KR20100138533A - Led driver - Google Patents

Abstract

PURPOSE: An LED driver is provided to suppress a driving power loss by providing a current balancing between LED strings. CONSTITUTION: A DC-AC converter(101) changes a DC voltage into an AC voltage. A rectifier(107) rectifies an AC voltage and supplies the rectified AC voltage to an LED string(103). A balancing capacitor(105) is positioned on the current path of each LED string. A path control element(108) controls the current path of each LED string. A controller(104) controls the path control elements. A transformer(102) transmits the converted AC voltage to the rectifier.

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 typically consist of one or more strings of LEDs connected in series.

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 can suppress the heat loss, and to provide an LED driver capable of individually controlling the LED string.

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, at least two LED strings; A rectifier for rectifying an AC voltage and supplying the LED strings; At least two balancing capacitors positioned in the current path of each LED string to match current balancing of the LED strings; At least two path control elements for controlling the current path of each LED string; And a controller for controlling the path control elements.

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 portion 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; At least one second rectifying diodes for forming a unidirectional current path for rectification between the first strings and the second balancing capacitors; First path control elements for controlling a current path of each of the first LED strings; And second path control elements for controlling a current path of each of 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 capacitor positioned between the output port of the transformer portion and the second LED strings; At least one second balancing capacitor positioned between the output port of the transformer portion and the first LED strings; At least one first rectifying diodes for forming a unidirectional current path between the first LED strings and the first balancing capacitor; At least one second rectifying diodes for forming a unidirectional current path between the second LED strings and the second balancing capacitor; First path control elements for controlling a current path of each of the first LED strings; And second path control elements for controlling a current path of each of the second LED strings.

By implementing the LED driver of the present invention according to the above configuration, there is an advantage to suppress the heat loss of the LED driver, and to individually control the LED string.

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 maintained uniformly even if 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; At least two current balancing capacitors (105) located in the current path of each of the LED strings to match the current balancing of the LED strings; Path control elements (108) for individually controlling the current supply of each of said LED strings (103); And a control unit 104 for controlling the path control element 108, and on a power supply side, a DC-AC converter 101 for converting a DC voltage into an AC voltage together with a DC power supply 11; And a transformer unit 102 transferring the converted AC voltage to the rectifying unit 107.

4 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. 4 serves as the DC-AC converter 11 of FIG. 3, and the first and second rectifying diodes 170 and 180 and the first and second auxiliary rectifying diodes of FIG. 210 and 220 (or first and second LED strings 130 and 140) serve as the rectifier 107 of FIG. 3.

The first and second balancing capacitors 150 and 160 of FIG. 4 serve as the current balancing capacitor 105 of FIG. 3, and the first and second LED strings 130 and 140 of FIG. 4 are shown in FIG. 3. Serves as the LED strings 103.

The bipolar transistors 510 of FIG. 4 serve as the path control element 108 of FIG. 3.

The LED driver shown in FIG. 4 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 capacitor (150) positioned between the output port of the transformer section (120) and the first LED strings (130); At least one second balancing capacitor 160 positioned between the output port of the transformer unit 120 and the second LED strings 140; At least one first rectifying diode (170) for directing current through the second LED strings (140) to the transformer unit (120) through the first balancing capacitor (150); At least one second rectifying diode (180) for directing current through the first LED strings (130) to the transformer unit (120) through the second balancing capacitors (160); At least two first bipolar transistors 510 for adjusting a current path of each first LED string 130; And at least two second bipolar transistors 520 for adjusting a current path of each second LED string 140.

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

As illustrated, the first rectifying diodes 210 have an anode connected to each of the first balancing capacitors 150, and the second rectifying diodes 220 have an anode whose respective second balancing is performed. Are connected to the capacitors 160. The cathode of the first rectifying diode 210 is connected to the collector terminal of the first bipolar transistors 510, and the cathode of the second rectifying diode 220 is connected to the second bipolar transistors 520. It is connected to the collector terminal. Emitters of the first and second bipolar transistors 510 and 520 are commonly connected.

The current gathered at the emitter side common node C of the first / second bipolar transistors 510 and 520 is the anode side common node of the first rectifying diodes 170 and the second rectifying diodes 180. It flows to (D).

