Help with 700ma LED driver Ckt

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 .

Can anyone help please??

Thanks

That is some LED to pull almost 3/4 of an amp. What is it being used for. Can you pulse the LED to extend the battery life?

Can you provide more details.

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.

Here is the type of circuit you need:

**broken link removed**

Here's another example. Of course the components will need to e changed to give you 700mA.
https://www.electro-tech-online.com/threads/led-switching-regulator.41375/