The assignee for this patent, patent number 8766553, is
Reporters obtained the following quote from the background information supplied by the inventors: "The present invention relates to a light-emitting diode (LED) device. More particularly, the present invention relates to a serial-type LED device.
"An LED light source employs a plurality of LEDs to provide sufficient brightness. The LEDs can be coupled in series to drive so that each LED provides substantially the same brightness due to the same current flowing through each LED. However, the serial LEDs will not work if one of the LEDs does not work. In addition, the driving voltage applied to the serial LEDs increases as the number of the LEDs coupled in series increases, so that the driving voltage may be too high, resulting in higher cost and increasing complexity of the circuit design.
"To avoid the disadvantage of the serial LEDs, the LEDs can be divided into several groups. The LEDs of each group are coupled in series as a light string, and all light strings are coupled in parallel, so that the LEDs of each light string provide substantially the same brightness and so that each light string provides the same brightness by employing a current balance technology. In addition, if one of the light strings does not work, the others of the light strings can still work. However, as the number of the light strings increases, the circuit design of the current balance circuit becomes complex."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Accordingly, a serial-type LED device is provided for employing a simple current balance circuit while avoiding that all light strings will not work if one of the light strings does not work.
"According to an aspect of the invention, a serial-type LED device includes a direct-current to direct-current (DC to DC) converter, p light source units and a dimming circuit. The DC to DC converter receives a first DC voltage and converts the first DC voltage to a second DC voltage according to a feedback signal. Each light source unit includes a first terminal, a second terminal, m light strings and m current balance units, and each light string includes 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. The p light source units are first to p-th light source units, the first terminal of the first light source unit is coupled to the DC to DC converter to receive the second DC voltage, and 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). The dimming circuit coupled to the second terminal of the p-th light source unit and the DC to DC converter outputs the feedback signal according to a dimming signal and a current outputted from the p-th light source unit.
"In another embodiment, the m light strings of the q-th light source unit constitute a q-th light bar, where q is any integer from 1 to p. The first to p-th light bars are arranged to be a backlight of a display device.
"In another embodiment, each current balance unit of the q-th light source unit includes a transistor, where q is any integer from 1 to p. Each transistor includes 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. The control terminals of the transistors are coupled to each other and to the first terminal of one of the transistors, so that the transistors of the q-th light source unit constitute a q-th current mirror.
"In another embodiment, the dimming circuit includes a first switch including a first terminal coupled to the second terminal of the p-th light source unit, a second terminal coupled to the DC to DC converter, and a control terminal coupled to receive the dimming signal having a pulse-width modulation (PWM) waveform. The first switch is turned on or off according to the dimming signal.
"In another embodiment, the dimming circuit further includes a second switch including a first terminal coupled to the control terminal of the first switch, a second terminal coupled to a disable signal, and a control terminal coupled to receive an on-off signal. The second switch is turned on or off according to the on-off signal. When the second switch is turned on, the disable signal is coupled to the control terminal of the first switch through the second switch, so that the first switch is turned off, and when the second switch is turned off, the disable signal is not coupled to the control terminal of the first switch."
For more information, see this patent: Lin, Li-Wei; Lee, Chen-Chiang; Lee, Chi-Hsin. Serial-Type Light-Emitting Diode (LED) Device. U.S. Patent Number 8766553, filed
Keywords for this news article include: Electronics, Light-emitting Diode,
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