PTC Resistor: Properties & Application

The function of the PTC resistors simply explained

The PTC resistor is an electronic component with a positive temperature coefficient (PTC). Current always flows particularly well through the components when their temperature is low. If the ambient temperature rises, the resistance increases and less current flows. Due to this special behavior, experts speak of a PTC resistor as a PTC thermistor.

Barrier layers form when the temperatures rise

The components are composed of very small crystals through which the current flows. If the temperature rises, barrier layers form at their borders. Experts also speak of potential walls. These disrupt the movement of the electrons, which means that current can flow through them more poorly.

Types and suitable materials for the PTC thermistor

Depending on how the resistance changes with increasing temperatures, three classes of PTC resistors can be distinguished. These are:

• PTC thermistor with linear resistance curve (use as temperature sensor, for example)
• Ceramic-based non-linear PTC resistors (used, among other things, as a self-regulating heating element in the ceramic heater)
• Polymer-based non-linear resistors (used, for example, as self-resetting overcurrent protection)

While all metals have similar properties, these are much more pronounced with a PTC resistor.

Properties of various PTC resistors

The temperature-dependent behavior during production can be influenced. Silicon-based thermistors usually have a parabolic relationship between temperature and resistance. They are suitable for temperature ranges from minus 50 to plus 150 degrees Celsius and are characterized by their small size.

PTC resistors that are manufactured with barium carbonate achieve a very special temperature behavior due to their specific properties. They act like thermistors (NTC resistance) at low and high temperatures. The resistance decreases the warmer it gets. In the area in between, however, the resistance increases sharply with increasing temperatures.

PTC thermistors made of pure metals are characterized by a comparatively linear resistance. For example, platinum resistors like the PT100 are very suitable for temperature measurement. A control device interprets the resistance values ​​in order to recognize the current temperature values.

The most important parameters of the PTC resistors

If you want to select a PTC thermistor, you have to consider various parameters. The nominal resistance is particularly important. Because this indicates how high the resistance is at a temperature of 25 degrees Celsius. In addition, temperature ranges and temperature coefficients must be observed. The latter stand for the change in resistance values ​​with increasing ambient temperatures.

Typical areas of application for a PTC resistor

PTC thermistors or PTC thermistors are used today in very different technical areas. When it comes to heating technology, platinum sensors such as the PT100 are particularly suitable for temperature measurement. For example, they are installed in external sensors. In this way, the heating control measures the outside temperature and can correctly select the flow temperature of the heating depending on the individual heating curve.

PTC thermistors can also measure the liquid level in containers. Their temperature changes depending on whether they are in the moist or dry area. A regulation can interpret the different resistance values ​​and act accordingly.

However, it also makes sense to use it to protect against excessive temperatures. In this context, PTC resistors automatically reduce the current flow when it gets too hot in their environment. They represent an alternative to fuses, but in contrast to them, they are self-resetting and can be used multiple times. Once a fuse has tripped, it must be replaced.