2.1.7 Thermistors

• Thermistor


  A type of resistor whose resistance varies significantly with temperature
• Types of Thermistors

  • NTC (Negative Temperature Coefficient)
  • PTC (Positive Temperature Coefficient)
• NTC Thermistors

  • Resistance decreases as temperature increases
  • High resistance at low temperatures
  • Commonly used for temperature sensing
• PTC Thermistors

  • Resistance increases as temperature increases
  • Low resistance at low temperatures
  • Used as resettable fuses
• How NTC Thermistors Work

  1. High resistance at low temperatures

  2. Resistance decreases as temperature rises

  3. Increased charge carriers available for conduction
• How PTC Thermistors Work

  1. Low resistance at low temperatures

  2. Resistance increases significantly after threshold

  3. Structural changes inhibit charge flow
• 1. I Characteristics of NTC Thermistors

  Current increases rapidly with small voltage increase at higher temperatures
• 1. I Characteristics of PTC Thermistors

  Current increases linearly at low voltages, levels off after Curie point
• Applications of Thermistors

  • Temperature Sensing
  • Temperature Compensation
  • Over-Temperature Protection
  • Inrush Current Limiting
• Temperature Sensing

  • Digital thermometers
  • Temperature monitoring systems
• Temperature Compensation

  • Electronic devices maintaining stable performance
• Over-Temperature Protection


  • Circuits protecting against overheating
• Inrush Current Limiting

  • Power supplies
  • Motors
• Practical Experiment with Thermistors

  1. Connect thermistor in circuit

  2. Record initial resistance

  3. Heat thermistor and record data

  4. Plot resistance vs. temperature graph
• Analysis of NTC Thermistor Graph

  • Decrease in resistance with increasing temperature
• Analysis of PTC Thermistor Graph

  • Initial decrease in resistance followed by sharp increase
• Thermistors are crucial components for temperature sensing and control in various electronic applications
• Understanding thermistors helps in designing and troubleshooting temperature-dependent systems