LED driving device and lighting device

A light emitting diode (LED) driving device is provided. The LED driving device includes a rectifier configured to rectify alternating current (AC) power to generate rectified power; an AC driver configured to control operations of a plurality of LED groups so that the plurality of LED groups receive the rectified power generated by the rectifier; and a light amount controller configured to reduce an amount of current applied to the plurality of LED groups when a peak value of the rectified power is increased, and increase the amount of current applied to the plurality of LED groups when the peak value of the rectified power is reduced.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No. 10-2014-0077240 filed on Jun. 24, 2014 in the Korean Intellectual Property Office, the disclosure of which is herein incorporated by reference.

BACKGROUND

The present disclosure relates to an light emitting diode (LED) driving device and a lighting device.

2. Brief Description of the Related Art

Light emitting diodes (LEDs) are extensively used as light sources, because LEDs possess several positive attributes, such as low power consumption, high luminance, and the like. In particular, light emitting devices using LEDs have been employed in general illumination devices and in the backlight units of large-sized liquid crystal displays. Such light emitting devices are provided in the form of packages, facilitating the installation thereof in various apparatuses. In recent times, research into various LED driving devices using an alternating current (AC) step driver scheme capable of directly driving an LED using AC power without an AC-direct current (DC) converter have been conducted.

SUMMARY

One or more exemplary embodiments provide an LED driving device and a lighting device capable of simultaneously driving LEDs using AC power without an AC-DC converter.

According to an aspect of an exemplary embodiment, there is provided a light emitting diode (LED) driving device driving a plurality of LED groups, the LED driving device including a rectifier configured to rectify alternating current (AC) power to generate rectified power, an AC driver configured to control operations of the plurality of LED groups so that the plurality of LED groups receive the rectified power generated by the rectifier, and a light amount controller configured to reduce an amount of current applied to the plurality of LED groups when a peak value of the rectified power is increased, and to increase the amount of current applied to the plurality of LED groups when the peak value of the rectified power is reduced.

The light amount controller may include a voltage detector configured to detect the rectified power to generate a first voltage, and a current controller configured to adjust a level of a current applied to the plurality of LED groups according to the first voltage.

The voltage detector may include a regulator circuit configured to detect the rectified power and convert the rectified power into the first voltage, and the first voltage may have a substantially constant level.

The current controller may include a switching device that includes an output terminal, an input terminal, and a control terminal, the output terminal being connected to at least one of the plurality of LED groups, and an operational amplifier configured to receive the first voltage and a reference voltage and control a current flowing in the at least one LED group connected to the output terminal of the switching device.

The current controller may include a voltage follower configured to receive the first voltage, and a switching device that is configured to control a current flowing in the at least one of the plurality of LED groups through an output from the voltage follower circuit.

The AC driver may be configured to compare the rectified power with one or more threshold voltages and divides a single period of the rectified power into a plurality of sections, and may control operations of the plurality of LED groups in the plurality of sections.

The light amount controller may be configured to reduce a current applied to the plurality of LED groups in the plurality of sections when a peak value of the rectified power is increased, and increase a current applied to the plurality of LED groups in the plurality of sections when the peak value of the rectified power is decreased.

The one or more threshold voltages may include a first threshold voltage and a second threshold voltage that is higher than the first threshold voltage, and the AC driver may be configured to turn on a first LED group in a first section in which a level of the rectified power is lower than the first threshold voltage, and turn on the first LED group and a second LED group having a lower level of light output from the second LED group than that of the first LED group in a second section in which the level of the rectified power is higher than the first threshold voltage and lower than the second threshold voltage.

The one or more threshold voltages may include a first threshold voltage and a second threshold voltage that is higher than the first threshold voltage, and the AC driver may be configured to connect the first LED group and the second LED group to each other in parallel to then be turned on in the first section in which a level of the rectified power is lower than the first threshold voltage, and connect the first LED group and the second LED group to each other in series to then be turned on in the second section in which a level of the rectified power is higher than the first threshold voltage and lower than the second threshold voltage.

The first LED group and the second LED group may output substantially the same level of light.

According to an aspect of another exemplary embodiment, there is provided a lighting device including a light source that includes a plurality of LED groups, a rectifier configured to rectify AC power to generate rectified power, an AC driver configured to control operations of the plurality of LED groups to allow the light source to receive the rectified power and emit light, and a light amount controller configured to reduce an amount of current applied to the plurality of LED groups when a peak value of the rectified power is increased, and increase the amount of current applied to the plurality of LED groups when the peak value of the rectified power is reduced.

