KR20160000493A - Light emitting diode apparatus - Google Patents

Abstract

Provided is a light emitting diode (LED) apparatus, which comprises: a rectification unit for rectifying AC voltage to supply rectification voltage; the N (N is a nature number greater than or equal to two) number of LED modules which include at least one LED, and are connected to each other in series; the M (M is a nature number greater than or equal to two) number of switching elements which are connected to one LED module from the LED modules in parallel, and connected to each other in series; and a control unit for selecting a turned-off LED module from the LED modules in accordance with the size of the rectification voltage at a first section of a half-cycle section of the AC voltage, turning on the switching elements connected to the turned-off LED module in parallel, and sequentially turning on a part or the entire of the switching elements from a first switching element connected to a ground at a second section of the half-cycle section.

Description

[0001] LIGHT EMITTING DIODE APPARATUS [0002]

The present invention relates to an LED device. And more particularly to a technique for driving a plurality of LEDs connected in series with each other.

An LED is a semiconductor device that emits light by flowing current to a compound (for example, gallium arsenide) in another expression of a light emitting diode (LED). Recently, a semiconductor device using an electroluminescent phenomenon that emits light when a current flows in a fluorescent organic compound has been developed as an organic light emitting diode (OLED). Such an organic light emitting diode (OLED) It can be seen as a kind.

LEDs can save up to 90% of energy because of the high efficiency of converting electrical energy into light energy. As a result, attention has been paid to a next-generation light source that can replace incandescent and fluorescent lamps whose energy efficiency is only about 5%.

In order to drive the LED, a driver must supply a voltage equal to or higher than the threshold voltage V _TH to the LED. In the past, such a voltage was supplied as a direct current (DC).

Accordingly, a separate power conversion circuit is required for the LED driving device.

For example, a PFC (Power Correction Circuit) and a DC / DC converter have been essentially used in the case of a conventional LED driving apparatus for generating a voltage for driving an LED from a commercial power source having an AC form.

Here, the PFC performs the function of rectifying the AC voltage and the function of maintaining the power factor within a predetermined range, and the DC / DC converter converts the high-voltage DC voltage generated by the PFC into a voltage suitable for the LED Respectively.

Conventional incandescent lamps and fluorescent lamps are being replaced by LED devices for environmentally friendly energy consumption. However, a conventional LED device requires a separate power conversion device, for example, a PFC and a DC / DC converter as described above, which is a problem in terms of cost.

In view of the foregoing, an object of the present invention is, in one aspect, to provide a technique relating to an apparatus for driving an LED by using an AC voltage directly in order to reduce the number of components.

In another aspect, the present invention drives a plurality of LEDs connected in series to each other. In this aspect, an object of the present invention is to drive a plurality of LEDs (LEDs) High Side Gate Driver).

In order to achieve the above object, in one aspect, the present invention provides a rectifying part for rectifying an AC voltage to supply a rectified voltage, a module including at least one LED (LED) (M is a natural number of 2 or more) switching elements connected in series with each other in parallel with one of the LED modules of the LED modules, A non-pointing LED module of the LED modules is selected according to a magnitude of the rectified voltage in a first section, and a switching device connected in parallel with the non-pointing LED module is turned on, and a switch connected to the ground in a second section of the half- And a controller for sequentially turning on some or all of the switching elements starting from the first switching element.

According to another aspect of the present invention, there is provided a liquid crystal display device comprising: a rectifying section for rectifying an AC voltage to supply a rectified voltage; a plurality of LEDs (LEDs) connected in series to each other; And a non-lighting LED of the LEDs is selected according to the magnitude of the rectified voltage in a period in which the magnitude of the rectified voltage is equal to or greater than a first voltage in a half period of the AC voltage, And a control unit which turns on a part or all of the switching elements sequentially from a switching element connected to the ground in a period in which the magnitude of the rectified voltage is smaller than the first voltage in the half period of the half period, Lt; / RTI >

As described above, according to the present invention, it is possible to reduce the number of parts and reduce the cost by directly using an AC voltage for driving an LED (LED). In addition, according to the present invention, when driving a plurality of LEDs (LEDs) connected in series to each other, the gate drive voltage of the high side gate driver can be efficiently generated.

