Full of heat sensation, compact and powerful: Shunluo NTC thermistors make circuits safer

The image is sourced from the interior of Shunluo

A thermistor is a temperature sensitive resistor device whose resistance value changes with temperature. Therefore, thermistors can be divided into two types:

Positive temperature coefficient thermistorPTC Thermo Passive

TemperatureCoefficientThermistor)

Negative temperature coefficient thermistor(NTC Thermostor Negative TemperatureCoefficientThermostor)

Image sourced from the internet

Chip packaging features: small size, multiple specifications, high sensitivity, and automatic mounting.

Principle of resistance change: Metal oxides such as manganese, cobalt, nickel, and copper are the main materials. When the temperature is low, the number of charge carriers (electrons and holes) in oxide materials is small, and their resistance value is higher; As the temperature increases, the number of charge carriers increases and their resistance values decrease.

The (nominal) zero power resistance value R25 refers to the DC resistance value measured at the specified temperature (25 ℃), and the change in resistance value caused by self heating can be ignored for the total measurement error.

It is calculated from the values at two specific ambient temperatures, as shown in the following formula:

• T and T0 take the absolute temperature (K);

• The general comparison temperature is 25 ℃/50 ℃, and there are also options of 25 ℃/85 ℃.

  
  

A thermistor is a current that heats it up by 1 ℃ by heating itself in a still air environment at a temperature of 25 ℃.

The thermal time constant is the time required for a thermistor to change from the initial temperature to 63.2% of the final temperature when the ambient temperature suddenly changes at zero power.

The electrical power consumed by a thermistor to heat up by 1 ℃ through its own electrification.

The electrical power consumed by a thermistor to rise from 25 ℃ to 100 ℃.

The image is sourced from the interior of Shunluo

The image is sourced from the interior of Shunluo

The image is sourced from the interior of Shunluo

The image is sourced from the interior of Shunluo

The key parts of the camera module (such as CMOS sensors) generate a large amount of heat during operation, and if the temperature is too high, it can lead to performance degradation or malfunction. NTC thermistors can monitor temperature changes in these critical areas, adjust the working status of the circuit in a timely manner, and improve the stability and reliability of the module.

The heat generated during the use of LED lights can affect their brightness and lifespan. To prevent excessive temperature from having adverse effects on LED lights, it is necessary to use NTC thermistors to limit the maximum current of LED lights.

The WiFi/Bluetooth circuit module will generate a certain amount of heat during operation, especially when increasing the transmission and reception frequency. If the module temperature is too high, it may cause damage to circuit components or lead to performance degradation. To prevent this situation from happening, NTC thermistors can be used for monitoring and protection.

Monitoring the temperature of the charging interface, especially during charging, can easily generate high temperatures. When the interface temperature increases, the resistance value of the NTC thermistor decreases, and the current in the circuit also changes accordingly. By detecting current changes in the circuit, it is possible to adjust the output power of the charger or trigger a temperature alarm to pause charging, thereby controlling the temperature of the interface to avoid overheating.

When a mobile phone is processed with high performance for a long time, the CPU will generate a large amount of heat, and the thermal detection will react by reducing the frequency of the phone to avoid CPU overheating and damage.

The function of NTC thermistors in power amplifiers is not only temperature monitoring and protection, but also temperature compensation to improve the linearity and stability of power amplifiers and avoid amplification distortion. Specifically, the output voltage signal of the NTC thermistor is amplified by the power amplifier and combined with the control signal of the power amplifier to achieve adaptive temperature compensation through feedback control. In this way, when the temperature rises, the compensation circuit will automatically reduce the gain of the amplifier or adjust the bias current, thereby maintaining the linearity and stability of the amplifier and avoiding amplification distortion.

The image is sourced from the interior of Shunluo

Lithium batteries are also commonly used in TWS battery compartments, as there is also a thermal sensor on the battery protection board to monitor the battery temperature.

The internal space of the earphones is small and contains lithium batteries. It is necessary to monitor the heat dissipation and battery temperature to prevent high-temperature burns to people.

The image is sourced from the interior of Shunluo

The image is sourced from the interior of Shunluo

(The following table shows some product specifications)

The image is sourced from the interior of Shunluo

Meaning of □ and ◎ in the table:

※□: Tolerance code for resistors, with a maximum accuracy of ± 1%

※◎: Tolerance code for B value, with a maximum accuracy of ± 1%

According to the temperature perception requirements of the circuit, determine the R25 and B values, namely the R-T curve of the chip NTC. It is required that this curve be fitted with the sensitivity of the circuit temperature perception, so that the difference in resistance values is very small under the same temperature change;

If it is necessary to improve the temperature sensitivity requirements of the line, a chip NTC component with a high B value must be selected. The higher the B value, the greater the change in resistance value under the same temperature change, which is reflected in the greater the change in voltage and the more identifiable voltage points;

If it is necessary to reduce the temperature sensitivity requirement of the line, a linear resistor with extremely low temperature coefficient can be connected in series with the chip NTC to reduce the B-value of its R-T curve (making the partial voltage of the tested NTC smaller than that of the NTC with resistance when the same temperature rises).