The light amount controller may include a regulator circuit configured to generate a first voltage having a substantially constant level using the rectified power, and a constant current controller configured to control a current flowing in at least a portion of the plurality of LED groups by comparing the first voltage with a reference voltage.

The lighting device may further include a regulator circuit configured to generate a first voltage having a substantially constant level using the rectified power, a voltage follower configured to receive the first voltage; and a constant current controller that is configured to control a current flowing in at least a portion of the plurality of LED groups using an output from the voltage follower circuit.

The plurality of LED groups may have different levels of light output.

The plurality of LED groups may have substantially the same level of light output.

According to an aspect of another exemplary embodiment, there is provided a light emitting diode (LED) driving device including a rectifier that to rectify alternating current (AC) power and provide the rectified power directly to a plurality of LED groups, a light amount controller configured to control supply of the rectified power to the plurality of LED groups, and an AC driver configured to drive the plurality of LED groups according to the rectified power, wherein the light amount controller is configured to control the AC driver to reduce an amount of current applied to the plurality of LED groups when a peak value of the rectified power is increased, and increase the amount of current applied to the plurality of LED groups when the peak value of the rectified power is reduced.

DETAILED DESCRIPTION

Various embodiments will now be described more fully with reference to the accompanying drawings in which some embodiments are shown. The present disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough and complete and fully conveys the present disclosure to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity.

Meanwhile, when an embodiment can be implemented differently, functions or operations described in a particular block may occur in a different way from a flow described in the flowchart. For example, two consecutive blocks may be performed simultaneously, or the blocks may be performed in reverse according to related functions or operations.

Exemplary embodiments will now be described in detail with reference to the accompanying drawings.

FIGS. 1 and 2are block diagrams of an LED driving device according to an exemplary embodiment.

With reference toFIG. 1, an LED driving device100according to an exemplary embodiment may include a rectifier110, a light amount controller120, and an AC driver130. The rectifier110may receive commercially available AC power and output rectified power VREC. The AC driver130may control operations of a plurality of LED groups11,12,13and14included in a light source10such that the light source10may directly receive the rectified power VRECto operate. The light amount controller120may control light output from the light source10by detecting a voltage level of the rectified power VRECand adjust a level of current ILEDapplied to the light source10.

The LED driving device100operating according to the exemplary embodiment may control operations of the light source10including the plurality of LED groups11,12,13and14. The plurality of LED groups11,12,13and14included in the light source10may have the same level of light or different levels of light output therefrom. That is, in some exemplary embodiments, each LED group11,12,13, and14may have a different level of light output, such that the level of light output from LED group11is different than that of LED group12, which are different than that of LED group13, etc.

When the plurality of LED groups11,12,13and14have substantially the same level of light output therefrom, the AC driver130may change a serial or parallel connection structure of the plurality of LED groups11,12,13and14, according to a voltage level of the rectified power VRECwithin a single period of the rectified power VREC. The AC driver130may divide a level of the rectified power VRECinto several sections within a single period of the rectified power VRECand may increase the number of LED groups11,12,13and14connected to one another in parallel in a section in which the level of the rectified power VRECis relatively low, and may increase the number of LED groups11,12,13and14connected to one another in series in a section in which the level of the rectified power VRECis relatively high.

When the plurality of LED groups11,12,13and14have different levels of light output therefrom, the AC driver130may change the number of the plurality of LED groups turned on according to a voltage level of the rectified power VRECwithin a single period of the rectified power VREC. The AC driver130may divide a level of the rectified power VRECinto several sections within a single period of the rectified power VRECand may turn on a relatively large number of LEDs in a section in which the level of the rectified power VRECis relatively high.

The light amount controller120may detect a voltage level of the rectified power VRECto control a current ILEDapplied to the light source10. In detail, the voltage level of the rectified power VRECmay be determined by a voltage level of AC power applied to the rectifier110. However, actually in some exemplary embodiments, the voltage level of the rectified power VRECis not be constantly maintained and may be varied in each respective period of the rectified power VREC. For example, when the rectifier110includes a diode bridge circuit and the AC power generates a voltage signal having a peak value of 220V, the voltage level of the rectified power VRECgenerated by the rectifier110may have a peak value of 220V in each period. However, for several reasons, voltage levels of the rectified power VRECgenerated by the rectifier110may have different peak values, slightly changed in each period, which may be a factor changing light output from the light source10.

