NTC thermistor function and its application in LED lamps

What is NTC Thermistor and how does it relate to temperature?

NTC stands for Negative Temperature Coefficient, which is a kind of thermistor. NTC thermistor function is that its resistance value decreases with the increase of temperature, this means that when the temperature increases, the resistance value of the NTC will decrease; when the temperature decreases, the resistance value of the NTC will increase.

All resistors have a temperature dependence, given by the temperature coefficient. For most resistors (fixed and variable), this temperature coefficient is kept very low, such that changes in temperature do not significantly affect their resistance. Thermistors, however, have a fairly high temperature coefficient, so that their resistance varies according to temperature.

NTC are usually made of oxide materials such as nickel oxide and zinc oxide. They have high sensitivity and stability and are widely used in temperature measurement and temperature compensation.

Why does the resistance value of NTC decrease with the increase of temperature. This is because in NTC materials, as the temperature increases, the concentration of electrons and holes in the conductive material increases, resulting in a decrease in resistance.

Connect the NTC to key parts in the circuit, such as the LED drive circuit. When the temperature increases, the resistance value of the NTC decreases, causing the current and power in the circuit to decrease. This reduced current and power serves to protect circuits and components from overheating and damage.

The specific circuit diagram can vary according to specific application and design requirements. Generally speaking, the NTC is connected at a key position of the circuit, such as the input or output of the LED driving circuit. Connecting NTC at the input can realize temperature monitoring and temperature compensation to ensure the stability and safety of the circuit. Connecting NTC at the output can realize temperature protection. When the temperature exceeds the set value, the resistance value of NTC will drop, reducing the current and power, thus protecting LED and other components from overheating.

The following is the circuit diagram of the street lamp with NTC:

Characterization Curves – Typical NTC thermistors provide the most accurate readings over the -55℃ to 200℃ temperature range. However, some specially designed NTC thermistors are used at absolute zero temperature (-273.15℃) and some can be used up to 150℃ above.

The figure below shows the characteristic curve of an NTC thermistor:

From the figure we can see that they have a steep resistance temperature curve, indicating good temperature sensitivity.

In temperature measurement, NTC thermistor can be used as temperature sensor. By measuring the change in NTC resistance, the change in temperature can be deduced. The resistance-temperature characteristics of NTC thermistors can be accurately measured by methods such as calibration and look-up tables.

In addition, NTC thermistors can also be used for temperature compensation. In some circuits, the performance of electronic components may be affected by temperature. By connecting the NTC thermistor with other electronic components, the work of the circuit can be adjusted according to the change of the NTC resistance value to achieve temperature compensation.

The NTC thermistor temperature sensor RT relationship table is commonly referred to as the table that represents the different resistance values of the NTC at various temperatures. The accurate parameters of this table are crucial in software development.

A typical RT meter includes the following key parameters:

1. Nominal resistance value

2. B value

3. Tolerance resistance value within the ± range.

Please refer to the table below for specific parameters.

Nominal resistance value: 10kΩ @25℃

Tolerance accuracy: + / – 1%

B value: 3950K @25/50℃

B value accuracy: + / – 1%