Knowledge of LED drive power
At present, LEDs are driven by DC, so a power adapter, that is, LED driving power, needs to be added between the mains and the LED. Its function is to convert the AC mains into a suitable DC power for the LED. According to the power rules of the grid and the drive of the LED Characteristic requirements, the following points should be considered when selecting and designing LED drive power supplies:
1. High reliability
Especially like the driving power supply of outdoor LED street lights, it is installed at high altitude, which is inconvenient to maintain and costly to repair.
2. high efficiency
LED is an energy-saving product, and the efficiency of the drive power supply should be high. It is especially important for the structure of the power supply installed in the lamp. 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. , 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 the LED.
3. High power factor
The power factor is the requirement of the power grid on the load. Generally, there is no mandatory indicator for electrical appliances below 70 watts. Although the power factor of a single electrical appliance with low power is lower, the impact on the power grid is not large, but everyone lights up at night, and similar loads are too concentrated , It will cause serious pollution to the power grid. For 30 watts to 40 watts of LED drive power, it is said that in the near future, there may be certain indicator requirements for power factors.
4. Drive method
There are two types currently in use: one is a constant voltage source for multiple constant current sources, and each constant current source individually powers each LED. In this way, the combination is flexible, and one LED fails, and it does not affect the work of other LEDs. , But the cost will be slightly higher. The other is direct constant current power supply, LEDs run in series or in parallel. Its advantage is that the cost is lower, but the flexibility is poor, and it must solve the problem of a certain LED failure without affecting the operation of other LEDs. These two forms will coexist for a period of time. The multi-channel constant current output power supply method will be better in terms of cost and performance. It is also the mainstream direction in the future.
When we design the LED drive power supply, it is necessary to know the LED current and voltage characteristics. Due to the different LED Lights manufacturers and LED Lights specifications, the current and voltage characteristics are different. Now take the typical specifications of white LEDs as an example, according to the current and voltage changes of the LED According to the law, the general application forward voltage is about 3.0-3.4V, the typical value voltage is 3.2V, and the current is 60mA. When the forward voltage applied to both ends of the LED exceeds 3.6V, the forward voltage will increase slightly, and the positive The current may increase exponentially, causing the temperature of the LED luminous body to rise too fast, thereby accelerating the light attenuation of the LED, shortening the life of the LED, and even burning the LED in severe cases. According to the voltage and current change characteristics of the LED, the impact of the driving power supply The design puts forward strict requirements.
At present, the LED lamp products produced by many manufacturers (such as guardrails, lamp cups, and projection lamps) use resistance and capacitance to step down, and then add a zener diode to stabilize the LED to supply power to the LED. This way of driving the LED has great defects.
