Contents
What does a thermistor do in a power supply?
A thermistor is a resistor, and, just like any resistor, it produces heat energy whenever current passes through it. The heat energy causes the NTC thermistor’s resistance to reduce which then indicates a temperature slightly above ambient temperature.
How do you do thermistor experiment?
Pour boiling water into the beaker and take readings of the current through the thermistor as the temperature falls. Record the results. Plot a graph of current/ mA (y-axis) against temperature/ °C (x-axis). Assuming that the voltage is constant, describe how the conductance or resistance varies with temperature.
What is the function of a thermistor in a circuit?
Thermistors are thermally sensitive resistors whose prime function is to exhibit a large, predictable and precise change in electrical resistance when subjected to a corresponding change in body temperature.
What is thermistor diagram?
Definition: The thermistor is a kind of resistor whose resistivity depends on surrounding temperature. The variation in the thermistor resistance shows that either conduction or power dissipation occurs in the thermistor. The circuit diagram of thermistor uses the rectangular block which has a diagonal line on it.
Where is thermistor used?
Thermistors are used as temperature sensors. They can be found in every day appliances such as fire alarms, ovens and refrigerators. They are also used in digital thermometers and in many automotive applications to measure temperature.
What is a power thermistor?
A Power Thermistor, also called Power NTC or inrush current limiter, is an electronical component which suppresses inrush currents of electric circuits. Switching power supplies, AC motors, and lighting ballasts can induce an inrush current of more than 100 times the nominal current when the circuit is switched on.
How do you read a thermistor?
Thermistor Specifications Usually expressed in percent (e.g. 1%, 10%, etc). For example, if the specified resistance at 25°C for a thermistor with 10% tolerance is 10,000 ohms then the measured resistance at that temperature can range from 9,000 ohms to 11000 ohms.
What are the two basic types of thermistor?
The main two types of thermistors are NTC (Negative Temperature Coefficient) and PTC (Positive temperature coefficient).
What happens when thermistor increases?
With an NTC thermistor, when the temperature increases, resistance decreases. Conversely, when temperature decreases, resistance increases. A PTC thermistor works a little differently. When temperature increases, the resistance increases, and when temperature decreases, resistance decreases.
How does a NTC thermistor reduce power loss?
An NTC thermistor limits an inrush current with its high initial resistance, and then its temperature rises because of energization and its resistance falls to a few percent of its level at room temperature, thus achieving a power loss that is lower than when a fixed resistor is used.
How much voltage do you need for a thermistor?
If we were powering on a device that needed higher power such as a 12V DC motor, for instance, we would need at least 12V of power. However, for an LED, 5V is sufficient. How this circuit works is based on the principle of a voltage divider. The voltage supplied to the circuit is 5VDC.
Why is the resistance of the thermistor so low?
Since at room temperature, the thermistor offers 100KΩ of resistance and the fixed resistor offers 50KΩ, most of the voltage will drop across the thermistor and very little across the fixed resistor. Thus, the voltage across the fixed resistor is very low, lower than the reference voltage set by the potentiometer.
How are PTC thermistors used for current protection?
PTC thermistors can withstand such loading without suffering any damage. If a fixed resistor is used for inrush current limiting, as was common in the past, the high operating current can thermally overstress the resistor and even destroy the resistor or cause a fire to break out. Figure 1 Inrush current limiting in a switch-mode power supply