PTC Thermistors

PTC Thermistors: Definition, Function, Applications, and Selection Criteria

Definition:
A PTC (Positive Temperature Coefficient) thermistor is a type of resistor whose resistance increases with an increase in temperature. This unique characteristic is due to the material's composition, which typically includes ceramic or polymer materials with conductive particles.

Function:
PTC thermistors serve as self-regulating devices that can protect electronic circuits from thermal overloads. They function by increasing their resistance as they heat up, which reduces the current flow and thus the heat generated in the circuit. This self-limiting behavior prevents damage from excessive heat and can also be used for temperature sensing and control.

Applications:
1. Overcurrent Protection: In power supplies and motor controls to prevent damage from overcurrent conditions.
2. Temperature Sensing: In thermostats and temperature systems to detect and respond to temperature changes.
3. Heating Elements: In self-regulating heaters where the resistance increase with temperature helps maintain a constant temperature.
4. Battery Protection: In battery packs to prevent overcharging and overheating.
5. Automotive Applications: For temperature control in engine management systems and cabin heating systems.

Selection Criteria:
1. Temperature Range: Choose a PTC thermistor that operates within the required temperature range of the application.
2. Resistance at Ambient Temperature: Ensure the resistance at room temperature meets the circuit requirements.
3. Resistance at Operating Temperature: The resistance should be high enough at the operating temperature to limit the current effectively.
4. Time Constant: Consider the time it takes for the thermistor to respond to temperature changes.
5. Power Rating: Select a thermistor that can handle the expected power dissipation without overheating.
6. Physical Size and Shape: The thermistor should fit within the available space and be compatible with the mounting and integration requirements.
7. Environmental Resistance: Consider the thermistor's resistance to environmental factors such as humidity, chemicals, and mechanical stress.
8. Certifications and Standards: Ensure the thermistor meets any necessary industry standards or certifications required for the application.

When selecting a PTC thermistor, it's important to consult with manufacturers or datasheets to ensure the chosen component meets all the necessary specifications for the intended application.
Please refer to the product rule book for details.