1 shows a configuration of an LED device according to an embodiment.
Fig. 2 shows a structure of an LED included in the LED module of Fig.
3 is a flowchart of a method of lighting control of the LED modules of FIG.
FIG. 4 is a view for explaining the number of LED modules turned on according to the lighting control method of FIG. 3. FIG.
5 is a diagram for explaining a detailed configuration of the control unit of FIG.
6 is a diagram for explaining a detailed configuration of the high side gate driver of FIG.
7 is a diagram showing a lighting control section and a charge control section in an embodiment.
8 is a diagram for explaining the turn-on sequence of the switching elements in the charge control period.
9 is a diagram for explaining the rectified voltage of the charge control section.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference numerals even though they are shown in different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

1 shows a configuration of an LED device according to an embodiment.

Referring to FIG. 1, the LED device 100 is connected to an AC power source 110. The AC power source 110 may be a commercial power grid, but is not limited thereto, and may be a generator for generating an AC voltage.

The LED device 100 includes a rectifier 120, a controller 130, a plurality of switching elements SW_1, SW_2, ..., SW_m and a plurality of LED modules LED__1, LEDM_2, ..., LEDM_n .

The rectifying unit 120 rectifies an AC voltage supplied from the AC power source 110 to form a rectified voltage V _R.

The rectifying unit 120 can rectify an alternating voltage using a diode. At this time, when the rectifying unit 120 includes one diode, the AC voltage corresponding to the half period is formed with the rectified voltage V _R and the zero voltage (0 V) is formed with the rectified voltage V _{R in the} other half period . And, there is the rectification part 120 is formed by an alternating current voltage is rectified voltage (V _R) corresponding to a half period if the selection includes four diodes, a rectified voltage (V _R) of the rest of half period are repeated.

The LED device 100 may include a plurality of LED modules LEDM_1, LEDM_2, ..., LEDM_n connected in series with each other.

For convenience of explanation, the LED device 100 is described as including N LED modules (LEDM_1, LEDM_2, ..., LEDM_n) (N is a natural number of 2 or more). In describing an example that can be commonly applied to the LED modules (LEDM_1, LEDM_2, ..., LEDM_n), when the reference symbol LEDM is used and an example that can be individually applied to each LED module is described 1 with reference to the respective reference symbols.

The N LED module (LEDM_n) located at the uppermost one of the plurality of LED modules (LEDM_1, LEDM_2, ..., LEDM_n) is connected to the high voltage terminal of the rectifying part 120 V _R ) and the other side is connected to the (N-1) th LED module LEDM_n-1. The first LED module LEDM_1 located at the lowermost one of the LED modules LEDM_1, LEDM_2,..., LEDM_n is connected to the second LED module LEDM_2, and the other LED module is connected to the ground.

The LED module (LEDM) includes a plurality of LEDs (LEDs), which may be connected to each other in series or in parallel with each other.

Reference is made to Fig. 2 to see the structure of an LED included in the LED module (LEDM).

Fig. 2 shows a structure of an LED included in the LED module of Fig.

Referring to FIG. 2 (a), the LED module (LED M) may include only one LED (LED). In this case, it can be understood that the LED module (LED M) and the LED (LED) are substantially the same.

Referring to FIG. 2B, the LED module LEDM includes a plurality of LEDs connected in series with each other.

Referring to FIG. 2 (c), the LED module LEDM includes a plurality of LEDs connected in parallel to each other.

2, one or more LEDs (LEDs) may be connected to one another in series or in parallel. Although not shown in FIG. 2, a plurality of LEDs (LEDs) may be connected in series or in parallel with each other.

Referring again to FIG. 1, the LED device 100 may include a plurality of switching elements SW_1, SW_2, ..., SW_m.

For convenience of explanation, the LED device 100 will be described as including M switching elements SW_1, SW_2, ..., SW_m (where M is a natural number of 2 or more). Here, when explaining an example that can be commonly applied to the switching elements SW_1, SW_2, ..., SW_m, the reference symbol SW is used, and when an example that can be individually applied to each switching element is described 1 with reference to the respective reference symbols.

The switching element SW is connected in parallel with the LED module LEDM and is connected in series between the switching elements SW. The first switching device SW_1 located at the lowermost one of the plurality of switching devices SW_1, SW_2, ..., SW_m has one side connected to the second switching device SW_2 and the other side connected to the ground.

