Nothing, the “R” represents a decimal point. R10000000 would also be the same thing, they are just trailing zeros.
It looks like a 1206, but I’d measure it if I wasn’t sure.
I’d also still consider an order from Mouser. For <$10 you should be able to get out of there with a decent assortment of precision sense resistors. They’ll get to you faster and if you choose the right values you’ll be in a good position to tune your output exactly as you want.
OTOH I always feel a lot of pressure to pile everything I can into a Mouser order so I don’t have to order again right away. With FT you just buy what you want, one item at a time.
BTW, for the record, I’ve added the emitter leads and tested the other board (the one with the blob) and it’s performing the same way as the first one did before I added the R300 resistor in parallel with the original R200 resistor.
So my paranoia about the blob of solder was unfounded :)…
I’ve ordered some of the R100 and R200 from Digikey, just in case, so I’ll have a pile of them :)… Shipping actually wasn’t bad… they apparently ship via USPS first class now, so it was about $3+ for the shipping.
As we can see from ohaya’s pictures, pins 3 and 4 appear to be “not connected” on the unmarked SOT23-6 package. If that’s correct it can’t be CX2829.
The pinout we appear to have on this driver is :
Vin or PWM (probably Vin.)
GND (sort of…)
PWM or Vin (probalby PWM)
Assuming any of that is correct, pins 3 and 4 probably need to be pulled to GND or Vin in order to change mode groups, if it’s possible at all. If ohaya will set the driver on “medium” and probe those pins for voltage with a DMM we can get a better idea what’s going on and then recommend an action.
I’m not ignoring you all - I’ll try to get those physical measurements you all have asked for, today, after work.
EDIT: Also, BTW, I only have one working driver (I KNEW I should’ve ordered more of them). I used a heatgun to pull the R200 off last night, and a bunch of the components came off at the same time. I’m planning to try to re-construct the driver when the new resistors come in, but not now since it won’t work anyway - that was part of the reason I asked about shorting the resistor…
Also killed one XM-L2 so far on this “project”… kind of amazing that it’s not more :)…
Tough luck on the components that came off. Putting them back on would be good practice for you…
The buck circuit rapidly switches a FET which puts a current through an inductor. The inductor smooths out the voltage to an intermediate voltage between the full “on” voltage and the 0v off state. The duty cycle of the FET is determined by the voltage drop across the sense resistor. Duty cycle means what percentage of the time it’s turned on. Shorting the resistor will produce negligible voltage drop and push the circuit to 100% duty cycle. At 100% duty cycle Vin = Vout and Iin = Iout (more or less). In other words the buck circuit will stop stepping the voltage down and go into DD (direct drive).
Since the purpose of using buck drivers in flashlights is generally to run a much higher input voltage than output voltage (MT-G2 on 3s/4s, XP- or XM- on 2s or 3s), DD is catastrophic for the LED.
Taking those measurements isn’t directly useful to me either, as I don’t plan to run this driver for anything, but I think it would be a nice thing to do for other people. Maybe bridging some of those pins enables even more blinky modes ;-).
Don’t worry about it! Despite the time we find to chat online, I know most of us have limited time for experiments. It sounded like a joke with a grain of truth and I took it as such, but if you never find time to do the test I couldn’t blame you either.
Did you lose any of the stuff for the driver that fell apart? I was at least half serious about putting it back together. It’s definitely doable if you want to, there are orientation marks for all the components with critical orientation. I feel a little bad about that one since I pushed you to steal the resistor!
I see what you mean. Maybe an accurate figure for wire thickness would be useful instead?
I think 4 amps could be a bad idea. The freewheeling diode (SS34) is not OK for that current, and I think the little shrimpy FET is also not going to be a fan of the higher current. You may be able to run this thing that way, but your losses will be high and if you get a failure it won’t be a surprise. Also, pushing a buck driver too far can zap LEDs due to spikes in the current. In short: no, do not do that.