Designing with DOB leds, Seoul Semiconductors Acrich 3.


Seoul Semiconductors started the idea of doing DOB leds. DOB stands for Driver On Board. They are also called AC LED or Driverless LED.

I started working on these as soon as they came out with the first serie, the Acrich 2. I loved the 10W 100mm. It was easy to dissipate because of the large surface and provided so much light! 1200 lumens, 120 lumens/watt.  This fantastic led is now out of production and the new Acrich 3 comes in 17W.

Actually the 10W had a marketing problem. People tend to measure the led power in watt and not in lumens. Even if I told salespeople and highlighted the lumens factor, when you tell a customer that “comes with a 10W led” they immediately think of dim light!

The Acrich3 17W works great, I had to test again temperature, luckily my dissipators are well designed that there is a small increase in temperature but still way below the TC set limit.

Why LED needs to be dissipated? This is something that everyone asks. If LED are so efficient, they should produce less heat. True. The difference is that the heat produced is not dispersed with infrared light like the unefficient incandescent bulbs do. Even if the wattage is low, heat tends to accumulate on the pcb and the led temperature raises. LED emits ligth because of a peculiar unbalanced way the silicon is added with other elements . With heat these elements tend to move and the light emitted reduces and the quality get worse. The standard is 50,000 hours if the PCB is below a certain temperature at the TC (temperature check) point.

That’s 17 years if it’s lit 8 hours every day. After that it does not break, just reduces the light output 20%.  If the temperature is 5 or 10 celsius lower the manufacturer indication, probably the life time is exponentially higher. That means that a well built  led will last a century or more.

The 70 and 100 mm Acrich 3 are easier to dissipate because of the larger surface. It’s a SMD and not a COB led. Although COB are nicer to see, they concentrate the heat and the middle leds are easily overheated. Unless there is a need of being small, SMD are better than COB.

The weak point are the other elements that are making the Led. The current feeding the LED has to be straightened and filtered. So this is the key importance of using a top manufacturer for DOB leds. The first Acrich 2, the small ones, encountered problems for surge peaks. Now the new ones have a filter and many good features (dimming, less flickering etc)

See this video for more information on the Acrich3.

 

 

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