Analysis of key parameters of LED lighting driver power supply

The LED driving power supply is a voltage converter that converts the power supply into a specific voltage and current to drive the LED to emit light. Usually, the input of the LED driving power source includes high-voltage power frequency AC, low-voltage direct current, high-voltage direct current, low-voltage high-frequency alternating current (such as electronic Transformer output) and so on. The output of the LED driver is mostly a constant current source that changes the voltage as the LED's forward voltage drop changes. The core components of the LED power supply include a switch Controller, an inductor, a switching component (MOSfet), a feedback resistor, an input filter component, an output filter component, and the like. According to the requirements of different occasions, there are also input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.

To do a good LED lighting product, the key lies in heat dissipation, driving power supply and light source, and heat dissipation is particularly important. The heat dissipation effect directly affects the quality of life of the lighting product, while the life of the driving power supply itself and the stability of the output current and voltage are on the product. The overall quality of life also has a large impact, and the light source is the core of the entire product. The following provides some knowledge about LED driver power.

Constant current drive:

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.

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.

Electrolytic capacitor:

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 selection of high-quality electrolytic capacitors has no effect on the life of the drive power.

Cooling:

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, if possible, increase the heat dissipation area of ​​the LED light source as much as possible, and try to reduce the operating temperature of the LED itself. If conditions permit, it is better to separate the power supply part from the light source part.

reliability:

Especially like the driving power supply of LED street lamps , it is installed at high altitude, the maintenance is inconvenient, and the maintenance cost is also large.

effectiveness:

LEDs are energy-saving products, and the efficiency of driving power supplies is high. It is very important to dissipate heat from the power supply installed in the fixture. The power supply has high efficiency, its power consumption is small, and the heat generated in the lamp is small, which reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LEDs.

Power Factor:

The power factor is the grid's load requirements. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the power factor of a single power consumer with low power has little effect on the power grid, the amount of lighting used at night is large, and the similar load is too concentrated, which will cause serious pollution to the power grid. For 30 watts to 40 watts of LED driver power, it is said that in the near future, there may be certain indicators for power factors.

Surge protection:

The ability of LEDs to withstand surges is relatively poor, especially against reverse voltage capability. It is also important to strengthen protection in this area. Some LED lights are installed outdoors, such as LED street lights. Due to the start of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, and some surges will cause LED damage. Therefore, the analysis of the "Zhongke Huibao" drive power supply should have a certain lack of surge protection, and as the power supply and lamps are frequently replaced, the LED drive power supply must have the ability to suppress the intrusion of surges and protect the LED from damage.