As the next generation of lighting source, high power LEDs have a number of advantages such as power saving, efficiency and cold start. They are environment friendly and have a long life which reduces the cost of maintenance. It is reported in research that an LED lamp of 100W or so can reach the lighting intensity of a 250W high voltage sodium lamp, presenting significant power efficiency. LEDs require low voltage DC supply, and therefore AC/DC conversion is necessary if they are powered by AC mains. The power supply for LEDs should meet the following requirements:
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- 1. PF>0.9;
- 2. Power Efficiency > 85%;
- 3. Compliant with Energy Regulations;
- 4. Constant Current Output;
- 5. High Reliability;
- 6. Surge Protection;
- 7. Low Ripple;
- 8. Operation Temperature -40℃ - +70℃
The requirements list above indicates that a typical LED street lighting solution have the following modules - bridge-diode, PFC, isolated DC-DC converter, LED constant current controller，and LED fixture which includes LED, Lens & heat sink. Depending on the output power, PFC may operate in either Discontinuous Conduction (DCM)，Continuous Conduction (CCM) or Critical Conduction (DRM) mode. Generally, PFC has a stable 400Vdc output to feed the isolated DC-DC converter when the input is within the range from 90V to 264V. The Isolated DC-DC converter can be either fly-back or LLC type. For the LED lamps higher than 100W, the design theory of using CCM PFC or CRM PFC and LLC isolated conversion is commonly adopted. LED constant current control can be implemented by buck, boost or buck-boost topology.
The environment in which LED street lamps will be operating should obviously be taken into consideration to ensure that adequate protection is provided. [-LESS]
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