Which converter?

[Lumbee1]

I am building a Cree bike light but I need some help with choosing which converter to use.

The P4 cree has a Vf of 3.3 to 3.9. The battery pack I would like to use is 3.7V Li-Ion. I know that I could run two Cree's for a higher total Vf and then choose a boost converter, but I would like to keep this as small as possible.

I already have a Fatman for another dual Cree bikelight.

 

[ROVER]

So just to be straight, for this application you're running a single lithium ion cell and connecting two Seoul p4s or is it just one?


If one, that GD500 looks good for running with your battery. You can choose your sense resistors to dial the current in to your liking too.

 

[LED Zeppelin]

The GD as Rover suggested would be a good choice, and give you the longest regulated output.

But if you want the longest output period, you might also consider a buck converter like the Downboy. It would start out regulated on a full charge, but when the pack voltage dropped below the Vf, it would drop out of regulation and gradually dim.

With the GD on the other hand, as the pack voltage dropped, the converter would ramp up the current from the pack and drain it faster to stay in regulation, and your pack would deplete sooner in exchange for regulated output.

 

[Lumbee1]

The GD as Rover suggested would be a good choice, and give you the longest regulated output.

But if you want the longest output period, you might also consider a buck converter like the Downboy. It would start out regulated on a full charge, but when the pack voltage dropped below the Vf, it would drop out of regulation and gradually dim.

With the GD on the other hand, as the pack voltage dropped, the converter would ramp up the current from the pack and drain it faster to stay in regulation, and your pack would deplete sooner in exchange for regulated output.

My requirements have changed. I built an enclosure for two CREE's (Vf ~3.4) in series. The battery pack is still 3.7V Li-Ion. It appears that the GD is designed for a total Vf of less than 5.4V.

So what are my options now?
Vf = 6.8V
Vin = 3.7V
Current requirement 700mA (either 650 or 750 will also work)

 

[Ms_SS]

The Shark will run multiple LEDs in series.