JP2009194202A - Current balancing transformer and discharge tube current uniform partition circuit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease the number of current balancing transformers that are required, to reduce cost and to facilitate circuit board design, thereby miniaturizing a mounting board. <P>SOLUTION: The current balancing transformer includes a magnetic core 10 that forms a closed magnetic path; two discharge tube windings N1 and N2, that are wound on the magnetic core for flowing of a discharge tube current, and a magnetic flux adjusting winding S, which is wound on the magnetic core for adjusting the magnetic flux generated by the discharge tube current that flows both discharge tube windings. The two discharge tube windings are wound so that the number of turns of winding is equal and the windings have the same polarity. The magnetic flux adjusting winding is so wound as to produce magnetic coupling with the two discharge tube windings. A plurality of such current balancing transformers are arranged. A discharge tube is connected to both discharge tube windings of each of the current balancing transformers. The magnetic flux adjusting windings of all the current balancing transformers are connected, together in series and form a closed loop. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a current balancing transformer for connecting a large number of discharge tubes to an inverter circuit and balancing the currents flowing in the respective discharge tubes during lighting, and a discharge tube current equalizing circuit using the current balancing transformer. This technique is particularly useful for backlights of large liquid crystal panels.

  As is well known, in a liquid crystal TV of a medium size or larger, four or more discharge tubes (cold cathode tubes) are used as a backlight for the liquid crystal panel. In the backlight, it is important to illuminate the entire liquid crystal panel as uniformly as possible. For this purpose, it is necessary to flow current as uniformly as possible to each discharge tube.

  In the past, one inverter circuit was provided for one discharge tube, and the discharge tube current was controlled independently by each inverter circuit, so that all the discharge tube currents were balanced. However, this method requires the same number of inverter circuits as the number of discharge tubes, so that it is difficult to reduce the size, and a large number of parts are used, resulting in high costs.

  In order to solve such a problem, a technique has been proposed in which a current balancing transformer is interposed between the inverter circuit and the discharge tube to evenly distribute the current flowing through each discharge tube. For example, a so-called common balance system (refer to Patent Document 1) in which current balancing transformers for supplying discharge tube current to two windings wound in opposite polarities are arranged in a tree shape, or primary winding for supplying discharge tube current, respectively. There is a so-called gin balance system (see Patent Document 2) in which a current balance transformer having a secondary winding connected in a loop with a line is provided for each discharge tube. As a result, the number of inverter circuits can be reduced. However, the former requires the number of discharge tubes-1 and the latter requires the same number of current balance transformers as the number of discharge tubes.

In the case where the liquid crystal panel is relatively small, the number of discharge tubes (cold cathode tubes) used for the backlight is small, so that no significant problem occurs. However, in recent years, the number of discharge tubes used for backlights has increased remarkably due to the increase in size of liquid crystal panels. Specifically, 20 discharge tubes are used for a 40 inch panel and 24 discharge tubes are used for a 46 inch panel. Therefore, in the configuration as described above, almost the same number of current balancing transformers as the number of discharge tubes are required. As a result, not only the circuit board design becomes complicated, but also the cost and mounting area of the current balancing transformer increases, and the mounting board becomes large. Can not be ignored.
JP-A-6-269125 Special table 2007-507855 gazette

  The problem to be solved by the present invention is to reduce the number of current balancing transformers required, thereby reducing costs, facilitating circuit board design, and reducing the size of the mounting board.

  The present invention relates to a magnetic core that forms a closed magnetic circuit, two discharge tube windings that are wound around the magnetic core and through which a discharge tube current flows, and a discharge tube that is wound around the magnetic core and flows through both of the discharge tube windings. A magnetic flux adjusting winding for adjusting a magnetic flux generated by an electric current, and the two discharge tube windings are wound with the same number of turns and the same polarity. The current balance transformer is wound so as to be magnetically coupled with two discharge tube windings.

  Here, the magnetic core is typically composed of a combined core that has a central leg and outer legs located on both sides thereof, thereby forming a closed magnetic circuit, and each of the magnetic cores is connected to a discharge tube at a portion near both ends of the central leg. Windings are wound, and a magnetic flux adjusting winding is wound around the central portion of the central leg between them.

  In the present invention, a plurality of such current balance transformers are arranged, and the discharge tubes are connected to the discharge tube windings of each current balance transformer, and the magnetic flux adjusting windings of all the current balance transformers are connected in series. It is a discharge tube current equal distribution circuit that is connected to form a closed loop.

