KR100478412B1 - Inverter for external electrode fluorescent lamp - Google Patents

Abstract

The present invention discloses an inverter for an external electrode fluorescent lamp that can be used in an LCD TV. The inverter includes a control unit for outputting a control signal for controlling the output of the power supplied from the outside; A driving unit which switches and converts power in response to the control signal; A transformer including a primary winding end to which a primary voltage is applied and a secondary winding end to which a secondary voltage derived from the primary voltage is applied to transform the power applied from the driving unit; A detector for detecting a current induced in the primary winding stage of the transformer is provided, and the external electrode fluorescent lamp is connected to both ends of the secondary winding stage in a floating type to drive the fluorescent lamp.

Description

Inverter for external electrode fluorescent lamp {INVERTER FOR EXTERNAL ELECTRODE FLUORESCENT LAMP}

 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for external electrode fluorescent lamps mounted on a backlight unit of a liquid crystal display (LCD), and more particularly, to a stable alternating current for an external electrode fluorescent lamp used as a light source of a thin film transistor liquid crystal display device. The present invention relates to an inverter for supplying power. Generally, flat panel displays are classified into light emitting and light receiving types. Among them, there is a liquid crystal display device as a light receiving type. Since the liquid crystal display itself is a light-receiving flat panel display device which emits light and does not form an image, but receives light from the outside to form an image, a backlight unit is separately provided on the back of the liquid crystal display device to irradiate light. However, unlike LCD monitors for notebook computers and LCD monitors employing LCDs, LCD TVs require high brightness and long lifespan, which cannot be satisfied with conventional cold cathode fluorescent lamps (CCFL). An external electrode fluorescent lamp (EEFL) is being developed as a replacement. On the other hand, the backlight unit may be classified into an edge light emitting method using a light guide panel and a direct light emitting method arranged in a plane according to the arrangement of the light source on the display surface. An edge type backlight unit in which a plurality of external electrode fluorescent lamps are arranged at the edge of the light guide plate or a direct backlight type backlight unit in which a plurality of external electrode fluorescent lamps are arranged on a plane may be driven by one inverter by connecting external electrode fluorescent lamps in parallel. Because the external electrode fluorescent lamp is not exposed to the discharge space, the current does not flow to the electrode, wall charges are accumulated on both electrode portions, and the discharge is stopped by the formation of a reverse voltage by wall charges at both ends of the lamp. Then, after the other lamps are discharged and likewise the wall charges are formed, the other lamps are discharged sequentially so that a plurality of lamps can be driven by one inverter. 1 is a view schematically illustrating the configuration of a conventional inverter for external electrode fluorescent lamps. The entire inverter circuit is controlled through the control unit 12 which generates a driving frequency by receiving power from an applied DC power source and performs a function such as duty control for the driving unit. The primary winding 32 and the secondary winding ( The transformer 18 including the 36 is supplied with alternating current power from the driving unit 14 that is a power switch to transform the voltage. One of the secondary windings 36 of the transformer 18 is grounded at G1 and the other is connected to the first electrode 22 of the external electrode fluorescent lamp 26. The second electrode 24 of the external electrode fluorescent lamp 26 is grounded at G2 via a resistor 38, where the detector 16 detects a current in the resistor 38 to sense the state of the external electrode fluorescent lamp. When the signal containing the information is transmitted to the control unit 12, the control unit detects the state of the external electrode fluorescent lamp 26 through the signal containing the information on the induced current transmitted from the detection unit 16 to the entire inverter The feedback acts as a control again. However, the above-described conventional external electrode fluorescent lamp inverter has a problem in that it extends the life of the external electrode fluorescent lamp by adopting a grounding method in which the second electrode side of the external electrode fluorescent lamp is grounded, and the luminance is not uniform. There was a problem.

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The present invention solves the problems of the ground-type inverter as described above, by detecting the state of the external electrode fluorescent lamp at the primary winding end of the transformer to achieve a high efficiency while maintaining a constant current on the fluorescent lamp side of the external electrode fluorescent lamp An object of the present invention is to provide an inverter.

