WO2014208999A1 - Driver circuit for light-emitting device and operation method therefor, and semiconductor chip employing said driver circuit - Google Patents

Abstract

The present invention provides a driver circuit for a light-emitting device and an operation method therefor, and a semiconductor chip employing the driver circuit, the driver circuit being configured to detect sensing voltages corresponding to the headroom voltages of light-emitting diode strings, control an output voltage provided to the light-emitting diode strings by using the sensing voltages, and accordingly control the headroom voltages.

Description

Driving circuit and driving method of light emitting device, and semiconductor chip employing said driving circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device, and more particularly to a driving circuit and a driving method of a light emitting device, and a semiconductor chip employing the driving circuit.

The LCD backlight including the LED string is configured to be controlled by a driver. The driver generally includes a voltage converter for supplying a forward voltage corresponding to one light emitting diode string and a current regulator for determining a current of the light emitting diode string.

Current regulators can include resistors and transistors, which can be embedded in integrated circuits or configured as passive elements on a PCB. If the resistor and the transistor included in the current regulator is embedded in the integrated circuit, manufacturing cost can be reduced, but there is a problem in that heat generation needs to be solved. Therefore, when it is desired to reduce heat generation, the resistors and transistors included in the current regulator may be configured outside the integrated circuit.

The transistor included in the current regulator may be selected from a MOSFET (Metal Oxide Silicon Field Effect Transister), npn Bipolar Junction Transistor (BJT), and pnp BJT. Among them, BJT is advantageous in terms of unit price, and npn BJT is advantageous in consideration of integrated circuits.

In a conventional current regulator, when npn BJT is used and npn BJT is configured outside of the integrated circuit, the integrated circuit includes an emitter pin connected with a resistor for determining the amount of current in correspondence with the externally configured npn BJT, A base pin for driving the base current and a collector pin for monitoring the headroom voltage must be configured. That is, an integrated circuit incorporating a conventional current regulator has three pins for an external npn BJT.

The npn BJT is configured to correspond to the number of light emitting diode strings (number of channels). Therefore, an integrated circuit incorporating a current regulator must be configured with an increased number of pins as the number of LED strings (number of channels) increases.

In order to solve the above problems, circuits and algorithms that can be configured to have a small number of pins and to adjust the headroom voltage of the LED string corresponding to npn BJTs configured externally need to be presented. .

On the other hand, the brightness of the LED string may be independently controlled using a PWM signal. However, in some cases, the PWM signal may not be provided. If no PWM signal is provided, the current regulator is turned off and no headroom voltage is detected. In this case, a reference voltage for driving the DC-DC converter must be maintained to detect the headroom voltage. If the reference voltage for driving the voltage converter is not maintained, the reference voltage is reduced due to the leakage current of the capacitor to which the reference voltage is applied, and correspondingly, the output voltage is also reduced.

When the PWM signal is re-applied, flicker may occur if the lowered output voltage does not satisfy the light emitting voltage level of the LED string. Therefore, in order to eliminate the flicker generated as described above, it is necessary to maintain the reference voltage when the PWM signal is not applied for a long time.

<Preceding technical literature>

Korean Laid-Open Patent Publication No. 2008-0020723 (published March 6, 2008)

The present invention can reduce the number of pins of the integrated circuit for the npn BJT used to adjust the headroom voltage of the light emitting diode string used as the LCD backlight, and can reduce the area of the integrated circuit by reducing the number of pins. A driving circuit and method for a light emitting device and a semiconductor chip employing the driving circuit are provided.

In addition, the present invention provides a driving circuit and method for a light emitting device capable of equalizing a current flowing in the light emitting diode strings by providing the light emitting diode strings with an output voltage equal to or greater than a maximum forward voltage among the forward voltages of the light emitting diode strings, and the driving circuit. It provides a semiconductor chip employing.

The present invention relates to a driving circuit and method of a light emitting device capable of maintaining a reference voltage for driving a voltage converter in response to a case where a PWM signal provided for determining the current of light emitting diode strings is not provided. Provided is a semiconductor chip.

In order to achieve the above object, a driving circuit of a light emitting device for driving at least one light emitting diode string of the present invention comprises: a voltage converter for providing an output voltage to the light emitting diode string; A driving controller controlling the voltage converter in response to a compensation signal; And a head configured to perform current regulation on at least one LED string, provide a reference voltage corresponding to headroom voltages of at least one LED string, and provide the compensation signal using the reference voltage. And a room voltage control unit, wherein the headroom voltage control unit receives at least one control signal for current regulation control corresponding to at least one of the light emitting diode strings, and corresponds to at least one control signal in a predetermined state. The reference voltage is maintained in order to maintain the output voltage.

The semiconductor chip of the present invention may include: a reference voltage holding determination unit determining whether a predetermined state is referred to by referring to at least one control signal for current regulation control corresponding to at least one LED string; A reference voltage unit configured to supply a sustain voltage in response to the predetermined state by a control of the reference voltage sustain determination unit to provide an output voltage to at least one LED string; And a voltage supply controller for switching the transfer of the sustain voltage to a node that outputs a reference voltage used to provide the output voltage.

A method of driving a light emitting device of the present invention includes a first step of controlling light emission by providing a control signal to a current regulator connected to at least one light emitting diode string; And when the control signal is provided to correspond to a predetermined state corresponding to at least one of the current regulation of the entirety of the light emitting diode string is stopped or no headroom voltages are detected. And a second step of maintaining the provided output voltage.

According to the present invention, the headroom voltage of the LED string used as the LCD backlight can be adjusted, and the number of pins of the integrated circuit corresponding to npn BJT for adjusting the headroom voltage can be reduced. Therefore, the integrated circuit can be designed to have a reduced area as the number of pins is saved.

Further, according to the present invention, since the driving circuit controls the output voltage provided to the LED strings based on the maximum forward voltage among the forward voltages of the LED strings, the current flowing through the LED strings can be equalized.

Further, according to the present invention, it is possible to maintain a reference voltage for driving the voltage converter when no PWM signals are provided, and consequently to maintain a reference voltage for adjusting the output voltage when not detected. As a result, when the PWM signal is re-applied, it is possible to maintain a sufficient output voltage that satisfies the light emitting voltage level of the light emitting diode string, and prevent flickering.

1 shows a driving circuit of a light emitting device according to an embodiment of the present invention;

2 is a graph illustrating a relationship between a sensing voltage and a headroom voltage according to an embodiment of the present invention.

3 is a flowchart illustrating a control operation according to an embodiment of the present invention.

4 is a detailed circuit diagram of a driving circuit according to an embodiment of the present invention.

FIG. 5 is a circuit diagram illustrating the current regulator and the current sensing unit of FIG. 4. FIG.

6 is a circuit diagram of a current compensator further configured in the embodiment of FIG. 5;

FIG. 7 is a circuit diagram of the reference voltage controller of FIG. 4. FIG.

8 is a diagram illustrating a reference voltage holding unit of FIG. 7.

9 is a circuit diagram of a reference voltage holding unit of FIG. 8.

