The first circuit is a low efficiency converter. It uses two NE555 timing ciruits, the first supplies a 21.5 khz trigger to the second which is voltage controlled by the output of an operational amplifier. The output of the second ne555 control a BJT. The second converter has a faster startup and increases its efficiency from 40% to 84%. This result is achieved by replacing the bjt with a N channel mosfet, the diode with a Schottky diode, the coil with a low resistance coil.