  Further, the current balancing transformer according to the present invention may be configured such that a detection winding for detecting a discharge tube current flowing through the discharge tube winding is wound around the central portion of the center leg together with the magnetic flux adjustment winding.

  In the present invention, a plurality of such current balance transformers are arranged, and the discharge tubes are connected to both discharge tube windings of each current balance transformer, and the magnetic flux adjusting windings of all the current balance transformers are connected in series. It is a discharge tube current equal distribution circuit which forms a closed loop by connecting, returns the detection output of the detection winding to the control unit, and controls the operation of the inverter circuit.

  According to the present invention, basically, one inverter circuit and half the current balance transformer of the discharge tube are used for the required number of discharge tubes, so that the current flowing through all the discharge tubes can be made uniform. The discharge tube current equal distribution circuit can be configured, so that the mounting board can be reduced in size and cost can be reduced.

  FIG. 1 is an explanatory view showing an embodiment of a current balancing transformer according to the present invention. In the figure, A shows the plane of the current balance transformer, B shows the equivalent circuit, and C shows the shape of the magnetic core and the magnetic flux flowing through it (indicated by a broken line). This current balancing transformer includes a magnetic core 10 forming a closed magnetic circuit, two discharge tube windings N1 and N2 wound around the magnetic core 10 and through which a discharge tube current flows, and both of the windings wound around the magnetic core 10 A magnetic flux adjusting winding S for adjusting the magnetic flux generated by the discharge tube current flowing through the discharge tube windings N1 and N2 is provided.

  As shown in FIG. 1C, the magnetic core 10 has a combination structure in which a central leg 12 and outer legs 14 located on both sides thereof are formed, thereby forming a sun-shaped closed magnetic circuit. Here, a combination of a rectangular frame core (shaped core) serving as an outer leg and an I-shaped core serving as a central leg is used. Discharge tube windings N1 and N2 are wound around portions near both ends of the I-shaped core serving as the central leg, and a magnetic flux adjusting winding S is wound around the central portion of the I-shaped core therebetween.

  In this current balance transformer, the two discharge tube windings N1, N2 have the same number of turns and are wound with the same polarity, and the magnetic flux adjusting winding S includes the two discharge tube windings N1, N2. Are wound so that magnetic coupling occurs (see B in FIG. 1). For example, the two discharge tube windings N1 and N2 are 800 turns, the magnetic flux adjusting winding S is 24 turns, and the like. Accordingly, the discharge tube current flowing through the two discharge tube windings N1 and N2 flows in the same direction using a common closed magnetic circuit (indicated by a broken line) as shown in FIG. A magnetic flux adjusting current is induced in the magnetic flux adjusting winding S by the magnetic flux generated by the discharge tube current.

  In the above description, a combination of a square frame core (shaped core) and an I core is used as the magnetic core 10, but a combination of two E cores may be used. In practice, as shown in FIG. 1A, the magnetic core 10 is assembled in the bobbin 18 in which the terminal 16 is implanted, and the winding terminal is entangled with the terminal 16 and soldered. Although not shown, a structure in which a cover for improving the withstand voltage is arranged between the magnetic core and the winding is also possible.

  FIG. 2 is a circuit diagram showing an embodiment of a discharge tube current equalizing circuit according to the present invention. Here, the simplest example using four discharge tubes is shown. Two current balancing transformers 20 described in FIG. 1 are juxtaposed on the high voltage side of a discharge tube (cold cathode tube) 22. One end of the discharge tube 22 is connected to one end of each of the discharge tube windings of both current balance transformers 20, and the other end of the discharge tube 22 is grounded. The other end (winding start end) of the discharge tube winding is connected in common and connected to the output winding of the inverter transformer 26 of the inverter circuit 24. Accordingly, regarding each current balancing transformer 20, the discharge tube current flowing through the two discharge tube windings N1 and N2 flows in the same direction using a common closed magnetic circuit. The magnetic flux adjusting windings S of both current balance transformers 20 are connected in series in the same direction to form a closed loop.

