I have a lamp with this hookup. Can someone confirm whether the electrical specs match up such that these can be connected in this way. ld009d-cu03036-m9 - MagTech Constant Current 24-36v output driver AC Input: 120Vac 0.15A 60Hz DC Output: 300mA,24-36V (7% current tolerance) Rated Max Power: 9W -- Weird - seems like this power supply isn't sold anymore, and when I calculate 36*.300 I get 10.8W which makes me scratch my head. The others on the page calculate to about 9W as the series supposedly supports. Here's a page listing the others of the same style: http://www.esop-power.com/products_detail/productId=196.html

These are the COB LEDs, two connected in parallel: http://www.edison-opto.com/get.php?f=Edison+Opto_EdiPower®+V+2PHM03xWxxP32020_Eng_V1.pdf&s=Edison+Opto_EdiPower®+V+2PHM03xWxxP32020_Eng_V1.pdf&path=doc

I'm struggling to figure out whether the electrical hookup is causing the LEDs to blink sometimes at power on. I have two lamps that have the same issue - and one of them has now burnt out one of the COB LEDs.

  • \$\begingroup\$ If you can cool the LED case to 60'C=Tc or 85'C=Tj then you can regulate the max current this way. \$\endgroup\$ – Tony Stewart EE75 May 1 '19 at 15:08
  • \$\begingroup\$ @SunnyskyguyEE75 No. These CoBs have a 5 V spread @ 85° C. There is no way to get these CoBs to work in parallel with a constant current source without a balancing circuit (e.g. LM3466). I would recommend using a constant voltage source, measuring the Vf, and using a resistor matched to the Vf of each CoB. Use a supply voltage that is fairly close to the Vf (e.g. 38 V) if efficiency is of any consequence. I like the Mean Well adjustable LRS series supplies. meanwell.com/Upload/PDF/LRS-150/LRS-150-SPEC.PDF \$\endgroup\$ – Misunderstood May 8 '19 at 2:56
  • \$\begingroup\$ Yes this would be optimal solution \$\endgroup\$ – Tony Stewart EE75 May 8 '19 at 14:01

Two LED strings (no series resistors) in parallel rated at 180 mA max each cannot be expected to share the current from a 300 mA constant source equally. One may hog the current and be stressed. Even if they did share equally, 150 mA is far more than the nominal LED rating of 90 mA. This is a bad design.

A good design would use a 90 mA constant current source and put the LED strings in series. Or use a constant voltage with series resistors.

  • \$\begingroup\$ Thank you. What is the difference for the LED of nominal rating of 90mA vs absolute of 180mA? Is the LED able to handle any current from 90mA to 180mA, and what would determine what the current is? The internal resistance of the LED? I'm also trying to figure out why I measure 37.5v between +/- of the COB LED. \$\endgroup\$ – nachum May 1 '19 at 7:01
  • \$\begingroup\$ The are designed to be run at 90 mA. You can overdrive them a little but you must be able to dissipate the extra heat or their life may be shortened. At 180 mA they may be damaged, so you should leave a good margin. White LEDs with good CRI are often UV LEDs with phosphor. The voltage drop of UV LEDs is on the high side, so 12 LEDs x 3V each is reasonable. \$\endgroup\$ – Mattman944 May 1 '19 at 7:22
  • \$\begingroup\$ Two resistors (each matched to each CoB's Vf) with a constant voltage is better because in series you will need an 80 V supply. I recommend a 35 W Mean Well LRS-35-36 with an adjustable voltage from 32.4 to 39.6V, $13.50 at Digikey. meanwell.com/Upload/PDF/LRS-35/LRS-35-SPEC.PDF \$\endgroup\$ – Misunderstood May 8 '19 at 3:06

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