Tuesday, 18 January 2011

LED’s (technical) issues

LED is a diode characteristics of the LED, it can only power one direction. LED light output is usually proportional to the current through the LED, but the white LED will appear in the high current saturation, a significant reduction in luminous efficiency, or even failure, so LED using current rating can not exceed its specifications. In addition, LED light output with temperature is inversely proportional to, so should minimize the use of well-designed power supply heating and cooling system.

LED are driven by DC current, so power and the LED in the city will need an adapter between the LED drive power. Its function is to convert into a suitable AC power LED's current. According to the electricity grid rules and LED drive feature requirements, selection and design of LED drive power to take into account the following:

1. High reliability

Especially as the drive power
LED street
lamps, installed in the high altitude, convenient maintenance and repair cost is also large.

2. High efficiency

LED energy-saving products, driving higher power efficiency. Installed in the fixture for the power structure, is particularly important. Because the LED luminous efficiency with LED temperature decreased, so the LED's heat is very important. High efficiency power supply, its power loss is small, the heat in the fixture on the small temperature rise will reduce the lamp. LED light on the slow decline favorable.

3. High power factor

Power factor is the power to the load requirements. 70 watts under normal use of electrical appliances, there is no mandatory targets. Although not a single power with a lower electrical power factor has little effect on the power grid, but at night we light lamps, the same load is too concentrated, would produce power more serious pollution. 30 watts to 40 watts for the LED drive power, it is said in the near future, perhaps there would be power factor requirements of certain indicators.

4. Drive

Now prevailing in two ways: one is a constant voltage constant current source for multiple sources, each current source separately to each channel LED power supply. In this way, the combination of flexibility, all the way LED failure does not affect the LED's work, but the cost will be slightly higher. The other is a direct constant current power supply, LED series or parallel operation. It has the advantage of lower cost, but flexibility is poor, but also to resolve a fault LED, LED operation does not affect other issues. These two forms coexist in a period of time. Multi-channel constant current output power supply, cost and performance will be better. Perhaps the main direction of the future.

5. Surge Protection

LED Surge capacity is relatively poor, especially the anti-reverse voltage capability. Enhance this protection is also very important. Some LED lights installed in the outdoors, such as LED lights. Since the start grid load rejection and lightning sensors, a variety of intrusion from the grid system will surge, the surge can cause some damage to the LED. LED drive power should therefore inhibit the surge of the invasion to protect the LED from damage ability.

6. Protection

In addition to the conventional power protection, the best increase in the constant current output LED temperature feedback, to prevent the LED temperature is too high.

7 protection aspects

Lighting and outdoor installation type, the power structure should be waterproof, moisture, shells and Fast.

8, the life of drive power LED lifetime compared with the fit.

9 to comply with safety regulations and electromagnetic compatibility requirements.

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