KR100877884B1 - Apparatus for controlling lamp and method thereof - Google Patents

Abstract

The embodiment relates to a lamp driving control apparatus and a control method thereof.

Lamp driving control apparatus according to the embodiment includes a plurality of lamps; A switching unit for switching the supplied power to output an AC signal; A transformer unit converting the AC signal of the switching unit into high voltage signals having different phases and supplying the signal to a plurality of lamps; An open ramp detector for detecting an open state of a lamp by adding signals of low voltage having different phases fed back from the transformer; And a control unit controlling the operation of the switching unit by the detected signal of the open ramp detection unit.

Lamp, open, transformer

Description

Lamp driving control device and its control method {APPARATUS FOR CONTROLLING LAMP AND METHOD THEREOF}

1 is a block diagram showing a lamp driving control apparatus according to an embodiment.

FIG. 2 is a circuit diagram illustrating the switching unit and the transformer unit of FIG. 1. FIG.

3 is a block diagram illustrating an open ramp detector of FIG. 1;

4 is a waveform diagram illustrating an example of detecting a feedback signal in a normal lamp state in an open ramp detector according to an embodiment;

5 is a waveform diagram illustrating an example of detecting a feedback signal in an open ramp state in an open ramp detector according to an exemplary embodiment;

6 is a configuration diagram of a first circuit of the lamp driving control apparatus according to the embodiment;

7 is a second circuit diagram illustrating a lamp driving control apparatus according to an embodiment.

8 is a third circuit diagram illustrating a lamp driving control apparatus according to an embodiment.

9 is a flowchart illustrating a lamp driving control method according to an embodiment.

<Explanation of symbols for main parts of the drawings>

100: lamp driving control device 101: inverter

110: control unit 120: switching unit

121 ~ 12N: Switching circuit 130: Trans part

131 ~ 13N: Transformer 140: Lamp unit

141 ~ 14N: Lamp 160: Open lamp detector

161 to 168: signal detection circuit 171 to 177: addition circuit

181 ~ 184: Protection circuit 191: Drive control circuit

The embodiment relates to a lamp driving control device and a control method thereof.

BACKGROUND ART Liquid crystal displays (hereinafter referred to as "LCDs") are becoming increasingly wider in scope due to their light weight, thinness, and low power consumption. According to this trend, LCDs are used for office automation equipment and audio / video equipment.

The LCD displays a desired image on a screen by adjusting the amount of transmission of image signals and light applied to a plurality of switch elements arranged in a matrix form.

Since the LCD is not a self-luminous display device, a light source such as a backlight is required. As a light source used in the backlight, a cold cathode fluorescent lamp (hereinafter referred to as "CCFL") is used.

The lamp is driven by an AC signal having a high voltage by a lamp driving circuit. However, in driving the lamp, a state in which the lamp is opened may occur due to a failure of the lamp, an abnormality in an input voltage of the lamp, or the like. There is a demand for an open lamp protection circuit capable of detecting an open state of such a lamp and protecting a lamp driving circuit.

The embodiment provides a lamp driving control apparatus and a control method thereof capable of detecting an open state of a lamp to protect a circuit for driving the lamp.

The embodiment provides a lamp driving control apparatus and a control method thereof which add a forward signal and a reverse signal fed back from a transformer to detect an open state of a lamp and an abnormal voltage of a transformer.

The embodiment provides a lamp driving control apparatus and a method of controlling the same, which can simplify a circuit by reducing the number of parts used in an open lamp detector.

Lamp driving control apparatus according to the embodiment includes a plurality of lamps; A switching unit for switching the supplied power to output an AC signal; A transformer unit converting the AC signal of the switching unit into high voltage signals having different phases and supplying the signal to a plurality of lamps; An open ramp detector for detecting an open state of a lamp by adding signals of low voltage having different phases fed back from the transformer; And a control unit controlling the operation of the switching unit by the detected signal of the open ramp detection unit.

Lamp driving control apparatus according to the embodiment includes a plurality of lamps having a first and a second electrode; An inverter connected to at least one electrode of the lamp, the inverter comprising: a switching unit for switching the supplied power and outputting an AC signal; A transformer for converting the AC signal of the switching unit into a positive signal and a reverse signal of a high voltage and supplying the alternating signal to the lamp; An open ramp detector for detecting an open state of a lamp by adding a low voltage positive signal and a reverse signal fed back from the transformer; And a control unit controlling the operation of the switching unit by the detected signal of the open ramp detection unit.

