So i have just built a constant current led driver for 30-60V LEDs that can drive them at up to 3.5A from a ~20V source. The chip i use is the LT3795.
The circuit is identical to the one at the top of the datasheet (obviously with adjusted component values), which should have efficiencies of >90%, but at only 400mA output current.
So far the design is working well, but i am only getting ~80% efficiency. One thing that i found was that there is a very odd gate drive waveform of the Low side mosfet (see below), if i understand correctly the biggest losses occur while the mosfet is changing from on to off, which is taking longer than it should (i think). I have no idea where it is coming from; i have checked FB, IntVcc and LED Current Sense for a possible fault conditions, that would cause the chip to force the Gate low, but have not found anything.
So now i am wondering if that reduction in efficiency is even because of that switching weirdness of if i just got pulled down the rabbit hole. Also i am not sure if the efficiency at this point is just a fundamental limit, after all this is a 200W boost converter.
EDIT: i have just checked and the chip also momentarily disables the PFet at the same time as the glitch on the NFet (i have no picture of that though), no idea what to make of that though
