KR20120026949A - Led lighting driving circuit - Google Patents

Abstract

PURPOSE: A light emitting diode drive circuit for illumination is provided to reduce EMI(Electro-Magnetic Interference) or EMC(Electro-Magnetic Compatibility) by reducing switching noise. CONSTITUTION: A bridge circuit part(410) outputs positive voltage from Vac voltage. A voltage detector(420) determines the size of input voltage. The voltage detector controls an upper switch(440) and a lower switch(450). A voltage-current converter(430) generates current proportional to the input voltage. The upper switch and the lower switch change a connection state of light emitting diode groups(460).

Description

LED Driving Circuit for Lighting {LED LIGHTING DRIVING CIRCUIT}

The present invention relates to a light emitting diode driving circuit.

Conventional light emitting diodes have been widely used as backlights of liquid crystal displays used in mobile phones, PDAs, notebooks, and the like. In addition, the light emitting diode is not only used as a light source of a large liquid crystal display device such as a TV, but also widely used in general lighting, security lamps, and street lights. Light-emitting diodes are characterized by long lifespan and eco-friendliness, and are expected to be widely used in Hwangwoo general lighting due to continuous efforts to improve light efficiency.

In general, a light emitting diode uses a current driving method. When a light emitting diode is used for general lighting, commercial power AC 220V or 110V is used. The driving method can be classified into a converter method using an inductor and a capacitor such as a switching mode power supply (SMPS) and a linear method without using an SMPS. 1 is a view for explaining a converter-type LED driving circuit. In the case of the converter method as shown in FIG. 1, the electrical efficiency and the light efficiency are higher than those of the linear method, but the configuration of the system is complicated and the noise appearing at the time of switching is large, thereby generating EMI and EMC. In addition, in case of the converter type, a power factor correction circuit must be used to improve the power factor, and the system configuration cost is high and the life of the capacitor is shorter than that of the LED. 2 is a view for explaining a linear LED driving circuit. In general, the linear system is simple in configuration but low in electrical efficiency and power factor. In the case of the linear method as shown in FIG. 2, the current flows only when the input voltage is high, and thus the power factor is low. When the input voltage is low, the light emitting diode does not operate, resulting in low light efficiency.

The technical problem of the disclosed technology is to provide a light emitting diode driving circuit having high efficiency, high power factor and high light efficiency while reducing the occurrence of EMI or EMC by reducing noise during switching because it does not include an inductor or a capacitor.

A first aspect of the disclosed technology to achieve the above technical problem is a control unit for changing the connection state of the LED groups based on a plurality of LED groups, the input voltage input to the LED groups, and the input voltage To provide a light emitting diode driving circuit comprising a voltage-to-current converter for determining the magnitude of the current flowing in the LED groups based on.

The disclosed technique may have the following effects. It is to be understood, however, that the scope of the disclosed technology is not to be construed as limited thereby, as it is not meant to imply that a particular embodiment should include all of the following effects or only the following effects.

The LED driving circuit according to an exemplary embodiment does not include an inductor or a capacitor, thereby reducing noise during switching to achieve high efficiency, high power factor, and high light efficiency while reducing EMI or EMC.

In addition, the LED driving circuit according to an exemplary embodiment may achieve high efficiency, high power factor, and high light efficiency by adjusting the LED voltage optimized for increasing or decreasing the AC input by changing the parallel connection of the LED groups.

In addition, the LED driving circuit according to an embodiment minimizes the average current difference flowing through each LED even when the LED groups are connected in parallel and parallel, so that the brightness of each LED does not change even when a wide AC input is changed. And it is possible to drive a light emitting diode of high light efficiency.

