Constant Current LED Diver LDH-25-350W


I’m trying to run a string of leds at 350ma. The forward voltage of these LEDs is around 35VDC. I’ve tried running the input voltage from 12VDC up to about 24VDC, but I get no output to the LEDs.

On the datasheet, they say to leave the dimming leads open if the dimming function is not required. Still, I get no output.

Also, I ordered a couple of these to try out, but neither worked. Any ideas?



Likely explanations could include an incorrect connection of some sort, damage to one or more components, and/or selection of an unsuitable power source.

Accidentally connecting the input backwards has potential to permanently damage the driver, and should be ruled out at a possibility. Sometimes things that look connected aren’t; take a meter, work your way from input to output, and when things go from “how they should be” to not, that’s a good clue as to where the problem may lie.

What’s the power source? It needs to be capable of supplying at least 13 watts or so based on the information given. Things won’t work so well if that’s not the case.

Hi Rick,

Thanks for the reply. I’m using a benchtop supply, capable of up to 3amps at up to 30VDC, similar to this one. Actually, it might be this exact one --> BK1670A-ND

Having tried two different drivers, I’ve received the same results. I would think the possibility of receiving two defective units would be fairly remote, but I suppose it’s possible.

I’m pretty sure I hooked it up per the datasheet, that I have read through a few times. That being said, I will go through the wiring again carefully to make sure I have everything hooked up per the datasheet.

Thanks a lot!

Hi NickW,

LED are pretty non-linear, thus you’ll need to power them from 35V or above and
let the current limiter to find the correct operating voltage. With 24V they probably are all off.


Note that the named driver is a boost-mode product, which stipulates the Vin be < Vout.

Hi Rick,

Oops. You are right. Assumed that RickW is testing the LED string directly with the PSU.

I guess the first thing to do is to measure the voltage at the output of the boost block while the LED string is connected. If the voltage is around 72V then the problem is in the strip, if the voltage is 0V even after removing the strip connection, then it is the boost block.

Seen that sometimes boost converters do not start up if the input voltage ramps up too fast.