Honestly, that makes two of us. I get the shakes every time I go near a driver. I could solder pipe all day, but it’s the tiny stuff that usually bites me in the butt. Especially when trying to make the master/slave mod. Those legs on the 7135 chips are so tiny and trying to solder two wires to one tiny leg on the first one (master), is plain murderous. The connections are delicate, as the legs are so small and the traces on the board can’t take a lot, before they will lift off.
The thread on the drivers is still on the site here, somewhere. Basically, the one micro controller on the master board, now controls PWM to all the 7135 chips on all three boards. The wiring to the LEDs is parallel, but because each led is wired to a board, the amperage is controlled, instead of uncontrolled.
In a regular parallel setup without regulating the amperage, the differences in three LEDs Vf can cause one led to see more amperage than the others (the one with the lowest Vf) and as LEDs heat, Vf lowers, making imbalance even worse, but this way each led still only sees a regulated amperage from the board it is wired to. It keeps parallel LEDs from having the issue of different Vf causing a possible thermal runaway, but still allows for the lower voltage found in a parallel circuit.
The reason I like the circuit is the fact that I don't have to use higher voltage found in series circuits. I like NiMHs and the higher the voltage, the more room I need for NiMHs. It allows me to still do a 1D with three LEDs, using NiMH batteries. With the Nichias only getting 1400ma each, I am still only drawing 4.2 amps from the Eneloops. That's a lot, but still within their ability. It won't run a long time on high, but that's why there's modes. It should run quite a while on low or medium. I am using 4 Eneloops due to the voltage drop that is going to happen from 4.2 amps and with four in series, I should still have good run time, even with the sag. Even at 1v each, I will still be putting 4v to the drivers.
The reasons I don't like it are, the added costs of using 3 drivers and the added risks of having some old fart wire it up wrong or solder things together that shouldn't be, due to the close quarters I'm dealing with. Really, I should farm out this stuff to someone who does this all the time and does it right.
Of course, with all that I don't know about this stuff, I could be just shooting my mouth off and be totally wrong.