Lamp driving control method according to the embodiment includes the step of operating the switching unit in response to the control signal of the controller; Supplying a high voltage positive signal and a reverse signal to a plurality of lamps according to an operation of the switching unit; Detecting an open state of a lamp by adding a low voltage positive signal and a reverse signal fed back from the transformer; And outputting a driving stop signal to the controller when an open state of the lamp is detected.

Hereinafter, exemplary embodiments will be described with reference to the accompanying drawings.

1 is a block diagram illustrating a lamp driving control apparatus according to an exemplary embodiment.

Referring to FIG. 1, the lamp driving control apparatus 100 includes an inverter 101 and a lamp unit 140 in which a plurality of lamps 141 to 14N are disposed.

The inverter 101 converts the lamp driving power supplied from the outside into an AC signal, and converts the converted AC signal into a positive-phase signal S1 having a high voltage and a negative-phase. The signal is converted into the signal S2 and supplied to the plurality of lamps 141 to 14N. The signals S1 and S2 of the positive phase and the reverse phase have a phase difference of 180 ° with each other.

A plurality of lamps 141 to 14N are disposed in parallel to the lamp unit 140, and two signals S1 and S2 of different phases are respectively supplied to the lamps 141 to 14N. Here, the lamps 141 to 14N may be any one of a Cold Cathode Fluorescent Lamp (CCFL), an External Electrode Fluorescent Lamp (EEFL), a Hot Cathode Fluorescent Lamp (HCFL), and an External & Internal Electrode Fluorescent Lamp (EIFL). The lamps 141 to 14N include a glass tube, inert gases Ar and Ne in the glass tube, and electrodes provided at both ends of the glass tube. Inert gases are filled in the glass tube, and phosphors are coated on the inner wall of the glass tube.

The inverter 101 includes a control unit 110, a switching unit 120, a transformer unit 130, and an open lamp detection unit 160. The control unit 110 controls the switching operation of the switching unit 120 in response to the input pulse width modulation signal PWM. The switching unit 120 switches the lamp driving power supplied from the power terminal by the control signal of the control unit 110 and converts it into an AC signal.

The transformer 130 converts the AC signal of the switching unit 120 into a positive phase signal S1 having a high voltage and an antiphase signal S2 and supplies the converted signal to the lamp unit 140. The transformer 130 may adjust the magnitude and output phase of the secondary voltage according to the winding ratio and the winding direction of the internal transformer.

Each of the lamps 141 to 14N is connected to the high voltage terminal of the secondary winding, and the open lamp detection unit 160 is connected to the low voltage terminal of the secondary winding.

The open ramp detector 160 detects the signals FB1 to FBn fed back from the transformer 130. The open ramp detection unit 160 detects a signal of a positive phase having a low voltage (hereinafter, referred to as a positive signal) and a signal of a reverse phase (hereinafter, referred to as a reverse signal) and detects the detected positive signal and the reverse signal. It adds each other as a pair and outputs the added result. In this case, since the positive signal and the reverse signal have the same signal magnitude and opposite phases, the sum of the two normal signals becomes a low signal. However, when one lamp is open, the sum of the positive signal and the reverse signal becomes a high signal.

In this case, the open ramp detection unit 160 may add each reverse signal with a different inverse signal and output the result. In addition, the open ramp detector 160 may add and output different positive signals with respect to each reverse signal. This means that even if two lamps are opened at the same time, by double checking for each signal, it is possible to accurately detect whether the lamp is open.

The open ramp detector 160 detects an intermediate level (or sum level) of the positive signal and the reverse signal and outputs a driving stop signal or a driving sustain signal to the controller 110. The open lamp detector 160 may detect whether the voltage of the transformer 130 is over or whether the lamps 141 to 14N are open.

FIG. 2 is a circuit diagram illustrating the switching unit 120 and the transformer unit 130 of FIG. 1.

Referring to FIG. 2, the switching unit 120 is implemented with a plurality of switching circuits 121 to 12N, and each of the switching circuits 121 to 12N includes transformers 131 to 13N of the transformer unit 130. Connected.

Here, the switching circuits 121 to 12N are switched by the control signal of the controller 110 to output the AC signals to the transformers 131 to 13N. The circuit configurations of the switching circuits 121 to 12N and the transformers 131 to 13N may be changed, but are not limited thereto.