Directions of the first bipolar transistors 510 are connected such that a collector-emitter is arranged in a forward direction of the first LED strings 130 forming the same current path, and the second bipolar transistors 520 Direction is connected such that the collector-emitter is arranged in the forward direction of the second LED strings 140 forming the same current path. The common connection node C of the emitters of the first bipolar transistors 510 and the second bipolar transistors 520 may be grounded.

In addition, although not shown, the LED driver may include a controller for individually adjusting the base terminal currents of the first bipolar transistors 510 and the second bipolar transistors 520.

The controller may apply an on / off current to each base terminal so that each of the first bipolar transistor 510 and the second bipolar transistor 520 operates as a kind of switch. Alternatively, the controller may apply a current having a linear value to each base terminal so that the first bipolar transistor 510 and the second bipolar transistor 520 linearly adjust the width of the current path. .

In addition, the common connection node C of the emitters of the first bipolar transistors 510 and the second bipolar transistors 520 and the first rectifying diodes 170 and the second rectifying diodes 180. A measurement resistor (not shown) may be disposed between the anode side common node D.

The measurement resistor does not perform a function for driving the LED in the LED driver, but is used to easily sense the total current of the LED driver. That is, the current flowing through the measurement resistor can be calculated from the voltage across the measurement resistor. This is because current measuring devices are burdened in size and cost, while voltage measuring devices are small in size and cost.

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

On the other hand, the control unit for controlling the first / second bipolar transistors (510, 520), the control signals (C1, C2) for controlling the four switching transistors of the DC-AC converter 110, the four It can be applied to the switching transistor. In this case, the control unit receives the current flowing through the measurement resistor and performs feedback control so that the current is constant, and the control signals C1 and C2 may be used.

The LED driver of another implementation may further include a first offset applying unit for applying an offset voltage to the C node, and a second offset applying unit for applying an offset voltage to the D node.

The operation of the illustrated LED driver is as follows.

A current of an alternating current pattern (for example, a sine wave) flows through the coil of the output end side of the transformer unit, and the alternating current is applied to the first / second LED strings via a first balancing capacitor and a second balancing capacitor.

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.

Current passing through the first LED strings 130 is collected at the node C and flows out to the node D via the measurement resistor 190. However, due to the voltage drop caused by the first LED strings 130 and the first auxiliary rectifying diode 210 through which current flows, the first rectifying diodes 170 are reverse biased so that the current path is blocked. The second diodes 180 are forward biased to open the current path by the electromotive force of the coil of the output end side of the transformer for flowing the current. As a result, the current flowing into the node D is circulated to the transformer unit 120 via the second balancing capacitors 160.

 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, the respective first balancing capacitors 150 may be caused by the deviation in a current flowing in the A direction. Only different charges accumulate. Charges accumulated in different amounts in each of the first balancing capacitors 150 are erased in a section in which current flows 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.

On the other hand, looking at the A direction current path and the B direction current path, there is no resistance component on the two current path. Therefore, it can be seen that the illustrated LED driver can greatly suppress the heat loss due to the resistive component.

On the other hand, by adjusting the base current of each of the first bipolar transistor 510 or each of the second bipolar transistor 520 appropriately, each of the first LED string 130 or each of the second LED string 140 is individually brightnessed I can regulate it. For example, the on / off current may be applied as the base current to individually adjust the brightness by the PWM control method.

The LED driver of FIG. 5 provides first stabilization resistors 530 connected between the connection node of the first LED strings 130 and the first ripple cancellation capacitor 250 and the first auxiliary rectifier diodes 210. And further comprising first stabilizing resistors 540 connected between the connection node of the second LED strings 140 and the second ripple cancellation capacitor 260 and the second auxiliary rectifying diodes 220. . This is different from the LED driver of FIG. 4.

When the emitter terminal is switched using the first bipolar transistors 510 and the second bipolar transistors 520 grounded, the grounding property may be deteriorated. The first stabilization resistors 530 and the first bipolar transistors 520 may be deteriorated. The two stabilization resistors 240 are for preventing this.

Since the remaining components of FIG. 5 except for the first stabilization resistors 530 and the second stabilization resistors 240 are the same as those of FIG. 4, redundant description thereof will be omitted.

The LED driver of FIG. 6 applies first MOS transistors 511 instead of the first bipolar transistors 510 of FIG. 4, and second MOS transistors 521 instead of the second bipolar transistors 520 of FIG. 4. ) Was applied. In addition, the measurement resistance 190 is not shown in FIG. 4.

