Portable lighting device and method thereof

A method for powering a light emitting diode (LED) light source, comprising:

• powering said LED light source by a power source under control of a controller;
• receiving a sensing signal indicating a voltage of said power source by said controller;
• regulating a current of said LED light source by said controller to a first current level if said sensing signal indicates that said voltage of said power source is greater than a first voltage level;
• regulating said current of said LED light source by said controller to a second current level if said sensing signal indicates that said voltage of said power source is less than a second voltage level, wherein said second voltage level is less than said first voltage level;
• and
• regulating said current of said LED light source by said controller to vary according to a voltage of said sensing signal if said sensing signal indicates that said voltage of said power source is between said first voltage level and said second voltage level.

A controller for controlling power of a light emitting diode (LED) light source, comprising:

• a power input terminal, coupled to a power source, that is operable for receiving a voltage from said power source;
• a sensing terminal, coupled to said power source, that is operable for receiving a sensing signal indicating said voltage of said power source;
• and
• a feedback terminal that is operable for receiving a feedback signal indicating an instant current of said LED light source,
• wherein said controller is operable for generating a reference signal indicating a target current of said LED light source based on said sensing signal and regulates a current of said LED light source based on said feedback signal and said reference signal, wherein a voltage of said reference signal is at a first voltage level if said sensing signal indicates that said voltage of said power source is greater than said first voltage level, wherein said voltage of said reference signal is at a second voltage level if said sensing signal indicates that said voltage of said power source is less than said second voltage level, and wherein said voltage of said reference signal varies linearly according to said voltage of said sensing signal if said sensing signal indicates that said voltage of said power source is between said first voltage level and said second voltage level.