  With this configuration, a discharge tube current flows through each discharge tube 22 through the discharge tube windings N1 and N2 wound around each current balancing transformer 20 by the inverter circuit 24. Both of the discharge tube windings N1 and N2 use a common closed magnetic circuit, and have the same number of turns and are wound with the same polarity. Therefore, the magnetic fluxes of both the discharge tube windings N1 and N2 act, Both discharge tube currents work to be equal to each other. Further, since the magnetic flux adjusting winding S is wound so as to be magnetically coupled with the two discharge tube windings N1 and N2, a magnetic flux adjusting current is induced in the magnetic flux adjusting winding S. . At this time, since the magnetic flux adjusting windings S of the current balancing transformers 20 are connected in series, the currents flowing through the magnetic flux adjusting windings S of the current balancing transformers 20 are equal. As a result, the currents flowing through all four discharge tubes are uniform.

  Therefore, in this discharge tube current equalizing circuit, even if the number of discharge tubes increases, the current balance transformer is only half the number of necessary discharge tubes. Therefore, the mounting board can be reduced in size and cost.

  FIG. 3 is a circuit diagram showing another embodiment of the discharge tube current equalizing circuit according to the present invention. In this example, unlike the embodiment shown in FIG. 2, the current balancing transformer 20 is arranged on the low pressure side of the discharge tube (cold cathode tube) 22. In this way, the current balance transformer 20 can be arranged on the low pressure side of the discharge tube 22. One end of each discharge tube 22 is connected in common and connected to the output winding of the inverter transformer 26 of the inverter circuit 24, and the other end of each discharge tube 22 has the same polarity of the discharge tube windings N 1 and N 2 of the current balancing transformer 20. Connected to the winding end. The magnetic flux adjusting windings S of each current balance transformer 20 are connected in series so as to form a closed loop. The function of evenly distributing the discharge tube current by the current balance transformer is the same as in the case of FIG.

  FIG. 4 is a circuit diagram showing still another embodiment of the discharge tube current equalizing circuit according to the present invention. 2 to 3 are examples in which the discharge tube is driven with a single voltage, the example shown in FIG. 4 uses a two-output transformer with an intermediate tap grounded as the inverter transformer 28 of the inverter circuit 24. The discharge tube 22 is configured to be driven with both voltages. In this discharge tube current equalizing circuit, it is necessary to use a two-output transformer, but two one-output transformers may be used. One end of the output winding of the inverter transformer 28 is connected to the winding start end of the discharge tube winding N1 of one current balancing transformer 20, and the winding end end is connected to one end of two discharge tubes 22 connected in series. The other end is connected to the winding start end of the other current balancing transformer 20, and the winding end end is connected to the other end of the output winding of the inverter transformer 28. Here again, the magnetic flux adjusting windings S of both current balancing transformers 20 are connected in series to form a closed loop.

  FIG. 5 is a circuit diagram showing another embodiment of the discharge tube current equalizing circuit according to the present invention. This is also an example of the dual voltage drive method. In this circuit example, a plurality of single-output transformers are used, and the current balance transformer 20, the inverter circuit 24, and the inverter transformer 26 are symmetrically arranged on both sides of the discharge tube 22. All of the magnetic flux adjusting windings S of the four current balancing transformers 20 are connected in series to form a closed loop. Although this circuit configuration can drive both voltages of the discharge tube, it requires two inverter circuits and the same number of current balancing transformers as the discharge tube. Although it is not preferable in terms of the number of parts, it is possible to use the current balance transformer of the present invention in such a circuit system. Incidentally, if such a circuit is configured in the prior art, a larger number of current balancing transformers are required, so that the number of current balancing transformers can be reduced by the present invention.

  FIG. 6 is an explanatory view showing another embodiment of the current balancing transformer according to the present invention. A shows a plane, and B shows an equivalent circuit.

  This current balancing transformer includes a magnetic core 10 forming a closed magnetic circuit, two discharge tube windings N1 and N2 wound around the magnetic core 10 and through which a discharge tube current flows, and both of the windings wound around the magnetic core 10 A magnetic flux adjusting winding S for adjusting the magnetic flux generated by the discharge tube current flowing through the discharge tube windings N1 and N2, and a detection winding D for detecting the discharge tube current flowing through the discharge tube windings N1 and N2 are provided. is doing.

  This magnetic core is also composed of a combination core having a central leg and outer legs located on both sides thereof, thereby forming a sun-shaped closed magnetic circuit. Here, a combination of a rectangular frame core (shaped core) serving as an outer leg and an I-shaped core serving as a central leg is used. Discharge tube windings N1 and N2 are wound around the ends of the I-shaped core serving as the central leg, respectively, and the magnetic flux adjusting winding S and the detection winding D are wound around the central portion of the I-shaped core between them. It is done.

