Various embodiments of the present invention relate to a switch-mode regulator, and more particularly, to systems, devices and methods of using a switch-mode regulator to regulate an LED current to improve overall LED system efficacy and suppress power consumption of a dimmable LED illumination system. Both high and moderate brightness modes are implemented in an LED driver based on the switch-mode regulator. In the high brightness mode, the LED current is larger than a preferred LED current. In the moderate brightness mode, the LED current is smaller than the preferred LED current, and the LED driver sustains the preferred driver efficiency while the LED current remains as a direct current. Such a switch-mode power supply or regulator may also be used in applications other than the LED illumination system.