Morse transistors differ from bipolar transistors in that they do not control the current path linearly, but only on / off control is possible. In addition, there is a difference even if it is controlled by a voltage rather than a current. However, as a kind of switch, the on / off operation is the same as in the case of the bipolar transistor, and thus redundant description of the function will be omitted.

Since the remaining components of FIG. 6 except for the first MOS transistors 511, the second MOS transistors 521, and the measurement resistor 190 are the same as those of FIG. 4, redundant description thereof 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 B from an output port of the transformer unit 320; At least one second LED string 340 that receives a current in a second direction A from an output port of the transformer unit 320; At least one first balancing capacitor (350) coupling the output port of the transformer unit (320) and the first LED strings (330); At least one second balancing capacitor 360 coupling the output port of the transformer unit 320 and the second LED strings 340; At least one first rectifying diodes (370) for directing current supplied from the transformer unit (320) to the second LED strings (340) via the first balancing capacitors (350); At least one second rectifying diodes (380) for directing current supplied from the transformer unit (320) to the first LED strings (330) via the second balancing capacitors (360); And at least two first bipolar transistors 610 for adjusting a current path of each of the first LED strings 130. And at least two second bipolar transistors 620 for adjusting a current path of each second LED string 140.

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

In addition, in order to prevent breakage of the LED due to a high voltage reverse current momentarily, the same as the first LED strings 330 between the first balancing capacitors 350 and the first LED strings 330. At least one first auxiliary rectifying diode 410 connected in a direction, and between the second balancing capacitor 360 and the second LED string 340 and the second LED string 340. At least one second auxiliary rectifying diode 420 connected in the same direction may be disposed.

In addition, at least one first ripple cancellation capacitor 450 connected in parallel with the first LED strings 330; And at least one second ripple cancellation capacitor 460 connected in parallel with the second LED strings 340.

As shown, the first rectifying diodes 410 have a cathode connected to each of the first balancing capacitors 350, and the second rectifying diodes 420 have a cathode of each of the second balancing capacitors. Are connected to the field 360. An anode of the first LED string 330 is connected to an emitter terminal of the first bipolar transistors 610, and an anode of the second LED strings 340 of the second bipolar transistors 620. It is connected to the emitter terminal. The collectors of the first and second bipolar transistors 610 and 620 are commonly connected.

The current gathered at the collector side common node C of the first and second bipolar transistors 610 and 620 is the cathode side common node of the first rectifying diodes 370 and the second rectifying diodes 380. It flows to (D).

Directions of the first bipolar transistors 610 are connected such that collector-emitters are arranged in the forward direction of the first LED strings 330 forming the same current path, and the second bipolar transistors 620 Direction is connected such that the collector-emitter is arranged in the forward direction of the second LED strings 340 forming the same current path. The common connection node C of the collectors of the first bipolar transistors 610 and the second bipolar transistors 620 may be grounded.

In addition, although not shown, the LED driver may include a controller for individually adjusting the base terminal currents of the first bipolar transistors 610 and the second bipolar transistors 620.

The controller may apply an on / off current to each base terminal so that each of the first bipolar transistor 610 and the second bipolar transistor 620 operates as a kind of switch. Alternatively, the controller may apply a current having a linear value to each base terminal so that the first bipolar transistor 610 and the second bipolar transistor 620 linearly adjust the width of the current path. .

In addition, the common connection node C of the collectors of the first bipolar transistors 610 and the second bipolar transistors 620 and the caching of the first rectifying diodes 370 and the second rectifying diodes 380. A measurement resistor (not shown) may be disposed between the node side common node D. FIG.

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

On the other hand, the control unit for controlling the first / second bipolar transistors (610, 620), the control signals (C1, C2) for controlling the four switching transistors of the DC-AC converter 110, the four It can be applied to the switching transistor. In this case, the control unit receives the current flowing through the measurement resistor and performs feedback control so that the current is constant, and the control signals C1 and C2 may be used.

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

The LED driver of FIG. 8 may include first stabilization resistors 630 connected between the connection node of the first LED strings 330 and the first ripple cancellation capacitor 450 and the first auxiliary rectifying diodes 410. And further comprising first stabilizing resistors 640 connected between the connection node of the second LED strings 340 and the second ripple cancellation capacitor 460 and the second auxiliary rectifying diodes 420. . This is different from the LED driver of FIG.

