Ok, I'm building an LED flashlight. It uses 12 high power LEDs, and what it all comes down to is that at 4.5V (3 "D" cells), I only need 5 Ohms of resistance. Now, a whole lot of energy goes into heating up that 5 Ohm resistor a whole lot. Is there a more effecient way? What I'd like is to be able to perhaps use PWM to short the battery out through the leds in quick bursts or something to that effect. I can use discreet components, but preferably stuff I could control from a uC. (Transistor, ADC for voltage/current sense built-in with the uC I'm using, a PIC16F876).
Thanks!