In order to significantly reduce a change in light output according to a change in a voltage level of the rectified power VRECas described above, the light amount controller120may detect a voltage level of the rectified power VRECand control the current ILEDapplied to the light source10. For example, when the peak value of the rectified power VRECis increased, the light amount controller120may reduce an amount of current ILEDapplied to the light source10within a single period of the rectified power VREC. On the other hand, when the peak value of the rectified power VRECis reduced, the light amount controller120may increase an amount of current ILEDapplied to the light source10within a single period of the rectified power VREC. Thus, even in a case in which a voltage level of the rectified power VRECis changed in each respective period of the rectified power VREC, a change in light output from the light source10may be significantly reduced.

The light amount controller120may include a voltage detector123and a current controller125. The voltage detector123may include a voltage regulator circuit capable of detecting a voltage level of the rectified power VREC. The current controller125may compare an amount of voltage output from the voltage detector123with a predetermined amount of reference voltage so as to control a magnitude of the current ILEDapplied to the light source10. The operation of the light amount controller120will be described in detail below with reference toFIG. 3.

Next, with reference toFIG. 2, an LED driving device200according to an exemplary embodiment may include a rectifier210, a light amount controller220, and an AC driver230. The rectifier210may receive commercially available AC power and output rectified power VREC. The AC driver230may control operations of a plurality of LED groups21,22,23and24included in a light source20such that the light source20may directly receive the rectified power VRECto operate. The light amount controller220may control light output from the light source20by detecting a voltage level of the rectified power VRECto adjust an amount of current ILEDapplied to the light source20.

Similar to the case in the exemplary embodiment ofFIG. 1, the AC driver230may control operations of the plurality of LED groups21,22,23and24according to a voltage level of the rectified power VREC. The AC driver230may change a serial or parallel connection structure of the LED groups21,22,23and24or change the number of turned-on LED groups21,22,23and24, according to a change in a voltage level of the rectified power VRECwithin a single period of the rectified power VREC. For example, the AC driver230may control operations of the plurality of LED groups21,22,23and24such that the light source20may directly receive the rectified power VREChaving AC characteristics to operate.

On the other hand, a magnitude of a current ILEDapplied to the light source20may be adjusted by the light amount controller220. The light amount controller220may adjust the magnitude of the current ILEDapplied to the light source20by detecting a voltage level of the rectified power VREC. In an exemplary embodiment, when a peak value of the voltage level of the rectified power VRECis increased, the light amount controller220may reduce the magnitude of current ILEDapplied to the light source20, and when a peak value of the voltage level of the rectified power VRECis reduced, the light amount controller220may increase the magnitude of current ILEDapplied to the light source20.

The light amount controller220may include a voltage detector223, a voltage follower225, and a current controller227. The voltage detector223may include a voltage regulator circuit capable of detecting a voltage level of the rectified power VREC. The current controller227may compare an amount of voltage output from the voltage detector223with an amount of reference voltage so as to control the magnitude of current ILEDapplied to the light source20. The amount of the reference voltage may be predetermined. The voltage follower225may be disposed between the voltage detector223and the current controller227so as to match levels of impedance. The operation of the light amount controller220will be described in detail below with reference toFIG. 4.

FIG. 3is a circuit diagram of a light amount controller applied to an LED driving device illustrated inFIG. 1. The operation of the light amount controller120illustrated inFIG. 3will be described together referring to the waveform diagrams ofFIGS. 5 and 6.

With reference toFIG. 3, the light amount controller120according to the exemplary embodiment may include the voltage detector123detecting a voltage level of the rectified power VRECgenerated by the rectifier110, and the current controller125comparing the voltage detected by the voltage detector123with an amount of reference voltage VREFso as to control the current ILEDapplied to the light source10. The amount of the reference voltage VREFmay be predetermined. The current controller125may include an operational amplifier U1and a switching device TR1. For example, when the switching device TR1is a bipolar junction transistor (BJT), a collector terminal of the switching device TR1may be connected to the light source10and the current ILEDapplied to the light source10may flow to the collector terminal of the switching device TR1.

The voltage detector123may detect a voltage level of the rectified power VRECoutput by the rectifier110. The voltage detector123may include a voltage regulator circuit, and an output from the voltage detector123may be input to a non-inverted terminal of the operational amplifier UI to be compared to the reference voltage VREF.

In terms of operational amplifier characteristics, since levels of voltages input to a non-inverted terminal and an inverted terminal should be equal to each other, when a voltage level of the rectified power VRECis increased, a level of current flowing in a resistor R1may be increased. On the other hand, when a voltage applied to both terminals of a resistor Rs is denoted as Vs, a voltage V+ input to the non-inverted terminal of the operational amplifier UI may be defined as illustrated in Equation Expression 1. I2in Equation Expression 1 denotes the current flowing in a resistor R2.
V+VREF=I2*R2+Vs[Equation Expression 1]

When the voltage level of the rectified power VRECis increased, the current I2flowing in the resistor R2may increase and the voltage Vs may decrease. Since an emitter current of the switching device TR1may be provided by a difference between the current I2and a current flowing in the resistor Rs, the emitter current of the switching device TR1may be reduced according to an increase in the voltage level of the rectified power VREC. Thus, a collector current of the switching device TR1may be decreased and the current ILEDflowing in the light source10may also be decreased.