Since the remaining components of FIG. 8 except for the first stabilization resistors 630 and the second stabilization resistors 640 are the same as those of FIG. 7, redundant descriptions thereof will be omitted.

The LED driver of FIG. 9 applies first MOS transistors 611 instead of the first bipolar transistors 610 of FIG. 7, and second MOS transistors 621 instead of the second bipolar transistors 620 of FIG. 7. ) Was applied. In addition, the measurement resistance 190 is not shown in FIG. 7.

Morse transistors differ from bipolar transistors in that they do not control the current path linearly, but only on / off control is possible. In addition, there is a difference even if it is controlled by a voltage rather than a current. However, as a kind of switch, the on / off operation is the same as in the case of the bipolar transistor, and thus redundant description of the function will be omitted.

Since the remaining components of FIG. 9 except for the first MOS transistors 611, the second MOS transistors 621, and the measurement resistor 190 are the same as those of FIG. 7, redundant description thereof will be omitted.

10 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 DC-AC converter 110 of FIG. 10 serves as the DC-AC converter 11 of FIG. 3, and the first / second rectifying diodes 172 and 182 and the first / second auxiliary rectifying diode of FIG. 212 and 222 (or first and second LED strings 132 and 142) serve as the rectifier 107 of FIG. 3.

The first / second balancing capacitor 152, 162 of FIG. 10 serves as the current balancing capacitor 105 of FIG. 3, and the first / second LED strings 132, 142 of FIG. Serves as the LED strings 103.

The bipolar transistors 512 of FIG. 10 perform the role of the path control element 108 of FIG. 3.

The LED driver shown in FIG. 10 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 142 that receives a current in a first direction A from an output port of the transformer unit 120; At least one second LED string 132 receiving current in a second direction B from an output port of the transformer unit 120; At least one first balancing capacitor 152 positioned between the output port of the transformer unit 120 and the second LED strings 132; At least one second balancing capacitor 162 positioned between the output port of the transformer unit 120 and the first LED strings 142; At least one first rectifying diodes (172) for forming a rectifying unidirectional current path through the first balancing capacitor (152) to the first strings (142); At least one second rectifying diodes (182) for forming a rectifying unidirectional current path through the second balancing capacitor (162) to the second strings (132); At least two first bipolar transistors 512 for adjusting a current path of each first LED string 142; At least two second bipolar transistors 522 for regulating a current path of each second LED string 132; First bypass diodes 532 forming a bypass path when the first bipolar transistors 512 are blocked; And second bypass diodes 542 forming a bypass path when the second bipolar transistors 522 are blocked.

Due to the reverse current blocking function of the first / second LED strings 132, 142 itself, the first / second rectifying diodes 172, 182 and the first / second LED strings 132, 142 Can form a kind of rectifier circuit. This is because the first / second LED strings 132 and 142 basically have a diode characteristic.

However, in order to place the first / second ripple cancellation capacitors 252 and 262 or to prevent breakage of the LED due to instantaneous high voltage reverse current, the second bipolar transistor 522 and the first At least one first auxiliary rectifying diode 222 connected to the first LED strings 142 in the same direction as the first LED strings 142 is disposed, and the first bipolar transistor 512 and the second are arranged. At least one second auxiliary rectifying diode 212 may be disposed between the LED strings 132 in the same direction as the second LED strings 132.

In addition, at least one connected in parallel with the first LED strings 142 in order to suppress the ripple component of the current flowing through the transformer unit 120 and the first and second balancing capacitors 152 and 162. First ripple cancellation capacitors 262; And at least one second ripple cancellation capacitor 252 connected in parallel with the second LED strings 132.

In addition, the current measuring device may be located at an output port of the transformer unit 120 or at 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.

A first bypass diode 532 and a second bypass diode 542 are connected to the emitter terminal and the collector terminal of each of the first bipolar transistor 512 and the second bipolar transistor 522. Each bipolar transistor and bypass diode pair acts as a switch for a kind of one-way current. This is to prevent individual control of a specific LED string in the A direction section from affecting the B direction section.

In addition, although not shown, the LED driver may include a controller for individually adjusting the base terminal currents of the first bipolar transistors 512 and the second bipolar transistors 522.

