How does a thermistor change its resistance with temperature and its applications?
1 Answer
A thermistor is a type of temperature sensor that exhibits a significant change in resistance with variations in temperature. The word "thermistor" is derived from "thermal resistor." The resistance-temperature relationship of a thermistor can be described in two main types: negative temperature coefficient (NTC) and positive temperature coefficient (PTC).
Negative Temperature Coefficient (NTC) Thermistor:
In an NTC thermistor, the resistance decreases as the temperature increases. This is due to the behavior of the semiconductor material from which the thermistor is made. As temperature rises, more charge carriers (electrons or holes) become available, leading to increased conductivity and therefore decreased resistance. NTC thermistors are widely used in various applications, including:
Temperature Measurement: They are commonly used as temperature sensors in devices like thermostats, automotive engine temperature sensors, and industrial equipment.
Overcurrent Protection: NTC thermistors can be employed to protect circuits from excessive current by acting as a current-limiting device that increases in resistance as current increases, thus reducing power dissipation and preventing damage.
Compensation and Control: NTC thermistors can be used for temperature compensation in electronic circuits and as components in feedback loops for temperature control.
Positive Temperature Coefficient (PTC) Thermistor:
In a PTC thermistor, the resistance increases as the temperature rises. This behavior is typically observed in certain ceramic materials. As the temperature increases, the semiconductor material's structure changes, causing an increase in resistance. PTC thermistors find application in areas such as:
Temperature Compensation: PTC thermistors can be used in circuits to provide temperature compensation, maintaining a consistent output in devices like thermally sensitive resistors.
Motor Starting and Protection: PTC thermistors are used in applications like motor starting, where they act as a self-resetting current limiter. Initially, when the motor starts, the resistance is low, allowing a higher current to pass. As the motor heats up, the resistance increases, limiting the current and providing protection against overload.
Inrush Current Limiting: PTC thermistors are used to limit the inrush current when devices like power supplies or transformers are turned on. Their resistance starts high to limit the initial current surge and then decreases as the device stabilizes.
The key advantage of thermistors is their sensitivity to temperature changes, making them suitable for precise temperature measurements and control. However, it's important to note that thermistors have limitations, such as non-linear behavior and self-heating effects at high currents. Therefore, their use must be carefully considered in each specific application.
Negative Temperature Coefficient (NTC) Thermistor:
In an NTC thermistor, the resistance decreases as the temperature increases. This is due to the behavior of the semiconductor material from which the thermistor is made. As temperature rises, more charge carriers (electrons or holes) become available, leading to increased conductivity and therefore decreased resistance. NTC thermistors are widely used in various applications, including:
Temperature Measurement: They are commonly used as temperature sensors in devices like thermostats, automotive engine temperature sensors, and industrial equipment.
Overcurrent Protection: NTC thermistors can be employed to protect circuits from excessive current by acting as a current-limiting device that increases in resistance as current increases, thus reducing power dissipation and preventing damage.
Compensation and Control: NTC thermistors can be used for temperature compensation in electronic circuits and as components in feedback loops for temperature control.
Positive Temperature Coefficient (PTC) Thermistor:
In a PTC thermistor, the resistance increases as the temperature rises. This behavior is typically observed in certain ceramic materials. As the temperature increases, the semiconductor material's structure changes, causing an increase in resistance. PTC thermistors find application in areas such as:
Temperature Compensation: PTC thermistors can be used in circuits to provide temperature compensation, maintaining a consistent output in devices like thermally sensitive resistors.
Motor Starting and Protection: PTC thermistors are used in applications like motor starting, where they act as a self-resetting current limiter. Initially, when the motor starts, the resistance is low, allowing a higher current to pass. As the motor heats up, the resistance increases, limiting the current and providing protection against overload.
Inrush Current Limiting: PTC thermistors are used to limit the inrush current when devices like power supplies or transformers are turned on. Their resistance starts high to limit the initial current surge and then decreases as the device stabilizes.
The key advantage of thermistors is their sensitivity to temperature changes, making them suitable for precise temperature measurements and control. However, it's important to note that thermistors have limitations, such as non-linear behavior and self-heating effects at high currents. Therefore, their use must be carefully considered in each specific application.