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LED lighting constant current drive analysis

May 16, 2017

 LED is a feature-sensitive semiconductor device, but also has a negative temperature characteristics, and thus in the application process to its stable working conditions and protection, resulting in the concept of drive. LED devices on the drive power requirements near the harsh, LED is not like ordinary incandescent bulbs, you can directly connect 220V AC mains. LED is about 3 volts low voltage drive, you must design a complex conversion circuit, different uses of LED lights, to be equipped with different power adapter. The international market for foreign customers on the LED drive power efficiency conversion, effective power, constant current accuracy, power life, electromagnetic compatibility requirements are very high, the design of a good power supply must take into account these factors, because the power in the entire lamp The role is like an important as the heart of people.

Due to the level of LED power constraints, usually need to drive multiple LEDs at the same time to meet the brightness requirements, therefore, need a special drive circuit to light the LED. Here are the main mainstream of several LED drive:

1, RC capacity step-down

The use of capacitance in the AC impedance to limit the input current, so as to obtain the DC level to the LED power supply. This drive method is simple, low cost, but the input non-isolation program, there are security risks. And the conversion efficiency is very low, can not be constant current control.

2, Isolated flyback circuit

The use of flyback circuit, through the transformer in the secondary side of the DC level, and then through the optocoupler this level of the ripple back to the original side, and thus self-stabilization. Such circuits meet the safety requirements, and the output constant current accuracy is better, the conversion efficiency is higher. But because of the need for optocoupler and secondary constant current control circuit, resulting in complex system, large size, high cost. Has been gradually replaced by the original side program.

3, The original side of the program

The original side of the program is completely through the control of the output side of the power and current output, the most accurate can do 5% constant current accuracy, the secondary only a simple output circuit can be. The primary side relies mainly on the feedback of the auxiliary side to control the output voltage, relying on the current limiting resistor to control the primary current, and multiply the turns ratio to control the output current accuracy. The original side program inherits the advantages of the isolated flyback circuit, while the architecture is simple, can be small size and low cost, has become the mainstream drive.

The original side of the constant current accuracy problem: the production accuracy of the pressure is difficult to control, resulting in the original side of the program in the use of low-quality transformers, the output current drift larger. Therefore, the original side of the program by improving the secondary side of the constant current control circuit, so that although the original side of the original program than the complex, but compared to the flyback program, you can still save the optocoupler, the system cost-effective.

According to the power grid rules and LED drive power characteristics of the requirements, in the selection and design of LED drive power to take into account the following points:

1, High reliability

Especially as LED lights drive power, installed at high altitude, maintenance is not convenient, maintenance costs are also large.

2, High efficiency

LED is energy-saving products, drive power efficiency is higher. It is especially important for the power supply to be installed in the fixture. Because LED luminous efficiency with the LED temperature increases and decreased, so the LED heat is very important. Power efficiency is high, its power consumption is small, in the lamp heat is small, it will reduce the lamp temperature. To delay the LED light failure beneficial.

3, High power factor

The power factor is the load on the grid. Generally less than 70 watts of electrical appliances, there is no mandatory indicators. Although the power is not a single power factor low power on the power of the little impact, but at night we light, similar load is too concentrated, will produce more serious pollution of the grid. For 30 watts to 40 watts of LED drive power, it is said that in the near future, may have a certain degree of power factor requirements.

4, Drive the way

Now there are two kinds of traffic: one is a constant pressure source for a number of constant current source, each constant current source to each LED power supply. 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 is a direct constant current power supply, LED series or parallel operation. Its advantage is a little lower cost, but the flexibility is poor, but also to solve an LED failure, does not affect the other LED operation problems. These two forms coexist for a period of time. Multi-channel constant current output power supply, in terms of cost and performance will be better. Perhaps the future direction of the mainstream.

5, Surge protection

LED anti-surge capability is relatively poor, especially anti-reverse voltage capability. It is also important to strengthen this protection. Some LED lights installed in the outdoors, such as LED lights. Due to the load of the grid load and lightning induction, from the grid system will invade a variety of surges, and some surge will lead to LED damage. So the LED drive power to suppress the surge of intrusion, the protection of LED is not damaged capacity.

6, Protection function

Power supply In addition to the conventional protection function, it is best to increase the constant current output LED temperature negative feedback to prevent the LED temperature is too high.

7, Protection aspects

Lighting outside the installation type, the power structure to waterproof, moisture, the shell to light.

8, The life of the drive power to match the life of the LED.

9, To meet the requirements of safety and electromagnetic compatibility.

With the growing popularity of LED, LED drive power performance will be more and more suitable for LED requirements.



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