1 is a view for explaining a converter-type LED driving circuit.
2 is a view for explaining a linear LED driving circuit.
3 is a block diagram illustrating a light emitting diode driving circuit according to an embodiment of the disclosed technology.
4 is a block diagram illustrating a light emitting diode driving circuit according to another exemplary embodiment of the disclosed technology.
5 is a circuit diagram illustrating a light emitting diode driving circuit according to an embodiment of the disclosed technology.
FIG. 6 is a diagram for describing an operation region of the voltage detector of FIG. 5 according to the magnitude of an input voltage.
FIG. 7 is a diagram illustrating a connection state of grouped LEDs in each operation region of FIG. 6.
8 is a diagram for describing an input voltage and an input current.
9 is a diagram for describing a change in input current according to a change in input voltage.
10 is a view for explaining a voltage-to-current converter for limiting the maximum current.
FIG. 11 is another circuit diagram illustrating upper and lower switchers and LED groups according to an embodiment. FIG.
12 is a circuit diagram illustrating an upper and lower switch and a light emitting diode array applicable to two groups of light emitting diodes.
FIG. 13 is a view illustrating a connection state and a driving circuit of LED groups for respective regions when there are two groups of LEDs.
FIG. 14 is a circuit diagram illustrating a top and bottom switch and a light emitting diode array applicable to three groups of light emitting diodes.
FIG. 15 is a view illustrating a connection state and a driving circuit of LED groups for respective regions when there are three groups of LEDs.
FIG. 16 is a circuit diagram illustrating an upper and a lower switch and a light emitting diode array when there are six groups of light emitting diodes.
17 is a diagram illustrating a connection state and a driving circuit of LED groups for respective regions when there are six groups of LEDs.
FIG. 18 is a circuit diagram illustrating a light emitting diode driving circuit when four light emitting diode groups and four current sources are used.
FIG. 19 is a view illustrating a connection state and a driving circuit of LED groups for respective regions when four LED groups and four current sources are used.
20 is a circuit diagram illustrating a driving circuit in the case of using two LED groups and two current sources.
FIG. 21 is a view illustrating a connection state and a driving circuit of a light emitting diode group for each region when two light emitting diode groups and two current sources are used.
FIG. 22 is a circuit diagram showing a driving circuit in the case of using three LED groups and three current sources.
FIG. 23 is a view illustrating a connection state and a driving circuit of light emitting diode groups for respective regions when three light emitting diode groups and three current sources are used.
24 is a diagram illustrating a circuit diagram for driving a switch included in an upper and a lower switch.
FIG. 25 is a circuit diagram illustrating an example in which the voltage-current converter of FIG. 4 is implemented as a resistor.

The description of the disclosed technique is merely an example for structural or functional explanation and the scope of the disclosed technology should not be construed as being limited by the embodiments described in the text. That is, the embodiments may be variously modified and may have various forms, and thus the scope of the disclosed technology should be understood to include equivalents capable of realizing the technical idea.

On the other hand, the meaning of the terms described in the present application should be understood as follows.

Singular expressions should be understood to include plural expressions unless the context clearly indicates otherwise, and terms such as "include" or "have" refer to features, numbers, steps, operations, components, parts, or parts thereof described. It is to be understood that the combination is intended to be present, but not to exclude in advance the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof.

Each step may occur differently from the stated order unless the context clearly dictates the specific order. That is, each step may occur in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed technology belongs, unless otherwise defined. Terms defined in commonly used dictionaries should be interpreted to be consistent with meaning in the context of the relevant art and can not be construed as having ideal or overly formal meaning unless expressly defined in the present application.

3 is a block diagram illustrating a light emitting diode driving circuit according to an embodiment of the disclosed technology. Referring to FIG. 3, the LED driving circuit includes a controller 310, a voltage-to-current converter 320, and a plurality of LED groups 330.

The controller 310 changes the connection state of the LED groups 330 based on input voltages input to the LED groups 330. The controller 310 includes a voltage detector 312 and a switch 314.

The voltage detector 312 detects the magnitude of the input voltage and generates a control signal based on the magnitude of the input voltage. Here, when the magnitude of the input voltage increases, the voltage detector 312 increases the number of groups connected in series among the LED groups 330 and decreases the number of groups connected in parallel. In contrast, when the magnitude of the input voltage decreases, the voltage detector 312 reduces the number of groups connected in series among the LED groups 330 and increases the number of groups connected in series. For example, if there are n LED groups 330 and the voltage drop caused by one LED group is V _{LED , G1} , the voltage detector 312 has a voltage drop caused by the LED groups 330. _LED, and generates a control signal for changing the serial-to-parallel connection of the LED group 330 so that the _G1 more than n × V _{LED, G1} below.