In FIG. 1, all the switching devices SW_1, SW_2, ..., SW_m are shown to correspond one-to-one with the LED modules LED__1, LEDM_2, ..., LEDM_n. In this case, the number M of the switching elements SW_1, SW_2, ..., SW_m is equal to N of the LED modules LED__1, LED_2, ..., LEDM_n. The Mth switch element SW_m located at the uppermost one of the switching elements SW_1, SW_2, ..., SW_m has a high voltage terminal (a terminal forming the rectified voltage V _R ) And the other side is connected to the (M-1) th switching element SW_m-1.

The number M of the switching elements SW_1, SW_2, ..., SW_m and the number N of the LED modules LED__1, LEDM_2, ..., LEDM_n are not always the same, N may have different values.

For example, M = N-1, where M can be one less than N. At this time, the LED device 100 may not include a switching element connected in parallel to the Nth LED module LED_n connected to the high voltage terminal V _R of the rectifying unit 120. [

Since the switching element SW may be a BJT (Bipolar Junction Transistor), the use of a high-brightness LED (LED) or a large number of parallel LEDs (LED) requiring a large power may be limited have.

On the other hand, the switching element SW may be a metal oxide semiconductor field effect transistor (MOSFET). If the switching element SW is a MOSFET, a large power LED can be driven. For convenience of explanation, an embodiment in which the switching element SW is a MOSFET will be described below. However, the present invention is not limited thereto, and all the semiconductor elements capable of ON / OFF control can be applied as the switching element SW.

The controller 130 turns on or off the LED module LEDM connected in parallel with the switching module SW by controlling the turn-on or turn-off of the switching module SW. Since the switching element SW and the LED module LEDM are connected in parallel to each other, when the control unit 130 controls the switching element SW to be turned on, the LED module LEDM is not supplied with electric power, LEDM) are turned off. On the other hand, when the control unit 130 turns off the switching element SW, a driving voltage is supplied to both ends of the LED module LEDM to turn on the corresponding LED module LEDM. Of course, in this case, the magnitude of the driving voltage supplied to both ends of the LED module LEDM must be larger than the threshold voltage V _TH of the LED module LEDM.

The controller 130 turns on the LED modules (LEDM_1, LEDM_2, ..., LEDM_n ) selecting a non-lighting of the LED modules and non-lighting of these LED modules are connected in parallel with the switching element according to the magnitude of the rectified voltage (V _R) can do.

3 is a flowchart of a method of lighting control of the LED modules of FIG.

The controller 130 first measures the rectified voltage V _R (S310). The control unit 310 may further include a sensing line for sensing a high voltage terminal of the rectifier unit 120 or a high voltage side voltage of the Nth LED module LED_n to measure the rectified voltage V _R.

The controller 130 determines the number of the non-pointing LED modules among the LED modules LED__1, LEDM_2, ..., and LEDM_n according to the magnitude of the rectified voltage V _R and also selects the non-pointing LED module (S320). Determining the number of non-lighting LED modules can be understood as determining the number of lighting LED modules. Accordingly, in the following description, the controller 130 may determine the number of the non-lighting LED modules or determine the number of the lighting LED modules.

The control unit 130 may increase the number of the light-emitting diode modules and reduce the number of the non-light-emitting diode modules as the rectified voltage V _R increases. For example, the control unit 130 the rectified voltage (V _R) of the LED module to indicate the maximum size of (LEDM_1, LEDM_2, ..., LEDM_n) control, and the rectified voltage (V _R) so that all of the light is maximum It is possible to control the number of LED modules to be turned on to become smaller as the size of the LED module decreases.

So the more the control unit 130 relates to the rectified voltage (V _R) is a high power consumption, increasing the number of the lighting LED modules in a high rectified voltage (V _R) is generated an effect of power factor improvement. Accordingly, when the LED device 100 uses the control method of this type, the power factor can be maintained at a predetermined value or more even without PFC.

The controller 130 may quantize the rectified voltage V _R and control the number of LED modules to be turned on according to each quantization interval.

FIG. 4 is a view for explaining the number of LED modules turned on according to the lighting control method of FIG. 3. FIG.

