PTC Thermistor

Switching type positive temperature coefficient (PTC) thermistor

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Libraries:
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

$$R=\{\begin{array}{ll}{R}_0{e}^{{\alpha }_0\left(T-T_0\right)}\hfill & \text{for }T\text{ < }{T}_{\text{c}}\hfill \\ R_1{e}^{{\alpha }_1\left(T-T_1\right)}\hfill & \text{for }T\ge T_{\text{c}}\hfill \end{array}$$

$$T_c=\frac{\log \left(R_1\right)-\log \left(R_0\right)+{\alpha }_0{T}_0-{\alpha }_1{T}_1}{{\alpha }_0-{\alpha }_1}$$

where:

• T_c is the Curie temperature.

• R₀ is the resistance at nominal temperature T₀.

• R₁ is the resistance at reference temperature T₁.

• T₀ is the nominal temperature at which the resistance is quoted, usually room temperature. T₀ is less than the Curie temperature T_c.

• T₁ 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.

• α₀ is the temperature coefficient at nominal temperature T₀.

• α₁ is the temperature coefficient at reference temperature T₁.

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 before 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.

Use nominal values 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 these sources is the Nominal Values section in the block dialog box or Property Inspector. For more information, see System Scaling by Nominal Values.

Ports

Conserving

A — Thermal port

thermal

Thermal port.

+ — Positive port

electrical

Electrical conserving port associated with the PTC thermistor positive port.

- — Negative port

electrical

Electrical conserving port associated with the PTC thermistor negative port.

Parameters

Electrical

Nominal resistance R0 at T0 — Nominal resistance at nominal temperature

1000 Ohm (default)

Nominal resistance of the thermistor at the nominal temperature. Many datasheets quote the nominal resistance at 25°C and list it as R25.

Temperature coefficient alpha0 at T0 — Temperature coefficient at nominal temperature

-0.01 1/K (default) | negative scalar

Temperature coefficient at the nominal temperature. The value must be less than zero.

Nominal temperature T0 — Nominal temperature

298.15 K (default)

Temperature at which the nominal resistance is measured.

Reference resistance R1 at T1 — Reference resistance at reference temperature

10000 Ohm (default)

Reference resistance of the thermistor at the reference temperature.

Temperature coefficient alpha1 at T1 — Temperature coefficient at reference temperature

1 1/K (default) | positive scalar

Temperature coefficient at the reference temperature. The value must be greater than zero.

Reference temperature T1 — Reference temperature

398.15 K (default)

Temperature at which the reference resistance is measured. This temperature must be in the PTC regime.

Thermal

Thermal time constant — Thermal time constant

5.0 s (default)

Time it takes the sensor temperature to reach 63% of the final temperature change when a step change in ambient temperature occurs.

Dissipation factor — Dissipation factor

0.75e-3 W/K (default)

Thermal power required to raise the thermistor temperature by one K.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2012b