Patent ID: 8400077

Claim:
A power supply circuit for receiving an input voltage through a first positive output terminal and a first negative output terminal of a power-providing device, and outputting a driving voltage to at least one LED string, said power supply circuit comprising: a second positive output terminal connected to a first terminal of said LED string; a second negative output terminal connected to a second terminal of said LED string; a rear-stage converting circuit for receiving said input voltage and converting said input voltage into a compensating voltage, wherein said rear-stage converting circuit comprises a third positive output terminal and a third negative output terminal, said third positive output terminal is connected to said second positive output terminal, and said third negative output terminal is connected to said first positive output terminal; and a control circuit connected to said rear-stage converting circuit and said LED string for detecting the magnitude of a current passing through said LED string, thereby controlling said current passing through said LED string to be identical, wherein said driving voltage is outputted from said power supply circuit through said second positive output terminal and said second negative output terminal, and said driving voltage is a summation of said input voltage and said compensating voltage.