The switch 314 includes a switch and changes the connection state of the LED groups 330 in series, parallel or a combination of series and parallel according to a control signal. The switch 314 includes an upper switch and a lower switch. The upper switch has one end connected to a voltage source supplying an input voltage, and the other end connected to the LED groups 330. The upper switch is connected between the voltage source and the anode of the LED group 330, and changes the connection state of the anode of each LED group 330. The lower switch is connected at one end to the LED groups 330 and the other end is connected to the voltage-to-current converter 320. The lower switch is between the voltage-to-current converter 320 and the cathode of the LED groups 330. Is connected to and changes the connection state of the cathode of each LED group 330.

The voltage-to-current converter 320 determines the magnitude of the current flowing in the LED groups 330 based on the input voltage. The voltage-to-current converter 330 may be implemented with a resistor or may be implemented with a plurality of current sources.

The connection state of the plurality of LED groups 330 is changed under the control of the controller 310. Each LED group 330 includes light emitting diodes connected in series with each other. Each LED group 330 may be connected in series by a diode or in series by a switch.

4 is a block diagram illustrating a light emitting diode driving circuit according to another exemplary embodiment of the disclosed technology. 4 illustrates a plurality of light emitting diodes forming a group in parallel and four light emitting diode groups are connected to each other in series through a diode. Referring to FIG. 4, the LED driving circuit 400 includes a bridge circuit 410, a voltage detector 420, a voltage-to-current converter 430, an upper switch 440, a lower switch 450, and a light emitting diode. Groups 460.

The bridge circuit unit 410 performs a rectifying function of outputting only a + voltage from a V _AC voltage alternated with + and −. Here, the output of the bridge circuit unit 410 corresponds to the input voltage V _IN of the LED driving circuit.

The voltage detector 420 determines the magnitude of the input voltage V _IN and controls the upper switch 440 and the lower switch 450.

The voltage-to-current converter 430 generates a current proportional to the input voltage V _IN and provides it to the LED groups 460. The voltage-current converter 430 determines the magnitude of the current flowing to the light emitting diodes in the light emitting diode groups 460. The voltage-current converter 430 may be configured as a constant current source irrespective of the input voltage. When the voltage-current converter 430 is configured as a constant current source, the power factor may be decreased, but electrical and light efficiency may be increased.

The upper switch 440 and the lower switch 450 change the connection state of the LED groups 460 under the control of the voltage detector 420. The upper switch 440 and the lower switch 450 connect the LED groups 460 in series or in parallel so that the LED groups 460 can be connected to the input voltage V _IN . The LED groups 460 are connected to other LED groups through a diode, and constitute one LED array.

5 is a circuit diagram illustrating a light emitting diode driving circuit according to an embodiment of the disclosed technology.

Referring to FIG. 5, the voltage detector 520 includes voltage divider resistors R ₁ , R ₂ , R ₃ , R ₄ , comparator 522, reference voltage source V _ref , and logic / level shift 524. do. The voltage detector 520 determines the magnitude of the input voltage V _IN through the voltage divider resistors R ₁ , R ₂ , R ₃ , and R ₄ and the comparator 522, and inputs the input voltage through the logic / level shift 524. According to the size of V _IN , the switches in the upper switch 540 and the lower switch 550 are turned on and off.

The upper and lower switchers 540 and 550 include diodes and switches S _U1 , S _U2 , S _U3 , S _P1 , S _P2 , S _D1 , S _D2 , S _D3 , and the voltage detector 520. According to control, the switches S _U1 , S _U2 , S _U3 , S _P1 , S _P2 , S _D1 , S _D2 , and S _D3 are turned on to change the connection state of the LED groups 560.

