Could linear driver work this way?
AFAIK linear drivers regulate current to a certain value and burn excessive voltage as heat. Usually they are used with one Li-Ion battery and one led.
For example we have a 4V batteries a 2A linear driver and a XM-L leds.
In a 1 battery 1 led configuration led have 2A at 3,05V. The driver would burn 1,9W* as heat
*(4-3,05)V x 2A = 1,9W
And here’s my “thesis”:
In a 2 batteries and 2 leds configuration (as pictured above) leds would still have 2A but this time at 6,1V. The driver would burn 3,8W
(8-6,1)V x 2A = 3,8W
Since you didn't specify what linear drivers you want to use, the anwer is yes, linear drivers can do that, efficiency is 76% using your numbers.
However if you try that with a NANJG105C or NANJG101, it will burn...
(a) The chips on the driver are rated up to 5.5V (ATtiny13, the AMCs are 6V), so they would suffer from over-voltage.
(b) Also 1.9V*350mA=0.67W for each AMC7135 to burn up is near their limit (0.7W), especially if the environment is already heated by the LEDs.
A solution for (a) is to somehow drop supply voltage for the electronics, maybe using a diode, a diode-resistor combo, an additional connection to between the batteries, or between the LEDs (this is a common solution, see below), or a voltage regulator.
I thought it wouldn’t work since I didn’t see any builds using this configuration. I’m building a cave headlamp and linear drivers don’t interfere with compass (cave surveying) while most buck/boost drivers do.
Since the primary goal of this cave lamp is to be powerfull I’ll just use buck drivers.
I tested that mod up to 3 XML in series from 9 or 10 nimhs (I forget, it’s been awhile) and it was stable with all modes available from a multimode driver. The series LEDs drop the voltage for the 7135’s and a 78L05 regulator drops the voltage for the IC. The problem is you lose the low voltage detection which is not good with series cells. For a pack with the appropriate protection pcb and a battery fuel guage it would be fine.
you could set it up as a master-slave - each LED is supplied by it’s own Nanjg board, but only one of those boards has an MCU which controls both of them. It’ll allow you to use a 1S battery pack too, so you can carry back up cells or tailor the pack cell count to a particular situation.
This is the way to go, real easy. I currently have this setup with 3 xml’s running on either 9 nimh or 3 lithiums. The diagram actually has an extra wire on it. In real life you just series wire everything put the amc 7135’s on the negative side and pull the positive from just before the last led.
That’s a proven way to go dating back to P7’s but some had issues because of the lower Vf of newer LEDs. It might be less of an issue with the higher Vf XML-2 but in any case people using this circuit have to pay close attention to battery voltage since the driver won’t read this correctly any more. It also works better with single mode drivers(no IC).
Diver in the above pictured Seoul P7 setup still has to burn excessive voltage for all three leds. But I guess if it worked with two additional batteries and P7 leds it will work with one additional battery and XM-L led.
Batteries will be in 2s/2p (8.4V) and will connected to headlamp with 1m (3 feet) of cable. A master/slave configuration would require batteries in parallel and twice the current through the cable which would also mean 4x the loss.
Using a 0.75mm2 cable (the most I can get through cable gland) that would be 0,4W vs 1,6W (3A or 6A current)
The 2280mA KD 7135 V2 driver with 2 batteries in series and 2 XML in series worked on high for ten minutes. It got hot but not so much that I couldn’t hold it between my fingertips.
Its hard to tell from the pictures, but I'm with scaru, that shouldnt work. 8.4V on that driver is too much and I dont see an LED in the path of the cells.
On second thought: are you sure the driver is working? Have you tried modes? Maybe you bypassed the driver.^^
