hi Guys .
I have to design a circuit that would drive a 3.2 Volt LED @ 700ma from a 4.8Volt NiMh battrey Pack for atleast 5 hours , doing the math i think min. battrey capacity needed would be 4000mAH .
But the problem is driving the LED at a constant current of 700ma as the voltage drops down .
Are you sure it's designed to run at 700mA continuously or is that just the absolute maximum rating?
Obviously the LED will need a heatsink.
I'd recommend a switched mode power supply, even if it's a simple open-loop design. Using four 4000mAh C cells and an 80% efficient switching regulator it should last about 7 hours.