Voltage-to-current converter 530 includes resistors R ₅ , R ₆ , R _S , amplifier 532, and transistor 534. The voltage-to-current converter 530 generates a current proportional to the magnitude of the input voltage V _IN to satisfy the high power factor, and limits the maximum current to minimize the change in output due to the maximum change in the input voltage V _IN . Can be.

FIG. 6 is a diagram for describing an operation region of the voltage detector of FIG. 5 according to the magnitude of an input voltage.

The operating region of the voltage detector according to the magnitude of the input voltage V _IN is according to Equation 1 below.

Here, V _REF represents a reference voltage, R ₁ to R ₄ represent an input voltage divider resistor, and V _TH represents an input voltage division reference voltage.

The voltage detector 520 compares the reference voltage V _REF with a resistor divided input voltage through a comparator to set an operation region corresponding to the number of LED groups based on the maximum voltage.

FIG. 7 is a diagram illustrating a connection state of grouped LEDs in each operation region of FIG. 6. In FIG. 7, the voltage drop of the diode is very small compared to the voltage drop of the LED group, and thus is not shown in the circuit diagram for convenience.

As shown in FIG. 7, the voltage drop of all the light emitting diodes corresponds to a minimum voltage of one grouped light emitting diode, and may represent two, three, and four times the voltage drop depending on the connection state. In section A, where the input voltage V _IN is the lowest, all four LED groups are connected in parallel as shown in FIG. 7A so that the grouped LEDs can flow current even at a low input voltage. In the second section, section B, two series-connected groups are connected in parallel as shown in FIG. 7 (b) to change the connection state of the light emitting diode to be twice the minimum light emitting diode voltage in correspondence with the increased input voltage V _IN . . Therefore, the efficiency is improved by adjusting the voltage of the entire light emitting diode close to the input voltage. If the connection state as shown in (a) of FIG. 7 is maintained in the section B, the voltage applied to the current source is increased, causing a large power consumption and reducing the efficiency. In the same manner, as the input voltage V _IN increases, the connection state may be changed to have three times and four times the LED voltage enhancement of each LED group in the C and D sections, thereby improving efficiency. When the input voltage V _IN decreases, that is, in the sections D, C, B, and A of FIG. 6, the grouped light emitting diodes in the order of (d), (c), (b), and (a) of FIG. By changing the connection, the characteristic of maximum efficiency can be achieved. The turn on and turn off states of the switches for each section are shown in Table 1 below.

Upper switch Lower side changer SU1 SU2 SU3 SP1 SD1 SD2 SD3 SP4 A section ON ON ON OFF ON ON ON OFF B section OFF ON OFF OFF OFF ON OFF OFF C section
(Two combinations) OFF OFF OFF ON OFF OFF ON OFF ON OFF OFF OFF OFF OFF OFF ON D section OFF OFF OFF OFF OFF OFF OFF OFF

As shown in FIG. 7 and Table 1, two connection states are possible in the section C, using the switch SP1 included in the upper switch 540 of FIG. 5, or SP2 included in the lower switch 550. Can be used. Since the C section occurs twice in one period of the input voltage V _IN , the two combinations may be alternately used to keep the average current of the light emitting diode constant. If only one of the two is used, the unused switch can be omitted.

The driving efficiency of the light emitting diode is shown in Equation 2 below.

Here, V _IN represents an input voltage, and V _LED represents a voltage across a light emitting diode.

V _LED when input voltage V _IN fluctuates V _IN voltage Maintaining close to the voltage and emitting all LEDs at the same time can increase the electrical efficiency and the light efficiency of the light emitting diode, and prevent the change of brightness of each LED. According to the present exemplary embodiment, the electrical efficiency and the light efficiency can be greatly improved by changing the connection state of the LED group according to the increase or decrease of the input voltage V _IN .

The voltage-to-current converter 530 may include voltage distribution resistors R ₅ and R ₆ , an amplifier 532, a transistor 534, and a sensing resistor R _S. Since the circuit for generating a current proportional to the voltage can be implemented in various ways, the circuit presented in this embodiment is just one example. For example, a resistor may be used instead of a current source to limit the current.