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In order to achieve the above object, an inverter for an external electrode fluorescent lamp according to a preferred embodiment of the present invention is an inverter for driving a lamp by supplying power to the external electrode fluorescent lamp, to control the output of the power supplied from the outside A control unit for outputting a control signal for the control unit; a driving unit for switching and converting power in response to the control signal; derived from the primary winding stage to which the primary voltage is applied to transform the power applied from the driving unit, and the primary voltage A transformer including a secondary winding end to which a secondary voltage is applied; and a detector configured to detect a current induced in the primary winding end of the transformer. Here, the primary winding end includes a first winding to which a voltage is applied from the driver and a second winding to which an induced current is applied from the first winding. In particular, the detector is configured to detect a current induced in the second winding. On the other hand, the above-described inverter of the present invention is characterized in that the drive by connecting the external electrode fluorescent lamp in the floating type to both ends of the secondary winding end. Here, the control unit is the 2 from the induced current detected by the detection unit The state of the external electrode fluorescent lamp connected to the secondary winding end is determined. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 2 is a view schematically showing that an external electrode fluorescent lamp is connected to and driven by an inverter for an external electrode fluorescent lamp according to an exemplary embodiment of the present invention. Although only one external electrode fluorescent lamp is illustrated in the drawing, a plurality of external electrode fluorescent lamps may be connected and driven in parallel, and the use thereof is not limited to the external electrode fluorescent lamp. 2, the external electrode fluorescent lamp inverter according to a preferred embodiment of the present invention includes a control unit 112 for outputting a control signal for controlling the output of the power supplied from the outside; A driving unit 114 for switching and converting a power supply in response to the power supply, and a primary winding stage to which the primary voltage is applied and a secondary voltage derived from the primary voltage are applied to transform the power applied from the driving unit 114. A transformer 118 including a secondary winding end, and a detector 116 for detecting a current induced in the primary winding end of the transformer 118. In detail, the discharge tube of the lamp 120 is provided. In order to drive this by supplying a predetermined voltage to the external electrode fluorescent lamp 126 in which the hot electrode 122 and the cold electrode 124 are provided, the inverter of the present invention externally supplies a DC power source indicated by "Vin" in the figure. Robu In general, the DC power supplied is in the range of 16 V to 24 V. In order to control the driving unit 114 for switching the pulse current, when the control signal is output from the control unit 112, the driving unit 114 is operated. In response to this, a switching step is performed to undergo a rectifying process of converting the pulse power into an AC power, thereby outputting a predetermined AC power to an input terminal of the transformer 118. Meanwhile, a transformer for performing step-up or step-down of the AC power ( 118) includes a primary winding corresponding to an input and a secondary winding corresponding to an output, wherein the primary winding of the present invention includes a first winding 132 and a second winding 134. The winding connected to the driving unit 114 to which the voltage is directly applied from the driving unit 114 is the first winding 132 of the primary winding end of the transformer 118, and the second winding 134 is connected to the driving unit 114. Direct voltage is applied However, the second winding 134 forms the primary winding end together with the first winding 132 to form an input terminal of the transformer, and the secondary winding, which is the output end of the transformer 118, is the third winding ( 136). In the third winding 136, a voltage is generally boosted and induced from the first winding 132, which is an input terminal, by an electromagnetic induction action. The boosted voltage induced in the third winding 136 drives the external electrode fluorescent lamp 126 to which the present invention is applied. That is, both ends of the third winding 136 are connected to the first electrode 122 and the second electrode 124 formed on both ends of the lamp 120 to drive the external electrode fluorescent lamp 126. On the other hand, the second winding 134 of the transformer 118 forms a primary winding end as in the first winding 132, the current is also induced between the first winding and the second winding. Therefore, the voltage is converted and induced from the first winding 132 to which the voltage is applied from the driver 114 to the third winding 136, and at the same time, the second winding 134 is applied to the voltage applied to the third winding 136. The corresponding induced current is applied. Through this process, the induced current applied to the second winding 134 is detected by the detection unit 116 connected to the second winding, and information about it is passed to the controller 112. The controller 112 receives information about the induced current from the detector from the detector 116 and transmits a new control signal to the driver 114 to apply a predetermined power to the external electrode fluorescent lamp 126 based on the information. The driving unit 114 operates in response to the control signal. In this process, when the controller 112 determines that the induced current detected by the detector 116 is excessive, the controller 112 controls the driver 114 by transmitting a control signal for lowering it to the driver 114. On the contrary, if it is determined that the induced current detected by the detection unit 116 does not reach a predetermined value, the control unit 114 controls the driving unit 114 by transmitting a control signal for increasing the driving current to the driving unit 114. Through this process, the voltage induced in the secondary winding end of the transformer can be maintained at a constant uniform range at all times, and can be adjusted by the controller if necessary. In the case of the inverter according to the present invention, a method of checking the state of the external electrode fluorescent lamp connected to the third winding 136, which is the transformer output terminal, through an induced current induced in the second winding 134 of the primary winding terminal, which is the transformer input terminal. Therefore, advance information on the relationship between the induced current induced in the second winding 134 and the voltage applied to the external electrode fluorescent lamp 126 should be given to the controller 112. Accordingly, the controller 112 controls the entire inverter based on this information, and thus, the predetermined power can be applied to the external electrode fluorescent lamp 126 to stably drive the lamp. On the other hand, unlike the prior art, the electrical connection configuration of the external electrode fluorescent lamp 126 on the transformer output end side of the present invention is not a ground (ground) method of grounding to form a feedback structure. In the case of the present invention, it corresponds to a floating method that is not grounded. In general, a power source for applying AC power to a lamp when driving an external electrode fluorescent lamp having external electrodes formed on one or both sides of an electrodeless glass tube In terms of the output unit, that is, the inverter, there are a floating method and a ground method according to the driving method. If both methods drive the lamp with the same current, the voltage across the lamp is the same. 3 is a view illustrating a lamp driving using a ground method as in the conventional technique shown in FIG. 1 when driving an external electrode fluorescent lamp, and FIG. 4 illustrates a lamp driving having a floating method when driving an external electrode fluorescent lamp. It is a figure for demonstrating. In the ground method shown in FIG. 3, the voltage across the external electrode fluorescent lamp 26 is the same as that of the floating method, but the potential between the positive (+) and the negative (-) voltages during the alternating current driving is determined by the first electrode ( In the case of 22), the potential is about twice that of the voltage applied to both ends, and the potential is 0V because the second electrode 24 side is ground. Therefore, the potential is gradually lowered from the first electrode to the second electrode. Here, since the potential is high on the first electrode side, there is a problem that the electrode is damaged. For reference, the plasma potential inside the tube of the lamp 20 is ignored. On the other hand, in the floating method shown in Fig. 4, the voltage across the lamp is the same as the ground method for the same time t1 and t2, but in terms of potential, the first electrode 122 and the second electrode 124 The same applies to both sides of the lamp, and the potential of the voltage across the lamp is different, and the center between the electrodes is a low potential, and the overall voltage transition of the "V" shape is different. The floating method has an advantage in that the lifetime of the fluorescent lamp of the external electrode of the lamp is improved as compared with the conventional ground method. On the other hand, in order to check the state of the external electrode fluorescent lamp driven by this floating method, the detection unit 116 does not detect the current directly from the external electrode fluorescent lamp, it detects the induction current at the primary winding end of the transformer, the actual inverter Even when the external electrode fluorescent lamp is not connected, it is possible to indirectly detect information about a power source applied to the transformer output terminal.

