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The relationship between LED lamps and power supply

Oct 02, 2019

The relationship between the quality of LED lamps and the power supply

LED has many advantages such as environmental protection, long life, high photoelectric efficiency (current light efficiency has reached to 130LM/W~140LM/W), earthquake resistance, etc. In recent years, its application has been rapidly developed in various industries. In theory, the service life of LED is 100,000 hour, but in the actual application process, some LED lighting designers have insufficient understanding or improper selection of LED driving power or blindly pursue low cost. As a result, the life of LED lighting products is greatly shortened. The life of poor LED lamps is less than 2000 hours and even lower. The result is that the advantages of LED lamps can not be showed in application.

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 rules of LED, a brief description is given. Generally, the forward voltage of 1W white light application is about 3.0-3.6V, that is, when it is labeled as 1W LED. When the current flows through 350 mA, the voltage across it may be 3.1V, or it may be other values at 3.2V or 3.5V. To ensure the life of 1WLED, the general LED manufacturer recommends that the lamp factory use 350mA current. When the forward current through the LED reaches 350 mA, the small increase in the forward voltage across the LED will cause the LED forward current to rise sharply, causing the LED temperature to rise linearly, thereby accelerating LED light decay. To shorten the life of the LED and even burn out the LED when it is serious. 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 driver 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.

Many high-power LED packaging plants now seal many individual LEDs in parallel and in series to produce a single 20W, 30W or 50W or 100W or higher power LED. Even though before the package, they are strictly selected and matched, there are dozens and hundreds of individual LEDs due to the small internal quantity. Therefore, the packaged high-power LED products still have great differences in voltage and current. Compared with a single LED (generally a single white light, green light, blue light operating voltage of 2.7-4V, a single red light, yellow light, orange light working voltage of 1.7-2.5V) parameters are even more different!

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. When the current is larger, the power consumed on the step-down resistor would be larger, the LED current cannot be guaranteed to exceed its normal working requirements. When designing the product, the voltage across the LED is used to drive the power supply, which is 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 the low cost. Therefore, some LED lighting companies still use this method.

Some manufacturers, in order to reduce the cost of the product, using constant voltage to drive the LED, also brings a series of questions about the uneven brightness of each LED in the mass production, the LED can not work in the best state, etc.

Constant current source driving is the best LED driving method. It is driven by constant current source. It does not need to connect current limiting resistors in the output circuit. The current flowing through the LED is not affected by external power supply voltage changes, ambient temperature changes, and discrete LED parameters. The effect is to keep the current constant and give full play to the various excellent characteristics of the LED.