Patent ID: 8766553

Claim:
A serial-type light-emitting diode (LED) device comprising: a direct-current to direct-current (DC to DC) converter for receiving a first DC voltage and converting the first DC voltage to a second DC voltage according to a feedback signal; p light source units each comprising a first terminal, a second terminal, m light strings and m current balance units, with each light string comprising a plurality of LEDs coupled in series to have a first terminal coupled to the first terminal of a corresponding light source unit and a second terminal coupled to the second terminal of the corresponding light source unit through a corresponding current balance unit, wherein the p light source units are first to p-th light source units, wherein the first terminal of the first light source unit is coupled to the DC to DC converter to receive the second DC voltage, and wherein the second terminal of the i-th light source unit is coupled to the first terminal of the (i+1)-th light source unit, where m and p are integers greater than or equal to 2 and i is any integer from 1 to (p−1); and a dimming circuit coupled to the second terminal of the p-th light source unit and the DC to DC converter for outputting the feedback signal according to a dimming signal and a current outputted from the p-th light source unit, wherein each current balance unit of the q-th light source unit comprises a transistor, where q is any integer from 1 to p, wherein each transistor comprises a first terminal coupled to the second terminal of a corresponding light string; a second terminal coupled to the second terminal of the q-th light source unit; and a control terminal, and wherein the control terminals of the transistors are coupled to each other and to the first terminal of one of the transistors, with the transistors of the q-th light source unit constituting a q-th current mirror.