Returning to BLF after a break, and it would appear things have moved on since I was last here.
What would be an appropriate driver for the 4000k SST-20 in single or triple config? Most of the small single cell lights I built used the yellow PCB A17DD-L FET+1 drivers from banggood and I still have a few of these left over, but I have no idea if using them with the SST-20 in either triple or single LED configs is safe or not.
Also, when it comes to the led4power LD-A4, what output levels would be appropriate for both single and triple setups? I was thinking 3A for the singles and 6A for the triples, but not clear if I can go higher with SST-20. I would like a powerful light, but also one that doesn’t instantly melt if I run it on full power.
You don’t want to use a FET driver on a single SST-20. They have a pretty low forward voltage, and they will cook themselves on direct drive. Triple/quads SST-20 should be a safer bet with a DD FET.
Djozz tested the sst-20 to about 7 amps before the emitter died, so a triple should be able to go up past 10 amps safely. 3 amps on a single should be very safe.
Even though it’s for the 3000k, if you look at the ouput graph in the first post of Djozz’s test you can get an idea of how much extra output you’ll get for your extra power. At a quick glance, the way i read the graph is that:
1A gives me about 300 lumens
2A gives me about 200 lumens more than 1A
3A gives me about 160 lumens more than 2A
4A gives me about 100 lumens more than 3A
so i would personally favour somewhere between 2-3amp as best bang for buck and around 4-5 if i wanted to push it, i think the visual difference between 4 and 6 would be bugger all practically. Obviously it’s a personal choice but it tops out at 6amp so it’s detrimental to go above that.
With a triple it would be 6-9amp for best bang for buck, 12-15 to push it and topping out at 18, justy multiply your single choice by 3.
But you also want to look at the heat your host can handle, this is generally what drives my driver choice.
Edit: Just seen Maukka produced an output graph for the 4000K in this post , slightly higher peak but roughly the same.
Looking at the graphs, yeah, I’d stick with a 2.1A driver (6×7135), which even at 0.1V saturation should still have headroom down to 3.3V at the cell (for 3.2V at the LED).
After (surprisingly if not amazingly) seeing some cells (eg, Samsung) down to like 10% SOC at 3.6V, you ain’t buying much extra runtime going lower.
Just in case you’re unaware, the B4 requires an external MOSFET, it won’t power an LED on it’s own. It’s like the A4 but with the MOSFET removed to allow you to connect to a MOSFET mounted in a place more conducive to heat transfer, such as the LED boards L4P sells with such a provision. Heat transfer from an LED board to the body is generally better than from the driver to the body.