The controller may apply an on / off current to each base terminal so that each of the first bipolar transistor 512 and the second bipolar transistor 522 operates as a kind of switch. Alternatively, the controller may apply a current having a linear value to each base terminal so that the first bipolar transistor 512 and the second bipolar transistor 522 linearly adjust the width of the current path. .

The controller may apply control signals C1 and C2 to control the four switching transistors of the DC-AC converter 110 to the four switching transistors. In this case, the controller may receive the current flowing through the measurement resistor 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 alternating current pattern (for example, a sine wave) flows in the coil of the output end of the transformer unit, and the alternating current flows through the first / second balancing capacitors 152 and 162 through the first / second LED strings. 132, 142.

According to the positive direction pattern of the sine wave, when a current flows in the direction A of the transformer, the current in the A direction passes through the first LED strings 142 and the first auxiliary rectifier diode 222 subjected to the forward bias. However, the second LED strings 132 and the second auxiliary rectifier diode 212 that are reverse biased cannot pass.

Current for the first LED strings 142 flows to the node C via the first balancing capacitors 152, the first rectifying diodes 172, and the first bipolar transistors 512. The current in the A direction is circulated through the current path.

As a result, in the period in which current flows in the A direction, the first LED strings 142 are driven and the second LED strings 132 are not driven. Similarly, in the period in which current flows in the B direction, the second LED strings 132 are driven and the first LED strings 142 are not driven.

That is, the first rectifying diodes 172 and the first auxiliary rectifying diodes 222 (or the first LED strings 142) form a kind of half-wave rectifying circuit. In addition, the second rectifying diodes 182 and the second auxiliary rectifying diodes 212 (or the second LED strings 132) form a half-wave rectifying circuit. In both cases, the half-wave rectification circuit structure, but since the first LED string 142 is driven in the current section of the A direction, the second LED string 132 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 deviation of each of the first LED strings 142, 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 field 152 and the second balancing capacitors 162. Charges accumulated in the different amounts are canceled in a period in which the capacitors 152 and 162 cancel each other or a current flows 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 142, a current deviation (or a resulting luminance deviation) occurs in the first LED strings 142. I never do that. Similarly, even if there is a deviation in the forward voltage drop of each of the second LED strings 132, no current deviation (or a resulting luminance deviation) occurs in the second LED strings 132.

On the other hand, looking at the A direction current path and the B direction current path, there is no resistance component on the two current path. Therefore, it can be seen that the illustrated LED driver can greatly suppress the heat loss due to the resistive component.

On the other hand, by adjusting the base current of each of the first bipolar transistor 512 or the second bipolar transistor 522 appropriately, each of the first LED string 142 or each of the second LED string 132 is individually brightness I can regulate it. For example, the on / off current may be applied as the base current to individually adjust the brightness by the PWM control method.

The LED driver of FIG. 11 includes first stabilization resistors 562 connected between the first LED strings 142 and the connection nodes of the first ripple cancellation capacitor 262 and the first auxiliary rectifier diodes 222. It includes more. The device further includes first stabilizing resistors 552 connected between the second LED strings 132 and the connection nodes of the second ripple cancellation capacitor 252 and the second auxiliary rectifier diodes 212. This is different from the LED driver of FIG.

When the emitter terminal is switched using the first bipolar transistors 512 and the second bipolar transistors 522 grounded, the grounding property may be deteriorated. The two stabilization resistors 552 are for preventing this.

Since the remaining components of FIG. 11 except for the first stabilization resistors 562 and the second stabilization resistors 552 are the same as those of FIG. 10, redundant description thereof will be omitted.

The LED driver of FIG. 12 applies first MOS transistors 513 instead of the first bipolar transistors 512 of FIG. 10 and replaces the second MOS transistors instead of the second bipolar transistors 522 of FIG. 523) was applied. In general MOS transistor switches, since a substrate diode is formed, the first bypass diode 532 and the second bypass diode 542 of FIG. 10 are removed. However, if implemented with a field effect transistor (FET) other than the MOS transistor, the first bypass diode 532 and the second bypass diode 542 may be provided in some cases.

Morse transistors differ from bipolar transistors in that they do not control the current path linearly, but only on / off control is possible. In addition, there is a difference even if it is controlled by a voltage rather than a current. However, as a kind of switch, the on / off operation is the same as in the case of the bipolar transistor, and thus redundant description of the function will be omitted.

