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Technical support
1.  Why does LED need high-quality driver?  
LED is non-toxic, environmental-friendly and long-life with high photoelectric efficiency. The design and manufacturing process of LED chips are quite mature. Nowadays, the LED lighting system failure mainly arises from a damaged LED driver. If the LED driver is of poor quality, due to low constant-current precision and wide current fluctuation, it can not provide enough protection and will cause damages to the LED chips. Therefore, the LED driver is very critical to the LED lighting. High quality LED driver is a must for fine, efficient LED lighting in order to meet the severe working environment and save expensive repair cost.
2. What are the root causes of LED driver quality problem? 
1: It is not designed and manufactured by a professional power supply manufacturer (diversified requirements and small quantity); 2: It is not designed according to the severe working environment requirements of LED lighting. 
a)  Ambient temperature: -35℃ ~ 70℃
b)  Poor waterproof design
c)  Poor lightning protection design
3. How to guarantee the quality and reliability of LED driver? 
1)Standard & professional design and flow control
Technical pre-research, feasibility assessment, preliminary design, detailed design, prototype, pilot run 
2)Reasonable design margin of components
3)High quality elements and components
Electrolytic capacitor, IC, power semiconductor, magnetic elements, etc.
4)Strict quality assurance and test procedures
 Stress analysis, EVT, SVT & DVT tests as well as MTBF calculation and experimental certification
4. Why does LED driver require high efficiency? 
For the LED lighting system, high efficiency is required for the energy saving purpose, and is a foundation and guarantee for low temperature rise, long operating life and high reliability. 
1) High efficiency, low loss, low temperature rise 
For example, for a 100W LED driver, when the efficient is 95%, the loss is 5.2W, and when the efficiency is 85%, the loss is 17.6W, that is, the loss of the latter is 3.4 times that of the former. Experiments have also shown that under the same conditions, the temperature of the former is 10~15℃ lower than the latter. 
2) Reduced operating temperature and delayed luminous decay
The temperature rise of LED chip will lead to performance degradation and electrical-to-optical conversion efficiency decay, and even failure, of light emitting device. Experiments have shown that luminous flux will drop by 3% for every 5 degree Celsius increase in the LED temperature. 
3) High efficiency, low temperature rise, long operating life
Take the high temperature electrolytic capacitor (105℃, 10000 hours) for example, according to the prevailing formula for life expectancy of electrolytic capacitor - “life of a capacitor double for every 10 degree Celsius decrease in temperature”, then, its operating life will be 20000 hours under 95℃ and 40000 hours under 85℃. When the tyjb driver normally operates below 60℃, the electrolytic capacitor temperature will be roughly 85℃, then the capacitor life will be 40000 hours, and can be used for about 15 years when calculating on a basis of 12 working hours per day. 
4) High efficiency, low temperature rise, high reliability
As the driver temperature decreases and the operating environment of IC and power semiconductor is improved, the MTBF (mean time between failures) will be significantly improved. 
5. What is PF? PFC? Why is high PF required?
As the abbreviation for “Power Factor”, PF refers to the ratio of active power to apparent power. PFC is the abbreviation for “Power Factor Corrector” . High PF can: 1) reduce current harmonics; 2) increase electric power system capacity; and 3) reduce line loss and save energy. Low PF means poor power efficiency, to be more specific, the lower the PF, the higher proportion of power loss in the distribution network. If such low PF is not corrected, the electric power company has to provide much more reactive power in addition to active power, which means it needs generators, transformers and transmission lines of higher capacities to compensate such loss. Therefore, when is provided with PFC function, the power supply device is able to increase it energy efficiency, reduce loss and lessen harmonic pollution to power grid. 
PCB of LED driver and design specification 
The physical design of PCB is last segment in the design of power supply device, which plays a decisive role in the electromagnetic interference and power supply stability. The following is the detailed analysis of these segments: 
    I. From schematic diagram to establishing element parameters in PCB design flow ->entry of schematic net list ->design parameter setup->manual layout->manual routing->design verification->review->CAM output. 
    II. During parameter setup, the spacing between adjacent conductors must satisfy the electrical safety requirements, and for ease of operation and production, shall be as wide as possible. The minimum spacing shall be at least enough for the withstanding voltage. In case of a relatively lower routing density, the spacing between signaling wires may be enlarged properly. Those signal wires with a big level gap shall be as short as possible and the spacing thereof shall be enlarged accordingly. Generally, the line to line spacing is 8mil. 
    The distance from the rim of pad hole to the PCB edge shall be over 1mm, to avoid damaging the pad during processing. For the fine lines connected to the pad, tear-shaped connections shall be made between the pad and these lines, so that the pad is less liable to peel and the connections are unlikely to broken. 
III. It has been proved that even with a correct schematic circuit diagram, defective design of PCB will have negative effects on the reliability of electronic equipment. For instance, when two fine parallel lines on the PCB are close to each other, it will result in a delay of signal waveform and generate reflecting background at the terminal of transmission line. And the interference caused by improper layout of power and ground wires could degrade the product performance. Therefore, proper approaches shall be adopted in the PCB design.
IV. When HF signals are contained in the routing of switching power supply, any printed wire on the PCB could serve as antenna wire; the length and wide of printed influence its impedance and wire inductive reactance, and thereby influence the frequency response. Those printed wires carrying DC signals could also be coupled by RF signals from adjacent printed wires, resulting in problems in the circuit (even radiating interfering signals again).
    V. After the routing design is finished, carefully check whether the routing design meets the rules set by the designer and confirm such rules meet the manufacturing process requirements of PCB. Check whether the distances between lines, lines and component pads, lines and through holes, component pads and through holes, as well as through holes are proper and meet manufacturing requirements. Check the widths of power and ground wires and see if it is possible to widen the ground wire in the PCB. Please note, some errors may be ignored, e.g., part of outline of connectors may go beyond the board outline, and an error may be made when checking the spacing. In addition, after the routing or through hole is modified, copper pouring shall be conducted once again. 
VI. Review according to the PCB checklist, including design rules, layer definition, wire width, spacing, pad, through hole setting. Special attention shall be paid to the component layout, routing of power and ground wire network, routing and shielding of high-speed clock network, placement and connection of decoupling capacitor, etc.

Please contact Evada for detailed technical parameters. The above information is for reference only, please subject to the actual product.


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