Lasersaber's use of a ferrite rod will likely generate lots's of EMI since the gap is at the maximum it acts as a dipole and is a very effectivre radiator of EMI. As such it is difficult to get a lot of inductance, which means you need to add more wire, which has resistance and will contribute to losses. A closed magnetic circuit or one with a small gap such as EI ferrites or the appropriate toroidal material will be more efficient pound for pound. It will also require fewer turns. Losses generally go up as a function of frequency, so keeping the inductance high and the frequency low is one path toward higher efficiency. If size is not a constraint, you can take this to the limits and be very efficient. Going the other way, attempting to get the smallest size and highest power transfer, you are compounding switching losses. This latter (compact design) has always been the aim of switchmode power supply designers, so they are constantly tweaking the switching circuit to get fast transition times for low loss. Auto radios of the forties and fifties used a vibrator switch at low frequency ( around 100 to 120 Hz.) to chop the DC battery supply into AC, and very large magnetics to get an efficiently derived plate supply for the tubes Here's a fun walk through of the old vibrator circuits which were used before power transistors were developed. http://www.youtube.com/watch?v=Fp6PkRTmb8U

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