LED as a new light source of the semiconductor industry has become more and more attention, and the backlight LED lamp has been widely used in many fields, object article describes some of the features of the LED semiconductor light source and related thermal management (Thermal management) of Preliminary experimental results of the comparison of "hot Ohm's law", heat flow transmission and node temperature detection analysis methods, thermal graphite and aluminum heat sink applications, for reader's reference.
LED semiconductor light source features
Unlike incandescent lamps, conventional fluorescent lamps, and halogen lamps, LED semiconductor light sources are made of semiconductor materials. They are formed by a PN structure. Hole-to-electron pairs produce light, working in the positive direction of the PN junction, and the P region is positive ( Yang) pole, N zone is negative (female) pole. The LED semiconductor light source has small volume, high luminous efficiency, short response time and energy saving. In addition, it has features not found in traditional light sources:
1. Similar characteristics to general PN junction devices such as diodes:
The forward voltage must exceed a certain threshold to have current;
Both forward voltage and forward current are negative temperature coefficients, which decrease with increasing temperature;
In the reverse direction, no current does not work.
2. Like all semiconductor devices, their operating temperature is subject to the following factors:
The junction temperature must be kept below the rated value of 95 °C to 125 °C (depending on the light-emitting device), otherwise it will cause failure;
If the surface has a plastic lens, it will also be limited by the melting temperature of the lens material;
The brightness of the LED is related to the forward current, and after the junction temperature exceeds a certain value, the forward current decreases and the brightness decreases.
There are two possibilities for LED failure modes: Light degradation and Total failure. Light decay occurs when the emitted light drops to 50% of its initial value; in addition to exceeding the maximum allowable junction temperature, the overall failure occurs due to internal open circuit, which includes: between the chip and the lead frame, the chip and Between the bonding wires, and between the bonding wires and the lead frame. One of the causes of failure is that the LDE resin glass lens is overheated, softened, and the stress generated after cooling causes an internal open circuit.
It is important for users to understand these characteristics, especially their thermal characteristics. This can't help reminding me of the situation when transistors were replaced by electronic tubes in electronic circuits. Due to the sensitivity of transistors as semiconductor devices to temperature, at the beginning of the application, some engineers who used to be familiar with tube applications thought that transistors have many advantages. However, its reliability is not as good as that of electronic tubes. However, the power of new things is unstoppable. With the advancement of application technology, the use of temperature compensation and negative feedback to suppress temperature drift and stable operating points has made transistors and semiconductor integrated circuit technology become today. The core technology of electronic information technology. In the field of light source technology, LED application technology will also experience how to develop and avoid short.
Thermal Management Design and "Thermal Ohm's Law"
The purpose of the thermal management design is to:
· Ensure that the device is operating under the right conditions to achieve high reliability;
· Prevent driving under super-stress conditions and prolong the working life of LEDs;
• Operates at the maximum possible current to improve light output performance.
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