  FIG. 7 is a circuit diagram showing an embodiment of a discharge tube current equalizing circuit using this current balance transformer. This example also shows the simplest configuration using four discharge tubes. Two current balancing transformers 30 described in FIG. 6 are juxtaposed on the high voltage side of the discharge tube (cold cathode tube) 22. One end of the discharge tube 22 is connected to one end of each of the discharge tube windings N1, N2 of both current balance transformers 30, and the other end of the discharge tube 22 is grounded. The other ends (winding start ends) of the discharge tube windings N1 and N2 are connected in common and connected to the output winding of the inverter transformer 26 of the inverter circuit 24. Accordingly, for each current balancing transformer 30, the discharge tube current flowing through the two discharge tube windings N1 and N2 flows in the same direction using a common closed magnetic circuit. Further, the magnetic flux adjusting windings S of both current balance transformers 30 are connected in series to form a closed loop. The reason why the current flowing through each discharge tube is made uniform is the same as described with reference to FIG.

  In this embodiment, the detection winding D is wound around the current balance transformer 30 as described above, and the output of each detection winding D is sent to the control unit 32, and the control unit 32 generates an inverter circuit. 24 is configured to control. For example, when an abnormality occurs, such as when one discharge tube is cut off, the magnetic flux of the current balance transformer 30 changes, so that it can be detected by the detection winding D, and the inverter 32 in the control unit 32 in consideration of safety. Can be stopped.

  In the above embodiments, the number of discharge tubes is four, but it goes without saying that the present invention can also be applied to a large number of discharge tubes, such as twenty or twenty-four. In a normal circuit configuration, 10 current balanced transformers are used when 20 discharge tubes are driven to light, and 12 current balanced transformers are used when 24 discharge tubes are driven to be lighted. Therefore, as the number of discharge tubes increases, the reduction effect of the current balance transformer increases.

Explanatory drawing which shows one Example of the current balance transformer which concerns on this invention. The circuit diagram which shows one Example of the discharge tube current equal distribution circuit which concerns on this invention. The circuit diagram which shows the other Example of the discharge tube current equal distribution circuit which concerns on this invention. The circuit diagram which shows the further another Example of the discharge tube electric current equal distribution circuit which concerns on this invention. The circuit diagram which shows the other Example of the discharge tube current equal distribution circuit which concerns on this invention. Explanatory drawing which shows the other Example of the current balance transformer which concerns on this invention. The circuit diagram which shows the Example of the discharge tube current equal distribution circuit which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Magnetic core 12 Central leg 14 Outer leg 16 Terminal 18 Bobbin 20 Current balance transformer 22 Discharge tube 24 Inverter circuit 26 Inverter transformer N1, N2 Discharge tube winding S Magnetic flux adjustment winding

Claims (5)

  A magnetic core that forms a closed magnetic circuit, two discharge tube windings that are wound around the magnetic core and through which a discharge tube current flows, and a discharge tube current that is wound around the magnetic core and flows through both of the discharge tube windings are generated. And the two discharge tube windings are wound with the same number of turns and the same polarity, and the magnetic flux adjustment winding includes the two discharge tube windings. A current balance transformer which is wound so as to generate magnetic coupling with a wire.   The magnetic core has a central leg and outer legs located on both sides thereof, and is composed of a combination core that forms a closed magnetic circuit by them, and discharge coil windings are wound around portions near both ends of the central leg, respectively. 2. A current balancing transformer according to claim 1, wherein a magnetic flux adjusting winding is wound around a central portion of the central leg between the two.   3. A current balancing transformer according to claim 2, wherein a detection winding for detecting a discharge tube current flowing through the discharge tube winding is wound around the central portion of the center leg together with the magnetic flux adjustment winding.   A plurality of current balancing transformers according to claim 1 or 2 are provided, the discharge tubes are connected to the windings for both discharge tubes of each current balancing transformer, and the magnetic flux adjusting windings of all the current balancing transformers are connected in series. The discharge tube current distribution circuit is designed to form a closed loop.   A plurality of current balancing transformers according to claim 3 are provided, and the discharge tubes are respectively connected to the windings for both discharge tubes of each current balancing transformer, and the flux adjusting windings of all the current balancing transformers are connected in series and closed. A discharge tube current equalizing circuit which forms a loop and returns the detection output of the detection winding to the control unit to control the operation of the inverter circuit.

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