LED knowledge: LED lighting power supply for LED lighting

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 LED driver power supply is also an accessory product. The power quality on the market is currently uneven. Some knowledge about LED driver power is provided below.

1. What is the LED driver power supply?

The LED drive power source converts the power supply into a specific voltage and current to drive the LED light-emitting voltage converter. Usually, the input of the LED drive power source includes high-voltage power frequency AC (ie, mains), low-voltage DC, high-voltage DC, low-voltage high-frequency. AC (such as the output of an electronic transformer). 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.

2, LED drive power features

(1) High 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.

(2) High efficiency LED is an energy-saving product, and the efficiency of driving the power supply 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.

(3) High 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.

(4) Driving method

There are two types of traffic: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED separately. In this way, the combination is flexible, and all the LED faults do not affect the work of other LEDs, but the cost will be slightly higher. The other is direct constant current power supply, which is the drive mode adopted by “Zhongke Huibao”. The LEDs run in series or in parallel. Its advantage is that the cost is lower, but the flexibility is poor, and it is necessary to solve a certain LED failure without affecting the operation of other LEDs. These two forms coexist for a while. Multi-channel constant current output power supply mode will be better in terms of cost and performance. Perhaps it is the mainstream direction in the future.

(5) 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.

(6) Protection function

In addition to the conventional protection function, the power supply preferably increases the LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high; it must meet the requirements of safety regulations and electromagnetic compatibility.

3. Classified by driving method

(1) The current output by the constant current constant current driving circuit is constant, and the output DC voltage varies within a certain range according to the magnitude of the load resistance. The load resistance is small, the output voltage is low, and the load resistance is low. The larger the output voltage is, the higher the output voltage is. The constant current circuit is not afraid of load short circuit, but the load is completely open. The constant current drive circuit is ideal for driving LED, but it is relatively expensive. Pay attention to the maximum withstand current used. The voltage value, which limits the number of LEDs used.

(2) Regulator type When the parameters in the voltage regulator circuit are determined, the output voltage is fixed, and the output current changes with the increase or decrease of the load; the voltage regulator circuit is not afraid of the load open circuit, but the load is strictly prohibited. Short circuit; drive the LED with a voltage-stabilized drive circuit, each string needs to add a suitable resistor to make each string of LED display brightness average; brightness will be affected by the rectified voltage change.

4. Advantages and disadvantages of overall constant current and path-by-channel constant current operation

Compared with the overall constant current, the constant current is more disadvantageous and the cost is higher. But it can really protect the LED and extend the life of the LED, so the constant current is the future trend.

5, the shortage of LED power

The technicians of the company producing LED lighting and related products have insufficient understanding of the switching power supply, and the power supply is working properly, but some key evaluations and electromagnetic compatibility considerations are not enough, there are certain hidden dangers; most LED power supplies Production enterprises are transforming from ordinary switching power supply to do LED power supply. It is not enough to know the characteristics and use of LEDs. At present, there are almost no standards for LEDs, most of which are standards for reference switching power supplies and electronic rectifiers; now most LEDs The power supply is not uniform, so most of the amount is relatively small. The purchase volume is small, the price is high, and the component suppliers are not very cooperative; the stability of the LED power supply: wide voltage input, high temperature and low temperature operation, over temperature, over voltage protection and other problems are not solved one by one.

The first is the overall life of the driver circuit, especially the critical components such as: the life of the capacitor at high temperatures directly affects the life of the power supply; secondly, the LED driver should challenge higher conversion efficiency, especially when driving high-power LEDs, Because all the power that is not used as the light output is dissipated as heat, the power conversion efficiency is too low, which affects the energy-saving effect of the LED; currently, in the application of low power (1-5W), the cost of constant current driving power is occupied. The proportion has been close to 1/3, which is close to the cost of the light source, which has affected the market to some extent.