I've noticed something about the XP-L over the past several days (also ruined 5-6 XP-L's in the process). Sometimes when I dedome I purposely remove the ESD diode (I've ALWAYS done this on XM-L2's without issue, as has ComfyChair) but when I do this with XP-L's it seems to raise the vF even higher. Before the dedome I was getting 5.2A DD off a KK26650 (didnt measure vF), after initial dedome I was still getting >5A, (gasoline method) but after going in and cleaning the loose silicone and removing the EDS diode (but verifying the 2 main bond wire's are intact and perfect) the max draw I can get off a KK or a 25R is 3.8A and at that level the measured vF is 3.835v.
This is a strange phenomenon, I can’t figure out why this should change the Vf of the led, because the esd diode is connected in inverse parallel so wouldn’t normally be conducting.
But I’ve not done this experiment and you have, so thank you for sacrificing your leds in the name of experimental science C-K :)!
It really makes me wonder about the LZ1’s I’ve been mounting on XML-color sinkPAD’s since they have their ESD protection diode mounted externally and I don’t use them.
This is very interesting. I’m going to suggest this is a field diode.
Something like a bias voltage to get the most out of the LED portion.
Somewhat of a gate function.
If you pull that wire and power it separately with a variable voltage, you can probably get an idea of what you can do with this or what it is doing.
there is no “gate” in an led.
my theory?
its a tvs/zener and when you shove enough through the led that vf rises it starts clamping.
without it you can abuse the led with impunity.
well till the smoke escapes.
That would mean that all the extra power we are putting in there is just being driven through the esd diode with no extra Vf through the die.
A proper zener circuit is a closed loop with a load drawing up to the zener’s voltage when the zener starts to function. this requires a “bleed” load for the zener to function.
A bias voltage is something completely different than a gate for sure. I wasn’t suggesting the “need” for a gate… I was suggesting that a bias voltage was being supplied to act on the structure in some unknown way. A gate does this in a special way.
Zener diodes are not only used to regulate voltage.
They are also used to limit the voltage across a parallel load.
Instead of using a resister in your circuit, replace it with a fuse rated higher than the maximum desired current.
If the input voltage exceeds the maximum allowed for the load ( set by the zener voltage ) current is shunted around the load.
If the current exceeds the fuse value, the fuse blows and saves the load.
