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I have a question about a LED array I am designing for a home-made 3D SLA printer. I find the subject of high power led drivers quite confusing but I believe I understand how it works now and I need someone to confirm my findings.

My total LED array will consist of 80, 3W UV LEDs. Their rated direct voltage is 3.2-3.4v and their rated direct current is 700ma.

The LEDs are connected to a large cooling fin with active cooling.

I want to connect them to a 50W constant current power supply at 1500ma, I want to connect them 2 parallel series of 8 LEDs. This would give them 750ma per serie.

I have three questions:

  1. Is my conclusion correct?
  2. Would the LED's be able to sustain the additional 50ma above their rated current?
  3. Would this lead to a shortened lifespan or just kill the LED outright?
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  • \$\begingroup\$ Welcome to EE.SE. Some simple math puts the power levels much higher than you expected. If all 80 of them are in series than you need 80*3.2V minimum to turn them ON. 80*3W = 240 watts. Also you should be driving them at no more than 80% of full power to get any life out of them. If rated 700mA max then drive them at 500mA. You should rethink your layout and power needs. NEVER overdrive semiconductors-they will have a short life. \$\endgroup\$ – Sparky256 Nov 11 '18 at 21:44
  • \$\begingroup\$ @Sparky256, Thanks, so if I decide to use a 600ma CC driver of 20W I could connect 6 of them in series, correct? Or could that be 7 since I am running them at 600ma instead of 700ma? \$\endgroup\$ – Milan van Dijck Nov 12 '18 at 10:13
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Is my conclusion correct?

No. It is very unlikely that the current will be evenly divided between the two strings. I have found with white high power LEDs the mismatch in current typically exceeds 20%

I rad some tests on three Bridglux EB Gen 2 strips wired in parallel. Bridgelux uses "binned" LEDs so the strips Vf are fairly close. I measured each strip individually at 500 mA.

enter image description here


The above strips used binned LED. I made some strips using 16 Luxeon Rebel white LEDs from the same reel. You can expect results similar to 40-60% mismatch like this:

enter image description here


I would recommend using a Texas Instruments LM3466 Multi-String LED Current Balancer for Use with Constant-Current Power Supplies




Would the LED's be able to sustain the additional 50ma above their rated current?

Would this lead to a shortened lifespan or just kill the LED outright?

Most high power LED have a "test current" at which they are spec'd. The maximum current is usually higher than the test current.

I doubt an additional 7% current would damage the LEDs. What is more important is that the temperature of the LEDs do not get too hot.

I want to connect them to a 50W constant current power supply at 1500ma, I want to connect them 2 parallel series of 8 LEDs.

Eight 3.5V LEDs would need a 30V CC driver. I would recommend a Mean Well HLG 60H-36A with a current adjustment range of 1000 - 1700 mA or a HLG 60H-36B where the max current can be set with a resistor.

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