# PSU drops both current and voltage when connecting to an LED

I'm connecting a DC PSU to a high power LED. I'm setting the maximal current, and a voltage. For the first few seconds, I'm in the c.c mode (voltage drops from its initial value to a lower one). But after a few seconds, probably since the LED heats up, something strange happens: both the current, and the voltage drop to very low values.

If the heating causes the resistance to increase, I would expect the voltage to increase.

A few more details:
It's an unbranded 100W LED I got from ebay (link)
Unfortunately, there is no spec.

I'm setting the voltage to 30V, and maximum current to 2.7A.
The LED heats up, there's a fan attached to it, that does its best to keep it cool.

Thank you.

• More information will help us help you. Link to LED datasheet or at least specs part number ... / What current and voltage are you setting the psu to? Why? | What are the initial values OC / on 1st connection / after a few seconds / is the LED hot? | ???????????????? Commented Sep 12, 2019 at 12:54
• Is your LED Vf and current within spec of your power supply? Commented Sep 12, 2019 at 13:01
• I've attached the additional information. Regarding the Vf: The power supply of the led supplies 40V. I'm intentionally using the PSU, and not the power supply since I found out you can use less the 40V to turn on the led (to a reasonable power for the cause), and hopefully, it'll heat less that way. Surprisingly, when I'm using the "official" power supply, there's no drop in lighting as appears when I'm connecting the LED to the PSU (when there's a drop in Voltage and Current, there's also drop in light intensity). Commented Sep 12, 2019 at 13:08
• On t=0, the psu shows v=~21V, and A=~2.7A. But after few seconds, V drops to less then 5V, and C to less then 0.5A. And it flickers up and down in that region. Commented Sep 12, 2019 at 13:14
• Re, "both current and voltage drop to very low values." Sounds like what I would expect if your power supply had a foldback mode, and your circuit tripped it. Commented Sep 12, 2019 at 15:07