KR101033732B1 - LED Driver - Google Patents

Abstract

The LED driver of the present invention, the first LED string; Second LED strings; A first rectifying unit rectifying current in a first direction of an AC voltage and supplying the first LED string to the first LED strings; A second rectifying unit rectifying current in a second direction of an AC voltage and supplying the second LED strings; And a balancing unit positioned between the first LED strings and the second LED strings to balance current balancing of the first LED strings and the second LED strings.

LED Driver, DC-AC Conversion, Light Emitting Diode, Backlight

Description

LED Driver {LED Driver}

The present invention relates to an LED driver for supplying driving power to LEDs (Light Emitting Diodes).

LED light source devices consisting of a plurality of strings of light emitting diodes (LEDs) are rapidly spreading for a wide range of applications for lighting applications or backlights of LDC panels.

LEDs with high brightness as a whole can be used in many applications, including backlights of liquid crystal displays (LCDs) based on monitors and televisions (collectively referred to as monitors hereinafter). In large LCD monitors, LEDs are typically supplied to one or more strings of LEDs connected in series to share a common current.

To provide backlight for LCD monitors, one of two basic techniques is commonly used. The first technique uses one or more strings of white LEDs, which typically include blue LEDs with phosphors (materials). This phosphor absorbs the blue light generated by the LED and emits white light. In the second technique, one or more individual strings of colored LEDs are placed adjacent to each other so that the light combined with each other looks like white light.

However, due to the deviation of characteristics (eg, forward voltage drop) between each LED element constituting the LED string, LED strings of the same type of LEDs also exhibit different electrical characteristics (eg, voltage drop). Thus, in order to allow the same current to flow through each of the LED strings, a controllable constant current source, etc., connected in series to each of the LED strings to compensate for different voltage drops is additionally required.

That is, a dissipative active element that operates to compensate for different voltage drops of the LED strings may be applied. However, the lossy active element is a significant heat source, which increases the heat dissipation cost for the entire LED driver and lowers the power transfer efficiency, causing a problem that the capacity of the power supply is large.

The present invention is to provide an LED driver that can suppress the heat loss.

Another object of the present invention is to provide an LED driver that can suppress power waste.

Another object of the present invention is to provide an LED driver capable of providing current balancing between LED strings in an inexpensive structure.

LED driver according to an embodiment of the present invention, the first LED string; Second LED strings; A first rectifying unit rectifying current in a first direction of an AC voltage and supplying the first LED string to the first LED strings; A second rectifying unit rectifying current in a second direction of an AC voltage and supplying the second LED strings; And a balancing unit positioned between the first LED strings and the second LED strings to balance current balancing of the first LED strings and the second LED strings.

LED driver according to another embodiment of the present invention, the transformer unit for receiving an AC voltage to the input port; At least one first LED string receiving current in a first direction from an output port of the transformer unit; At least one second LED string receiving current in a second direction from an output port of the transformer unit; At least one first balancing capacitors positioned between the output port of the transformer section and the first LED strings; At least one second balancing capacitor positioned between the output port of the transformer portion and the second LED strings; At least one first rectifying diodes for forming a unidirectional current path for rectification between the second strings and the first balancing capacitors; And at least one second rectifying diode for forming a unidirectional current path for rectification between the first strings and the second balancing capacitors.

By implementing the LED driver of the present invention according to the above configuration, there is an advantage that the heat generation loss of the LED driver can be suppressed.

Alternatively, the LED driver of the present invention has an advantage of suppressing driving power loss of the LED driver.

Or the LED driver of this invention has the advantage that the manufacturing cost can be reduced.

Alternatively, the LED driver of the present invention has the advantage of providing a current balancing between the LED strings in a simple structure.

1 illustrates a structure of an LED driver for smoothing driving power of LED strings in a linear driving scheme.