4, the controller 130 of the interval in the interval [t _k t _{k +1]} j of the lighting LED modules in the control and t _{k +1} at t _k to t _{k +1} to t _{k +2} and controls the lighting of j + 1 LED modules at [t _{k +1} t _{k +2} ].

At this time, the difference between the rectified voltage (V _R) the rectified voltage (V _R) in the t _{k +1} at t _k may be the same as the LED module (LEDM) a threshold voltage (V _TH).

Meanwhile, when the number of LED modules to be lit is determined, the LED module to be unlit is also determined, and the controller 130 determines the unlit LED module and also selects the non-lit LED module. The lifetime of the LED may be proportional to the lighting time. Accordingly, the controller 130 can select the non-lighting LED module so that the lighting time is maintained to be similar.

Referring to FIG. 3 again, the controller 130 selects a non-illuminated LED module and controls the switching elements connected in parallel with the corresponding LED module to turn on (S330).

Here, the controller 130 may include a plurality of gate drivers for controlling the switching elements SW_1, SW_2, ..., SW_m, respectively.

5 is a diagram for explaining a detailed configuration of the control unit of FIG.

5, the control unit 130 includes M gate drivers corresponding to the respective switching devices SW_1, SW_2, ..., SW_m and a controller 510 for transmitting control signals to the M gate drivers. . ≪ / RTI >

The gate driver connected to the first switching device SW_1 of the M gate drivers is a low side gate driver and the gate driver connected to the second switching devices SW_2 to SW_m is a low side gate driver. May be a high side gate driver.

The source terminal of the switching element connected to the low side gate driver (hereinafter LSGD) is connected to the ground. Accordingly, the LSGD can directly drive the switching element by directly using the DC power supply voltage VDD connected to the LSGD. Here, the DC power supply voltage VDD may be supplied from the outside as a DC voltage used for the operation of the controller 130, or may be generated by itself. The control unit 130 includes a line connected to the high voltage terminal of the rectifier unit 120 to generate the DC power source voltage VDD itself and uses the rectified voltage V _R supplied through the line to generate the DC power source voltage VDD (For example, a DC / DC converter or a regulator circuit) that generates a DC voltage (e.g., DC voltage).

On the other hand, the source terminal of the switching element to which the high side gate driver (hereinafter referred to as HSGD) is connected is not directly connected to the ground terminal. Thus, the HSGD can store a constant electrical energy in the capacitor to supply the gate drive voltage to the switching element in the floating state.

6 is a diagram for explaining a detailed configuration of the high side gate driver of FIG.

Referring to FIG. 6, the HSGD may include a driving circuit 610, a capacitor 620, and a diode 630.

The first pin of the driving circuit 610 is connected to the DC power supply voltage VDD and the second pin is connected to the ground. The fifth terminal of the capacitor 620 is connected to the other terminal of the capacitor 620 and the gate of the switching element SW is connected to the fourth terminal of the capacitor 620, The source terminal is connected.

The driving circuit 610 may further include a signal pin (not shown) connected to the controller 510. The driving circuit 610 may receive a signal pin (not shown) using the DC power supply voltage VDD And outputs a gate driving voltage to the gate terminal of the switching element SW according to the result of the processing.

The diode 630 is connected to the DC power supply voltage line and one side of the capacitor 620. At this time, if the DC power supply voltage VDD is greater than one side voltage VC1 of the capacitor 620, So that the DC power supply voltage VDD charges the capacitor 620.

One side voltage V _C1 of the capacitor 620 is determined by the sum of the other voltage V _C2 of the capacitor and the charging voltage V _C of the capacitor 620. V _C1 = V _C2 + V _C. At this time, when the voltage V _C2 is floating or forming a high voltage, VDD becomes smaller than V _C1 , so that the capacitor 620 is not charged.

When substantially V _C2 is coupled to ground, capacitor 620 can be charged. V _C2 is equal to the source voltage VS of the switching element SW so that the source terminal of the switching element SW is grounded with the ground for a predetermined time (for example, a capacitor 620) during the charging time.

If the AC voltage rectified by the rectifying unit 120 is directly used as in the embodiment, the voltage is low in a certain section due to the characteristics of the AC voltage, so that the LED can not be driven or only one LED . The control unit 130 according to the embodiment can control the charging of the capacitor 620 of the HSGD in this interval.

