Relationship between LED lamp quality and driving power supply

LED is the abbreviation of "LIGHT EMITTING DIODE" in English, and its Chinese abbreviation is light emitting diode. Due to its many advantages such as environmental protection, long life, high photoelectric efficiency (the current luminous efficiency has reached 100LM/W), and earthquake resistance, its application in various industries has been rapidly developed in recent years. In theory, the service life of LED is about 100,000 hours, but in actual application, some LED lamp designers lack understanding of LED driver power or make improper selection or blindly pursue low cost, resulting in greatly shortening the life of LED lamp products. The life of poor LED lamps is less than 2,000 hours, and some are even lower. As a result, the advantages of LED lamps cannot be fully utilized.

Due to the particularity of LED processing and manufacturing, the current and voltage characteristics of LEDs produced by different manufacturers or even the same manufacturer in the same batch of products have large individual differences. Taking the typical specifications of high-power 1W white light LED as an example, a brief description is given according to the current and voltage change law of LED. Generally, the forward voltage of 1W white light is about 3.0-3.6V. That is to say, when the nominal 1W LED flows through 350 mA current, the voltage across its two ends may be 3.1V, 3.2V or 3.5V, or other values. In order to ensure the life of 1W LED, LED manufacturers generally recommend that lighting manufacturers use 350mA current to drive. When the forward current through the two ends of the LED reaches 350 mA, a small increase in the forward voltage across the two ends of the LED will cause the LED forward current to rise significantly, causing the LED temperature to rise linearly, thereby 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 LEDs, strict requirements are placed on the power supply that drives the LED.

LED driver power is the key to LED lamps, it is like a person's heart, to manufacture high-quality LED lamps for lighting, we must give up the constant voltage driving method.

Now many high-power LED packaging factories seal many single LEDs together in parallel and series to produce single 20W, 30W or 50W or 100W or even higher power LEDs. Although these single LEDs are strictly selected and matched before packaging, there are dozens or hundreds of single LEDs inside, so the voltage and current of the packaged high-power LED products are still very different, and compared with single LEDs (generally single white light, green light, blue light working voltage is 2.7-4V, single red light, yellow light, orange light working voltage is 1.7-2.5V), the parameter difference is even greater! (Remind the newly launched LED lighting factory that the packaging quality of LED light source cannot be ignored)

At present, many manufacturers produce LED lighting products (such as guardrails, lamp cups, projection lamps, garden lights, etc.), which use resistors and capacitors to reduce voltage, and then add a voltage regulator diode to stabilize the voltage to supply power to the LED. This way of driving LED has great defects. First, it is inefficient, consumes a lot of power on the voltage-reducing resistor, and may even exceed the power consumed by the LED, and cannot provide high current drive, because the larger the current, the greater the power consumed on the voltage-reducing resistor, and it cannot be guaranteed that the current passing through the LED does not exceed its normal working requirements. When designing products, they will use the voltage reduction at both ends of the LED to power the drive, which is at the expense of the brightness of the LED. When driving LEDs by using resistors and capacitors to reduce voltage, the brightness of the LED cannot be stable. When the power supply voltage is low, the brightness of the LED becomes dim, and when the power supply voltage is high, the brightness of the LED becomes brighter. Of course, the biggest advantage of driving LEDs by resistors and capacitors is low cost, so some LED lighting companies are still using this method.

Some manufacturers use constant voltage to drive LEDs to reduce product costs, which also brings a series of problems such as uneven brightness of each LED during mass production and LEDs not working in the best state.

Constant current source drive is the best LED drive method. With constant current source drive, there is no need to connect a current limiting resistor in series in the output circuit. The current flowing through the LED is not affected by changes in external power supply voltage, ambient temperature, and discreteness of LED parameters, so that the current can be kept constant and the various excellent characteristics of LEDs can be fully utilized.

LED constant current power supply is used to power LED lamps. Since the current flowing through the LED will be automatically detected and controlled during the operation of the power supply, there is no need to worry about excessive current flowing through the LED at the moment of power on, nor is there any need to worry about the load short circuit burning the power supply. Constant current

drive can avoid current changes caused by changes in the forward voltage of the LED. At the same time, the constant current stabilizes the brightness of the LED, and it is also convenient for LED lamp manufacturers to ensure product consistency when implementing mass production. Therefore, many manufacturers have fully realized the importance of driving power supply. Many LED lamp manufacturers have abandoned the constant voltage method and selected the slightly more expensive constant current method to drive LED lamps.

Some manufacturers are worried that the use of electrolytic capacitors in the power driver board will affect the life of the power supply. In fact, this is a misunderstanding. For example, if a high-temperature electrolytic capacitor with a life of 8,000 hours at 105 degrees is selected, according to the popular electrolytic capacitor life estimation method, "every 10 degrees lower, the life doubles", then its working life in a 95-degree environment is 16,000 hours, in an 85-degree environment, it is 32,000 hours, and in a 75-degree environment, it is 64,000 hours. If the actual working temperature is lower, the life will be longer! From this point of view, as long as high-quality electrolytic capacitors are selected, it will have no effect on the life of the driving power supply!

There is another point that LED lamp companies should pay attention to: Since LEDs release a lot of heat during operation, the junction temperature of the tube core rises rapidly. The higher the LED power, the greater the heating effect. The increase in the temperature of the LED chip will lead to changes in the performance of the light-emitting device and the attenuation of the electro-optical conversion efficiency, and even failure in severe cases. According to experimental tests, the luminous flux decreases by 3% for every 5 degrees Celsius increase in the temperature of the LED itself. Therefore, LED lamps must pay attention to the heat dissipation of the LED light source itself, and try to increase the heat dissipation area of ​​the LED light source itself when possible, and try to reduce the operating 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 blindly pursue small size and ignore the operating temperature of the lamp and power supply.