So i just finished building two P60 drop-in’s using the convoy drivers with biscotti. I stacked the same amounts of 7135’s on both drivers. One is using a XP-L Hi and the other a 219c.
Here is something I don’t quite understand. Both drivers draws 4.2 amps on a VTC6. The 219c also draws 4.2 amps on a NCR18650B. However the XP-L Hi only draws 3.7 amps with the NCR18650B.
How can this be possible?
These lineair drivers deliver a fixed current to the led, they do it by giving the led the voltage needed to get the specified current through the led, and any voltage leftover is burnt off as heat. For this to work, the battery voltage must be higher than the led voltage. Once this is not the case (i.e. during drainage battery voltage goes down), the 7135 chips can not deliver their rated current anymore but less, the driver is out of regulation, in fact the leds experience direct drive.
Higher voltage leds like the XP-L Hi are closer to the battery voltage than lower voltage leds like the 219C and so falls out of regulation sooner, and a low-drain battery like the NCR18650B has so low voltage under load that the 7135 chips even with a fully charged battery do not have the voltage overhead at hand to deliver their rated current.
Thanks for the explanation, djozz! :+1:
Another question. What happens if one of the 7135’s stops working? Will I just lose the mA it gives or does anything else happen?
You will just lose that one chip working.