NTC sensor elements are the basis for the realization of NTC temperature sensors in various applications. In fact, they are not only used in temperature sensors, but also very common in other electronic product applications, such as resettable fuses and self-adjusting heaters. As a type of semiconductor sensing element, the application of NTC can be roughly divided into two categories, one is for temperature measurement, and the other is for circuit protection.
Realize high sensitivity and high precision temperature measurement
Due to their high sensitivity and high precision, NTC thermistors have been well used for temperature measurements where durability, reliability, and stability are important. Although there are many materials for thermistors, compared with conductors such as metals, semiconductor resistors such as NTC have the advantages of being easier to process, smaller and lighter. In addition, due to its fast response, it is also suitable for small diameter precision equipment.
In a low-cost temperature measurement scheme, a pull-up resistor is generally connected in series between the NTC thermistor and the positive pole of the power supply, and the ambient temperature change is determined by collecting the voltage divider change across the NTC thermistor. In most cases, a resistor with the same value as the normal temperature resistance of the NTC is connected in series, and the current flowing through is guaranteed to be small enough to avoid self-heating to ensure the accuracy of the measurement process.
Avoid self-heating to ensure the accuracy of the measurement process. On the other hand, since NTC thermistors are non-linear resistors in nature, they must be linearly processed before temperature measurement, and ensure that the measurement is within a suitable temperature range, otherwise the result will be Far from it. At present, it can generally cover the measurement of -50°C to 150°C, and some industry-leading NTC manufacturers can cover -55°C to 175°C. With a special coating, the NTC thermistor can be covered up to 300°C without any problem.
The resistance temperature coefficient of the NTC thermistor is reduced by 3 to 5% per 1°C. Compared with other metal resistance values, the change per 1°C is only about a few percentage points. It can be seen that the NTC thermistor shows a small temperature change. large resistance changes. From these characteristics, it is not difficult to see that within a suitable temperature range, NTC thermistors can detect small temperature differences with high precision and sensitivity.
(NTC sensor element, TDK)
Chip embeddable NTC thermistors can be directly integrated into IGBT modules and IPM modules, such as TDK’s new chip L860 NTC thermistors, which do not require leads and can be directly embedded into the power supply by sintering and heavy aluminum wire bonding module, completely different from traditional SMD NTC components. We all know that power modules are typically most efficient when operating close to their power limits, but maintaining extreme operation requires precise temperature control. Compared with the traditional NTC element, the thermal coupling between the chip NTC thermal element and the power module is more stable, which means that the element can achieve ultra-fast response, which is more conducive to high-precision temperature measurement and control.
Whether in industrial, automotive or consumer applications, monitoring the temperature of all power components is a critical task and a fundamental requirement to ensure the safety, reliability and service life of the entire system, where NTC thermistors are widely used.
NTC suppresses surge and improves system reliability
In terms of circuit protection control, NTC has many applications. Generally, when it is turned on, a large current will flow through the diode. If the current is too large, the diode may be damaged. There are many ways to suppress inrush current. Generally, resistance current limiting is used in small and medium power power supplies to suppress power-on inrush current.
With traditional fixed-value current-limiting resistors, the power consumption wasted on the resistor cannot be changed. An NTC thermistor is connected in series on the line. Before starting the machine, the temperature of the thermistor is low and the resistance is relatively large, which can well limit the inrush current when starting up. After the power is turned on, the temperature of the thermistor increases, the resistance value is greatly reduced, and there is no excessive loss.
(Source: Fenghua Hi-Tech)
This process occurs very quickly in practical applications. The NTC thermistor heats up rapidly as the temperature increases, and its resistance value will rapidly drop to a very small level in milliseconds, generally only a few tenths of ohms to a few ohms. the size of. In contrast, the power dissipated in the resistance is reduced by dozens or even hundreds of times.
The suppression method based on NTC thermistor has high power, strong ability to suppress surge current, high reliability, long life and small residual resistance. Under normal circumstances, the NTC of the low-power power supply does not need to add a relay, and the high-power needs to add a relay. However, it should be noted that the power supply equipment that uses NTC to suppress the power-on surge cannot be turned on and off frequently. It takes tens of seconds to several minutes for the NTC to cool down, and it can be turned on again after it recovers to its cold resistance value.
As an NTC that suppresses power-on surges to ensure that electronic equipment is not damaged, it can be said to be the simplest and most effective. Of course, NTC only plays the role of power-on protection. When the circuit is working normally or short-circuited, NTC has no way to deal with the surge.
summary
As a typical type of temperature-sensitive semiconductor resistor, NTC thermistor, its resistance value will decrease as the temperature increases. On the one hand, NTC thermistor elements also have the advantages of small loss, almost no hysteresis, and can also play a very good protective role.