What Happens When Your Total Voltage Drop is Outside of Your Driver’s Constant Current Region?

In this video, we’ll have a look at what happens when the sum of your COB voltage drop in a circuit is below the minimum constant current region voltage of your driver, as well as what happens when it’s above the maximum constant current region voltage of your driver.


  1. Thats impressive that the driver can handle going all the way down to one cob, mine makes a whistling sound when dimming as well. Just got a delivery today with 2 Seoul Semiconductor SDW87F1C-N2E11J 4000k chips, and an HLG-120H-54A driver for my next project. I’m going to mount them to a couple of the heat sinks that came from china, and cool them with the dual fans out of the old xbox 360, want to make it all one unit with the driver mounted all together. Just have to get some aluminum angle then I can put it all together, going without holders on this one and just solder the wires on, it seems like the plastic holders for the chips with the mounting holes put the hold down pressure on the bolt hole area anyways.

    • LEDGardener

      March 21, 2017 at 6:50 pm

      Interesting that yours makes the same noise. It’s crazy how many new COBs are coming to market now – those Seoul Semis look like another affordable option. Have you seen many builds with them? What will you grow with this light?

      • Got all my parts today and pulled an all dayer and got it fired up, never saw anyone use these chips before, figured for 17 bucks what the heck. I have to say they are bright, especially for being only driven at 1.15ma they are a good sized chip and they cast a wide area of light. Put them about 14″ apart, it makes for a fairly even spread it seems, not sure where exactly to sat the voltage though, the specs say 51v at 1.5ma so I set it a little less, the fans are a little noisy but not too bad though and the heat sinks stay nice and cold. As for what Im going to grow I just put 8 different pepper plants into kratky containers the other day, I plan on topping all of them and trying to keep whatever I don’t run out of room for and keeping an indoor garden all the time from now on

  2. Yea, I figured for less than 10 bucks it would be more reliable than a wall wort to power the fan. My father in law gave me the meter, he ordered it at work but said it won’t read high enough, it’s the first real meter I have ever owned. A huge step up from my old one, didn’t know what I was missing, it does everthing.

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