Patent ID: 8120323

Claim:
A charging circuit for charging an energy storage element, said charging circuit comprising: a main power circuit comprising at least a first switching element and electrically connected to a power source for converting an input voltage from said power source into a first voltage; a DC-to-DC converting circuit electrically connected to said main power circuit for converting said first voltage into a second voltage to charge said energy storage element; a detection circuit electrically connected to output terminals of said main power circuit and said DC-to-DC converting circuit for detecting a terminal voltage of said energy storage element and said first voltage from said main power circuit, thereby generating a feedback signal; and a controller electrically connected to said detection circuit and said first switching element of said main power circuit for controlling operations of said first switching element in response to said feedback signal, so that said first voltage is adjustable according to said second voltage; wherein said feedback signal has a feedback voltage, and a feedback ratio of said feedback voltage to said first voltage is changed as said second voltage, wherein said first voltage outputted from said main power circuit is adjusted under control of said controller according to said feedback ratio such that said DC-to-DC converting circuit is operated at a constant duty cycle or a variable duty cycle within a predetermined range.