PT4115 LED module – upgraded to Nichia NT2x757D LEDs

First the old version, using the best small LEDs I could get hold of at that time: Nichia NSSL157 and NSSW157 types driven at about 100mA.


The new boards were ordered at, one of the many Chinese board houses / factory front-ends. I’m quite pleased with the quality, no extra charge for black solder mask, excellent silkscreen quality / resolution (no inkjet dots visible).


The new LEDs are from Nichia again, of course high efficiency ones. I used these types: NT2L757D (warm white ~ 3500K), NT2W757D (white ~ 5000K). They are driven with about 180mA, which is a still safe value without mandatory additional heat-sinks or even active cooling. The absolute maximum constant current is 300mA (400mA pulsed). Total light output is at least 400lm per board.

As you can see, the new LEDs are larger, about double the size. As the forward voltage is the same as of the previous ones, I suspect each package contains 2 chips in parallel. This time I used a whole lot more thermal vias to help keep them cool enough.

I used a different inductor model, still 100µH, but a lot smaller and less prone to stress fractures as the old ‘top-hat’ one. Internal resistance of the new inductor is about 1.35 Ohm, the old one has about 1 Ohm. The new inductor is also a lot flatter, just 2mm high, removing any chance of accidentally ripping it off the board or of breaking the ferrite material.

The Schottky diode was changed too. I chose a smaller SS14L model (sub SMA package) with similar specs: 1A, 40V.


All of the back side copper is used as a heat-sink.


The footprint provided in the LED datasheet worked reasonably well using hot-air reflow soldering. I added some extra flux and only had to nudge 2 LEDs into position. I blame uneven heating for their ‘misbehaviour’, I probably used too small an air-nozzle.


Footprint download: [1], [2]

Please note: the thermal vias are NOT part of the footprint, you will have to add them yourself. The same is true for additional copper pour acting as a heat-sink. You cannot operate these LEDs at their rated current without some sort of heatsink.

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