In the reverse case, when the voltage level of the rectified power VRECis reduced, the current I2may be reduced and the voltage Vs may be increased. Thus, since the current flowing in the resistor R2is increased, the emitter current and the collector current of the switching device TR1may be increased. As a result, since the magnitude of the current ILEDflowing in the light source10is increased, a level of light output from the light source10may be increased.

FIGS. 5 and 6are waveform diagrams illustrating operations of an LED driving device according to an exemplary embodiment. First, the operation of the LED driving device100performed when the voltage level of the rectified power VRECis increased will first be described with reference toFIG. 5.

With reference toFIG. 5, in a first period T1, the rectified power VRECmay have a first peak voltage Vpeak1, and the first period T1may be divided into a total of eight sections t1to t8. The eight sections t1to t8configuring the first period T1may be defined by the rectified power VRECand a plurality of threshold voltages Vth1, Vth2and Vth3. Similarly, a second period T2may also be divided into eight sections t1′ to t8′ by the rectified power VRECand a plurality of threshold voltages Vth1′, Vth2′and Vth3′. In the respective sections t1to t8of the first period T1, the AC driver130may set the number of turned-on LED groups11,12,13and14to be different from one another among the plurality of LED groups11,12,13and14included in the light source10, or may set a serial connection structure or a parallel connection structure between the LED groups11,12,13and14to be different from one another.

In a case in which the plurality of LED groups11,12,13and14have substantially the same level of light output therefrom, the AC driver130may increase the number of the LED groups11,12,13and14connected to one another in parallel when the voltage level of the rectified power VRECrelatively low, and may increase the number of LED groups11,12,13and14connected to one another in series when the voltage level of the rectified power VRECis relatively high. For example, the AC driver130may connect all of the LED groups11,12,13and14to one another in parallel in the first and eighth sections t1and t8of the first period T1, and may connect all of the LED groups11,12,13and14to one another in series in the fourth and fifth sections t4and t5of the first period T1.

In a case in which the plurality of LED groups11,12,13and14have different respective levels of light output therefrom, the AC driver130may reduce the number of operating LED groups11,12,13and14when the voltage level of the rectified power VRECis relatively low, and may increase the number of operating LED groups11,12,13and14when the voltage level of the rectified power VRECis relatively high. In this case, in order to significantly reduce a difference in levels of light output within the respective periods T1and T2of the rectified power VREC, the LED group11operating when the voltage level of the rectified power VRECis relatively low may have a relatively high level of light output therefrom as compared to those of the other LED groups12,13and14.

In some exemplary embodiments, the AC driver130may only turn on the first LED group11having a highest level of light output from the light source in the first and eighth sections t1and t8of the first period T1, and may turn off the remaining LED groups12,13and14. In the fourth and fifth sections t4and t5of the first period T1, the AC driver130may turn on all of the LED groups11,12,13and14.

On the other hand, the light amount controller120may adjust the magnitude of the current ILEDapplied to the light source10in each respective period T1or T2. With reference toFIG. 5, the voltage level of the rectified power VRECmay have a smaller value in the second period T2than in the first period T1. Further, referring toFIG. 5, the first peak voltage Vpeak1of the rectified power VRECrepresented in the first period T1may be greater than that a second peak voltage Vpeak2of the rectified power VRECrepresented in the second period T2.

In a case in which the current ILEDis applied to the light source10regardless of a change in a voltage level that may occur in each period of the rectified power VREC, a level of light output from the light source10in the second period T2in which the voltage level of the rectified power VRECis reduced may be significantly reduced as compared to that of light output from the light source10in the first period T1. This degree of reduction in the level of light output from the light source in the second period T2may be recognized by a user as a variation in the output of light, and this leads to deteriorations in reliability of the LED driving device100.

In the exemplary embodiment, when the voltage level of the rectified power VRECis reduced, the light amount controller120may increase the amount of current ILEDflowing in the light source10as illustrated with reference toFIG. 3. Thus, as illustrated inFIG. 5, in the second period T2in which the voltage level of the rectified power VRECis reduced, the magnitude of the current ILEDflowing in the light source10may be rather increased. In addition, lengths of the sections t4′ and t5′ in which a greatest magnitude of current ILEDflows in the light source10may be shorter than those of the first period T1. Therefore, a difference in levels of light output from the light source10between the first period T1and the second period T2may be significantly reduced.