An inverter for an external electrode fluorescent lamp according to a preferred embodiment of the present invention has the same effect. First, when driving an external electrode fluorescent lamp connected to a plurality of parallel, each of the external electrode fluorescent lamps may exhibit uniform luminance to each other. There is an advantage. Second, since the induction current can be detected through the detector under no load where the fluorescent lamp is not connected, the inverter and the backlight unit can be protected. Third, the lifetime of the lamp can be maximized by connecting the external electrode fluorescent lamp in a floating manner. In the above, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible. . Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

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1 is a configuration diagram schematically showing a configuration of a conventional inverter for external electrode fluorescent lamps.

2 is a configuration diagram schematically showing the configuration of an inverter for an external electrode fluorescent lamp according to an embodiment of the present invention.

3 is a view illustrating a lamp driving using a ground method when driving an external electrode fluorescent lamp. FIG. 4 is a view illustrating a lamp driving using a floating method when driving an external electrode fluorescent lamp. * Description of the symbols for the main parts of the drawings * 112: control unit 114: drive unit 116: detection unit 118: transformer 120: lamp 122: first electrode 124: second electrode 126: external electrode fluorescent lamp 132: first winding 134: first 2 windings

136: third winding

Claims (5)

In the inverter for driving external electrode fluorescent lamp to supply power to the external electrode fluorescent lamp, A control unit for outputting a control signal for controlling the output of power supplied from the outside; A driving unit which switches and converts power in response to the control signal; A transformer including a primary winding end to which a primary voltage is applied and a secondary winding end to which a secondary voltage derived from the primary voltage is applied to transform the power applied from the driving unit; Inverter for an external electrode fluorescent lamp having a detector for detecting a current induced in the primary winding of the transformer. The method of claim 1, And the primary winding end comprises a first winding to which a voltage is applied from the driving unit and a second winding to which an induced current is applied from the first winding. The method of claim 2, And the detection unit detects a current induced in the second winding. The method of claim 3, wherein Inverter for external electrode fluorescent lamp, characterized in that for driving by connecting the external electrode fluorescent lamp in the floating type on both ends of the secondary winding end. The method of claim 4, wherein And the control unit determines the state of the external electrode fluorescent lamp connected to the secondary winding end from the induced current detected by the detection unit.