The voltage divider resistors R ₅ and R ₆ generate a reference voltage proportional to the input voltage V _IN , and the amplifier 532, transistor 534 and sensing resistor R _S form a current source proportional to the input voltage V _IN . And determine the amount of current to drive the light emitting diodes. Here, the size of the current source is shown in Equation 3 below.

Where I _LED is the current through the light emitting diode, I _IN is the input current, V _{IN is the} input voltage, R _S is the sensing resistor, and R ₅ and R ₆ are the distribution resistors.

Since the current determined by the current source flows from the input voltage to the light emitting diode, the current of another block for controlling is very small compared to the current of the light emitting diode. In addition, since the current source has a current shape proportional to the input voltage and is in the same phase, it exhibits the same characteristics as the resistance load, thereby achieving a high power factor.

8 is a diagram for describing an input voltage and an input current, and FIG. 9 is a diagram for describing a variation of an input current according to a variation of an input voltage. FIG. 9A is a diagram showing an input voltage and an input current when the input voltage changes by ± 20%. When the input current changes according to the input voltage, the power factor may theoretically be “1”, but in this case, the output change of the light emitting diode may occur according to the change of the input voltage. Therefore, it is necessary to limit the maximum current as shown in FIG. 9B to minimize the change in output of the LED according to the input voltage variation and to protect the LED. Limiting the maximum current has the effect of reducing the power factor, but the overall current form is maintained, so that the power factor standard threshold of "0.9" or more can be easily achieved.

10 is a view for explaining a voltage-to-current converter for limiting the maximum current. As shown in FIG. 10A, the maximum current may be limited by limiting the maximum value of the voltage divided by the input voltage. FIG. 10B is an example in which the voltage limiting circuit 1010 of FIG. 10A is simply implemented as the transistor 1020 and the voltage source 1030. The circuit for limiting the maximum current is different from the various circuits. Can be implemented. The maximum current is given by Equation 4 below.

Where I _MAX is the maximum light-emitting diode current, V _MAX is the amplifier "+" input maximum voltage, V _REF is the reference voltage, V _GS is the gate-source voltage of the MOSFET, and R _S is the sensing resistor.

FIG. 11 is another circuit diagram illustrating upper and lower switchers and LED groups according to an embodiment. FIG. In comparison with FIG. 5, FIG. 11 used switches S ₁ , S ₂ , and S ₃ instead of diodes in the LED group 1130. The diodes in LED group 1130 may all be replaced with switches, as shown in FIG. 11.

In the present embodiment, the light emitting diode driving circuit in the case where there are four groups in which a plurality of light emitting diodes are connected in series is described as a reference. However, the present invention is not limited thereto, and the present invention may be applied to two or more groups. The range and number of operating regions in the voltage detector can be determined according to the number of LED groups, and the voltage drop of the LEDs has a maximum LED drop in which all groups are connected in series, and all groups are connected in parallel. The state has a minimum light emitting diode voltage drop, and the light emitting diode voltage drop may be changed for each region by a series-parallel combination of groups.

FIG. 12 is a circuit diagram illustrating a top and bottom switch and a light emitting diode array applicable to two groups of light emitting diodes. FIG. 13 is a connection state and a driving circuit of LED groups for respective regions when two groups of light emitting diodes are used. It is a figure which shows. The input voltage section may be divided into two regions, and the parallel connection of FIG. 13A may be used in the low voltage region, and the series connection of FIG. 13B may be used in the high voltage region.

FIG. 14 is a circuit diagram illustrating an upper and lower switch and an LED array applicable when three groups of LEDs are used. FIG. 15 is a connection state and a driving circuit of LED groups for respective regions when there are three groups of LEDs. It is a figure which shows. The entire parallel represents the smallest LED drop and the entire series represents the largest LED drop. That is, when there are three groups, when the minimum light emitting diode voltage drop is "1", the voltage drop may be 1, 2, 3 times. When the voltage drop is twice, the same voltage drop of the two LEDs is shown even when the upper two groups are connected in parallel or the lower two groups are connected in parallel. If you use only one of the two cases, you can omit one switch.