Then, with reference toFIG. 6, the voltage level of the rectified power VRECmay be further increased in the second period T2than in the first period T1. For example, the second peak voltage Vpeak2of the rectified power VRECin the second period T2may be greater than the first peak voltage Vpeak1of the rectified power VRECin the first period T1.

As illustrated above with reference toFIGS. 1 to 6, the light amount controller120may significantly decrease the magnitude of the current ILEDflowing in the light source10when the voltage level of the rectified power VRECis increased. With reference toFIG. 6, the magnitude of the current ILEDflowing in the light source10in each respective section t1′˜t8′ of the second period T2may be smaller than the current ILEDflowing in the light source10in each respective section t1˜t8of the first period T1. In addition, lengths of the sections t4′ and t5′ in which a greatest magnitude of current ILEDflows in the light source10in the second period T2may be longer than those in the first period T1. Therefore, a difference in levels of light output from the light source10between the first period T1and the second period T2may be significantly reduced.

FIG. 4is a circuit diagram of a light amount controller applied to an LED driving device illustrated inFIG. 2.

With reference toFIG. 4, the light amount controller220may include a voltage detector223, a voltage follower225, and a current controller227. The voltage detector223may include a voltage regulator circuit and may generate a voltage proportional to a peak value of the rectified power VREC. A voltage output by the voltage detector223may be input to a non-inverted terminal of an operational amplifier U2included in the voltage follower225. The voltage output from the operational amplifier U2may be proportional to the voltage output by the voltage detector223and input to the non-inverted terminal of the operational amplifier U2in terms of circuit characteristics of the voltage follower225. On the other hand, the voltage follower225may be a circuit used for impedance matching between the voltage detector223and the current controller227.

An output from the voltage follower225may be connected to an emitter terminal of a first switching device TR1′ and a base terminal of a second switching device TR2′ through a resistor Rs′. A driving voltage Vcc may be supplied to a collector terminal of the second switching device TR2′ through a driving resistor Rcc, and a current ILEDflowing in a light source20may be input to a collector terminal of the first switching device TR1′.

Since the emitter terminal of the first switching device TR1′ and the base terminal of the second switching device TR2′ are connected to each other, an emitter voltage of the first switching device TR1′ may be the same voltage as a base-emitter voltage of the second switching device TR2′. On the other hand, the emitter voltage of the first switching device TR1′ may be defined as illustrated in the following Equation Expression 2. In Equation Expression 2, Is′ denotes a current flowing in the resistor Rs′, and Vo denotes a voltage output from the operational amplifier U2.
VE=Is′*Rs′+Vo[Equation Expression 2]

Since the emitter voltage of the first switching device TR1′ is fixed as the base-emitter voltage VBEof the second switching device TR2′, when the voltage Vo output by the operational amplifier U2is increased, the current Is′ may be decreased, and when the voltage Vo output by the operational amplifier U2is decreased, the current Is′ may be increased. Since the rectified power VRECoutput by the rectifier210and the voltage Vo output by the operational amplifier U2are in proportion to each other, when the voltage level of the rectified power VRECis increased, the current Is' may be decreased. The current Is′ may be provided as the collector current of the first switching device TR1′ and may be in proportion to the current ILEDflowing in the light source20, the emitter current of the first switching device TR1′. Thus, when the voltage level of the rectified power VRECis increased, the current ILEDflowing in the light source20may be decreased. On the other hand, when the voltage level of the rectified power VRECis reduced, the current ILEDflowing in the light source20may be increased.

The light amount controller220illustrated inFIG. 4may operate in a manner similar to the light amount controller120illustrated inFIG. 3, and when the rectified power VRECis applied to the light source20in the manner as illustrated inFIGS. 5 and 6, a deviation in light output from the light source20may be significantly reduced.

With reference toFIG. 5, the voltage level of the rectified power VRECmay have a lower peak value in the second period T2than that in the first period T1. The light amount controller220may significantly reduce a deviation in the levels of light output from the light source20in the first period T1and the second period T2by increasing the magnitude of the current ILEDflowing in the light source20during the second period T2by reflecting the reduction in the voltage level of the rectified power VREC.

Subsequently, with reference toFIG. 6, the voltage level of the rectified power VRECmay have a higher peak value in the second period T2than that in the first period T1. The light amount controller20may significantly reduce a deviation in the levels of light output from the light source20in the first period T1and the second period T2by decreasing the magnitude of the current ILEDflowing in the light source20during the second period T2by reflecting the increase in the voltage level of the rectified power VREC.

