LED lamp quality and drive power relationship

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 3.2V or 3.5V may be other values. To ensure the life of 1WLED, the general LED manufacturer recommends that the lamp factory use 350mA current. Drive, 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 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.

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 before the package. They are strictly selected and matched, but 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, and 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), the parameter difference is even greater! (Remind that the LED lighting factory just launched the LED light source packaging quality can not be ignored)

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 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.

LED constant current power supply is used to supply power to LED lamps. Since the current flowing through the LEDs is automatically detected and controlled during power supply operation, there is no need to worry that excessive current flows through the LEDs at the moment of power-on, and there is no need to worry about short-circuiting of the load. Bad power supply.

Constant current driving 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 also convenient for LED lamp factory to ensure product consistency when mass production is implemented. Therefore, many manufacturers have already Fully aware of the importance of the drive power, many LED luminaire manufacturers have abandoned the constant voltage mode, and chose a relatively high-cost constant current mode to drive the LED luminaire.

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 105 degrees is used, the high temperature electrolytic capacitor with a life of 8000 hours will be reduced by 10 degrees according to the current life expectancy of electrolytic capacitors. , 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!

Another point worthy of attention of LED lighting companies: As the LED will release a lot of heat during the working process, the junction temperature of the die will rise rapidly, the higher the LED power, the greater the heating effect. The increase of the temperature of the LED chip will lead to the performance of the light-emitting device. The change and the electro-optical conversion efficiency are attenuated, and even fail when it is serious. According to the experimental test, the luminous flux decreases by 3% for every 5 degrees Celsius increase of the LED's own temperature. Therefore, the LED lamp must pay attention to the heat dissipation of the LED light source itself, if possible. Try to increase the heat dissipation area of ​​the LED light source as much as possible, and try to reduce the working temperature of the LED itself. If conditions permit, it is best to separate the power supply part from the light source part. It is not advisable to pursue the small volume blindly and ignore the operating temperature of the lamp and the power supply. of.