In the transformers 131 to 13N of the transformer unit 130, a first winding N1 may be wound on a primary side, and a second winding N2 and a third winding N3 may be wound on a secondary side. The high voltage terminals of the second winding N2 and the third winding N3 supply two signals S1 and S2 of different phases to each lamp, and the sum of the phases of the two signals is zero.

Here, the number of the transformers (131 ~ 13N) may be arranged in the same number as the lamp. In an embodiment, two or more signals may be provided. For example, N (e.g., 2? N? 36) drive signals such that 360 ° is divided by N (e.g., 2? N? 36) lamp units with respect to the phase of the signal supplied to the lamp. In addition, the sum of each phase of the N driving signals should be zero.

The transformers 121 to 12N are respectively output as the positive signal S1 and the reverse signal S2 having high voltage through the high voltage terminals of the secondary side second winding N2 and the third winding N3. Positive signals FB1 to FBm and reverse signals FB2 to FBn having low voltage are fed back to the low voltage terminals of the secondary windings N2 and third windings N3 of the transformers 121 to 12N. . Here, the feedback signals FB1, ..., FBn are low voltage signals having the same phase as the phases of the signals S1, S2 output to the secondary high voltage terminals of the transformers 131, ..., 13N.

Here, the feedback signals FB1 to FBn are output between the secondary low voltage terminals of the transformers 121 to 12N and the resistors R1 to Rn of which the other end is grounded.

3 is a block diagram illustrating an example of the open ramp detection unit 160 according to an exemplary embodiment. The open ramp is detected through four feedback signals FB1 to FB4.

Referring to FIG. 3, the open ramp detection unit 160 may include first to eighth signal detection circuits 161 to 168, first to seventh addition circuits 171 to 177, and first to fourth protection circuits 181 to. 184, a drive control circuit 191.

The first to eighth signal detection circuits 161 to 168 branch and detect the feedback signals FB1 to FB4 in two paths. Here, the first and third feedback signals FB1 and FB3 are positive signals, and the second and fourth feedback signals FB2 and FB4 are inverse signals.

The first and fifth signal detection circuits 161 and 165 detect a positive signal as a first feedback signal, and the second and eighth signal detection circuits 162 and 167 detect a reverse signal as a second feedback signal. The seventh signal detection circuit 163 and 168 detects the positive signal as the third feedback signal, and the fourth and sixth signal detection circuits 164 and 166 detect the reverse signal as the fourth feedback signal.

Here, the first to fourth addition circuits 171 to 174 are primary addition nodes, the fifth and sixth addition circuits 175 and 176 are secondary addition nodes, and the seventh addition circuit 177 is third addition. Can be implemented as a node. The fifth to seventh addition circuits 175 to 177 may be implemented as one secondary addition node, but are not limited thereto.

The first to fourth adding circuits 171 to 174 add one positive signal and an inverse signal in pairs. For example, the first addition circuit 171 adds the positive signal and the inverse signal detected by the first and second signal detection circuits 161 and 162, and the second addition circuit 172 adds the third and fourth signals. The two signals detected by the signal detection circuits 163 and 164 are added, and the third addition circuit 173 adds the two signals detected by the fifth and sixth signal detection circuits 165 and 166, and the fourth addition circuit ( 174 adds two signals detected by the seventh and eighth signal detection circuits 167 and 168.

Here, as shown in FIG. 4, the first adding circuit 171 outputs a low signal (eg, 0V) when the normal first feedback signal FB1 and the second feedback signal FB2 are added.

In addition, as shown in FIG. 5, the first addition circuit 171 outputs the first feedback signal FB1 when the normal first feedback signal FB1 and the second feedback signal FB2 in the open ramp state are added. do. For example, when the lamp associated with the second feedback signal FB2 is opened, the second feedback signal FB2 is detected at a low level (eg, 0V) or at a reduced level. In addition, since the phase difference of the first feedback signal and the second feedback signal does not occur exactly 180 °, the high signal can be detected as a result of the addition of the two signals (FB1 + FB2).

The fifth addition circuit 175 re-adds the addition results of the first and second addition circuits 171 and 172, and the sixth addition circuit 176 adds the addition results of the third and fourth addition circuits 173 and 174. Will be added again. The seventh addition circuit 177 re-adds the addition results of the fifth and sixth addition circuits 175 and 176.

The first to seventh adder circuits 171 to 177 re-add the result of adding each of two positive signals to one positive signal. Alternatively, the first to seventh addition circuits 171 to 177 may re-add and output a result obtained by adding two positive signals to one reverse signal, respectively.