FIGS. 7A to 8Dare circuit diagrams illustrating a connection structure of a plurality of LED groups according to operations of an LED driving device according to an exemplary embodiment.

First, operations of the LED driving device100illustrated inFIG. 1will be described with reference toFIGS. 5 to 7D. Referring toFIGS. 5 and 6, the rectified power VRECgenerated by the rectifier110may be divided into a plurality of sections in a single period T1or T2. AlthoughFIGS. 5 and 6illustrate cases in which one period T1or T2of the rectified power VRECis divided into a total of 8 sections t1to t8or t1′ to t8′, respectively, these cases are only provided as examples, and thus, the present disclosure is not necessarily limited thereto. Hereinafter, operations of the LED driving device100will be described, based on the first period T1illustrated inFIGS. 5 and 6for convenience of explanation. However, operations of the LED driving device100in the first period T1may also be applied to the operations of the LED driving device100in the second period T2ofFIGS. 5 and 6. In addition, operations described with reference toFIGS. 7A to 7Dmay also be applied to the LED driving device200illustrated inFIG. 2.

In sections t1and t8in which the level of the rectified power VRECis higher than a reference potential 0V and is lower than a first threshold voltage Vth1, the AC driver130may perform controlling so that the current ILEDmay only flow in the first LED group11. In this case, the first LED group11may have a relatively high level of light output therefrom than that in the remaining LED groups12,13and14. In some exemplary embodiments, the reference potential may alternatively be a non-zero value. Moreover, the reference potential may be determined experimentally.

In sections t2and t7in which the level of the rectified power VRECis higher than the first threshold voltage Vth1and is lower than a second threshold voltage Vth2, the AC driver130may perform controlling so that the first and second LED groups11and12may be connected to each other in series to emit light. In addition, in sections t3and t6in which the level of the rectified power VRECis higher than the second threshold voltage Vth2and is lower than a third threshold voltage Vth3, the first to third LED groups11to13may emit light. In sections t4and t5in which the level of the rectified power VRECis higher than the third threshold voltage Vth3and is lower than the first peak voltage Vpeak1of the first period T1of the rectified power VREC, all of the LED groups11,12,13and14may emit light.

FIGS. 7A to 7Dare equivalent circuit diagrams illustrating a connection structure of respective LED groups11,12,13and14according to a level of the rectified power VRECin a single period of the rectified power VREC. First,FIG. 7Aillustrates a connection structure of the plurality of LED groups11,12,13and14in sections t1and t8in which the level of the rectified power VRECis higher than the reference potential 0V and is lower than the first threshold voltage Vth1. Referring toFIG. 7A, in the sections t1and t8in which the level of the rectified power VRECis higher than the reference potential 0V and is lower than the first threshold voltage Vth1, only the first LED group11may emit light. A current flowing in the first LED group11may be defined as a constant current I1.

FIG. 7Billustrates a connection structure of the respective LED groups11,12,13and14in sections t2and t7in which the level of the rectified power VRECis higher than the first threshold voltage Vth1and is lower than the second threshold voltage Vth2. Referring toFIG. 7B, in the sections t2and t7in which the level of the rectified power VRECis higher than the first threshold voltage Vth1and is lower than the second threshold voltage Vth2, the first LED group11and the second LED group12may be connected to each other in series to emit light. In this case, a constant current flowing in the first LED group11and the second LED group12may be defined as I2.

Similarly,FIGS. 7C and 7Dillustrate a connection structure of the LED groups11,12,13and14in sections t3and t6in which the level of the rectified power VRECis higher than the second threshold voltage Vth2and lower than the third threshold voltage Vth3and in sections t4and t5in which the level of the rectified power VRECis higher than the third threshold voltage Vth3and lower than the first peak voltage Vpeak1of the rectified power VREC. For example, with reference toFIGS. 7A and 7D, as the level of the rectified power VRECis increased so as to approximate the peak voltage Vpeakwithin a single period T1, a relatively large number of LED groups11,12,13and14may be connected to one another in series and may thus emit light. In the reverse case, as the level of the rectified power VRECis reduced so as to approximate the reference potential 0V within a single period T1, a relatively small number of LED groups11,12,13and14may be connected to one another in series and may thus emit light. Thus, in order to significantly reduce a change in light output from the light emitting unit10depending on a change in a level of the rectified power VRECwithin a single period, the first LED group11may have a highest level of light output therefrom, and the fourth LED group14may have a lowest level of light output therefrom.