Accordingly, the controller 130 distinguishes between a section (first section) for lighting control of the LED modules (LEDM_1, LEDM_2, ..., LEDM_n) and a section (second section) for controlling the charging of the HSGD.

7 is a diagram showing a lighting control section and a charge control section in an embodiment.

Referring to FIG. 7, the controller 130 sets a period in which the magnitude of the rectified voltage V _R is greater than or equal to the reference voltage V _A in a half period of the AC voltage as a first period for lighting control, (V _R ) is smaller than the reference voltage (V _A ) as a second section for charging control.

The controller 130 may display the section where the magnitude of the rectified voltage V _R is less than the reference voltage V _A twice in one half period, as shown in FIG. 7, Alternatively, only a section in which one side section, for example, the rectified voltage V _R falls may be set as the second section.

In this second period, the controller 130 may turn on some or all of the switching elements SW_1, SW_2, ..., SW_m sequentially from the first switching element SW_1 connected to the ground. For example, when the number M of the switching elements SW_1, SW_2, ..., SW_m and the number N of the LED modules LEDM_1, LEDM_2, ..., LEDM_n are equal to each other, The first switching device SW_1 can sequentially turn on the other switching devices except for the switching device SW_m. As another example, when the number M of the switching elements SW_1, SW_2, ..., SW_m is smaller than the number N of the LED modules LED__1, LEDM_2, ..., LEDM_n, The switching elements SW_1, SW_2, ..., SW_m can be sequentially turned on from the first switching element SW_1.

8 is a diagram for explaining the turn-on sequence of the switching elements in the charge control period.

Referring to FIG. 8, the controller 130 turns on the first switching device SW_1 connected to the ground first in the second period. When the first switching device SW_1 is turned on, the source voltage VS_2 of the second switching device SW_2 connected to the first switching device SW_1 becomes the ground voltage. At this time, since the source voltage VS_2 of the second switching device SW_2 becomes the ground voltage, the capacitor 620 of the HSGD connected to the second switching device SW_2 is charged.

The control unit 130 sequentially turns on the switching elements located at the upper end in accordance with the ON direction shown in FIG. 8. For example, after the K-th switching element SW_k is turned on, The switching element SW_k + 1 is turned on.

At this time, when the Kth switching element SW_k is turned on, all of the K-1th and lower switching elements are in a turned-on state, but some of the K + 1th and higher switching elements are in a turned-off state.

After the M-1th switching device SW_m-1 is turned on according to the sequential turn-on, the Mth switching device SW_m may be turned on or not turned on. The M-th switching device SW_m does not need to be turned on since the source voltage VS_m of the M-th switching device SW_m becomes the ground voltage in accordance with the turn-on of the (M-1) th switching device SW_m-1.

In HSGD, the capacitor 620 starts to be charged when the DC power supply voltage VDD is greater than V _C1 . At this time, the DC power supply voltage VDD is not supplied from the external power supply but the rectified voltage V _R is used If it is generated, the rectified voltage V _R in the second section needs to be maintained at a certain magnitude or more.

9 is a diagram for explaining the rectified voltage of the charge control section.

Referring to FIG. 9, the controller 130 controls the second section as a charge control section in a section where the rectified voltage V _R is less than the first rectified voltage V _{B1 and} is greater than the second rectified voltage V _B2 .

At this time, the second rectified voltage V _B2 may be larger than the magnitude of the DC power supply voltage VDD. When the control unit 130 generates the DC power supply voltage VDD using the rectified voltage V _R as described above, the rectified voltage V _R must be greater than the DC power supply voltage VDD, Thereby making it possible to generate the DC power supply voltage VDD. If the DC power supply voltage VDD is normally generated, the capacitor 620 of the HSGD can be normally charged in the charge control period.

On the other hand, the charging control for the capacitor 620 can be performed only during a period in which one LED module (LEDM) is not turned on. Accordingly, the controller 130 can determine that the maximum voltage V _B1 of the rectified voltage in the second section is smaller than the threshold voltage V _TH for one LED module and greater than the DC power source voltage VDD.

When the LED module includes a single LED or a plurality of LEDs connected in series, the maximum voltage V _B1 of the rectified voltage in the second section may be a threshold voltage of the LED or a plurality of LEDs ) And may be larger than the DC power supply voltage (VDD).

