# Thermal Resistor

Model resistor with thermal port

Passive Devices

## Description

The Thermal Resistor block represents a temperature-dependent resistor. The resistance when the temperature at the thermal port is T is

R = R0(1+α(TT0))

where:

• R0 is the nominal resistance at the reference temperature T0.

• α is the temperature coefficient.

The following equation describes the thermal behavior of the block:

$Q={K}_{d}{t}_{c}\frac{dT}{dt}-{i}^{2}R$

where:

• Q is the net heat flow into port A.

• Kd is the Dissipation factor parameter value.

• tc is the Thermal time constant parameter value.

• dT/dt is the rate of change of the temperature.

• i is the current through the resistor.

## Dialog Box and Parameters

### Electrical Tab

Nominal resistance

The nominal resistance of the thermistor at the reference temperature. Many datasheets quote the nominal resistance at 25°C (298.15 K) and list it as R25. The default value is `1` Ω.

Reference temperature

The temperature at which the nominal resistance was measured. The default value is `298.15` K.

Temperature coefficient

The coefficient α in the equation that describes resistance as a function of temperature. The default value is `5e-05` 1/K.

### Thermal Tab

Thermal time constant

The time it takes the resistor temperature to reach 63% of the final temperature change when a step change in ambient temperature occurs. The default value is `10` s.

Dissipation factor

The thermal power required to raise the thermal resistor temperature by one K. The default value is `0.001` W/K.

Initial temperature

The temperature of the thermal resistor at the start of the simulation. The default value is `298.15` K.

## Ports

The block has the following ports:

`A`

Resistor thermal port

`+`

Positive electrical port

`-`

Negative electrical port