The present invention discloses a driving circuit and method for a light emitting device and a semiconductor chip employing the driving circuit. The drive circuit of the device of the present invention may be implemented by driving a string of light emitting diodes (LEDs) constituting a backlight for supplying light to a liquid crystal display (LCD).

The driving circuit of the present invention senses sensing voltages corresponding to headroom voltages of a plurality of LED strings connected in parallel with each other, and based on the sensed sensing voltages, the current headroom. Adjust the voltage. Here, the headroom voltage refers to the voltage of the node between the light emitting diode string and the corresponding headroom voltage controller, and may be, for example, a voltage corresponding to a product of a current flowing through the light emitting diode string and a resistor electrically connected to the light emitting diode string. have.

In general, light emitting devices are designed such that the currents flowing through the light emitting diode strings are uniform. However, the actual forward voltage of the LED strings may vary due to various reasons. As a result, the headroom voltages of the LED strings may also vary.

The present invention can sense the sensing voltages corresponding to the headroom voltages and control the output voltage provided to the LED strings to satisfy the maximum forward voltage of the forward voltages of the LED strings in response to the sensing voltages. .

In this case, the reason for controlling the output voltage based on the maximum forward voltage is that when the output voltage provided to the LED strings is controlled based on a voltage smaller than the maximum forward voltage, the LED strings corresponding to the maximum forward voltage are normally This is because the light emitting operation may not be performed.

That is, when the light emitting diode string corresponding to the maximum forward voltage is provided to the light emitting diode strings with an output voltage that can normally operate, for example, an output voltage of a DC-DC converter, which is a voltage converter, the light emitting diode corresponding to the maximum forward voltage Not only the string but also the remaining LED strings may normally perform light emitting operations. Therefore, the present invention can control the output voltage provided to the LED strings to be equal to or greater than the maximum forward voltage.

In addition, the present invention proposes a circuit structure in which pins (eg, pads) are configured in an integrated circuit to sense a sensing voltage corresponding to a headroom voltage and the number of pins can be reduced while adjusting the headroom voltage.

On the other hand, in order to individually control the LED strings, respective control signals, for example PWM signals, may be provided to the LED strings. When there is no need to drive the LED strings, for example when the LCD power is off and there is no need to drive the backlight, the control signals may not be provided to the LED strings.

For example, a state in which the current regulation for the whole of the light emitting diode string is stopped or the headroom voltages of the entire light emitting diode string are not detected may be defined as a predetermined state, and the state of the light emitting diode strings may correspond to the predetermined state. The control signal for the current regulation control may not be provided as described above.

At this time, the reference voltage used to adjust the output voltage is gradually down by the influence of leakage current, etc., and as a result, the output voltage may be lowered. In such an environment, when the control signals are provided back to the LED strings, the lowered output voltage may not satisfy the maximum forward voltage. As a result, the brightness of the light emitting device is not constant, and a flicker phenomenon in which the brightness changes with time may occur.

Therefore, it is necessary to maintain the reference voltage even if the control signals are not provided in the light emitting diode strings, and the present invention proposes a circuit structure for maintaining the reference voltage. Detailed description thereof will be described later.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. For convenience of explanation, the light emitting device is assumed to be a backlight including LEDs.

Referring to FIG. 1, the light emitting device of the present embodiment includes a driving circuit 110 and a light emitting unit 102.

The driving circuit 110 may include a voltage converter 100, a driving controller 104, and a headroom voltage controller 106. According to an exemplary embodiment, the driving circuit 110 may be implemented as an integrated circuit, that is, a single semiconductor chip, including all or a part of components. However, the LED of the headroom voltage controller 106 may be used for current regulation. The transistor T1 and the resistor R3 connected to the string may be formed outside the semiconductor chip. Its structure is shown in FIG. Here, the transistor T1 may be composed of npn BJT.

The light emitting unit 102 may include at least one light emitting diode string, and for example, may include three light emitting diode strings ST1 to ST3. Each of the LED strings ST1 to ST3 may include a plurality of LEDs connected in series with one or more LEDrks. In addition, the LED strings ST1 to ST3 are connected in parallel with each other. In FIG. 1, only three LED strings ST1 to ST3 are illustrated, but at least one LED string is sufficient. In addition, although only three LEDs are shown for each LED string ST1 to ST3 in FIG. 1, at least one LED is sufficient, and at least one of the LED strings ST1 to ST3 may include a different number of LEDs. have. Meanwhile, the LED strings ST1 to ST3 may be individually controlled.

The voltage converter 100 converts the input voltage Vin to generate an output voltage Vout, and provides the output voltage Vout to the light emitting unit 102. For example, the voltage converter 100 may be a DC-DC converter as a boosting converter. That is, the voltage converter 100 may boost the input voltage Vin to generate an output voltage Vout. The output voltage Vout should be controlled to have a sufficient size to emit all of the LEDs of the LED strings ST1 to ST3.

The driving controller 104 controls the voltage converter 100 to provide the light emitting unit 102 with an output voltage Vout through which the LEDs of the LED strings ST1 to ST3 can emit light. According to an embodiment, the driving controller 104 may control the voltage converter 100 using a pulse width modulation (PWM) scheme. However, the control method of the drive control unit 104 may be used other than the PWM method, for example, a constant current control method may be used.

The headroom voltage controller 106 is connected to the LED strings ST1 to ST3, respectively, and senses sensing voltages corresponding to the headroom voltages that are voltages applied to the LED strings ST1 to ST3. According to the design, forward voltages of the LED strings ST1 to ST3 should be the same. However, due to various reasons, the forward voltages of the LED strings ST1 to ST3 may vary. Accordingly, headroom voltages of the LED strings ST1 to ST3 may vary. Here, the forward voltage refers to the total voltage required to emit the LEDs of the LED strings ST1 to ST3 of FIG. 1.

The headroom voltage controller 106 adjusts the headroom voltages by sensing sensing voltages corresponding to the headroom voltages of the LED strings ST1 to ST3.

According to an embodiment, the headroom voltage controller 106 controls the drive controller 104 to satisfy the maximum forward voltage among the forward voltages, and correspondingly, the drive controller 104 controls the voltage of the voltage converter 100. Adjust the magnitude of the output voltage (Vout). Preferably, the headroom voltage controller 106 controls the output voltage Vout in response to the sensing voltages such that the output voltage Vout is equal to or greater than the maximum forward voltage.

According to another embodiment, the headroom voltage controller 106 determines whether headroom voltages corresponding to the sensing voltages exist in the headroom voltage range, and according to the determination result, the current headroom voltage is the headroom voltage. Adjust the output voltage (Vout) to be in range.

According to another embodiment, the headroom voltage control unit 106 receives control signals CS1, CS2 and CS3, which are, for example, PWM signals. However, the headroom voltage controller 106 may maintain a reference voltage for adjusting the output voltage Vout so that the output voltage Vout is not lowered when the control signals CS1, CS2, and CS3 are not received. Meanwhile, the control signals CS1, CS2, and CS3 may be provided to corresponding current regulators and reference voltage controllers, respectively. By the control signals CS1, CS2, and CS3, current regulation of each current regulator with respect to the light emitting diode strings ST1 to ST3 may be individually controlled, and a reference voltage provided by the reference voltage controller may be maintained. Detailed description thereof will be described later.