On the other hand, the charge control period (second period) for the capacitor 620 may include a period during which one LED module LEDM is turned on. At this time, the maximum voltage V _B1 of the rectified voltage in the second period May be greater than the threshold voltage (V _TH ) for one LED module and less than the threshold voltage (2 · V _TH ) of the two LED modules.

The LED device 100 according to the embodiment of the present invention has been described above. According to these embodiments, it is possible to reduce the number of parts and reduce the cost by directly using the AC voltage for driving the LED (LED). According to these embodiments, when driving a plurality of LEDs connected in series to each other, the capacitor 620 of the HSGD can be efficiently charged in the non-lighting period.

It is to be understood that the terms "comprises", "comprising", or "having" as used in the foregoing description mean that the constituent element can be implanted unless specifically stated to the contrary, But should be construed as further including other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (13)

A rectifying unit for rectifying the AC voltage to supply a rectified voltage;
A module including at least one LED (LED), wherein N (N is a natural number of 2 or more) LED modules connected in series with each other;
M (M is a natural number of 2 or more) switching elements connected in series with each other as a switching element connected in parallel with one of the LED modules of the LED modules; And
And a switching element connected in parallel to the non-lighting LED module is turned on in accordance with the magnitude of the rectified voltage in a first period of the half period of the AC voltage, A first switching element connected to the ground in a second period, and a control part sequentially turning on some or all of the switching elements,
. The method according to claim 1,
Each of the LED modules including two or more LEDs,
Wherein the at least two LEDs are connected to each other in series or in parallel with each other. The method according to claim 1,
Wherein,
And controls the switching elements so that the LED modules are turned on when the rectified voltage indicates a maximum size, and the number of LED modules turned on as the rectified voltage becomes smaller. The method according to claim 1,
Wherein the number M of switching elements is smaller than the number N of the LED modules and there is no switching element connected in parallel with the Nth LED module connected to the high voltage terminal of the rectifying unit. The method according to claim 1,
The number M of switching elements is equal to the number N of the LED modules,
Wherein,
Wherein the switching device sequentially turns on the first switching device except for the Mth switching device connected to the high voltage terminal of the rectifying part in the second section. The method according to claim 1,
Wherein,
M gate drivers,
The gate driver connected to the first switching device is a low side gate driver,
And the gate drivers connected to the second to Mth switching elements are high side gate drivers. The method according to claim 6,
The high-side gate driver includes:
And a diode connected to the DC power supply voltage and connected to the DC power supply voltage (VDD) and ground, and a capacitor connected to the diode, wherein one of the switching elements On state. 8. The method of claim 7,
Wherein a magnitude of the rectified voltage in the second section is greater than a magnitude of the DC power supply voltage. 8. The method of claim 7,
Wherein a maximum voltage of the rectified voltage in the second section is smaller than a threshold voltage V _TH for one LED module and is greater than the DC power supply voltage. The method according to claim 1,
LED apparatus is smaller than a threshold voltage (V _TH) the threshold voltage (2 · V _TH) of the two LED modules is larger than for the highest voltage of the rectified voltage is a single LED module in the second section. A rectifying unit for rectifying the AC voltage to supply a rectified voltage;
A plurality of LEDs (LEDs) connected in series with each other;
A plurality of switching elements connected in parallel with at least one of the LEDs and connected in series with each other; And
Selecting a non-pointing LED among the LEDs according to a magnitude of the rectified voltage in a period in which the magnitude of the rectified voltage is equal to or greater than a first voltage in a half period of the AC voltage and turning on a switching element connected in parallel with the non- A control unit for turning on a part or all of the switching elements sequentially from a switching element connected to the ground in a period in which the magnitude of the rectified voltage is smaller than a first voltage in the half period,
. 12. The method of claim 11,
Wherein,
And controls the switching elements to turn on all of the LEDs when the rectified voltage indicates a maximum size, and to reduce the number of LEDs that illuminate as the rectified voltage decreases in size. 12. The method of claim 11,
The control unit is connected to the DC power supply voltage VDD and the ground,
Wherein the first voltage is smaller than a sum of threshold voltages of LEDs connected in parallel with one switching device or threshold voltages of LEDs connected in parallel with one switching device, and is greater than the DC power supply voltage.

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