In the case of using four LED groups, the two groups connected in parallel can be connected in parallel as in the case of making a connection with a voltage drop of three times, but the average current is reduced in the two groups connected in parallel compared to the other groups. The combination of the two groups can be used to change the connection alternately, or the average value can be controlled in consideration of the connection state of one cycle.

When using n groups of light emitting diodes as described above, the voltage drop of the adjustable light emitting diodes also increases to n. Since the maximum input voltage is already set to AC 220V or AC 110V, the number of comparator, bonsai resistor, switch, and diode of the voltage detector increases as the number of LED groups increases, but finely adjusts the voltage of the LED against the input voltage. It is possible to further increase the efficiency. Efficiency reductions can occur with added diodes and switches, but switch turn-on resistance values of several to several tens of Ohms provide much higher efficiency than without changing the connection state as the input voltage increases or decreases.

FIG. 16 is a circuit diagram illustrating an upper and a lower switch and a light emitting diode array when there are six groups of light emitting diodes. FIG. 17 illustrates a connection state and a driving circuit of LED groups for each region when there are six groups of light emitting diodes. Drawing. In FIG. 16 and FIG. 17, the case where all are parallel shows the minimum voltage drop, and when it is all series, the maximum voltage drop is shown. When the voltage drop is twice or three times the minimum value, it is easily determined as shown in the circuit diagram. In the case of four times and five times, the connection state may vary depending on which group is parallelized. The same can be applied to the other groups 5, 7, 8, 9, ... which are not explained.

FIG. 18 is a circuit diagram illustrating a light emitting diode driving circuit when four light emitting diode groups and four current sources are used. Each current source supplies a current corresponding to one quarter of the current source of FIG. Even in the case where more than one current source is used, the driving method and operation description when using one of the above current sources can be applied in the same manner.

FIG. 19 is a view illustrating a connection state and a driving circuit of LED groups for respective regions when four LED groups and four current sources are used. When the four current sources are shorted, the LED driving circuit of FIG. 19 becomes the same as the LED driving circuit of FIG. As shown in (a) and (b) of FIG. 19, there is an advantage that the same current can flow even if there is a variation in LED voltage drop for each group. However, there is a disadvantage in that the number of switches and the number of voltage-to-current converters increase. 19C and 19D are the same as when one current source is driven.

FIG. 20 is a circuit diagram illustrating a driving circuit in the case of using two LED groups and two current sources, and FIG. 21 is a connection state of the LED groups for each region in the case of using two LED groups and two current sources. It is a figure which shows a drive circuit.

FIG. 22 is a circuit diagram illustrating a driving circuit in the case of using three LED groups and three current sources, and FIG. 23 is a connection state and driving circuit of each LED group in each region when three LED groups and three current sources are used. It is a figure which shows a furnace. This approach can be easily applied even when using five or more groups of light emitting diodes which are not described.

24 is a diagram illustrating a circuit diagram for driving a switch included in an upper and a lower switch. In the circuit diagrams of FIGS. 6 to 23, switch driving parts are omitted to reduce complexity. The driving switch is not only an N-type MOSFET but also a variety of semiconductor switches. The circuit for driving other types of switches is omitted, and an embodiment of the driving circuit of the N-type MOSFET is most commonly used.

The switch driving stage includes a bootstrap diode forming a floating power supply, a resistor, a capacitor and a voltage clamp, and a level shift and driving stage for driving a switch in response to a signal of a voltage detector.

Floating power supplies receive a voltage from a voltage higher than the source (emitter) of the switch at switch turn-off to charge the bootstrap capacitor and limit the voltage clamp block from rising above a certain voltage. Bootstrap diodes prevent capacitors from discharging due to rising voltages at switch turn-on. Level shift receives the signal of the voltage detector and transfers the output signal of the ground level to the drive terminal connected to the bootstrap power source, and the drive level amplifies the signal to shorten the turn-on and turn-off time of the switch. To function. The switching driving stage may apply a high voltage driving method that is generally used, and may omit a floating power supply when using a P-type driving device.