Since the remaining components of FIG. 12 except for the first MOS transistors 513 and the second MOS transistors 523 are the same as those of FIG. 10, redundant description thereof will be omitted.

FIG. 13 shows a structure of another embodiment of an LED driver that smoothes the driving power of LED strings in a split AC drive scheme.

The LED driver shown in FIG. 13 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 332 which receives a current in a first direction A from an output port of the transformer unit 120; At least one second LED string 342 that receives a current in a second direction B from an output port of the transformer unit 120; At least one first balancing capacitors 352 positioned between the output port of the transformer unit 120 and the first LED strings 332; At least one second balancing capacitor (362) located between the output port of the transformer section (120) and the second LED strings (342); At least one first rectifying diodes 382 for forming a rectifying unidirectional current path through the first balancing capacitor 352 to the first strings 332; At least one second rectifying diodes (372) for forming a rectifying unidirectional current path to the second strings (342) via the second balancing capacitor (362); At least two first bipolar transistors 612 for adjusting a current path of each first LED string 332; At least two second bipolar transistors 622 for regulating a current path of each second LED string 342; First bypass diodes 632 forming a bypass path when the first bipolar transistors 612 are blocked; And second bypass diodes 642 forming a bypass path when the second bipolar transistors 622 are blocked.

Due to the reverse current blocking function of the first / second LED strings 332, 342 itself, the first / second rectifying diodes 372, 382 and the first / second LED strings 332, 342 Can form a kind of rectifier circuit. This is because the first / second LED strings 332 and 342 basically have a diode characteristic.

However, to place the first / second ripple cancellation capacitors 452 and 462 or to prevent breakage of the LED due to instantaneous high voltage reverse current, the first bipolar transistor 612 and the first Placing at least one first auxiliary rectifying diode 412 connected in the same direction as the first LED strings 332 between the LED strings 332, the second bipolar transistor 622 and the second At least one second auxiliary rectifying diode 422 connected in the same direction as the second LED strings 342 may be disposed between the LED strings 342.

In addition, at least one connected in parallel with the first LED strings 332 to suppress the ripple component of the current flowing through the transformer unit 120 and the first and second balancing capacitors 352 and 362. First ripple cancellation capacitors 452; And at least one second ripple cancellation capacitor 462 connected in parallel with the second LED strings 342.

In addition, the current measuring device may be located at the output port of the transformer unit 120. 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.

The first bypass diode 632 and the second bypass diode 642 are connected to the emitter terminal and the collector terminal of each of the first bipolar transistor 612 and the second bipolar transistor 622. Each bipolar transistor and bypass diode pair acts as a switch for a kind of one-way current. This is to prevent individual control of a specific LED string in the A direction section from affecting the B direction section.

In addition, although not shown, the LED driver may include a controller for individually adjusting the base terminal currents of the first bipolar transistors 612 and the second bipolar transistors 622.

The controller may apply an on / off current to each base terminal so that each of the first bipolar transistor 612 and the second bipolar transistor 622 operates as a kind of switch. Alternatively, the controller may apply a current having a linear value to each base terminal so that the first bipolar transistor 612 and the second bipolar transistor 622 linearly adjust the width of the current path. .

The controller may apply control signals C1 and C2 to control the four switching transistors of the DC-AC converter 110 to the four switching transistors. In this case, the control unit receives the current flowing through the measurement resistor and performs feedback control so that the current is constant, and the control signals C1 and C2 may be used.

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

The LED driver of FIG. 14 includes first stabilization resistors 652 connected between the first LED strings 332 and the connection nodes of the first ripple cancellation capacitor 452 and the first auxiliary rectifying diodes 412. It includes more. The apparatus further includes first stabilizing resistors 662 connected between the second LED strings 342 and the connection nodes of the second ripple cancellation capacitor 462 and the second auxiliary rectifying diodes 422. . This is different from the LED driver of FIG.

When the emitter terminal is switched using the first bipolar transistors 612 and the second bipolar transistors 622 which are grounded, the grounding property may be deteriorated. The two stabilization resistors 662 are for preventing this.

Since the remaining components of FIG. 14 except for the first stabilization resistors 652 and the second stabilization resistors 662 are the same as those of FIG. 13, redundant descriptions thereof will be omitted.