As shown, each LED string is supplied with driving power from a common power supply 11, and the bipolar transistor 13 and the op amp 12 are fixed in the current path formed by each of the LED strings 14. Current sources 19 are connected. In the illustrated circuit, the same current is supplied to each of the LED strings by the fixed current sources 19, so that the luminance of each of the LED strings 14 can be kept uniform even when there is a slight characteristic variation between the LED strings. have.

While the illustrated LED driver has the advantage of accurate current control and easy implementation of additional functions such as dimming, LED strings having different forward voltage drop values are unilaterally the same size. By forcing a current to flow, there is a disadvantage in that heat generation loss caused by the resistive component 16 on the current path occurs.

2 shows the structure of an LED driver that smoothes the driving power of the LED strings in a switching manner.

Each LED string 24 of the illustrated LED driver is provided with DC-DC converters 21 for switching driving, respectively. As shown in the figure, time-sharing control of the switching transistor 32 of each DC-DC converter 21 according to the current detected by the switching control IC 31 sensing the output current of each LED string, the corresponding LED string 24 Adjust the average current flowing to).

While the illustrated LED driver has an advantage of suppressing heat dissipation due to a resistive component, an accurate current control process is relatively complicated, costs are increased, and additional functions are difficult to implement.

3 is a block diagram illustrating the concept of an LED driver according to the spirit of the present invention.

The illustrated LED driver includes at least two LED strings 103; A rectifier 107 for rectifying an AC voltage to supply the LED strings; A DC-AC converter (101) including a balancing unit (105) for matching the current balancing of the LED strings, and on the power supply side, together with the DC power supply unit (11), converting a DC voltage into an AC voltage; And a transformer unit 102 transferring the converted AC voltage to the rectifying unit 107.

FIG. 4 is a block diagram illustrating a concept of an LED driver that divides the concept of the LED driver of FIG. 3 according to the spirit of the present invention into a half-wave rectification method by dividing the concept of the LED driver into an AC current again.

The illustrated LED driver includes: first LED strings 103; Second LED strings 104; A first rectifying unit (107) for rectifying current in a first direction of an AC voltage and supplying the first LED strings (103); A second rectifier 108 for rectifying a current in a second direction of an AC voltage and supplying the second LED strings 104 to each other; And a balancing unit positioned between the first LED strings 103 and the second LED strings 104 so as to match the current balancing of the first and second LED strings 103 and 104. A DC-AC converter 101 which includes a 105, and converts a DC voltage into an AC voltage on the power supply side together with the DC power supply 11; And a transformer unit 102 transferring the converted AC voltage to the LED strings 103.

The LED driver of the illustrated structure alternately drives the first LED strings 103 and the second LED strings 104 in accordance with the direction of the alternating current, and the first LED strings 103 and the second LEDs. By the balancing unit 105 disposed between the strings 104, the currents flowing into the respective LED strings are uniformly adjusted. The balancing unit 105 may have the characteristics of a capacitor for inexpensive and efficient current balancing.

5 shows the structure of one embodiment of an LED driver that smoothes the drive power of LED strings in a split AC drive scheme.

The DC-AC converter 110 of FIG. 5 serves as the DC-AC converter 11 of FIG. 4, and the first rectifying diode 170 and the first auxiliary rectifying diode 210 (or the first LED) of FIG. The strings 130 serve as the first rectifying unit 107 of FIG. 4, and the second rectifying diode 180 and the second auxiliary rectifying diode 220 (or the second LED strings 140) of FIG. 5. ) Serves as the second rectifier 108 of FIG. 4.

The first and second balancing capacitors 150 and 160 of FIG. 5 serve as the balancing capacitor unit 105 of FIG. 4.

The LED driver shown in FIG. 5 includes a DC-AC converter 110 as an AC power source for applying an AC voltage to the LED driver; A transformer unit 120 for receiving an AC voltage of the DC-AC converter 110 to an input port; At least one first LED string 130 receiving a current in a first direction A from an output port of the transformer unit 120; At least one second LED string 140 receiving a current in a second direction B from an output port of the transformer unit 120; At least one first balancing capacitors (150) having one ends connected to a common node (C) and forming a current path for each of the first LED strings; At least one second balancing capacitors 160 having one ends connected to the common node C and forming a current path for each of the second LED strings;

At least one first rectifying diodes (170) for forming a rectifying unidirectional current path through the first balancing capacitor (150) to the second strings (140); At least one second rectifying diode 180 may be formed to form a rectifying unidirectional current path through the second balancing capacitor 160 with respect to the first strings 130.

