I bought some IRLML2502 MOSFET transistors to repair a toy quadcopter and had a bunch left over. I decided to add one to my convoy S2 with a nanjg 101-AK-A1 driver to give it an extra bright strobe mode. They were pretty small, and they can handle 4.2A. They might be slightly undersized for a direct drive turbo mode, but with a lower duty cycle they will be fine. The datasheet says it can handle up to 33A pulsed, as long as the junction temperature stays under the maximum rating.
My original plan was to remove a 7135 and stack it on another one, then use the space for the FET (rotated because they don’t share the same footprint), but the pill wouldn’t fit back together with the extra height from the stacked 7135. I didn’t want to give up 350mA, so I put the 7135 back and found another spot with enough room for the FET with access to battery negative and LED negative. I scraped away some solder mask and tinned the copper. It’s on the lower right side near the Q3 screenprint.
I found a 10K resistor to act as the pull down resistor on the gate, and I bent one of the FET lugs upwards.
I used some kapton tape to hold everything in place and I soldered the resistor to the fet with some copper wire to connect everything.
Then I carefully soldered it in place using lots of flux and covered it with some kapton tape to insulate it. I used that red wire to connect the gate to pin 5 (PB0) of the attiny13.
Then I assembled the light and flashed the firmware. If anyone wants to try it just define STROBE_PIN as PB0 in my firmware: GitHub - alexvanh/basic_off_time_driver: Flashlight driver firmware demonstrating method of using off-time to switch modes on attiny13 nanjg drivers.
At first I wasn’t sure if it was worth all of the hassle and the tiny soldering because the brightness wasn’t that much greater. I added some copper braid to the springs and now the strobe is definitely a lot brighter and seems a little whiter as well (the led is normally a little warm). My driver was only a 4*7135 driver at 1.4A, if you are already running your light at a higher brightness this mod might not be worth it for you.
This could also be useful for a low moonlight mode since the 7135’s seem to have some trouble turning on fast enough for lower PWM values, especially when there are a lot of them.