On the other hand, the level of the current ILEDflowing in the light source10in the respective sections t1to t8may be determined by the light amount controller120. The light amount controller120may compare a voltage level of the rectified power VRECto a level of reference voltage and may determine the level of the current ILEDflowing in the light source10according to the comparison result. The level of the reference voltage may be predetermined, and may be determined experimentally. With reference to the embodiment ofFIG. 5as an example, the level of the current ILEDflowing in the light source10in the first section t1of the first period T1may be higher than that of the current ILEDflowing in the light source10in the first section t1of the second period T2. With reference to the exemplary embodiment ofFIG. 6as an example, the level of the current ILEDflowing in the light source10in the first section t1of the first period T1may be lower than that of the current ILEDflowing in the light source10in the first section t1of the second period T2. Here, in a case in which the voltage levels of the rectified powerRECare different from each other in the first period T1and the second period T2, the light amount controller120may determine that the magnitudes of the currents ILEDflowing in the light source10are different from each other. As the light amount controller120controls the current ILEDflowing in the light source10, based on the voltage level of the rectified power VREC, even in a case in which the voltage levels of the rectified power VRECare different in respective periods T1and T2, a deviation in the levels of light output from the light source10may be significantly reduced.

Subsequently, operations of the LED driving device200illustrated inFIG. 2will be described with reference toFIGS. 5 and 6andFIGS. 8A to 8D. The rectified power VRECgenerated by the rectifier210may be divided into a plurality of sections t1to t8or t1′ to t8′ in a single period T1or T2. AlthoughFIGS. 5 and 6illustrate the cases in which one period T1or T2of the rectified power VRECis divided into a total of 8 sections t1to t8or t1′ to t8′, respectively, the cases are provided as only examples, and thus, the present disclosure is not necessarily limited thereto. Hereinafter, operations of the LED driving device200will be described below, based on the first period T1illustrated inFIGS. 5 and 6for convenience of explanation. However, operations of the LED driving device200in the first period T1may also be applied to the operations of the LED driving device200in the second period T2ofFIGS. 5 and 6. In addition, operations described with reference toFIGS. 8A to 8Dmay be applied to the LED driving device100illustrated inFIG. 1.

In sections t1and t8in which the level of the rectified power VRECis higher than the reference potential 0V and is lower than the first threshold voltage Vth1, the AC driver230may perform controlling so that the LED groups21,22,23and24are connected to one another in parallel as illustrated inFIG. 8A. Here, a sum of currents flowing in the respective LED groups21,22,23and24may be defined as IF.

In sections t2and t7in which the level of the rectified power VRECis higher than the first threshold voltage Vth1and lower than the second threshold voltage Vth2, the first LED group21and the second LED group22may be connected to each other in series and the third LED group23and the fourth LED group24may be connected to each other in series as illustrated inFIG. 8B. Further, the first LED group21and the second LED group22, and the third LED group23and the fourth LED group24may be connected to each other in parallel. In sections t3and t6in which the level of the rectified power VRECis higher than the second threshold voltage Vth2and lower than the third threshold voltage Vth3, the first LED group21, the third LED group23, and the fourth LED group24may be connected to one another in series, and the second LED group22may be connected to the first LED group21in parallel as illustrated inFIG. 8C.

In sections in which the level of the rectified power VRECis higher than the third threshold voltage Vth3and is lower than the first peak voltage Vpeak1of the rectified power VREC, all of the LED groups21,22,23and24may be connected to one another in series. For example, according to the exemplary embodiment, the LED groups21,22,23and24may emit light constantly, regardless of a change in a voltage level within a single period t1of the rectified power VREC. However, a connection structure of the respective LED groups21,22,23and24may be changed depending on a change in a voltage level within a single period t1of the rectified power VREC. On the other hand, according to the exemplary embodiment, the levels of light output from the respective LED groups21,22,23and24may be substantially identical to each other.

The level of the current ILEDflowing in the light source20in the respective sections t1to t8may be determined by the light amount controller220. The light amount controller220may detect a voltage level of the rectified power VREC, and may determine the level of the current ILEDflowing in the light source20using the voltage level of the detected rectified power VREC. With reference to the exemplary embodiment ofFIG. 5as an example, the level of the current ILEDflowing in the light source20in the first section t1of the first period T1may be higher than that of the current ILEDflowing in the light source20in the first section t1of the second period T2. With reference to the exemplary embodiment ofFIG. 6as an example, the level of the current ILEDflowing in the light source20in the first section t1of the first period T1may be lower than that of the current ILEDflowing in the light source20in the first section t1of the second period T2. For example, in a case in which the voltage levels of the rectified powerRECare different from each other in the first period T1and the second period T2, the light amount controller220may determine that the magnitudes of the currents ILEDflowing in the light source20are different from each other. As the light amount controller220controls the current ILEDflowing in the light source20, based on the voltage level of the rectified power VREC, even in a case in which the voltage levels of the rectified power VRECare different in respective periods T1and T2, a deviation in the levels of light output from the light source20may be significantly reduced.

