NTC Thermistor: Working, Characteristics & Applications
NTC Thermistors (Negative Temperature Coefficient thermistors) are temperature-sensitive resistors that decrease in resistance as temperature increases. These are widely used in temperature sensing, compensation, and inrush current limiting.
🔧 How NTC Thermistors Work
NTC thermistors are made from metal oxides like manganese, nickel, cobalt, and copper. As the temperature increases, more charge carriers are released, reducing the resistance. This behavior makes them ideal for precise temperature measurements.
📉 Resistance-Temperature Relationship
The resistance of an NTC thermistor follows the Steinhart-Hart equation:
1/T = A + B * ln(R) + C * (ln(R))^3
Where:
- T = Temperature in Kelvin
- R = Resistance in Ohms
- A, B, C = Thermistor constants
📦 Applications of NTC Thermistors
- Temperature sensors in HVAC, automotive, and appliances
- Battery pack temperature monitoring
- Overcurrent and inrush current protection
- Temperature compensation in electronic circuits
📊 NTC Thermistor vs PTC Thermistor
| Feature | NTC Thermistor | PTC Thermistor |
|---|---|---|
| Resistance Change | Decreases with Temperature | Increases with Temperature |
| Use Case | Temperature Sensing | Overcurrent Protection |
| Cost | Generally Lower | Slightly Higher |
📷 Common Types of NTC Thermistors
- Bead Thermistors
- Disk and Chip Thermistors
- Glass-encapsulated Thermistors (for harsh environments)
🛠️ Example Circuit
Below is a simple voltage divider circuit using an NTC thermistor and resistor to measure temperature with a microcontroller like Arduino:
Vcc | | [R] ----> A0 (Analog Pin) | | [NTC] | GND
🧠 Conclusion
NTC thermistors are cost-effective, reliable, and easy-to-use components for temperature measurement and compensation. Their non-linear resistance behavior is predictable and can be easily interpreted using calibration tables or formulas.
Pro Tip: Always check the datasheet for the thermistor's Beta value and resistance at 25°C (R25) when designing your circuit.