I’m trying to use some ir leds but seem to be having earthing issues. With a multimeter i placed the negative probe on the copper base and positive probe on both the + & - of the pcb and i get a reading on both pads…???
Does this mean the led is soldered in reverse polarity? And the direct thermal pad has negative potential…?
Btw led is osram sfh 4715as
If I see correctly the first photo is right.
There is no connection between ground - and positive +
This looks like the Anode (+) is shorted to the copper base - not sure if intentional or missoldered. Probably the latter, I’ve not seen a single flashlight with + on the copper PCB.
Second image you have black lead on base (shorted to anode) and red lead on - pad (cathode), so you are measuring the LED in reverse direction, which tests the integrated protection diode of the led. Most LEDs have that. A value of 900ish mV looks about right for that.
Have you tried isolating led mcpcb? Most IR Leds I was dealing with required it.
In times of Led4Power store Neven had special pcb (isolated) just for IRs.
Yeh seems like I’ll need to isolate the mcpcb’s. I wouldn’t have thought to do that, thanks
Ops sorry you are right! I have to check with my multimeter
Just looks like the top pic is a direct short (by design, I imagine, per the center-pad), and the bottom pic is through the IRLED itself (935mV drop?, which seems kinda low).
Reverse direction, so it’s the ESD protection diode which should be a generic Silicon diode (I guess). Even 6V white LEDs usually have such a draw in rev direction.
Huh. Okay, I did not expect that to be a thing. What the heck Osram.
Ah, that explains it.
Aharh, thanks mate. Isolating the mcpcb’s is going to be a pita but that’s what I’ll have to do. I agree with Moritz , wtf osram!?
You can find non-isolated thermal pad in many LED models. It’s just that we try to avoid them in flashlights.
They are usually negative potential though
It’s a problem the old Osram Black Flat had too, as well as the Black Flat S (IIRC remains the intensity king despite the weird size).
Would be nice if someone made a DTP MCPCB with the core isolated on the other side, maybe with solder mask or something else that’s still thermally conductive.
Correct me if I’m wrong but will this have fried the led?
Nice!!