Here, the first LED strings 130 are disposed to allow a current to flow in the direction from the first LED strings 130 to the first balancing capacitors 150, and the second LED strings 140. ) Is disposed such that a current flows in a direction from the second LED strings 140 to the second balancing capacitors 160.

Due to the reverse current blocking function of the first / second LED strings 130 and 140 itself, the first / second rectifying diodes 170 and 180 and the first / second LED strings 130 and 140 May form one type of rectifier circuit. This is because the first and second LED strings 130 and 140 basically have diode characteristics.

However, in order to place the first / second ripple cancellation capacitors 250, 260 or to prevent breakage of the LED due to an instantaneous high voltage reverse current, the first balancing capacitors 150 and the first At least one first auxiliary rectifying diode 210 connected between the first LED strings 130 in the same direction as the first LED strings 130, the second balancing capacitors 160, and the At least one second auxiliary rectifying diode 220 connected to the second LED strings 140 in the same direction may be disposed between the second LED strings 140.

In addition, at least one first resistor connected between the first auxiliary rectifying diodes 210 and the first LED strings 130 to protect the first / second LED strings 130 and 140. Field 230; And at least one second resistor 240 connected between the second auxiliary rectifying diodes 220 and the second LED strings 140.

In addition, in order to bypass the ripple component of the current flowing through the transformer unit 120 and the first and second balancing capacitors 150 and 160, at least connected in parallel with the first LED strings 130. One first ripple cancellation capacitor 250; And at least one second ripple cancellation capacitor 260 connected in parallel with the second LED strings 140.

In addition, the current measuring device may be located at an output port of the transformer unit or a common node of the first balancing capacitor. The current measuring device may be provided with a current measuring transformer.

The DC-AC converter 110 may convert a DC voltage into an AC voltage in a manner of changing the direction of the current applied to the input coil of the transformer unit 120 using four switching transistors.

Although not shown, the LED driver may include a controller that generates control signals C1 and C2 for controlling four switching transistors of the DC-AC converter 110.

The controller may receive the current measured by the current measuring device, and use the control signals C1 and C2 to feedback control the current to be constant.

The operation of the illustrated LED driver is as follows.

A current of an AC pattern (for example, a sine wave) flows through the output side coil of the transformer unit, and the AC current is applied to the first / second LED strings 130 and 140.

According to the positive direction pattern of the sine wave, when a current flows in the A direction of the output side coil of the transformer unit, the A direction current passes through the first LED strings 130 and the first auxiliary rectifier diode 210 subjected to the forward bias. However, the second LED strings 140 and the second auxiliary rectifier diode 220 that are reverse biased may not pass.

The current passing through the first LED strings 130 and the first auxiliary rectifier diode 210 is collected at the C node via the first balancing capacitor 150.

The current collected at the C node is circulated to the transformer unit 120 through the second balancing capacitor 160 and the second diodes 180 subjected to the forward bias.

As a result, the first LED strings 130 are driven and the second LED strings 140 are not driven in the section in which current flows in the A direction. In the same process, in the current flow in the B direction, the second LED strings 140 are driven and the first LED strings 130 are not driven.

That is, the first rectifying diode 170 and the first auxiliary rectifying diode 210 (or the first LED strings 130) form a kind of half-wave rectifying circuit. In addition, the second rectifying diode 180 and the first auxiliary rectifying diode 220 (or the first LED strings 140) form a kind of half-wave rectifying circuit. In both cases, the half-wave rectification circuit structure, but since the first LED string 180 is driven in the current section of the A direction, the second LED string 180 is driven in the current section of the B direction, the general half-wave rectifier circuit No power loss occurs.

