This switch mode step-down converter has very good efficiency, up to 94% can be obtained. This switch mode regulator uses LTC1266-3.3 controller with external N-Channel power mosfet, and need only a 5uH inductor because it uses high frequency switching. Here is the schematic diagram of this switch mode step down converter circuit:

high efficiency smps 3v3 regulator circuit schematic

To optimize efficiency, the LTC1266  automatically switches between two modes of operation, burst and continuous. The LTC1266 series uses a current mode, constant off-time architecture to synchronously switch an external pair of power MOSFETs. Operating frequency is set by an external capacitor at the timing capacitor Pin 6. [Circuit’s schematic diagram source: Linear Technology Application Notes]