FIG. 25 is a circuit diagram illustrating an example in which the voltage-current converter of FIG. 4 is implemented as a resistor.

The switch used in the figure represents an N-type MOSFET, but can be replaced with a transistor functioning as a switch regardless of the N and P types. In addition, the switches used in all the above drawings include metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), junction transistors (BJTs), junction field effect transistors (JFETs), and silicon controlled rectifiers. It may include at least one of triac (Triac).

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that

Claims (18)

A plurality of LED groups;
A controller configured to change a connection state of the LED groups based on input voltages input to the LED groups; And
And a voltage-to-current converter for determining a magnitude of current flowing through the LED groups based on the input voltage. The apparatus of claim 1, wherein the control unit
A voltage detector detecting a magnitude of the input voltage and generating a control signal based on the magnitude of the input voltage; And
And a switch configured to switch according to the control signal to change the connection state of the LED groups. The method of claim 2, wherein the voltage detector is
When the magnitude of the input voltage is increased, the number of groups connected in series among the LED groups is increased, and when the magnitude of the input voltage is decreased, the light emission is decreased as the number of groups connected in series among the LED groups is decreased. Diode driving circuit. The method of claim 2,
If the LED groups are n, and the voltage drop by one LED group is V _{LED , G1} ,
The voltage detector is configured to generate a light emitting diode driving circuit for changing the series-parallel connection state of the LED groups such that the voltage drop caused by the LED groups is V _{LED , G1} or more, n × V _{LED , G1} or less. . The method of claim 4, wherein the voltage detector is
Voltage divider resistors for dividing the input voltage;
Comparators for comparing a predetermined reference voltage with the divided voltages;
And a logic block configured to determine on / off of the switch according to an increase or decrease of the input voltage according to a comparison result of the comparator. The method of claim 2, wherein the LED groups are
A light emitting diode driving circuit comprising at least one light emitting diode. The method of claim 2,
A light emitting diode driving circuit in which each group of light emitting diodes is connected in series by a diode. The method of claim 2,
A light emitting diode driving circuit in which each group of light emitting diodes is connected in series by a switch. The method of claim 2, wherein the voltage-to-current converter
A light emitting diode driving circuit comprising a resistor. The method of claim 2,
And at least one voltage-to-current converter. The method of claim 2, wherein the voltage-to-current converter
Voltage divider resistors for dividing the input voltage;
An amplifier connected with the voltage divider resistor through a + input terminal; And
A transistor whose gate or base is connected to the output terminal of the amplifier and whose source or emitter is connected to the − input terminal of the amplifier and one end of a sensing resistor,
The other end of the sensing resistor is connected to the ground of the amplifier, the LED driving circuit for supplying a current proportional to the magnitude of the input voltage to the LED groups. The method of claim 2, wherein the switch
An upper switch having one end connected to a voltage source supplying the input voltage and the other end connected to the LED groups; And
And a lower switch, one end of which is connected to the LED groups and the other end of which is connected to the voltage-current converter. The method of claim 12, wherein the switch
And a light emitting diode driving circuit for changing the connection state of the LED groups in series, parallel or a combination of series and parallel according to the control signal. The method of claim 12, wherein the upper switch
A light emitting diode driving circuit connected between the voltage source and an anode of the light emitting diode group and changing a connection state of the anode of each light emitting diode group. The method of claim 14, wherein the upper switch
And at least one switch connected in parallel between the anode tabs of the LED group, the at least one switch connecting the LED group in parallel. The method of claim 12, wherein the lower switch
A light emitting diode driving circuit connected between the voltage-current converter and a cathode of the LED group, the LED driving circuit changing a connection state of the cathode of each LED group. The method of claim 16, wherein the lower switch
And at least one switch connected in parallel between the cathode tabs of the LED group, the at least one switch connecting the LED group in parallel. The method of claim 2, wherein the switch
At least one of a metal oxide semiconductor field effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), a junction transistor (BJT), a junction field effect transistor (JFET), a silicon controlled rectifier, and a triac LED driving circuit comprising a.

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