According to another embodiment, when the headroom voltage controller 106 cannot sense sensing voltages corresponding to the headroom voltages of the LED strings ST1 to ST3, the headroom voltage controller 106 may execute an operation for maintaining the reference voltage. Can be.

In summary, the light emitting device driving circuit 110 senses sensing voltages corresponding to the headroom voltages of the light emitting diode strings ST1 to ST3, and maximizes the forward direction with respect to the light emitting diode strings ST1 to ST3. The output voltage Vout provided to the light emitting unit 102 is adjusted using the sensing voltage to satisfy the voltage. Of course, if it is determined that the output voltage Vout satisfies the maximum forward voltage, the driving circuit 110 may maintain the output voltage Vout of the voltage converter 100.

In addition, the driving circuit 110 may not provide the control signals CS1, CS2, and CS3 to the LED strings ST1 to ST3 or sense the headroom voltages of the LED strings ST1 to ST3. The output voltage Vout is maintained when no voltages are detected, and as a result, flicker occurs when the control signals CS1, CS2, and CS3 are provided back to the LED strings ST1, ST2, and ST3. You can prevent it.

FIG. 2 illustrates a relationship between a headroom voltage Vheadroom and a sensing voltage Vsense obtained by converting a current flowing through a light emitting diode string into a voltage. Here, the sensing voltage Vsense is inversely related to the headroom voltage Vheadroom. This is because an npn Bipolar Junction Transistor (BJT) is used to sense currents flowing in the LED strings as described below.

As shown in FIG. 2, the set voltage range may be defined as a section between the lowest set voltage V _HL and the maximum set voltage V _HH , and the set voltage range is set by the user to control the headroom voltage Vheadroom. The headroom voltage range. The set voltage range may vary depending on the type of light emitting device, the structure of a circuit for sensing a current flowing through the light emitting diode strings, and the like.

According to one embodiment, the reference sensing voltages for determining the sensing voltage (Vsense) corresponding to the maximum set voltage (V _HH ) and the minimum set voltage (V _HL ) defining the set voltage range of the headroom voltage (Vheadroom) (V _REFH and V _REFL ) can be set. The driving circuit 110 compares the sensing voltage Vsense with the reference sensing voltages V _REFH and V _REFL , respectively, and maintains or adjusts the current headroom voltage based on the comparison result. Detailed description thereof will be described with reference to FIG. 3.

Referring to FIG. 3, when the voltage converter 100 outputs an output voltage Vout, LEDs of the LED strings ST1 to ST3 emit light (S300).

The headroom voltage controller 106 detects sensing voltages corresponding to currents flowing through the LED strings ST1 to ST3 (S302). For example, the headroom voltage controller 106 may detect sensing currents by sensing currents flowing through each LED string using npn BJT. Using npn BJT, the drive circuit 110 can be manufactured at low cost and can be advantageous for integration.

The headroom voltage controller 106 determines whether at least one of the headroom voltages of each of the LED strings ST1 to ST3 is smaller than the lowest set voltage V _HL in the set voltage range using the sensing voltages (S304). ). If the headroom voltage is less than the lowest set voltage (V _HL ), it means that the output voltage (Vout) does not satisfy the maximum forward voltage, so that the LEDs of the light emitting diode string with the maximum forward voltage will not operate normally. Most likely. Since the backlight does not operate normally when the headroom voltage is lower than the minimum set voltage V _HL for the above reason, the output voltage Vout of the voltage converter 100 so that all the headroom voltages are equal to or greater than the minimum set voltage V _HL . This must be adjusted. All headroom voltages above the minimum set voltage V _HL means that the output voltage Vout satisfies the maximum forward voltage. If the output voltage Vout satisfies the maximum forward voltage, all the LED strings ( ST1 to ST3) may operate normally.

If at least one of the headroom voltages corresponding to the sensing voltages is smaller than the lowest set voltage V _HL , the driving controller 104 controls the voltage converter 100 to raise the output voltage Vout (S306). ).

If all of the headroom voltages corresponding to the sensing voltages are equal to or greater than the minimum set voltage V _HL , the headroom voltage controller 106 determines whether all the headroom voltages are greater than the maximum set voltage V _HH ( S308). When all the headroom voltages are equal to or greater than the maximum set voltage V _HH , the LEDs of the LED strings ST1 to ST3 emit light normally. However, in this case, heat may occur considerably in the npn BJT sensing the sensing voltage, and there is a possibility that the npn BJT cannot perform normal operation due to the heat. Therefore, the driving circuit 110 preferably controls all the headroom voltages not to be greater than the maximum set voltage V _HH .

If all of the headroom voltages are greater than the maximum set voltage V _HH , the driving controller 104 controls the voltage converter 100 to lower the output voltage Vout (S306).

On the other hand, if all the headroom voltages are above the minimum set voltage V _HL and below the maximum set voltage V _HH , the driving circuit maintains the current output voltage Vout (S310).

However, step S308 may be omitted. In this case, when all of the headroom voltages are equal to or greater than the minimum set voltage V _HL , the driving circuit 110 maintains the current output voltage Vout (S310).

In summary, the driving circuit of the present invention controls the output voltage Vout such that all headroom voltages are at least the minimum set voltage V _HL .

Hereinafter, the detailed structure of the driving circuit 110 will be described with reference to the accompanying drawings.

4 is a detailed circuit diagram of a driving circuit according to an embodiment of the present invention. In FIG. 4, the sensing voltage detectors 400b and 400c may have the same or similar structure as the sensing voltage detector 400a. Therefore, only the sensing voltage detector 400a is illustrated in detail, and detailed description of the sensing voltage detectors 400b and 400 dml is omitted.

Referring to FIG. 4, the voltage converter 100 may be a DC-DC converter including one transformer, a diode, and a capacitor, and is preferably a boost converter. However, the voltage converter 100 may be configured of various circuits, and there is no limitation as long as it can boost the input voltage Vin.

The transformer and the diode are connected in series, and the node n1 between the transformer and the diode is connected with the transistor T3 of the driving controller 104. The output node n2 of the diode is connected to the light emitting unit 102.

The headroom voltage controller 106 may include sensing voltage detectors 400a to 400c and a headroom voltage controller 402. The sensing voltage detectors 400a to 400c are configured one-to-one with the LED strings ST1 to ST3.

The sensing voltage detector 400a may include a current regulator 410 and a current detector 412.

The current regulator 410 includes a sensing circuit, which senses a current flowing through the LED string ST1. For example, the sensing circuit may include a transistor T1 composed of npn BJT. The npn BJT has a characteristic that the current of the base increases in proportion to a decrease in the voltage between the collector and the emitter. Accordingly, as shown in FIG. 2, the headroom voltage Vheadroom is inversely related to the sensing voltage Vsense corresponding to the current flowing through the base of npn BJT.

