Patent ID: 8120263

Claim:
A portable lighting device comprising: a power source; a controller having a power input terminal, wherein said power input terminal is coupled to said power source through a switch; and a load comprising a light emitting diode (LED) coupled to a power output terminal of said controller and operable for providing a feedback signal, wherein said controller is operable for adjusting power of said LED based on said feedback signal and a conduction status of said switch, wherein said controller comprise: an under voltage lockout (UVLO) circuit coupled to said power input terminal and operable for generating a UVLO signal by comparing a voltage at said power input terminal with a predetermined voltage; a trigger circuit coupled to said power input terminal and operable for generating a trigger signal; a pulse generator operable for receiving said UVLO signal and said trigger signal and for generating a pulse signal; a reference selection circuit operable for receiving said pulse signal and for selecting a reference signal among a plurality of reference signals according to said pulse signal; and a dimming unit operable for generating a dimming signal based on said selected reference signal and said feedback signal to adjust power of said LED.