The LED driver of FIG. 15 applies first MOS transistors 613 instead of the first bipolar transistors 612 of FIG. 13, and second MOS transistors 623 instead of the second bipolar transistors 622 of FIG. 10. ) Was applied. There is also a difference in that the directions of the first and second bypass diodes 632 and 546 are symmetrical with FIG. 12.

The remaining components of FIG. 15 except for the directions of the first MOS transistors 613, the second MOS transistors 623, and the first / second bypass diodes 632 and 546 are the same as those of FIG. 13. , Duplicate 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 circuit diagram showing an embodiment of an LED driver for smoothing the driving power of LED strings in a split AC drive scheme.

Fig. 5 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. 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.

Fig. 9 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. 10 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. 11 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. 12 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. 13 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. 14 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. 15 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 (22)

At least two LED strings; A rectifier for rectifying an AC voltage and supplying the LED strings; At least two balancing capacitors positioned in the current path of each LED string to match current balancing of the LED strings; At least two path control elements for controlling the current path of each LED string; And Control unit for controlling the path control elements LED driver comprising a. The method of claim 1, A DC-AC converter for converting a DC voltage into an AC voltage; And Transformer unit for transmitting the converted AC voltage to the rectifier LED driver comprising a. The method of claim 1, The path control elements, LED drivers, the switch elements blocking the current path of the LED strings. The method of claim 1, The path control elements, LED drivers, which are transistors that adjust the width of the current path of a corresponding LED string according to a control signal applied to a base terminal. 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 positioned between the output port of the transformer portion 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; At least one second rectifying diodes for forming a unidirectional current path for rectification between the first strings and the second balancing capacitors; First path control elements for controlling a current path of each of the first LED strings; And Second path control elements for controlling a current path of each second LED string LED driver including. The method of claim 5, The path control elements, LED drivers, which are switch elements that block the current path of a corresponding LED string in response to a control signal. The method of claim 6, The switch elements are MOS transistors or bipolar transistors. The method of claim 5, The path control elements, LED drivers, which are transistors that adjust the width of the current path of a corresponding LED string according to a control signal applied to a base terminal. The method of claim 5, One end of the first path control element is commonly connected, The common connected node is a grounded LED driver. The method of claim 5, 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 10, 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 5, 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 5, The first LED strings are arranged such that a current flows from the first balancing capacitors to the first LED strings, The second LED strings are arranged such that current flows in the direction from the second balancing capacitors to the second LED strings, The first rectifying diodes have a cathode connected to each of the first balancing capacitors, an anode connected in common, And the second rectifying diodes have a cathode connected to each of the second balancing capacitors and an anode commonly connected to the first rectifying diodes. The method of claim 5, The first LED strings are arranged such that a current flows in the direction from the first LED strings to the first balancing capacitors, The second LED strings are arranged such that current flows in the direction from the second LED strings to the second balancing capacitors, The first rectifier diodes, the anode is connected to each of the first balancing capacitor, the cathode is commonly connected, And the second rectifying diodes have an anode connected to each of the second balancing capacitors and a cathode commonly connected to the first rectifying diodes. The method of claim 5, LED driver including a DC-AC converter for converting a DC voltage applied from the outside into an AC voltage. The method of claim 5, A measurement resistor connected between the first LED strings and the second rectifying diodes LED driver including. The method of claim 16, Control the path control elements; Control unit for controlling the operation of the DC-AC converter according to the current flowing through the measurement resistance LED driver including 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 capacitor positioned between the output port of the transformer portion and the second LED strings; At least one second balancing capacitor positioned between the output port of the transformer portion and the first LED strings; At least one first rectifying diodes for forming a unidirectional current path between the first LED strings and the first balancing capacitor; At least one second rectifying diodes for forming a unidirectional current path between the second LED strings and the second balancing capacitor; First path control elements for controlling a current path of each of the first LED strings; And Second path control elements for controlling a current path of each second LED string LED driver including. The method of claim 18, At least one first auxiliary rectifying diode connected between the second path control elements 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 first path control elements and the second LED strings in the same direction as the second LED strings LED driver including. The method of claim 18, At least one first resistor coupled between the second path control elements and the first LED strings; And At least one second resistor connected between the first path control elements and the second LED strings LED driver including. The method of claim 18, 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 18, First bypass diodes respectively connected to both ends of the first path control elements; And Second bypass diodes respectively connected to both ends of the second path control elements; LED driver including.

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