The current sensing unit 412 may sense a current flowing through the base of the transistor T1 through the current regulator 410. The collector of transistor T1 is connected to the output terminal of the last LED of light emitting diode string ST1, the emitter is connected to ground through resistor R3, and the base is connected to current sensing unit 412 through transistor T2. Can be connected. Although the sensing circuit has been described as including one transistor T1 which is npn BJT, the sensing circuit 412 may be variously modified to detect the current flowing through the LED string.

The current regulator 410 controls the current flowing through the sensing circuit in response to the current flowing through the light emitting diode string ST1, and more specifically, the current flowing through the base of the transistor T1. To this end, the current regulator 410 may include a transistor T2, a sensing resistor R3, a first comparator 430, and a switch SW.

Transistor T2 controls the current and may be configured as an N-channel MOS transistor. The drain of the transistor T2 is connected to the current sensing unit 412, and the source is connected to the base of the transistor T1.

The sensing resistor R3 is used to detect a current flowing through the light emitting diode string ST1. Specifically, when the current flowing through the light emitting diode string ST1 is changed, the voltage across the sensing resistor R3 (hereinafter, referred to as a “sampling voltage”) is changed, and the sampling voltage is inverted by the first comparator 430. Input to terminal (-).

The first comparator 430 compares the sampling voltage with the reference regulator voltage V _{REF_CH} and provides a voltage corresponding to the comparison result to the gate of the transistor T2. As a result, the amount of current flowing through the transistor T2 is controlled by the voltage output from the first comparator 430. That is, the current regulator 410 regulates the current provided to the current sensing unit 412 in response to the change of the current flowing through the light emitting diode string ST1.

The switch SW is connected between the first comparator 430 and the gate of the transistor T2, and the on / off may be controlled by the control signal CS1. Therefore, the light emission operation of the LEDs of the LED string ST1 may be controlled by the control signal CS1. Accordingly, the light emission operation of the LED strings ST1 to ST3 may be individually controlled by the control signals CS1, CS2, and CS3.

Unlike the above description, another embodiment may be configured. In another embodiment, the switch SW is not configured between the first comparator 430 and the transistor T2 and the control signal CS1 is configured as the first comparator 430 or It can be configured to directly control the transistor T2.

The current detector 412 detects a sensing voltage Vsense corresponding to the headroom voltage Vheadroom of the light emitting diode string ST1 using the current provided from the current regulator 410. Specific circuit structure and operation of the current sensing unit 412 will be described later.

The headroom voltage adjusting unit 402 determines whether to adjust the headroom voltage Vheadroom, and outputs a compensation signal COMP for adjusting the output voltage Vout when it is determined that adjustment is necessary, and the voltage adjusting determining unit 414. ), A reference voltage controller 416, and a second comparator 418.

The voltage regulation determiner 414 is connected to the current detectors 412 of the sensing voltage detectors 400a to 400c.

The voltage adjustment determiner 414 determines whether to adjust the current headroom voltages of the LED strings ST1 to ST3 by using the detection results provided by the current detectors 412 of the sensing voltage detectors 400a to 400c. Determine whether or not. For example, when the at least one headroom voltage is less than the lowest set voltage V _HL , the voltage regulation determiner 414 increases the output voltage Vout of the voltage converter 100 to increase the headroom voltage. You can decide to do so. In addition, the voltage regulation determining unit 414 may lower the output voltage Vout of the voltage converter 100 to bring the headroom voltages down when all sensed headroom voltages are greater than the maximum set voltage V _HH . You can decide.

According to an embodiment, the voltage adjustment determiner 414 outputs an UP signal UP when determining that the output voltage Vout is increased, and outputs a DOWN signal DOWN when determining the down of the output voltage Vout. do. However, the voltage adjustment determiner 414 may not output any signal when maintaining the output voltage Vout.

The reference voltage controller 416 adjusts the magnitude of the reference voltage REF input to the non-inverting terminal + of the second comparator 418 according to the signal provided from the voltage adjusting determiner 414. For example, the reference voltage controller 416 may increase the reference voltage REF when receiving the UP signal from the voltage adjustment determiner 414 and decrease the reference voltage REF when receiving the DOWN signal. .

According to one embodiment, control signals CS1, CS2, and CS3 provided to the current regulators 410 are also provided to the reference voltage controller 416. The reference voltage controller 416 maintains a reference voltage REF when all control signals CS1, CS2, and CS3 are not input. Here, not all control signals CS1, CS2, and CS3 are input, which means that no pulse is input in the case of a PWM signal. Detailed description thereof will be described later.

According to another embodiment, the reference voltage controller 416 may maintain the reference voltage REF when the sensing voltages corresponding to the headroom voltages of all the LED strings ST1 to ST3 are not detected.

The second comparator 418 may be configured as an error amplifier. The non-inverting terminal (+) is connected to the reference voltage controller 416 and the inverting terminal (-) is connected to the output voltage detector 428. do. As a result, the reference voltage REF is input to the non-inverting terminal + of the second comparator 418, and the detection voltage V _det is input to the inverting terminal −. The detection voltage V _det is a voltage formed by the voltage of the node n2, that is, the output voltage Vout is divided by the resistors R1 and R2, and the node n4 between the resistors R1 and R2. Means the voltage.

The second comparator 418 compares the reference voltage REF with the detection voltage V _det and outputs a compensation signal COMP. For example, if the reference voltage REF raised according to the UP signal is compared with the detection voltage V _det , the reference voltage REF is likely to be greater than the detection voltage V _det . In this case, the second comparator 418 may output the compensation signal COMP to increase the output voltage Vout. On the other hand, when the reference voltage REF reduced according to the DOWN signal and the detection voltage V _det are compared, the reference voltage REF is likely to be smaller than the detection voltage V _det . In this case, the second comparator 418 may output the compensation signal COMP to lower the output voltage Vout.

A capacitor C may be connected to a node between the second comparator 418 and the reference voltage controller 416, and the capacitor C may serve to stably maintain the reference voltage REF.

The driving controller 104 may include a third comparator 420, a PWM driver 422, a transistor T3, a resistor R4, and an output voltage detector 428 as a switch. Here, the transistor T3 may be configured as an N-channel MOS transistor.

The inverting terminal (-) of the third comparator 420 may be connected to the output terminal of the second comparator 418, and the non-inverting terminal (+) may be connected to a node n3 corresponding to the source of the transistor T3. The third comparator 420 compares the voltage of the node n3 with the compensation signal COMP output from the second comparator 418 and outputs a specific voltage.

The PWM driver 422 outputs a PWM signal according to the voltage output from the third comparator 420 to control the voltage converter 100, and as a result, the output voltage Vout is adjusted. For example, the PWM driver 422 may output a PWM signal having a variable duty ratio in response to the voltage output from the third comparator 420 to increase or decrease the output voltage Vout. According to one embodiment, the PWM driver 422 may include a PWM logic unit and a driver, the PWM logic unit is connected to the output terminal of the third comparator 420, the driver is the PWM logic unit and the transistor (T3) Can be connected between. The driver may be composed of one buffer or may be formed by combining several other circuit elements.

In the above, the output voltage Vout is adjusted through the PWM method, but another control method may be used.

