A high efficiency single-inductor dual-control loop power converter (SIDL) is proposed for converting unregulated DC input into regulated DC output to a power load. The SIDL includes: an energy storage loop having: a power inductor, a power capacitor and a power diode.A PWM switching power regulating loop for converting the unregulated DC input into the regulated DC output. a power-efficiency maximizing loop in parallel connection with the power diode.The power-efficiency maximizing loop includes: a power shunt transistor in parallel connection with the power diode and a real-time control loop adjusting, in response to a freewheeling current through the power diode, conductance of the power shunt transistor in a manner that a higher freewheeling current results in a higher conductance of the power shunt transistor.