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Relationship Analysis Between LED Lamp Quality And Driving Power Supply

08 Oct

Because LED is eco-friendly light source which does not contain toxic materials, and it has a long lifetime with high efficiency, the applications of LEDs in various industries have developed fast in recent years, theoretically, LED’s service life can reach about 100,000 hours, but in the practical application process, as a result of some LED lamps designers’ inadequate knowledge or improper selection of LED driving power supplies, the lifetime of LED lamp products is greatly reduced.

Due to the particularity of LED manufacturing, the current and voltage characteristics of LEDs produced by different manufacturers or even the same manufacturer in the same batch are of great differences. Now we can take 1W high power white LED with typical specifications as an example and do a brief description in accordance with the LED current and voltage change law, the general application forward voltage of 1W white LED is around 3.0-3.6V, in order to ensure the lifetime of the 1W LED, most LED manufacturers suggest the lamp factories to use 350mA current to drive, When the forward current which passes through both ends of LED reaches 350 mA, a small increase of forward voltage to both ends of LED will cause a significant increase of LED forward current and a linear increase of LED temperature, thus speeding up the LED light degradation, and shortening the lifespan of LEDs, or seriously burning out LEDs. Due to the particularity of LED’s voltage and current changes, the industry makes strict requirements to the power supplies that drive LEDs.

LED driving power supply is the key point to an LED lamp, it is just like a person’s heart, in order to manufacture high-quality LED lamps for illumination lighting, we must give up the constant voltage mode to drive LEDs.

Currently, LED lamp products produced by many manufacturers (such as rail lights, lamp cups, spotlights, garden lights etc.), use resistance or capacitance to reduce voltage, then add a voltage stabilizing diode to stabilize the voltage, and supply power to LEDs, such driving method has significant defects, first, the efficiency is low, much electricity will be consumed on quenching resistor, which may even exceed the LED’s power consumption, and can not provide large current driving, as when the current is large, consumption of energy on the quenching resistor will be high, and can not guarantee that the current passing through the LED does not exceed the work requirements of LED, when designing products, the designers use the method of reducing voltage of both ends of LED to supply power and drive LED, which is at the expense of sacrificing LED brightness. Using resistance or capacitance to reduce voltage and drive LED will cause unstable brightness of LED, when the power supply voltage is low, LED brightness becomes low, when the power supply voltage is high, LED brightness becomes high. Of course, biggest advantage of resistance or capacitance reducing voltage to drive LED is the low cost.

Some manufacturers, in order to reduce product costs, use constant voltage to drive LED, which also brings a series of problems when doing mass production, for instance, the brightness of LEDs is uneven, LEDs can not achieve their best performance and so on.

Constant current driving is the optimum driving method for LEDs. When driven by constant current, LED current will not be influenced by the change of external power supply voltage, environment temperature, and the discreteness of LED parameters, thus it can maintain the current constant, and fully demonstrate various excellent features of LED.

Utilizing constant current driving mode can avoid the current variation caused by LED forward voltage changes, meanwhile a constant current will stabilize LED brightness, also facilitate the LED lamp factory to implement mass production, therefore many manufacturers have been fully aware of the importance of driving power supply, many manufacturers have chosen constant current mode to drive LED lamps.

Some manufacturers worried that power supply driving board choosing electrolytic capacitors may affect the lifetime of power supplies, which is actually a misconception, for instance: if we choose 105 degree Celsius high-temperature electrolytic capacitors with a lifetime of 8,000 hours, according to the electrolytic capacitors life estimation fomula “Temperature drops by 10 degree Celsius, litime increases by 100%”, then when it works under the environment of 95 degrees Celsius,its lifetime is 16,000 hours, when it works under the environment of 85 degrees Celsius,its lifetime is 32,000 hours, when it works under the environment of 75 degrees Celsius,its lifetime is 64,000 hours, if the actual working environmental temperature is lower, then the lifetime will be longer! Therefore, as long as the manufaturers select high quality electrolytic capacitors, the lifetime of driving power supply will not be influenced!

There is another issue that should be noted: since LED will emit a lot of heat when working, which causes a rapid rise in junction temperature, the higher LED power is, the greater heating effect is. LED chip temperature rise will lead to changes in light-emitting device performance and the reduction or failure of electro-optical conversion efficiency, according to the experimental tests: when LED temperature increases by 5 degrees Celsius, luminous flux will decreases by 3%, so the thermal control of LED light source itself is very important, if possible the heat dissipation area of LED itself shall be enlarged in order to decrease the working temperature of LED.

 

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