In the illustrated LED driver, when there is a deviation in the forward voltage drop due to the characteristic variation of each of the first LED strings 130, in the current flow in the A direction, each of the first balancing capacitors is caused by the deviation. Different charges only accumulate in the coil 150 and the second balancing capacitors 160. The charges accumulated in different amounts are canceled in a period in which the capacitors 150 and 160 cancel each other or flow current in the B direction. As a result, in the case of the illustrated LED driver, even if there is a deviation in the forward voltage drop of each of the first LED strings 130, a current deviation (or a resulting luminance deviation) occurs in the first LED strings 130. I never do that. Similarly, even if there is a deviation in the forward voltage drop of each of the second LED strings 140, there is no current deviation (or a resulting luminance deviation) in the second LED strings 140.

Meanwhile, referring to the A direction current path and the B direction current path, except for the first resistor 230 and the second resistor 240 on the two current paths, there is no resistance component. Therefore, it can be seen that the illustrated LED driver can greatly suppress the heat loss due to the resistive component.

FIG. 6 is an LED driver according to another embodiment having a simpler structure than that of FIG. 5, wherein the LED driver has no resistance in the driving path. The configuration and operation of each illustrated LED driver can be easily inferred from the description of FIG. 5, and thus redundant descriptions will be omitted.

7 shows the structure of another embodiment of an LED driver that smoothes the drive power of LED strings in a split AC drive scheme.

The illustrated LED driver includes a DC-AC converter 310 as an AC power source for applying an AC voltage to the LED driver; A transformer unit 320 receiving an AC voltage of the DC-AC converter 310 to an input port; At least one first LED string 330 that receives a current in a first direction A from an output port of the transformer unit 320; At least one second LED string 340 that receives a current in a second direction B from an output port of the transformer unit 320; At least one first balancing capacitors (350) having one ends connected to a common node (C) and forming a current path for each of the first LED strings; At least one second balancing capacitors 360 having one ends connected to the common node C and forming a current path for each of the second LED strings;

At least one first rectifying diodes (370) for forming a rectifying unidirectional current path to the second strings (340) via the first balancing capacitor (350); At least one second rectifying diode 380 for forming the rectifying unidirectional current path through the second balancing capacitor 360 with respect to the first strings 330 may be included.

Here, the first LED strings 330 are arranged such that a current flows in the direction from the first balancing capacitors 350 to the first LED strings 330, and the second LED strings 340. ) Is disposed such that a current flows from the second balancing capacitors 360 to the second LED strings 340.

Due to the reverse current blocking function of the first / second LED strings 330, 340 itself, the first / second rectifying diodes 370, 380 and the first / second LED strings 330, 340 Can form a kind of rectifier circuit. This is because the first / second LED strings 330 and 340 basically have a diode characteristic.

However, in order to place the first / second ripple cancellation capacitors 450 and 460 or to prevent breakage of the LED due to a momentarily high voltage reverse current, the first balancing capacitors 350 and the At least one first auxiliary rectifying diodes 410 connected between the first LED strings 330 in the same direction as the first LED strings 330, the second balancing capacitors 360, and At least one second auxiliary rectifying diode 420 connected to the second LED strings 340 in the same direction may be disposed between the second LED strings 340.

In addition, at least one first resistor connected between the first auxiliary rectifying diodes 410 and the first LED strings 330 to protect the first / second LED strings 330 and 340. Field 430; And at least one second resistor 440 connected between the second auxiliary rectifying diodes 420 and the second LED strings 340.

In addition, in order to bypass the ripple component of the current flowing through the transformer unit 320 and the first and second balancing capacitors 150 and 160, at least connected in parallel with the first LED strings 330. One first ripple cancellation capacitors 450; And at least one second ripple cancellation capacitor 460 connected in parallel with the second LED strings 340.

