Cree XPG with Nexgen, full regulation over 600MA?

Wayne,

I recently bought several of your Nexgen 500MA converter boards, and a Nexgen 750. As expected the 500 boards go into full regulation with two AA batteries (both 1.2 and 1.5V) and the 750 does not. I was using a Cree XRE LED.

Do you know if an LED with a lower forward voltage can be driven at a higher current with full regulation? Supposedly the new Cree XPG has typically around 0.3V lower Vf at 700MA (3.2 vs 3.5).

There are several factors that you need to take into account. The total losses from all the components like the switch, housing impedance and of course the major one being the Vf of the LED.

It would be hard to determine, but, in genreal a lower Vf will be more likely to be in regulation with the Nexgen 750. One thing that may be working against this is the higher internal impedance of Alkaline batteries as they are put under a load. They sag more than NiMH/NiCD.

If you are using a Kroll switch it could be a major source of loss in the total system. I would grease the Kroll to ensure the contact resistance remains low. A dry contact Kroll will arc and the springs/contacts get dirty and raise the contact resistance quite fast. I used to fill my Kroll switches with Nyogel to eliminate this problem.

Wayne

Just to give you some encouragement, I've measured Vf of 3.10V at 1050mA drive current for an XP-G R4.