____ +V <------* *-----*-----@@@@@----- SW | L | | | | Power --- Shottkey \|/ IR supply /|\ diode --- emitting | | | diode | | -V <---------------*--------------- SW is actually a transistor which switches on and off at a fixed frequency with 25% time on, 75% time off. During the 25% on-time of each cycle, the Shottkey diode is off, the IR emitting diode is on. Current is drawn from the power supply. Due to the L in series, current builds up slowly and a magnetic field is also building up inside L. When SW turns off, the current from the power supply is cut off. The magnetic field inside L will generate an electrical potential to keep the current flowing. Thus the Shottkey diode will turn on and the IR emitting diode will still stay on. This will last about another 25% of a cycle. Thus the IR generated will still have about 50% duty cycle.