The selection and design considerations of LED driver power supply
LED is a light-emitting tube with diode characteristics, which can only be powered in one direction. Usually, the brightness output of LED is directly proportional to the current passing through the LED, but white LED will experience saturation under high current, greatly reducing the luminous efficiency and even failure. Therefore, the current used by LED cannot exceed its rated value. In addition, the brightness output of LED is inversely proportional to temperature, so it is important to minimize power generation and design a well-designed cooling system during use. At present, LEDs are all driven by DC, so a power adapter called LED driver power supply needs to be added between the mains and LED. Its function is to convert AC mains power into suitable LED DC power. According to the electricity consumption rules of the power grid and the driving characteristics requirements of LEDs, the following points should be considered when selecting and designing LED driving power sources:
1. High reliability
Especially like the driving power supply of LED street lights, installed at high altitude, maintenance is inconvenient and the cost of maintenance is also high.
2. High efficiency
LED is an energy-saving product, and the efficiency of the driving power supply needs to be high. For the structure where the power supply is installed inside the lamp, it is particularly important. Because the luminous efficiency of LED decreases with the increase of LED temperature, the heat dissipation of LED is very important. The power supply has high efficiency, low power consumption, and generates less heat inside the lamp, which reduces the temperature rise of the lamp. It is beneficial for delaying the light decay of LEDs.
3. High power factor
Power factor is the requirement of the power grid for the load. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the power factor of individual appliances with low power has little impact on the power grid, lighting up at night and concentrating similar loads can cause serious pollution to the power grid. For LED driver power supplies ranging from 30 watts to 40 watts, it is said that in the near future, there may be certain requirements for power factors.
4. Driving method
There are two types currently in use: one is a constant voltage source that supplies multiple constant current sources, with each constant current source supplying separate power to each LED. This method is flexible in combination, and if one LED fails, it will not affect the operation of other LEDs, but the cost will be slightly higher. Another method is direct constant current power supply, with LED series or parallel operation. Its advantage is that it has a lower cost, but poor flexibility, and it also needs to solve a certain LED malfunction without affecting the operation of other LEDs. These two forms coexist for a period of time. The multi-channel constant current output power supply method will have better cost and performance. Perhaps it is the mainstream direction in the future.
5. Surge protection
The ability of LED to withstand surges is relatively poor, especially in terms of resistance to reverse voltage. Strengthening protection in this area is also important. Some LED lights are installed outdoors, such as LED street lights. Due to the load shedding of the power grid and the induction of lightning strikes, various surges may invade the power grid system, some of which can cause damage to the LED. Therefore, the LED driver power supply should have the ability to suppress surge intrusion and protect the LED from damage.
6. Protection function
In addition to conventional protection functions, it is best to add LED temperature negative feedback in the constant current output of the power supply to prevent excessive LED temperature.
7 Protection aspects
The external installation type of the lamp should have a waterproof and moisture-proof power structure, and the outer shell should be sun resistant.
The lifespan of the 8 driver power supply should match the lifespan of the LED.
9 must comply with safety regulations and electromagnetic compatibility requirements.
