Did a test run on 100% for 10 to 15 secs and seen smoke coming from the reflector, upon inspection 1 to 2 mm black dot sitting on the led die
so pretty much semi cooked the led (was still working when shutdown)
Did i do something wrong ? or sold a fake led ? or driver malfunction ?
Photo of the MCPCB ?
A DTP 12V MCPCB must not have the middle connection between the 2 strings of two series LED chips going through the center pad, otherwise one string is shorted to ground, and the other string receive no current.
Thanks, a bit blurry but looking at it it’s the non isolated kind (=bad). DTP means direct thermal path, a normal MCPCB has a copper/Alu base, a dielectric layer and an electrical copper layer. In a DTP MCPCB the thermal pad is directly connected to the base without dielectric, this means much lower thermal resistance and it’s pretty much mandatory for high power LEDs.
The one you have is the non isolated kind, like shown in the XHP70.3 datasheet :
internally there is 2 strings of 2 LED chips, for 12V they must be externally connected in series, if they are connected through the middle pad, then the negative side of the top string is connected to the base, in contact with the flashlight body, which is the battery negative = short, that string received all the current the driver was capable to provide (more than the regulated current).
It looks like it’s sitting bit crooked on led board. That makes me think there might be too much or too little solder under the led thermal pad. There could also have been some flux residue or other dirt on top of the led that has burned and caused the damage. The led board could use some force pressing it towards the material the heat needs to transfer towards to. I don’t know if there was that. It could also be bad pcb without direct thermal pad. One of these is probably the case.
LEDs need to be cleaned after reflow. If there is any crud on it, dust, dirt, solder flux residue, VOCs, it can cause the silicone to burn. LEDs are often dirty straight from the reflow provider.
To clean LEDs I place the LED in a bath of 99.9% isopropyl alcohol and use a clean nitrile glove or a clean fine tip painters brush to gently rub the silicone. Then I hit it with an air blast to dry. Then I inspect the silicone with a 10x loupe to make sure it is perfectly clean.
Solder flux can get on the LED when you connect the wires too. I place a little guard over the LED when I connect the wires to prevent this.
But besides that, in the case of your LED it looks like the quality of the reflow wasn’t so great.
, thinking the 2 cells were used in series with boost driver. So ignore everything I said.