According to another embodiment, the driving controller 104 may further include a current sensing unit and a slope compensating unit. The current sensing unit may be connected between the node n3 and the non-inverting terminal + of the third comparator 420. The current detector detects a current input to the light emitter 102, that is, predicts a current flowing to the node n1 through a current flowing through the node n3. Subsequently, the current detector outputs a voltage corresponding to the predicted current.

The slope compensator compensates for the current flowing to the current detector. When the duty ratio of the current sensing unit is 50% or more, for example, current may oscillate, and the slope compensator serves to compensate for the current.

Next, the operation of the driving circuit 110 will be described.

The sensing voltage detectors 400a to 400c detect headroom voltages of the corresponding LED strings ST1 to ST3. In detail, the current sensing unit 412 of the sensing voltage sensing unit 400 senses a sensing voltage Vsense corresponding to the headroom voltage by using a current flowing to the base of the transistor T1 connected to the corresponding LED string. do.

Subsequently, the voltage adjustment determiner 414 determines whether to adjust current headroom voltages in response to a result of analyzing the sensing voltages Vsense sensed by the sensing voltage sensing units 400a to 400c.

When the voltage regulation determining unit 414 determines that the headroom voltages are adjusted, the reference voltage controller 416 varies the reference voltage REF under the control of the voltage regulation determination unit 414.

Subsequently, the second comparator 418 compares the variable reference voltage REF with the detection voltage V _det corresponding to the output voltage Vout provided to the light emitting unit 102, and compensates the compensation signal ( COMP) output.

The driving controller 104 compares the compensation signal COMP provided from the second comparator 418 with the voltage corresponding to the current input to the light emitting unit 102 and operates the voltage converter 100 in a PWM manner according to the comparison result. Control the output voltage (Vout).

The driving circuit of the present invention repeats the above process to provide the light emitting unit 102 with an output voltage Vout for ensuring a maximum forward voltage.

Hereinafter, operations of the current sensing unit 412 for sensing the current of the LED string and the voltage regulation determining unit 414 for determining the voltage regulation in response to the sensing result will be described.

Referring to FIG. 5, the current detector 412 of the present embodiment may include a mirror 500 and a headroom voltage determiner 502.

The mirror unit 500 may be configured as a current mirror circuit including two P-channel MOS transistors T4 and T5, and a gate of the MOS transistor T4 and a gate of the MOS transistor T5 are coupled to each other. . The drain and the gate of the MOS transistor T4 are connected to each other.

The mirror unit 500 may be configured such that current smaller than the base current of the transistor T1 flows through the transistor T5 by mirroring, thereby scaling the current. Of course, a current having the same magnitude as that of the base of the transistor T1 can be designed to flow through the transistor T5 by mirroring. However, in consideration of power consumption, it is preferable that a current smaller than the current of the base of the transistor T1 corresponding to the current flowing through the LED string flows through the transistor T5 by mirroring.

According to the operation of the mirror unit 500, a current corresponding to the current flowing through the LED string flows through the transistor T5, and the voltage of the drain of the transistor T5, that is, the sensing voltage Vsense, of the LED string It will reflect the headroom voltage (Vheadroom).

The headroom voltage determination unit 502 may determine whether the headroom voltage Vheadroom exists in the set voltage range V _HL to V _HH shown in FIG. 2 using the sensing voltage Vsense. For example, the headroom voltage determination unit 502 may sense the sensing voltage Vsense corresponding to the headroom voltage Vheadense by comparing the sensing voltage Vsense with the reference sensing voltages V _REFH and V _REFL . Is compared with the minimum set voltage V _HL and the maximum set voltage V _HH in the set voltage range V _HL to V _HH .

According to an embodiment, the headroom voltage determiner 502 may include a fourth comparator 510 and a fifth comparator 512.

The first reference sensing voltage V _REFL is input to the non-inverting terminal + of the fourth comparator 510, and the sensing voltage Vsense is input to the inverting terminal −. Accordingly, the fourth comparator 510 compares the first reference sensing voltage V _REFL with the sensing voltage Vsense and outputs a voltage V _HIGH according to the comparison result. Specifically, the fourth comparator 510 outputs a voltage V _HIGH , which is a digital signal having high logic, when the sensing voltage Vsense is equal to or less than the first reference voltage V _REFL . According to the graph of FIG. 2, the fourth comparator 510 outputs the voltage V _HIGH having the high logic such that the headroom voltage Vheadroom corresponding to the sensing voltage Vsense is equal to or greater than the maximum set voltage V _HH . it means. On the other hand, the fourth comparator 510 outputs a voltage V _HIGH , which is a digital signal having a low logic, when the sensing voltage Vsense is greater than the first reference voltage V _REFL . According to the graph of FIG. 2, the fourth comparator 510 outputs a voltage V _HIGH having a low logic such that the headroom voltage Vheadroom corresponding to the sensing voltage Vsense is smaller than the maximum set voltage V _HH . Means.

The sensing voltage Vsense is input to the non-inverting terminal + of the fifth comparator 512, and the second reference sensing voltage V _REFH is input to the inverting terminal −. Accordingly, the fifth comparator 512 compares the second reference sensing voltage V _REFH and the sensing voltage Vsense, and outputs a voltage V _LOW which is a digital signal according to the comparison result. Specifically, the fifth comparator 512 outputs a voltage V _LOW having a high logic when the sensing voltage Vsense is equal to or greater than the second reference voltage V _REFH . According to the graph of FIG. 2, the fifth comparator 512 outputs the voltage V _LOW having the high logic such that the headroom voltage Vheadroom corresponding to the sensing voltage Vsense is less than or equal to the minimum set voltage V _HL . it means. On the other hand, the fifth comparator 512 outputs a voltage V _LOW having a low logic when the sensing voltage Vsense is smaller than the second reference sensing voltage V _REFH . According to the graph of FIG. 2, the fifth comparator 512 outputs the voltage V _LOW having the low logic such that the headroom voltage Vheadroom corresponding to the sensing voltage Vsense is greater than the minimum set voltage V _HL . it means.

That is, the outputs V _HIGH and V _LOW of the comparators 510 and 512 have a headroom voltage Vheadroom which eodmds to the sensing voltage Vsense at any point of the set voltage range V _HL to V _HH . Express information about whether

Therefore, the voltage adjustment determination unit 414 may determine whether to adjust the output voltage Vout by determining the current headroom voltages Vheadroom of the LED strings ST1 to ST3.

Specifically, when the outputs V _HIGH of the fourth comparator 510 of the current sensing units 412 are zero and the outputs V _LOW of the fifth comparator 512 are zero, the voltage regulation determination unit 414. Determines that the headroom voltages Vheadroom are appropriate and maintains the output voltage Vout.

However, when at least one of the outputs V _LOW of the fifth comparator 512 of the current sensing units 412 is 1, the voltage regulation determination unit 414 may determine at least one of the headroom voltages Vheadroom of the LED strings. It is determined that one is smaller than the headroom voltage corresponding to the maximum forward voltage, and the output voltage Vout is increased.

