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How to choose the drive IC of LED and the heat generated by LED

Time:2018-12-26 Views:187
LED heat prevention and reduction:
Like traditional light sources, semiconductor light-emitting diodes (leds) generate heat during operation, depending on the overall luminous efficiency.Under the action of external electrical energy, the radiation of electrons and holes is combined to produce electroluminescence, and the light emitted near the p-n junction needs to pass through the semiconductor medium and packaging medium of the chip itself to reach the outside world (air).Based on the comprehensive current injection efficiency, radioluminescence quantum efficiency and chip external light removal efficiency, only about 30-40% of the input electric energy is converted into light energy in the end, of which 60-70% is mainly converted into heat energy in the form of non-radiation composite lattice vibration.
The increase of chip temperature will enhance the non-radiation compound and further weaken the luminous efficiency.Because, people think subjectively that high-power LED does not have heat, in fact it does.There is so much heat that problems occur during use.In addition, many people who use high-power LED for the first time do not know how to solve the thermal problem effectively, making the product reliability become the main problem.So do leds actually generate heat?How much heat can you generate?How much heat do leds generate?
Under the positive voltage of LED, electrons obtain energy from the power supply. Driven by the electric field, LED overcomes the electric field of PN junction and transitions from the N region to the P region. These electrons compound with the holes in the P region.Since the free electron drifting to the P region has higher energy than the valence electron in the P region, when the electron recombines, it returns to the low energy state and the excess energy is released in the form of photons.The wavelength of emission photon is related to energy difference Eg.
It can be seen that the luminous area is mainly near the PN junction, which is the result of energy released by the combination of electrons and holes.When a semiconductor diode is involved, the electrons will encounter resistance when they are all the way into and out of the semiconductor area.Simply put, the physical structure of a semiconductor diode in principle is that the number of electrons emitted from the negative electrode of the semiconductor diode is the same as the number of electrons returned to the positive electrode.In ordinary diodes, electron hole pair recombination occurs due to the factor of energy level difference Eg, and the released photon spectrum is not in the visible range.
Electrons consume power in the presence of resistance as they travel through the diode.
The power consumed conforms to the basic laws of electronics:
P is equal to I2, R is equal to I2 times RN plus plus RP plus IVTH
In the formula, RN is the resistance of n-region volume and RP is the resistance of p-region volume.
The heat generated by the power consumed is:
Q = Pt
Where: t is the time when the diode is energized.
In essence, an LED is still a semiconductor diode.Therefore, when LED is working forward, its working process conforms to the above description.The electric power it consumes is:
P LED = U LED &TImes;I LED
Where, U LED is the forward voltage at both ends of LED light source
I LED is the current flowing through the LED.
The electrical power consumed is converted into heat output:
Q = P LED & TImes;t
Where: t is the power on time
In fact, the energy released when the electron recombines with the hole in the P region is not directly provided by the external power source, but because the electron in the N region, in the absence of external electric field, its energy level is Eg higher than the valence electron energy level in the P region.When it gets to the P region, when it recombines with the hole to become a valence electron in the P region, it releases more energy than the N region.The size of Eg is determined by the material itself and has nothing to do with the external electric field.The effect of external power supply on the electron only pushes it to do directional movement and overcomes the effect of PN junction.
The heat produced by leds has nothing to do with light efficiency.There is no relation between what percentage of electrical power produces light and what percentage of electrical power produces heat.Through understanding the thermal generation, thermal resistance, junction temperature concept of high-power LED, derivation of theoretical formulas and thermal resistance measurement, we can study the actual packaging design, evaluation and product application of high-power LED.It needs to be explained that heat management is a key issue at the current stage when LED product luminous efficiency is not high. Fundamentally improving luminous efficiency to reduce the generation of heat energy is the fundamental solution, which requires technological progress in chip manufacturing, LED packaging and application product development.
LED IC driver to choose how?
Some people in the LED industry have found that constant voltage source drive cannot guarantee the consistency of LED brightness, and affects the reliability, life and light attenuation of LED.Therefore, super bright LED is usually driven by constant current source.Constant current power supply can eliminate the current change caused by forward voltage change.Therefore, constant LED brightness can be generated no matter how the forward current changes.It is easy to generate constant current power supply.Instead of adjusting the output voltage of the power supply, only the voltage of the resistor detected by the current needs to be adjusted.
Therefore, we need to choose high precision constant current source LED driver chip, which is easy to use in circuit of various LED lighting products.Its wide voltage input range, can ensure a very high output current accuracy, so that in a large area of light source lighting, LED lighting brightness can be maintained uniform.Due to its low drop-out voltage drop, stable load and power supply adjustment rate, this series of products can maintain stable LED brightness and fully extend LED service life even when the power supply and load in the lighting circuit vary widely.The VDD pin of this series of products can serve as the output enabling (OE) function, which can be combined with digital PWM control circuit to achieve more accurate dimming applications.
In addition, accurate undervoltage locking and overtemperature protection and anti-static protection design can ensure the safety of the entire lighting system in the design, installation and application.Display high quality LED lighting drive.
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