(a) Field of the Invention
The present invention relates to an LED light emitting device and a driving method thereof, and more particularly, to an LED light emitting device including a plurality of LED channels each of which a plurality of LEDs are connected in series.
(b) Description of the Related Art
A light emitting device using LEDs supplies currents to the LEDs so as to drive the LEDs. Then, the LEDs emit beams having brightness corresponding to the currents. Such an LED light emitting device can be used as a light source of an LCD or a lighting. A light emitting device that uses LEDs and is used as a light source of an LCD or a lighting is referred to as an LED light emitting device. An LED light emitting device provides a predetermined intensity by making a predetermined current flow in each LED channel including a plurality of LEDs connected in series. An LED light emitting device according to the related art includes a plurality of converters for supplying a current to each of a plurality of LED channels. Specifically, when an LED light emitting device includes a plurality of LED channels and the plurality of LED channels are connected in parallel, a plurality of converters for supplying currents to the individual LED channels are necessary. This type of LED light emitting device needs a large space for including the plurality of converters and the manufacturing cost of the LED light emitting device increases.
Unlike this, another type in which one power supply device supplies currents to a plurality of LED channels exists. This type cannot ensure supply of a constant current to the individual LED channels. Because of a deviation in the characteristics of LED elements, supply of the same voltage to the LED channels may not generate the same current. In order to solve this, a plurality of current control units for constantly linearly controlling current flowing in a plurality of LED channels are connected. This addition of the plurality of current control units causes power consumption.
FIG. 1 is a drawing schematically illustrating a configuration of an LED light emitting device according to the related art.
As shown in FIG. 1, an LED light emitting device includes a power supply device 1, an LED panel 2, and an LED driver 3.
The power supply device 1 includes a transformer 21, a gate driver 22, a power switch S, and a smoothing capacitor C1. The transformer 21 converts an input voltage Vin to an output voltage Vout, and supplies the output voltage to the LED panel 2. At this time, the operation of the transformer 21 is controlled by a switching operation of the power switch S. The controller 22 controls the switching operation of the power switch S according to the output voltage Vout and feedback information fb transmitted from the LED driver 3.
The LED panel 2 includes a plurality of LED channels same as an LED channel 21 in which a plurality of LEDs are connected in series.
The LED driver 3 includes a plurality of current control units (not shown) and constantly controls a current flowing in each of the plurality of LED channels. The LED driver 3 transmits information on currents of the plurality of LED channels and voltages applied to the LED channels as the feedback information fb to the power supply device 1.
The controller 22 controls the switching operation of the power switch according to the feedback information and the transformer generates the output voltage for driving the LED panel 2 according to the operation of the power switch.
However, a period in which a current is not supplied to the LED panel may occur during the operation of the LED light emitting device. During that period, an over-shoot phenomenon in which the output voltage rises occurs. Further, if a current necessary for the LED panel rapidly increases, a phenomenon in which the output voltage falls occurs. For example, when a current is supplied to the plurality of LED channels of the LED panel in an OFF state, a current necessary for the LED panel rapidly increases.
Further, when an LED of the LED channels is short-circuited or opened so as not to perform an appropriate function (hereinafter, a defective state), it is necessary to interrupt the switching operation of the power switch S. In the defective state, a channel voltage that is the end terminal voltage of the LED channel becomes an over voltage or an LED current does not flow. Further, when an LED is short-circuited, the LED driver 3 may be damaged by an overcurrent flowing in the LED channel, and when an LED is opened, a phenomenon in which the output voltage rises very highly may occur.
The controller 22 determines the state of the LED panel described in the above two paragraphs from the feedback information fb. If the primary side and secondary side of the transformer 21 are insulated, it is difficult for the controller 22 to exactly receive the feedback information. Then, it is difficult for the controller 22 to exactly control the operation of the power supply device 1. That is, the power supply device 1 may not supply power according to the state of the LED panel 2 or may supply an overvoltage to increase the power consumption. Heat generated in the LED driver may increase to damage the LEDs or the LED driver.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.