On the other hand, when the outputs V _HIGH of the fourth comparator 510 of the current sensing units 412 are all 1, the voltage regulation determination unit 414 determines that the headroom voltages of the LED strings are the maximum forward direction. It is determined that the headroom voltage corresponding to the voltage is exceeded, and the output voltage Vout is determined to be lowered.

As described above, the driving circuit 110 of the present invention compares the sensing voltage Vsense with the reference sensing voltages V _REFH and V _REFL , outputs the comparison result as a digital signal, and outputs the output voltage Vout. Decide if you want to adjust.

Although not described above, as illustrated in FIG. 5, the transistor T1 is configured outside the semiconductor chip, and the first comparator 430 and the transistor T2 are configured inside the semiconductor chip. Therefore, in the semiconductor chip, a first pad P1 connecting the base of the transistor T1 and the transistor T2, and an emitter of the transistor T1 and the inverting terminal (−) of the first comparator 430 are connected. There are two pads P2. The pads P1 and P2 refer to pins of an integrated circuit. That is, two pads P1 and P2 are used to correspond to the sensing voltage sensing units 400a to 400c, respectively.

The driving circuit 110 of the present invention includes both an emitter pin connected to the resistor R3 for connecting with the transistor T1, a pin for driving the current of the base, and a collector pin for monitoring the optimal headroom voltage. I don't need it. The drive circuit 110 of the present invention is configured to monitor the optimum headroom voltage using the current flowing to the base of the transistor T1, thereby eliminating the need for a collector pin for monitoring the headroom voltage.

As a result, the driving circuit 110 of the present invention can use one pin less in correspondence to each of the LED strings ST1 to ST3. That is, the driving circuit 110 of the present invention uses the first pin P1 and the emitter of the transistor T1 connected to the base of the transistor T1 to monitor the current flowing through the base of the transistor T1. Only the second pin P2 connected to the emitter of the transistor T1 is needed to monitor the flowing current, ie the current flowing through the corresponding LED string. Therefore, the driving circuit 110 can be simplified in configuration and can reduce the area of the semiconductor chip. Here, the second pin P2 may be connected to the collector instead of the emitter of the transistor T1 to monitor the current flowing through the corresponding LED string.

Based on the pins P1 and P2, the left circuits in FIG. 5 correspond to a semiconductor chip implemented as an integrated circuit, and the right circuits correspond to the outside of the semiconductor chip.

In addition to the circuit elements of FIG. 5, the driving circuit 110 of the present embodiment may further include a current compensator 600 as shown in FIG. 6. The current compensator 600 may have a mirror structure and include two transistors T7 and T8 having gates coupled to each other, and the two transistors T7 and T8 may be configured as PMOS transistors. The source of transistor T7 is connected to a node between emitter of transistor T1 and resistor R3 through panel P2, and the source and gate of transistor T8 are connected to each other. In addition, the transistor T8 is connected to the mirror part 500.

The current compensator 600 senses a base current i _b flowing to the base of the transistor T1 and compensates for the base current. Specifically, in the design of the driving circuit of the present invention, the current (collector current i _c ) flowing to the light emitting diode string may be designed to be the voltage / R3 of the node n5, but the current flows to the base of the transistor T1. The collector current i _c may actually be the voltage / R 3 -base current of node n5. Here, the voltage of the node n5 may be preferably V _{REF_CH} .

Accordingly, the present invention can compensate the collector current i _c by the base current i _b using the current compensator 600, and as a result, the collector current i _c is the voltage / R3 of the node n5. Can be made with

Meanwhile, the mirror unit 500 may further include a transistor T6 connected in parallel to the transistor T4 and transferring the mirrored current to the transistor T8. As a result, the base current i _b of the transistor T1 is mirrored to the line corresponding to the transistor T6. In addition, the current flowing to the transistor T6 is mirrored to the transistor T7. As a result, as shown in FIG. 6, the base current i _b flows through the transistor T7, so that the current flowing through the node n5 becomes equal to the collector current i _c . In this case, since the voltage of the node n5 is V _{REF_CH} , the current flowing through the node n5 is the voltage / R3 of the node n5. In other words, the collector current i _c may be the voltage / R3 of the node n5.

In summary, using the current compensator 600 of the present invention, even when a current flows through the base of the transistor T1, the collector current i _c can be made the voltage / R3 of the node n5.

7 is a diagram illustrating a reference voltage controller according to an embodiment of the present invention.

Referring to FIG. 7, the reference voltage controller 416 of the present exemplary embodiment may include a reference voltage booster 700, a reference voltage booster 702, and a reference voltage maintainer 704. The reference voltage booster 700, the reference voltage booster 702, and the reference voltage maintainer 704 are connected in parallel to the node n6. The reference voltage REF is applied to the node n6.

The reference voltage booster 700 boosts the reference voltage REF according to the UP signal UP output from the voltage adjustment determiner 414. According to an embodiment, the reference voltage booster 700 may include MOS transistors T10, T12, and T13 and an inverter of a P channel. The MOS transistors T10 and T12 are connected in series, an UP signal UP is applied to a gate of the MOS transistor T10 through an inverter, and an operating voltage Vcc which is a pull-up voltage to a source of the MOS transistor T10. Is applied. The drain of the MOS transistor T12 is connected to the node n6. In addition, the gates of the MOS transistors T12 and T13 are coupled to each other, and the gate and the drain of the MOS transistor T13 are configured to be commonly connected to a current source. The transistor T12 has a structure in which a current is mirrored with the transistor T13.

When the high logic UP signal UP is input to the reference voltage booster 700, a low logic is input to the gate of the transistor T10, and the transistor T10 is turned on. The reference voltage REF is raised in conjunction with the turn-on of the transistor T10. When the UP signal UP having the low logic is input to the reference voltage booster 700, the transistor T10 is turned off.

The reference voltage step-down part 702 performs a function of stepping down the reference voltage REF according to the DOWN signal DOWN output from the voltage adjustment determiner 414. According to an embodiment, the reference voltage step-down part 702 may include N-channel MOS transistors T11, T14, and T15. The MOS transistors T14 and T11 are connected in series, a DOWN signal DOWN is applied to the gate of the MOS transistor T11, and a ground voltage Vcc, which is a pull-down voltage, is applied to the source of the MOS transistor T11. . The drain of the MOS transistor T14 is connected to the node n6. In addition, the gates of the MOS transistors T14 and T15 are coupled to each other, and the gate and the drain of the MOS transistor T15 are configured to be commonly connected to the current source. The transistor T14 has a structure in which a current is preset with the transistor T15.

When the DOWN signal DOWN having the high logic is input to the reference voltage step-down unit 702, the transistor T11 is turned on so that the reference voltage REF is down. When the DOWN signal DOWN having the low logic is input to the reference voltage step-down part 702, the transistor T11 is turned off.

The reference voltage booster 700 and the reference voltage booster 702 may be a kind of charge pump.

