1, what is the LED driver
The LED driving power supply converts the power supply into a specific voltage and current to drive the LED light-emitting voltage converter. Under normal circumstances, the input of the LED driving power supply includes high-voltage power frequency AC (ie, mains), low-voltage DC, high-voltage direct current, and low-voltage high frequency. AC (such as the output of electronic transformers) and so on. The output of the LED driver is mostly a constant current source that changes the voltage as the forward voltage drop of the LED changes. The LED power core components include switch controllers, inductors, switching elements (MOSfets), feedback resistors, input filter components, output filter components, and the like. According to the requirements of different occasions, there must be input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.
2, LED drive power characteristics
(1) High reliability
In particular, the driving power source of LED street lights is installed at a high altitude, which is inconvenient to maintain and costs a lot for maintenance.
(2) High efficiency
LED is an energy-saving product, and the driving power supply is more efficient. It is very important for the heat dissipation of the power supply installed in the lamp. The efficiency of the power supply is high, its power consumption is small, and the heat generated in the lamp is small, which also reduces the temperature rise of the lamp. It is beneficial to delay the decay of the LED.
(3) High power factor
The power factor is the grid's load requirements. Electrical appliances below 70 watts generally have no mandatory targets. Although the single power device with low power has a low power factor, it has little impact on the power grid. However, the large amount of lighting used at night and the similar load is too concentrated can cause serious pollution to the power grid. For a 30-watt to 40-watt LED driver, it is said that in the near future, there may be certain indicators of power factor.
(4) Driving method
There are two types of traffic now: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED individually. In this way, the combination of flexible, all the way LED failure, does not affect the work of other LED, but the cost will be slightly higher. The other type is direct constant current power supply, which is the driving mode changed by “Zhongke Huibao”. The LEDs are operated in series or in parallel. Its advantages are low cost, but poor flexibility, but also to solve a LED failure, without affecting the operation of other LED. Both forms coexist for a period of time. Multiple constant current output power supply methods will be better in terms of cost and performance. It may be the main direction of the future.
(5) Surge protection
The ability of the LED to withstand surges is relatively poor, especially against reverse voltage capability. It is also important to strengthen this protection. Some LED lights are installed outdoors, such as LED street lights. Due to grid load kicking and induction by lightning strikes, various surges can be invaded from the grid system, and some surges can cause LED damage. Therefore, the analysis of "China Branch Hui Bao" drive power supply should have some shortcomings in the surge protection, and as for the frequent replacement of power supply and lighting, LED drive power to inhibit the intrusion of surge to protect the ability of the LED is not damaged.
(6) Protection function
In addition to the conventional protection function, it is better to increase the LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high; to meet the safety and electromagnetic compatibility requirements
3, classified by driving mode
(1) Constant current
The output current of the constant current drive circuit is constant, but the output DC voltage varies with a certain range with the magnitude of the load resistance, the load resistance is small, the output voltage is low, the greater the load resistance, the output voltage is also The higher the
The constant current circuit is not afraid of load short circuit, but the load is strictly prohibited;
The constant current drive circuit drives the LED is ideal, but relatively high price;
Pay attention to the maximum withstand current and voltage used, which limits the number of LEDs used.
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;
The LED is driven by a constant voltage driver circuit. The proper resistance of each string is required to make the brightness of each LED display average.
The brightness is affected by the voltage change from the rectification.
4. Advantages and Disadvantages of Overall Constant Current and Step-by-Step Constant Current Operation Modes
Compared with the overall constant current, although the disadvantages are more, the cost is higher. However, it can really protect the LED and extend the life of the LED, so the constant current is the trend in the future.
5, lack of LED power supply
LED drive power is currently lacking reasons:
The technical personnel of the company that manufactures LED lighting and related products do not have enough knowledge of the switching power supply, and the power supply that is made can work normally. However, some critical assessments and electromagnetic compatibility considerations are not enough, and there are certain hidden risks;
Most of the LED power supply manufacturers are transitioning from ordinary switching power supplies to LED power supplies, and their understanding of the characteristics and use of LEDs is not enough.
At present, there are almost no standards for LED. Most of them refer to the standard of switching power supplies and electronic rectifiers.
Most of the LED power supply is not uniform now, so the amount is relatively small. With small purchases, prices are high, and component suppliers are not very cooperative.
LED power supply stability: wide voltage input, high temperature and low temperature operation, over temperature, overvoltage protection and other issues have not been solved;
The first is the overall life of the drive circuit, especially the key devices such as: the life of the capacitor at high temperatures directly affects the life of the power supply;
It is the LED driver that should challenge higher conversion efficiency, especially when driving high-power LEDs, because all power that is not used as light output is dissipated as heat, and the power conversion efficiency is too low, which affects the energy-saving effect of LEDs. Play;
At present, in applications with small power (1-5W), the proportion of the cost of the constant current driving power has already approached 1/3, which is close to the cost of the light source, which has affected the market promotion to some extent.