\text{c}}\text{}\hfill \end{array}$$

$${T}_{c}=\frac{\mathrm{log}\left({R}_{1}\right)-\mathrm{log}\left({R}_{0}\right)+{\alpha}_{0}{T}_{0}-{\alpha}_{1}{T}_{1}}{{\alpha}_{0}-{\alpha}_{1}}$$

where:

*T*_{c}is the Curie temperature.*R*_{0}is the resistance at nominal temperature*T*_{0}.*R*_{1}is the resistance at reference temperature*T*_{1}.*T*_{0}is the nominal temperature at which the resistance is quoted, usually room temperature.*T*_{0}is less than the Curie temperature*T*_{c}.*T*_{1}is the reference temperature, equal or greater than the Curie temperature*T*_{c}, which means that at this temperature the PTC regime is in force.*α*_{0}is the temperature coefficient at nominal temperature*T*_{0}.*α*_{1}is the temperature coefficient at reference temperature*T*_{1}.

The following equation describes the thermal behavior of the block:

$$Q={K}_{d}{t}_{c}\frac{dT}{dt}$$

where:

*Q*is the net heat flow into port A.*K*_{d}is the**Dissipation factor**parameter value.*t*_{c}is the**Thermal time constant**parameter value.*dT/dt*is the rate of change of the temperature.

### Variables

To set the priority and initial target values for the block variables prior to simulation,
use the **Initial Targets** section in the block dialog box or Property
Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model.
Using system scaling based on nominal values increases the simulation robustness. Nominal
values can come from different sources, one of which is the **Nominal
Values** section in the block dialog box or Property Inspector. For more
information, see System Scaling by Nominal Values.

## Ports

### Conserving

## Parameters

## Extended Capabilities

## Version History

**Introduced in R2012b**