The reference voltage holding unit 704 maintains the reference voltage REF. Current regulators 410a to 410c in which the control signals CS1 to CS3 correspond to the LED strings ST1 to ST3. ) And the capacitor C connected to the node n6 are gradually discharged under the influence of the leakage current, and as a result, the reference voltage REF is lowered. The reference voltage holding unit 704 is operated to prevent the reference voltage REF from lowering.

Specifically, the reference voltage holding unit 704 receives the control signals CS1 to CS3. The reference voltage holding unit 704 does not operate when at least one of the control signals CS1 to CS3 is input, and maintains the reference voltage REF when all of the control signals CS1 to CS3 are not input. To perform.

Hereinafter, the structure and operation of the reference voltage holding unit 704 will be described.

Referring to FIG. 8, the reference voltage holding unit 704 of the present exemplary embodiment may include a reference voltage holding determining unit 800, a reference voltage unit 802, and a voltage supply control unit 804.

The reference voltage holding determination unit 800 determines whether to perform the reference voltage holding operation in response to the control signals CS1 to CS3. Specifically, when at least one of the control signals CS1 to CS3 is provided to the reference voltage holding determination unit 800, the reference voltage holding determination unit 800 does not perform the reference voltage holding operation. In contrast, when all of the control signals CS1 to CS3 are not provided to the reference voltage holding determination unit 800, the reference voltage holding determination unit 800 performs a reference voltage holding operation. Not all of the control signals CS1 to CS3 are provided to the reference voltage holding determination unit 800. Therefore, all of the control signals CS1 to CS3 are provided to the current regulator 410 of the LED strings ST1 to ST3. It means not. That is, not all of the control signals CS1 to CS3 are provided to the current regulator 410 as described above, the current regulator for the LED strings ST1 to ST3 is turned off, and current regulation is not performed. This corresponds to the headroom voltage not being detected. According to the present invention, when the current regulators for the LED strings ST1 to ST3 are turned off, the current regulation is not performed, and the headroom voltage is not detected by the control signals CS1 to CS3. To maintain the reference voltage to maintain.

The reference voltage unit 802 provides a voltage corresponding to the reference voltage REF to the node n6 in response to the control of the reference voltage holding determination unit 800 to perform the reference voltage holding operation. On the other hand, the reference voltage unit 802 does not provide a voltage corresponding to the reference voltage REF to the node n6 in response to the control of the reference voltage holding determination unit 800 not to perform the reference voltage holding operation. Do not.

The voltage supply controller 804 may switch a connection between the reference voltage unit 802 and the node n6 under the control of the reference voltage maintenance determiner 800. Specifically, the voltage supply control unit 804 electrically connects the reference voltage unit 802 and the node n6 in response to the control of the reference voltage holding determination unit 800 to perform the reference voltage holding operation. Therefore, the reference voltage REF is maintained. On the other hand, the voltage supply control unit 804 cuts off the electrical connection between the reference voltage unit 802 and the node n6 in response to the reference voltage holding determination unit 800 controlling not to perform the reference voltage holding operation. .

Referring to FIG. 9, the reference voltage maintaining determiner 800 may include a first counter 900, a second counter 902, and a comparator 904. The first counter 900 receives the control signals CS1, CS2, and CS3, and may be, for example, a PWM counter. The second counter 902 receives and counts the enable signal EN of the first counter 900 and may be, for example, a down counter. The comparator 904 can provide a comparison signal to the second counter 902.

The reference voltage unit 802 receives a signal for controlling a sustain voltage to be output from the second counter 902 and is connected to provide a sustain voltage to the voltage supply controller 804 and the comparator 904. According to an embodiment, the reference voltage unit 802 may be a digital analog converter (DAC).

The voltage supply control unit 804 is connected between the node n7 and the node N6, which are output terminals of the reference voltage unit 802, for example, transistors T16 and T17 and an inverter IN for configuring a transfer gate. It can be made of). The transistor T16 may be an N-channel MOS transistor, and the transistor T17 may be a P-channel MOS transistor. Therefore, when the set signal set is input to the high logic from the second counter 902, the transistors T16 and T17 are turned on, and as a result, the node n7 and the node, which are the output terminals of the reference voltage unit 802, are turned on. (n6) is electrically connected. On the other hand, when the set signal set is input to the low logic from the second counter 902, the transistors T16 and T17 are turned off, and as a result, the node n7, which is an output terminal of the reference voltage unit 802, is turned off. The electrical connection between the nodes n6 is cut off.

The operation of the reference voltage holding unit 704 will now be described.

When at least one of the control signals CS1 to CS3 is input to the first counter 900, the first counter 900 does not activate the second counter 902. That is, the deactivated enable signal EN is provided to the second counter 902. As a result, the reference voltage holding unit 704 does not perform the reference voltage holding operation.

On the other hand, if all of the control signals CS1, CS2, and CS3 are not input to the first counter 900, that is, if all of the control signals CS1 ˜ hold logic 0, the first counter 900 counts. Perform the action. The first counter 900 outputs an enabled enable signal EN when the first count value is greater than or equal to a preset value. Specifically, the first counter 900 checks whether the control signals CS1 to CS3 are input in units of a predetermined time, and gradually increases the first count value when the control signals CS1 to CS3 are not input. When the first count value is greater than or equal to the preset value, the enabled enable signal EN is output.

The second counter 902 drops a second count value (for example, 4) in response to the enabled enable signal EN, and a signal corresponding to the down second count value (for example, 3). To the reference voltage unit 802. Here, the signal may be a signal of n bits, where n is a positive integer.

The reference voltage unit 802 outputs a voltage 2.2V down from a preset voltage (eg, 2.5V) according to a signal provided from the second counter 902.

The comparator 904 receives the voltage output from the reference voltage unit 802 to the inverting terminal (-), and receives the voltage of the node n6 corresponding to the reference voltage REF (for example, 2V) from the non-inverting terminal (+). To receive. That is, the comparator 904 compares the voltage output from the reference voltage unit 802 with the voltage of the node n6.

When the voltage output from the reference voltage unit 802 is greater than or equal to the voltage of the node n6, the comparator 904 may provide a comparison signal having high logic to the second counter 902, for example. In this case, the second counter 902 may again down the second count value, and may provide a signal corresponding to the down second count value (for example, 2) to the reference voltage unit 802. In addition, the second counter 902 may provide the set signal SET having the low logic to the voltage supply controller 804, so that the voltage supply controller 804 maintains the off state. Therefore, the voltage output from the reference voltage portion 802 is not supplied to the node n6.

The reference voltage unit 802 may output a voltage (1.9V) down again from the preset voltage in response to the signal provided from the second counter 902.

The comparator 904 compares the voltage output from the reference voltage unit 802 (for example, 1.9V) with the voltage of the node n6 (for example, 2V). As a result of the comparison, the voltage output from the reference voltage unit 802 is smaller than the voltage of the node n6, and in this case, the comparator 904 outputs a comparison signal STOP having low logic, for example, to the second counter 902. Can be provided as

The second counter 902 may output the set signal SET having the high logic according to the comparison signal STOP having the low logic. As a result, the voltage supply control unit 804 is turned on, and the reference voltage unit 802 and the node n6 are electrically connected. Therefore, the voltage (holding voltage) output from the reference voltage unit 802 is supplied to the node n6, and as a result, the voltage of the node n6, that is, the reference voltage REF, can be maintained. Here, the voltage of the node n6 maintained may be a voltage which is equal to or slightly smaller than the reference voltage REF.

