Let's assume I have 3 LEDs which have forward voltage of 3.3 V and current rating is 300 mA. All the LEDs are in series and I have a power supply of 12 V. when I series a resistor to limit current it draws much power.
Voltage through LEDs =\$3.3v*3=9.9 V\$
Voltage drop through resistor=\$12v-9.9v=2.1 V\$
Resistor value for \$300 mA =2.1v/0.3A=7\Omega\$
Power loss through resistor \$= 7*0.3=2.1 W\$
I need to reduce this power loss. Is there any way with MOSFET or BJT transistors? I read this http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/. But I don't understand how to calculate values. Here is the circuit diagram in above site.
I don't need exactly this. I need a proper way to do that.