A switch mode power supply (SMPS) includes a buck converter circuit that includes a first inductor coupled to an output terminal and a switch device coupled the first inductor. A controller is configured for regulating the output current based at least in part on controlling a peak current in the first inductor according to a ratio between an instantaneous voltage to an average voltage at the negative output terminal. The controller is configured to cause the SMPS to operate in a boundary conduction mode (BCM). The controller is configured to maintain a constant average output current that is substantially independent of the input voltage and the output voltage, and also provide a high power factor.