In summary, if all control signals CS1 to CS3 are not input, the reference voltage holding unit 704 gradually lowers the voltage output from the reference voltage unit 802 and outputs the voltage from the reference voltage unit 802. When the voltage is smaller than the voltage of the node n6 corresponding to the reference voltage REF, the sustain voltage is supplied to the node n6 to maintain the reference voltage REF.

In another aspect, the reference voltage holding unit 704 may supply the holding voltage to the node n6 to maintain the reference voltage REF after a predetermined time elapses from when the control signals CS1 to CS3 are not all input. have.

The embodiments of the present invention described above are disclosed for purposes of illustration, and those skilled in the art having ordinary knowledge of the present invention may make various modifications, changes, and additions within the spirit and scope of the present invention. Should be considered to be within the scope of the following claims.

Claims (17)

1. A driving circuit of a light emitting device for driving at least one light emitting diode string,

   A voltage converter providing an output voltage to the light emitting diode string;

   A driving controller controlling the voltage converter in response to a compensation signal; And

   Headroom performing current regulation on at least one of the light emitting diode strings, providing a reference voltage corresponding to headroom voltages of at least one of the light emitting diode strings, and providing the compensation signal using the reference voltage. A voltage controller;

   The headroom voltage control unit receives at least one control signal for current regulation control corresponding to at least one of the LED strings, and maintains the output voltage when at least one control signal corresponds to a predetermined state. And the reference voltage is maintained.
2. The method of claim 1,

   And the predetermined state corresponds to any one of the current regulation for the entirety of the light emitting diode string being halted or the headroom voltages not being detected.
3. The method of claim 1,

   And the headroom voltage control unit controls the drive control unit such that the output voltage is equal to or greater than a maximum forward voltage among forward voltages of at least one LED string.
4. The method of claim 1,

   The headroom voltage controller includes a reference voltage controller providing the reference voltage corresponding to the headroom voltages.

   And the reference voltage controller includes a reference voltage holding unit configured to provide a sustain voltage for maintaining the reference voltage to a node outputting the reference voltage in response to the predetermined state.
5. The method of claim 4, wherein the reference voltage holding unit,

   A reference voltage holding determination unit determining whether the predetermined state is referred to by referring to at least one control signal;

   A reference voltage unit supplying the sustain voltage in response to the predetermined state by the control of the reference voltage sustain determination unit; And

   And a voltage supply controller to switch the transfer of the sustain voltage to the node.
6. The method of claim 5, wherein the reference voltage holding determination unit,

   A first counter configured to output an activated enable signal when the predetermined state is maintained for a predetermined time;

   A comparator comparing the sustain voltage with the reference voltage of the node and providing a comparison signal according to a comparison result; And

   In response to the enable signal of the first counter, controlling the reference voltage unit to output the sustain voltage from a high level to a gradually lower level, and if the sustain voltage is determined to be equal to or lower than the reference voltage by the comparison signal And a second counter for controlling the reference voltage portion to maintain the sustain voltage at a current level and for controlling the voltage supply controller to transfer the sustain voltage to the node.
7. The method of claim 1, wherein the headroom voltage control unit,

   At least one sensing voltage detector configured to correspond to at least one of the at least one LED string, and to detect sensing voltages corresponding to respective headroom voltages; And

   And a headroom voltage adjuster configured to control the reference voltage in response to the sensing voltage detected by the at least one sensing detector, and output the compensation signal corresponding to the controlled reference voltage. Circuit.
8. The method of claim 7, wherein

   At least one sensing voltage sensing unit includes an npn bipolar junction transistor (BJT) connected to corresponding LED strings, and detects the sensing voltage by sensing a base current of the npn BJT.
9. The method of claim 8, wherein the sensing voltage detecting unit,

   A current regulator including the npn BJT and performing regulation with respect to a base current of the npn BJT; And

   And a current sensing unit configured to detect the sensing voltage corresponding to the base current provided by the current regulator and to provide a sensing result of the sensing voltage to the headroom voltage adjusting unit.
10. The method of claim 7, wherein the headroom voltage adjusting unit,

    A voltage adjustment determining unit determining whether to adjust the output voltage in response to the sensing voltage detected by at least one sensing sensor;

    A reference voltage controller configured to adjust the reference voltage according to the determination of the voltage adjustment determiner; And

    And a comparator for comparing the reference voltage provided from the reference voltage controller with a detection voltage corresponding to the output voltage and providing the compensation signal corresponding to the comparison result to the driving controller.
11. The method of claim 10,

    And the reference voltage controller includes a reference voltage holding unit configured to provide a sustain voltage for maintaining the reference voltage to a node outputting the reference voltage in response to the predetermined state.
12. A reference voltage maintenance determination unit determining whether a predetermined state is referred to by referring to at least one control signal for current regulation control corresponding to at least one LED string;

    A reference voltage unit configured to supply a sustain voltage in response to the predetermined state by a control of the reference voltage sustain determination unit to provide an output voltage to at least one LED string; And

    And a voltage supply controller configured to switch the transfer of the sustain voltage to a node that outputs a reference voltage used to provide the output voltage.
13. The semiconductor chip of claim 12, wherein the predetermined state corresponds to any one of the current regulation of the entirety of the light emitting diode string being stopped or no headroom voltages detected.
14. The method of claim 12, wherein the reference voltage holding determination unit,

    A first counter configured to output an activated enable signal when the predetermined state is maintained for a predetermined time;

    A comparator comparing the sustain voltage with the reference voltage of the node and providing a comparison signal according to a comparison result; And

    In response to the enable signal of the first counter, controlling the reference voltage unit to output the sustain voltage from a high level to a gradually lower level, and if the sustain voltage is determined to be equal to or lower than the reference voltage by the comparison signal And a second counter for controlling the reference voltage unit to maintain the sustain voltage at a current level and for controlling the voltage supply controller to transmit the sustain voltage to the node.
15. A first step of controlling light emission by providing a control signal to a current regulator connected to the at least one light emitting diode string; And

    Provided to the at least one light emitting diode string when the control signal is provided to correspond to a predetermined state corresponding to at least one of either stopping current regulation for the entirety of the light emitting diode string or not detecting headroom voltages. And a second step of maintaining the output voltage.
16. The method of claim 15, wherein the second step,

    Determining the control signal corresponding to the predetermined state;

    Gradually lowering a predetermined sustain voltage in response to the predetermined state;

    Comparing the held down voltage with a current reference voltage used to provide the output signal; And

    And when the sustain voltage is determined to be equal to or lower than the reference voltage, maintaining the sustain voltage at a current level and transferring the sustain voltage to a node that outputs the reference voltage. .
17. The method of claim 15, wherein the headroom voltages sense and detect a base current of a bipolar junction transistor (BJT) connected to at least one or more of the light emitting diode strings, respectively.

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