FIGS. 9 and 10illustrate LED packages operated by the LED driving device according to an exemplary embodiment. The light emitting units of the light source10and the light source20may be packaged in the LED packages illustrated inFIGS. 9 and/or 10.

With reference toFIG. 9, a semiconductor light emitting device package1000may include a semiconductor light emitting device1001, a package body1002, and a pair of lead frames1003. The semiconductor light emitting device1001may be mounted on the lead frame1003to be electrically connected to the lead frame1003through a wire W. According to an exemplary embodiment, the semiconductor light emitting device1001may also be mounted in other regions instead of the lead frame1003, for example, in the package body1002. In addition, the package body1002may have a cut shape to improve light reflection efficiency. Such a reflective cup may be provided with an encapsulation body1005formed thereon, filled with a light transmitting material encapsulating the semiconductor light emitting device1001, the wire W, and the like.

With reference toFIG. 10, a semiconductor light emitting device package2000may include a semiconductor light emitting device2001, a mounting substrate2010, and an encapsulation body2003. In addition, a wavelength converter2002may be formed on a surface and a side of the semiconductor light emitting device2001. The semiconductor light emitting device2001may be mounted on the mounting substrate2010and electrically connected to the mounting substrate2010through a wire W and a conductive substrate209.

The mounting substrate2010may include a substrate body2011, an upper electrode2013, and a lower electrode2014. In addition, the mounting substrate2010may include a through electrode2012connecting the upper electrode2013and the lower electrode2014to each other. The mounting substrate2010may be provided as a substrate such as a printed circuit board (PCB), a metal-core printed circuit board (MCPCB), a multilayer printed circuit board (MPCB), a flexible printed circuit board (FPCB), and the like, and the structure of the mounting substrate2010may be variously applied.

The wavelength converter2002may contain a phosphor, a quantum dot, or the like. An upper surface of the encapsulation body2003may have a convex, dorm-shaped lens structure, but according to an exemplary embodiment, the surface thereof may be a convex or a concave shaped lens structure, so as to be able to adjust an angle of beam spread in light emitted through the upper surface of the encapsulation body2003.

FIG. 11illustrates an example in which an LED driving device according to an exemplary embodiment is applied to a lighting device.

Referring to an exploded perspective view ofFIG. 11, a lighting device3000may be a bulb type lamp by way of example. The lighting device3000may include a light emitting module3003, a driver3008, and an external connector3010. In addition, the lighting device3000may further include a structure of appearance such as external housing3006and internal housing3009and a cover3007. Although the exemplary embodiment illustrates the form in which one semiconductor light emitting device3001is mounted on a circuit board3002, a plurality of semiconductor light emitting devices may be mounted on the circuit board3002as needed. In addition, instead of directly mounting the semiconductor light emitting device3001on the circuit board3002, the semiconductor light emitting device may be manufactured as a package type light emitting device and then mounted thereon.

In addition, in the lighting device3000, the light emitting module3003may include the external housing3006serving as a heat radiating unit, and the external housing3006may include a heat radiating plate3004directly contacting the light emitting module3003to improve a heat radiation effect. In addition, the lighting device3000may include the cover3007mounted on the light emitting module3003and having a convex lens shape. The driver3008may be installed in the internal housing3009to be connected to the external connector3010having a structure such as a socket structure so as to receive power from an external power supply. In addition, the driver3008may convert the received power into a current source suitable for driving the semiconductor light emitting device3001of the light emitting module3003to then be supplied. The driver3008may include at least one LED driving device. For example, the at least one LED driving device may be a LED driving device100or a LED driving device200illustrated inFIGS. 1 to 5, and may receive a control command provided externally through a digital addressable lighting interface (DALI) communications protocol.

According to exemplary embodiments in the present disclosure, an AC driver may perform controlling so that an LED is operated using rectified power output by a rectifier without a separate AC-DC converter. In addition, as a light amount controller may perform control so that levels of currents applied to LEDs are changed depending on an increase or a decrease in peak values of rectified power, a deviation in levels of light output from the LEDs depending on the change in the rectified power input to the LEDs may be significantly reduced.