Also, as shown in Figs. 2 and 3, the first and second addition circuits 171 and 172 add signals FB1 and FB2 and FB3 and FB4 fed back from the same transformer to each other, and the third and fourth additions. The circuits 173 and 174 add signals FB1 and FB3 (FB2 and FB4) fed back from different transformers.

As such, the open level detector 160 may double-check each of the feedback signals, so that the lamp open state may be detected even if both feedback signals input to one adder circuit are at the open level.

The first to fourth protection circuits 181 to 184 are disposed at the output terminals of the first to fourth adder circuits 171 to 174 to block an overvoltage applied to the transformer and allow only a forward current to pass through. The arrangement positions of the protection circuits 141 to 144 may be changed, but are not limited thereto.

The driving control circuit 191 outputs a driving stop signal or a driving holding signal to the controller by the addition result of the seventh adding circuit 177. The driving control circuit 191 outputs a driving stop signal when the result of the addition of the seventh addition circuit 177 is a high signal and outputs a driving stop signal. When the seventh addition result 177 is a low signal, the driving control circuit 191 is normal. The drive maintenance signal is output by judging by the lamp.

FIG. 6 is a diagram illustrating a first circuit configuration of the lamp driving control apparatus 100A according to an exemplary embodiment, and illustrates an example of detecting whether lamps 141 to 144 connected to two transformers 131 and 133 are opened. Drawing.

Referring to FIG. 6, the switching unit 120 outputs an AC signal to the first and second transformers 131 and 132. The first electrodes 151 of the lamps 141 to 144 are connected to the high voltage terminals of the second windings N2 and the third windings N3 of the first and second transformers 131 and 132, respectively. The open ramp detector 160 is connected to the low voltage terminals of the second winding N2 and the third winding N3 of the transformers 131 and 132. High voltage capacitors Ca and Cb are connected in series to both electrodes 151 and 152 of the lamps 141 to 144.

The first and second signal detection circuits 161 and 162 of the open ramp detection unit 160 are connected to the low voltage terminals of the second winding 2N and the third winding N3 of the first transformer 131, respectively. . The third and fourth signal detection circuits 163 and 164 are respectively connected to the low voltage terminals of the secondary winding second winding N2 and the third winding N3 of the second transformer 132.

The first to fourth signal detection circuits 161, 162, 164, 164 may be implemented with voltage divider R1, R2, R3, R4, R5, R6, and R7, R8. The 161 and 162 detect the positive signal FB1 and the inverse signal FB2 fed back from the secondary side of the first transformer 131, and the third and fourth signal detection circuits 163 and 164 respectively detect the second transformer 132. The positive signal FB3 and the reverse signal FB4 respectively fed back from the secondary side of the signal are detected.

The first and second adder circuits 171 and 172 may be implemented as adder nodes, and the first adder circuit 171 may add a positive signal and a reverse signal detected by the first and second signal detection circuits 161 and 162. The second addition circuit 172 adds the positive signal and the inverse signal detected to the third and fourth signal detection circuits 163 and 164.

The first and second protection circuits 181 and 182 may be implemented as diodes, and are disposed at the output terminals of the first and second addition circuits 171 and 172 to block signals flowing in the reverse direction.

The third addition circuit 175 re-adds the result added to the first and second addition circuits 171 and 172. Here, the number of signal detection circuits and addition circuits may be changed according to the number of transformers.

The output signal of the third addition circuit 175 is removed from the noise through the resistors R9 and R10 and the capacitor C1 and input to the driving control circuit 191.

The driving control circuit 191 may be implemented with a transistor Q1, and the transistor Q1 is turned on or off by an output signal of the third addition circuit 175 input to a base. For example, the transistor Q1 is turned on when a high signal is applied to the base, and outputs a driving stop signal that is a low signal to the collector terminal. The transistor Q2 is turned off when a low signal is applied to the base, and outputs a driving sustain signal that is a high signal to the collector terminal.

The control unit 110 determines that specific lamps 141 to 144 are opened by the driving stop signal of the open lamp detection unit 160, and outputs an off control signal Ctrl to the switching unit 120, thereby switching. The unit 120 and the transformers 131 and 132 are turned off.

7 is a diagram illustrating a second circuit of the lamp driving control apparatus 100B according to the embodiment. In the description of the second circuit configuration diagram, redundant description of the same parts as the first circuit configuration diagram of FIG. 6 will be omitted.

