Hastily assembled a Convoy L21B and had a tall solder joint or two that shorted to the reflector. Now the 8A buck driver is dead. Interestingly, it actually lit up for a split second at a reasonable brightness, then dropped to a super low moon for a while. I took it through to programming mode so the mcu seemed intact. Now I can’t get anything out of it.
Anybody have ideas which component likely bit it? Maybe the op-amp? Buck controller? Switching fet?
Thanks in advance.
I don’t think it could be anything else than the buck regulator, though they usually have short circuit protection.
From the look of it it has integrated switchs. The FET in the middle being likely for RPP.
BTW I’d be interested to know what buck regulator is used if you could make out the markings.
I will update the thread, but it turns out I misdiagnosed the situation. I don’t think I shorted to the reflector at all, but rather torque on the star cut through the insulation of the wires. I killed the SST40 with DD from a (wait for it) fully charged 30T. Normally I test with M50T at like 3.3V to avoid killing things… that’s what I get for modding when I shouldn’t be.
The driver is fine!
The FET is AON7423 P-fet, Opamp is OPA333AIDBVR, and the buck controller has it’s markings destroyed.
Good then (well not for the poor LED )
Damn they really love doing this…
Can I ask for measurements of the package if it doesn’t bother you ? 3x4mm maybe ? Also from this pic it seems that the two pins next to the FET are Vin with the third being something else, on the other side, looking at Convoy’s pics, it seems that 2 pins are GND, can you confirm ? That’ll be easier to search which IC it is.
I will definitely get these measurements for you. I’ll see if it’s reasonable to de-solder it as well. I blew my second and last 5000K sst40 this morning before realizing how dumb I was, so there’s nothing else to put in the host until those YinDing emitters show up (which apparently are coming through US customs now. USPS awaiting parcel… Can’t wait. I have high hopes for that emitter.)
Looks to be the MPQ8612-12 , I think I already came across it before, 3Vin min without bias but maybe it can works down to 2.8V, the 10mΩ (18max) and 7.8mΩ (10 max) FETs are a little high for using it with at 9A IMO (e.g. with an SFT-40), there were a 16 and 20A version with lower Rdson FETS but they’re obsolete.
Additionally it’s not capable of 100% duty cycle, only about 96% at 500kHz and 93% at 1Mhz if I calculated it right, their DC-DC designer strangely gives a worse max duty cycle, about 90%, meaning Vout is less than Vin x 0.9, with isn’t great for a 1S to 1S buck LED driver.
Jared, does your picture show that the chip has a notched corner? That is a strange package for sure. i was thinking an MPS chip also but couldn’t find one with a notch.
The picture I linked doesn’t show a notch.
It’s probably from the sanding.
Any mods you’d suggest to increase efficiency or dropout performance? Still a bit above my knowledge at this time.
The ‘notch’ is actually some of the red goop that i didn’t cleanly cut away being backlit
Nothing really substantial, the max duty cycle can be increased by lowering the switching frequency, but then you’d need to use a higher inductance but it’ll have a higher DCR (which increases the dropout voltage) maybe a taller one could fit, looks like a 6030 ? Then a 6060, but then also more output capacitance…
Additionally the sense resistor could be lowered, like 6mΩ with 48mV Vsense for 8A, or even lower if you don’t care about the lowest mode.
The RPP FET could be shunted too, it’s a very good one though.
I’m not sure it’s worth the hassle.
What is that 10-pin device on the left side—looks like 5 of the pins aren’t even used in the back-lit photo.