In addition, the current measuring device may be located at the output port of the transformer unit 320 or the common node C of the first balancing capacitor 350. The current measuring device may be provided with a current measuring transformer.

Although not shown, the LED driver may include a controller that generates control signals C1 and C2 for controlling four switching transistors of the DC-AC converter 110.

The controller may receive the current measured by the current measuring device, and use the control signals C1 and C2 to feedback control the current to be constant.

Description of the operation and principle of the illustrated LED driver can be easily inferred from the description of FIG.

FIG. 8 is an LED driver according to another embodiment having a simpler structure than that of FIG. 7, wherein the LED driver has no resistance in the driving path. The configuration and operation of each illustrated LED driver can be easily inferred from the description of FIG. 5, and thus redundant descriptions will be omitted.

Although the technical spirit of the present invention has been described in detail according to the above embodiment, it should be noted that the above embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

1 is a circuit diagram showing a structure of an LED driver for smoothing the driving power of LED strings in a linear driving method.

2 is a circuit diagram showing the structure of an LED driver for smoothing the driving power of the LED strings in a switching manner.

3 is a block diagram illustrating the concept of an LED driver according to the spirit of the present invention.

4 is a block diagram illustrating the concept of another aspect of the LED driver according to the spirit of the present invention.

Fig. 5 is a circuit diagram showing the structure of one embodiment of an LED driver for smoothing the driving power of LED strings in a split AC drive scheme.

Fig. 6 is a circuit diagram showing the structure of another embodiment of an LED driver for smoothing the driving power of LED strings in a split AC drive scheme.

Fig. 7 is a circuit diagram showing the structure of another embodiment of an LED driver for smoothing the driving power of LED strings in a split AC drive scheme.

Fig. 8 is a circuit diagram showing the structure of another embodiment of an LED driver for smoothing the driving power of LED strings in a split AC drive scheme.

Claims (11)

delete delete A transformer unit receiving an AC voltage through an input port; At least one first LED string receiving current in a first direction from an output port of the transformer unit; At least one second LED string receiving current in a second direction from an output port of the transformer unit; At least one first balancing capacitors having one end connected in common and forming a current path for each of the first LED strings; At least one second balancing capacitors, one ends of which are connected to a common node of the first balancing capacitor and form a current path for each of the second LED strings; At least one first rectifying diodes for forming a unidirectional current path for rectification via said first balancing capacitor for said second strings; At least one second rectifying diodes for forming a unidirectional current path for rectification via said second balancing capacitor for said first strings; LED driver including. The method of claim 3, wherein At least one first auxiliary rectifying diode connected between the first balancing capacitors and the first LED strings in the same direction as the first LED strings; And At least one second auxiliary rectifying diode connected between the second balancing capacitors and the second LED strings in the same direction as the second LED strings LED driver including. The method of claim 4, wherein At least one first resistor coupled between the first auxiliary rectifying diodes and the first LED strings; And At least one second resistor connected between the second auxiliary rectifying diodes and the second LED strings LED driver including. The method of claim 3, wherein At least one first ripple cancellation capacitor connected in parallel with the first LED strings; And At least one second ripple cancellation capacitor connected in parallel with the second LED strings LED driver including. The method of claim 3, wherein The first LED strings are arranged such that a current flows from the first balancing capacitors to the first LED strings, An LED driver in which the second LED strings are arranged such that current flows in the direction from the second balancing capacitors to the second LED strings The method of claim 3, wherein The first LED strings are arranged such that a current flows in the direction from the first LED strings to the first balancing capacitors, An LED driver in which the second LED strings are arranged such that current flows in the direction from the second LED strings to the second balancing capacitors The method of claim 3, wherein LED driver including a DC-AC converter for converting a DC voltage applied from the outside into an AC voltage. The method of claim 9, Current measuring device located at the output port of the transformer unit or a common node of the first balancing capacitor LED driver comprising a. 11. The method of claim 10, According to the current measured by the current measuring device Control unit for controlling the operation of the DC-AC converter LED driver comprising a.

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