Referring to FIG. 7, first and second inverters 102 and 103 are disposed at both ends of the lamp unit 140, and open states of both electrodes 151 and 152 of the lamps 145 and 146 through the respective inverters 102 and 103, respectively. Will be detected.

The first inverter 102 includes a first control unit 111, a first switching unit 121, a first transformer 131A, and a first open lamp detection unit 160A, and the second inverter 103 includes a first inverter unit 111. And a second control unit 112, a second switching unit 122, a second transformer 131B, and a second open lamp detection unit 160B.

The first inverter 102 will be briefly described. In the first transformer 131A, the first electrodes 151 of the lamps 145 and 146 are connected to the high voltage terminals of the second and third windings N2 and N3 on the secondary side. ) Is connected. The first open lamp detection unit 160A is connected to the low voltage terminals of the second and third windings N2 and N3 of the secondary side of the first transformer 131A. The first open lamp detection unit 160A includes first and second signal detection circuits 161A and 162A, an addition circuit 171A, a protection circuit 181A, and a driving control circuit 191A, and lamps 145 and 146. It is detected whether the first electrode 151 of the opening is open.

The second inverter 103 will be described briefly. The second electrodes 152 of the lamps 145 and 146 are connected to the high voltage terminals of the second and third windings N2 and N3 of the secondary side of the second transformer 131B. This is connected. The second open lamp detection unit 160B is connected to the low voltage terminals of the second and third windings N2 and N3 of the secondary side of the second transformer 131B. The second open lamp detection unit 160B includes first and second signal detection circuits 161B and 162B, an addition circuit 171B, a protection circuit 181B, and a driving control circuit 191B, and lamps 145 and 146. The opening of the second electrode 152 on the side is detected.

8 is a third circuit diagram illustrating the lamp driving control apparatus 100C according to the embodiment. In the description of the third circuit configuration diagram, redundant description of the same parts as the first circuit configuration diagram of FIG. 6 will be omitted.

Referring to FIG. 8, signals of different phases are provided using one transformer 133 to drive all lamps 141a, 141b, 141c, 142a, 142b, and 142c of the lamp unit 140.

A plurality of lamps 141a, 141b, 141c, 142a, 142b, and 142c are respectively connected to the high voltage terminals of the secondary windings N2 and the third windings N3 of the transformer 133. At this time, the AC signal of the high voltage supplied through the second winding N2 of the transformer 133 and the AC signal of the high voltage supplied through the third winding N3 are different from each other.

Accordingly, the open ramp detection unit 160C adds the signal detected by the first signal detection circuit 161C and the signal detected by the second signal detection circuit 162C to the addition circuit 171C. The signal added to the addition circuit 171C is input to the non-inverting terminal (+) of the comparator 185, and the comparator 185 is applied to the signal input to the non-inverting terminal (+) and the inverting terminal (-). The reference voltage Vref is compared. At this time, the comparator 185 outputs a high signal when the input addition signal is large, and outputs a low signal when the input addition signal is small. Here, the reference voltage Vref applied to the inverting terminal (-) of the comparator 185 is a voltage according to the operation of the lamps connected to the second winding N2 and the third winding N3 of the transformer 133. The difference is compensated for.

The high signal of the comparator 185 drives the driving control circuit 191C to output the driving stop signal to the controller 110.

9 is a flowchart illustrating a lamp driving control method according to an exemplary embodiment.

Referring to FIG. 9, when the control unit outputs a control signal to the switching unit (S101), the switching unit operates by the control signal to output a lamp driving power to drive the transformer unit (S102).

The transformer converts an AC signal input from the switching unit into a high voltage forward phase signal and a reverse phase signal and supplies them to a plurality of lamps, respectively (S103).

The open ramp detector detects the low voltage forward phase signal and the reverse phase signal fed back from the transformer unit (S104), and adds the forward phase signal and the reverse phase signal to each other in a pair to output an addition result. (S105). The addition result at this time can be re-added with the addition result of another signal.

If the added value is a high signal, a drive stop signal is output to the controller (S106, S107). If the added value is a low signal, a drive maintenance signal is output to the controller (S108).

The lamp driving apparatus according to the exemplary embodiment may stably control the backlight assembly through driving control of the lamp, thereby improving reliability of the liquid crystal display.

