Application of NTC thermistor in LED lamp

　　Like any other semiconductor device, high brightness, high power LEDs (HBLEDs) generate heat. It is well known that high temperatures can significantly shorten the life of HBLEDs and have an impact on brightness, so temperature control is required. However, in order to control temperature, it is necessary to first determine how to monitor the temperature of the LED die, which is exactly the role of negative temperature coefficient (NTC) thermistors in LED lighting systems.

　　Different temperature sensing devices, including diodes, on-chip sensors, positive temperature coefficient (PTC) thermistors, and resistance temperature detectors (RTDs), can be used in LED lighting applications to protect HBLEDs from overheating. However, in many of these applications, NTC thermistors are often a good choice for temperature sensing and control, mainly because of their small package size and attractive price/performance ratio.

　　Comparing NTC thermistors with different temperature sensing solutions, diodes have low accuracy and limited temperature range; on-chip sensors have higher cost and limited temperature range; PTC thermistors have limited temperature range accuracy, and RTDs are often too costly, with the possible exception of Ni thin film RTDs.

　　Even a small increase in the sensitivity of an NTC thermistor to temperature changes enables the device to be used in temperature sensing/control applications. These devices allow the LEDs to withstand higher currents (by compensation) over the entire temperature range to increase the lifetime of the LEDs. The current can be controlled according to the ambient temperature through an NTC thermistor.

　　NTC thermistors allow the HBLED to be used at its full operating capacity for a given lifetime, which means higher currents at lower ambient temperatures, adapting lower currents as temperatures increase to increase lifetime still guaranteed well the lumen output, .

　　NTC thermistors are available in a variety of package options to accommodate remote sensing applications where the LED substrate and LED driver circuit are physically separated, as well as LED driver substrate combination applications.

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