"Andrew Sarangan" wrote in message
oups.com...
Actually, those are current sensing resistors, not current limiting.
The voltage across the resistor is compared with a fixed reference
voltage, and it is the FET which limits the current. So, a higher
resistor does not necessarily mean lower current.


Ahh yes. I saw the current sensing resistors but I overlooked the resistor
values for the divider that creates the fixed reference. I'm still wondering
about a few things though, hope you can elaborate a bit.

- You have the fuse placed in the ground wire. However, the largest
'touchable' area on your PCB and heatsinks are all attached to the area
behind the fuse. A simple protruding screw or rivet would be enough to turn
the circuit into an unfused system. Why not fuse the 12V line?

- The LM7805 really likes having a small decoupling capacitor at it's output
to prevent oscillation (and even self-destrucion on cheap non-brand 7805's).
How about adding 100nF between the 5V output and ground?

- The current sense resistor in the 1400mA version will dissipate about (1.4
x 1.4 x 1.3) 2.6W, so a 3W resistor is OK. The 700mA version would only
dissipate (0.7 x 0.7 x 0.69) about 0.36 W. You could do with a smaller
version (0.5W) there??

Mind you, I'm not trying to be negative about your design, but just curious
about some of your design decisions. The Luxeon's are really nice gadgets
8-)

Rob