Because LED does not contain toxic substances, environmental protection, long life, high photoelectric efficiency and many other advantages, it has been rapidly developed in various industries in recent years. In theory, the service life of LED is about 100,000 hours, but in actual application, some LEDs The luminaire designer has insufficient understanding or improper selection of the LED driver power , and the life of the LED lamp product is greatly shortened.
Due to the particularity of LED processing and manufacturing, the current and voltage characteristics of LEDs produced by different manufacturers and even the same manufacturer in the same batch of products have large individual differences. Taking the typical specification of high-power 1W white LED as an example, according to the current and voltage variation law of LED, a brief description is given. Generally, the forward voltage of 1W white light application is about 3.0-3.6V. To ensure the life of 1WLED, the general LED manufacturer recommends The lamp factory uses 350mA current to drive. When the forward current through the LED reaches 350 mA, the positive voltage at both ends of the LED increases slightly, which will increase the LED forward current and make the LED temperature straight. Rising, thus accelerating the LED light decay, shortening the life of the LED, and even burning the LED in severe cases. Due to the particularity of the voltage and current changes of the LED, strict requirements are imposed on the power supply for driving the LED.
LED drive power is the key to LED luminaires. It is like a person's heart. To manufacture high-quality LED luminaires for lighting, it is necessary to abandon constant voltage to drive LEDs.
At present, LED lamp products (such as guardrails, lamp cups, projection lamps, garden lights, etc.) produced by many manufacturers use resistance, capacitance and voltage reduction, and then add a Zener diode to supply power to the LEDs. There are great defects. First, it is inefficient. It consumes a lot of power on the step-down resistor. It may even exceed the power consumed by the LED, and it cannot provide high-current drive. Because the current is larger, the power consumed on the step-down resistor is The larger, the guarantee that the LED current does not exceed its normal working requirements, the design of the product will be reduced by the voltage across the LED to drive, so at the expense of LED brightness. The LED is driven by the resistance and capacitance step-down mode, and the brightness of the LED cannot be stabilized. When the power supply voltage is low, the brightness of the LED becomes dark, and when the power supply voltage is high, the brightness of the LED becomes brighter. Of course, the biggest advantage of resisting and capacitive step-down driving LEDs is low cost.
Some manufacturers, in order to reduce the cost of the product, using constant voltage to drive the LED, also brings a series of problems such as uneven brightness of each LED in the mass production, LED can not work in the best state.
Constant current source drive is the best way to drive LEDs. Driven by a constant current source, the current flowing through the LED will not be affected by changes in external power supply voltage, ambient temperature, and discrete LED parameters, thereby maintaining a constant current and giving full play to the various excellent characteristics of the LED.
Constant current drive mode, which can avoid the change of LED forward voltage and cause current fluctuation, while constant current makes the brightness of LED stable, and it is convenient for LED lamp factory to implement mass production. Therefore, many manufacturers have fully realized the driving power supply. Importance, many manufacturers have been using constant current to drive LED lamps.
Some manufacturers are worried that the choice of electrolytic capacitors on the power driver board will affect the life of the power supply. In fact, it is a misunderstanding. For example, if a high temperature electrolytic capacitor with a life of 8000 hours is used, the life expectancy of the electrolytic capacitor is estimated to be 10 degrees. , the life expectancy doubled, then it has a working life of 16,000 hours in a 95 degree environment, a working life of 32,000 hours in a 85 degree environment, and a working life of 64,000 hours in a 75 degree environment. If the actual operating temperature is lower, Then life will be longer! From this point of view, as long as the choice of high-quality electrolytic capacitors has no effect on the life of the drive power!
It is also worth noting that since the LED will release a large amount of heat during the working process, the junction temperature of the die rises rapidly, and the higher the LED power, the greater the heating effect. The increase of the temperature of the LED chip will lead to the change of the performance of the light-emitting device and the attenuation of the electro-optical conversion efficiency. In severe cases, it may even fail. According to the experimental test, the luminous flux decreases by 3% for every 5 degrees Celsius increase of the LED's own temperature, so the LED lamp must pay attention to the LED. The heat dissipation of the light source itself increases the heat dissipation area of ​​the LED itself when possible, and minimizes the operating temperature of the LED itself.
Article source: Technology Forum
(Editor: Fliuzhou)
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