LED display drivers general technical requirements
In recent years, the application of LED in various industries has developed rapidly, and driving power supply has become a hot spot in the industry. The LED driver can be regarded as a special power supply that supplies power to the LED, and can drive multiple LEDs in series, parallel or series-parallel as required to meet the requirements of the driving current. Theoretically, the service life of the LED is more than 100,000 hours, but in the actual application process, due to the improper design of the driving power supply and the selection of the galloping method, the LED is easily damaged. Common technical requirements when selecting and designing LED drivers are as follows.
High efficiency and high reliability. LED is an energy-saving product, and the efficiency of the driving power supply is high. This is especially important for structures where the power supply is installed within the luminaire. Because the luminous efficiency of the LED decreases with the increase of the LED temperature, the heat dissipation of the LED is very important. The efficiency of the power supply is high, the power consumption is small, and the heat generation in the lamp is small, which reduces the temperature rise of the lamp, and also slows down the light decay of the LED display, which is beneficial to prolong the service life of the entire lamp.
The working reliability of the LED driver must be high (such as mechanical connection, installation, maintenance and replacement), and the output power must be able to meet the requirements of the lamp (involving LED forward voltage range, current and LED arrangement), especially the driving of LED street lamps The power supply is installed at high altitude, which is inconvenient to maintain and the maintenance cost is also large.
High power factor. Power factor is the requirement of the grid for the load. Generally, there are no mandatory indicators for electrical appliances below 70W. Although the power factor of a single electrical appliance with low power is low, it has little impact on the power grid, but everyone lights up at night, and the same load is too concentrated, which will cause serious pollution to the power grid. For the 30~40W LED drive power supply, there may be certain index requirements for the power factor in the near future.
Drive method. LED displays are powered by DC power. There are two common driving methods. One of them is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED separately. This method is flexible in combination. When one LED fails, it will not affect the work of other LEDs, but the cost will be slightly higher. The other is direct constant current power supply, with LEDs running in series or parallel. Its advantage is that the cost is a little lower, but the flexibility is poor, and it also solves the problem that when one LED fails, it does not affect the operation of other LEDs. These two forms will coexist for some time. The multi-channel constant current output power supply method will be better in terms of cost and performance, and may be the mainstream development direction in the future.
The LED driver should maintain constant current characteristics as much as possible, especially when the power supply voltage changes by 15%, it should still be able to keep the output current within the range of 10%. At the same time, the driver should keep its own power consumption low, so that the system efficiency of the LED can always be kept at a high level.
Surge protection. The ability of LED to resist surge voltage and current is relatively poor, especially the ability to resist reverse voltage. Therefore, it is very important to strengthen the protection in this regard. For example, LED street lamps installed outdoors, due to the irregular activation and deactivation of grid loads, lightning strike induction, etc., will invade various surge voltages and currents from the grid system, and some surge voltages and currents will cause damage to the LED. Therefore, the LED driving power supply must have technical measures to suppress the intrusion of surge voltage and current to protect the LED from accidental damage by the surge voltage and current.
Protective function. The driver should be equipped with complete protection circuits, such as low-voltage latching, over-voltage protection, over-temperature protection, output open-circuit or short-circuit protection. In addition to the above-mentioned conventional protection functions of the LED driver, it is better to add a negative feedback circuit for the LED temperature in the constant current output to prevent the LED temperature from being too high.
Protective performance. For externally mounted lamps, the encapsulation structure of the driving power supply should be waterproof and moisture-proof, and the outer casing should be resistant to sunlight and ultraviolet radiation.
Functional requirements. The maximum current of the led display can be set, and the brightness of the LED can be adjusted during use. In some occasions, the driver is also required to have the function of light-emitting mode and effect conversion. The driver should meet the requirements of safety regulations and electromagnetic compatibility, and the interference to other electronic equipment and circuits during operation is small.