Hi. Not sure if this is the correct spot for this post. I am working on making a driver for a supplemental rear light for my motorcycle. I am needing it to power 13, 750ma red leds. They list the forward voltage as 2.2-2.6. Supply voltage will be 12v to around 13.5-14. I have some lm350 regulators. I am wanting to give the array maybe 300ma for running lights and maybe 650 for brake. Any help would be appreciated. Thanks Matt
Dropping 12v to 2.2-2.6 with a linear regulator will be burning off (wasting) a lot of power as heat.
Ebay has cheap buck regulators you could use.
You could buck down to 3 volts then use AMC7135 chips to provide 350mA & 700mA constant current.
Perhaps the lm350 can do constant current?
I'd probably use 3 or 4 in series with a resistor, switched by a 2 FETs, one with a bigger resistor for the lower light output.
You should consider a much bigger difference between running lights and brake lights, more in the range 10:1 to 20:1. 2:1 doesn't make much of a difference visually.
Is there enough room in or around the tail light for the regulator heatsinks? Each one would burn off roughly 2.5W, but I’m assuming the LED’s are wired 4 in series x 3 strings (12 LED’s total instead of 13).
Yes there is room. I plan to put the circuits under the seat. I plan to use 13 leds.
13 is an awkward number for laying out a good series+parallel circuit.
I could use 14 if that would help.
I would use 15 to have series of 5 and fine tune with resistors.
OEM car high-mount LED brake lights use series strings of 4 LEDs with a resistor, multiples of those in parallel. 5 LEDs in series wouldn't be fully driven until voltage was over 13. 4 in series would be controlled by the resistor at all times.
It'd probably be a lot easier to set it up as two separate circuits, a series string of 4 LEDs for the running light and all series strings (3 or 4 total) for the brake light.
I would do 4 also but he said he wanted a lower than max current for brake lights. I figured 5 would be close.
Thank you for all the input. I only wanted less than max current for the brake lights to increase life and reliability of the leds. I originally ordered 10 leds but have ordered another 5 and am awaiting arrival. After I receive them I will have to experiment.