Although the technical idea according to the embodiment has been described in detail as described above, it should be noted that the above-described embodiments are for the purpose of description and not of limitation. In addition, it will be understood that various implementations are possible within the scope of the technical idea according to the embodiment.

According to an exemplary embodiment of the present invention, a lamp driving control apparatus and a method of controlling the same may detect an open state of a lamp and an abnormal voltage of a transformer by using a calculation method of adding two signals having opposite phases into one pair. .

In addition, the circuit components of the open lamp detector can be simplified. In addition, the simplified circuit configuration of the open lamp detection unit may reduce the manufacturing cost of the inverter and reduce the probability of defective parts.

Claims (19)

A plurality of lamps; A switching unit for switching the supplied power to output an AC signal; A transformer unit converting the AC signal of the switching unit into high voltage signals having different phases and supplying the signal to a plurality of lamps; An open ramp detector for detecting an open state of a lamp by adding signals of low voltage having different phases fed back from the transformer; A control unit controlling an operation of the switching unit by the detected signal of the open ramp detection unit; And the open lamp detector adds and outputs signals having different phases fed back from the transformer as a pair. delete delete delete A plurality of lamps; A switching unit for switching the supplied power to output an AC signal; A transformer unit converting the AC signal of the switching unit into high voltage signals having different phases and supplying the signal to a plurality of lamps; An open ramp detector for detecting an open state of a lamp by adding signals of low voltage having different phases fed back from the transformer; A control unit controlling an operation of the switching unit by the detected signal of the open ramp detection unit; And the signals having different phases include a forward signal and a reverse signal having a phase difference of 180 ° from each other. delete The method of claim 5, And the open ramp detection unit re-adds each of the positive signals fed back from the transformer to different inverse signals and outputs the result of the addition. The method of claim 5, And the open ramp detection unit re-adds and outputs a result of adding each of the reverse signals fed back from the transformer into different positive signals. The method of claim 5, The open ramp detection unit includes a plurality of signal detection circuits for branching and detecting respective signals fed back from the transformer in a different path; An addition circuit for adding the positive signal and the inverse signal detected by the signal detection circuit to each other in a pair; And a drive control circuit for outputting a drive stop signal or a drive sustain signal to the controller in accordance with the added result of the addition circuit. The method of claim 9, The adder circuit includes a first adder circuit that adds a positive signal and a reverse signal fed back from the same transformer, respectively, as a pair, and a second adder that adds the positive signal and the reverse signal fed back from different transformers, respectively, to a pair; And an adder circuit and a third adder circuit for re-adding the addition result of the first and second adder circuits. The method of claim 9, And a protection circuit for blocking a voltage flowing in a reverse direction between the signal detection circuit and the driving control circuit, and a comparator for comparing the addition result of the addition circuit with a reference voltage. A plurality of lamps having first and second electrodes; An inverter connected to at least one electrode of the lamp, In the inverter, A switching unit for switching the supplied power to output an AC signal; A transformer for converting an AC signal of the switching unit into a high voltage positive signal and a reverse signal and supplying the lamp to a lamp; An open ramp detector for detecting an open state of a lamp by adding a low voltage positive signal and a reverse signal fed back from the transformer; And a control unit for controlling the operation of the switching unit by the detected signal of the open ramp detection unit. The method of claim 12, And the open ramp detector detects an intermediate voltage of a positive signal and a reverse signal fed back from the transformer. The method of claim 12, The open ramp detector may include: a divided resistor for branching and detecting the positive signal and the reverse signal fed back from the transformer in two paths; And a second adding node for re-adding a result added by the first adding node and a first adding node for respectively adding the detected one positive signal and an inverse signal in pairs. The method of claim 14, And a transistor configured to output a driving stop signal or a driving sustain signal to a controller in accordance with the addition result of the second adding node. Operating the switching unit by a control signal of the controller; Supplying a high voltage positive signal and a reverse signal to a plurality of lamps according to an operation of the switching unit; Detecting an open state of a lamp by adding a low voltage positive signal and a reverse signal fed back from the transformer; And outputting a driving stop signal to the control unit when the open state of the lamp is detected. The method of claim 16, The detecting of the lamp open state may include: branching each signal fed back from the transformer into a different path; Adding the detected positive signal and the reverse signal to each of a pair; And re-adding the added result to detect an open state of the lamp. The method of claim 16, And a phase of the positive signal and the reverse signal has a difference of 180 ° from each other. The method of claim 17, And the adding step adds two different inverse signals to one positive signal, respectively.

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