Inverter Transformer and Discharge Tube Drive Circuit Using the Same

Abstract

An inverter transformer to which coils for a balance transformer are integrally assembled. The inverter transformer is employed in a drive circuit for evenly driving a plurality of discharge tubes, and includes a primary coil and a secondary coil. The present invention proposes the inverter transformer which performs reduction in the number of components and in the size thereof by providing a through-hole a portion of a magnetic core section made from magnetic material configuring the inverter transformer, and by providing coils for a balance transformer through the through-hole.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views designating configurations of an inverter transformer according to a first embodiment of the present invention,

FIG. 2 is one example of a cold cathode discharge tube drive circuit to which the inverter transformer according to the first embodiment of the present invention is applied,

FIGS. 3A-3D are views of configurations of cores in the inverter transformers according to the second to fifth embodiments of the present invention, and

FIG. 4 is an exploded perspective view of the inverter transformer according to sixth embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiment 1

FIG. 1A shows an external perspective view of an inverter transformer 1 according to a first embodiment of the present invention. FIG. 1B shows only a core section of the inverter transformer 1 in FIG. 1A. In FIGS. 1A and 1B, the inverter transformer 1 is configured with an H-shaped core 2, I-shaped cores 3 and 4, and a bobbin 5 to be wound coil. The H-shaped core 2 and the I-shaped cores 3 and 4 are assembled with the bobbin 5. These cores 2, 3 and 4 are made from magnetic material. Further, the bobbin 5 is made from an insulating material having electric and magnetic insulating characteristics.

Primary coils T1-11 and T1-12 for the inverter transformer 1 are wound on a center core portion H1 of the H-shaped core 2, and secondary coils T1-21 and T1-22 for the inverter transformer 1 are respectively wound on the I-shaped cores 3 and 4. In addition, there is provided a through-hole 6 at one side core portion H2 of the side core portions H2 and H3 in the H-shaped core 2, and as shown in FIG. 1A, primary and secondary coils CT1-1 and CT1-2 for a balance transformer are wound through the through-hole 6. Reference 7 designates a terminal group divided into a plurality of terminals, and they are connected to respective end of the coils for the inverter transformer and the balance transformer for external wirings.

As described above, it becomes possible to present an inverter transformer achieving reduction of weight, size and fabrication costs by providing the through-hole 6 at a portion of the core section used in the inverter transformer 1, and by winding the coils CT1-1 and CT1-2 for the balance transformer.

A position of the through-hole 6 is set so that a magnetic flux generated by the primary coils T1-11 and T1-12 and the secondary coils T1-21 and T1-22 and flow through the H-shaped core 2 and a magnetic flux generated by the coils CT1-1 and CT1-2 for the balance transformer and flow through the H-shaped core do not interfere to each other.

For example, in FIG. 1A, if the relation between a length A1 and a length A2 is A1>A2, a fair amount of magnetic flux interferences can be suppressed. The inverter transformer according to the first embodiment of the present invention, it is able to achieve a downsized inverter transformer by integrating the coils for the balance transformer.

It is able to form the through-hole 6 by modification after the H-shaped core 2 is formed, or the through-hole 6 is formed simultaneously with the H-shaped core 2 using a mold for the H-shaped core 2 having a function to form the through-hole 6. In case of designing a size of the H-shaped core, it is preferable to design a size L2 of the core portion H2 on which the through-hole 6 is formed is longer than a size L1 of the core portion H3 on which the through-hole 6 is not formed. Thus formed balancer transformer is resultantly configured with quasi-toroidal core form by providing a through-hole at an end of a core portion made from magnetic material and on which coils for an inverter transformer are wound. Accordingly, costs of material are reduced, and the number of components is also reduced, so that it becomes possible to reduce the fabrication cost. Further, the inverter transformer of the invention becomes equivalent to such inverter transformer that is added a balance transformer with a toroidal core. Further, it is able to form a toroidal-shaped balance transformer so that a magnetic gap error and an assembling error do not occur, and only errors due to fluctuation of the material exist. Therefore, it becomes possible to fabricate an inverter transformer having less impedance fluctuation and high precision.

FIG. 2 shows one embodiment of a cold cathode discharge tube drive circuit to which the inverter transformer 1 shown in FIGS. 1A and 1B is applied.

A DC voltage is applied to power source terminals 21 and 22, and is supplied to a control circuit 23 and a switching circuit 24, respectively. In this case, the power source terminal 22 is connected to ground. The control circuit 23 includes an oscillator circuit or a PWM circuit inside, and a switching signal outputted there-from is modulated by a F/B signal that is described later. A switching circuit 24 includes a switch circuit configured with transistors, switches the DC voltage applied to the power source terminal 21 with the switching signal supplied from the control circuit 23, and outputs a pulse drive signals (drive voltage) generated by the switching. The cold cathode discharge tube drive circuit shown in FIG. 2 employs two inverter transformers illustrated in FIGS. 1A and 1B. Namely, each of inverter transformers T1 and T2 corresponds to the inverter transformer 1 in FIGS. 1a and 1B.

As shown in the figure, the primary coils CT1-1 and CT2-1 of the two balance transformers are connected in series, and at both ends of the series connection are applied with pulse drive signals (drive voltage) from the switching circuit 24.

The secondary coil CT1-2 for the balance transformer in the inverter transformer T1 is connected to the primary coils T1-11 and T1-12 in the inverter transformer T1 in series as shown in FIG. 2, and pulse drive signals are applied to both ends of the primary coils T1-11 and T1-12.

Further, the secondary coil CT2-2 for the balance transformer in the inverter transformer T2 is connected to the primary coils T2-11 and T2-12 in the inverter transformer T2 in series as shown in FIG. 2, and pulse drive signals are applied to both ends of the primary coils T2-11 and T2-12.

Further, one terminal of the secondary coil T1-21 in the inverter transformer T1 is connected to ground by way of a cold cathode discharge tube FL1-1 and a resister R1-1, and another terminal is connected directly to ground. Similarly, one terminal of the secondary coil T1-22 in the inverter transformer T1 is connected to ground by way of a cold cathode discharge tube FL1-2 and a resister R1-2, and another terminal is connected directly to ground.

Further, one terminal of the secondary coil T2-21 in the inverter transformer T2 is connected to ground by way of a cold cathode discharge tube FL2-1 and a resister R2-1, and another terminal is connected directly to ground. Similarly, one terminal of the secondary coil T2-22 in the inverter transformer T2 is connected to ground by way of a cold cathode discharge tube FL2-2 and a resister R2-2, and another terminal is connected directly to ground. Further, a connecting mid-point of the cold cathode discharge tube FL2-2 and the resister R2-2 is derived and supplied to the control circuit 23 as the F/B signal for controlling the current flowing through the cold cathode discharge tube FL2-2.

In the cold cathode discharge tube drive circuit using the inverter transformers T1 and T2 of the present invention such as shown in FIG. 2, the switching signal is modulated in accordance with an oscillation frequency of the oscillation circuit or a pulse width modulation by the PWM circuit included in the control circuit 23 by feeding back the F/B signal to the control circuit 23. Thereby, the current flowing through the cold cathode discharge tube FL2-2 is controlled to be constant and emission brightness thereof becomes constant. Further by providing coils for the balance transformer, the currents flowing through the inverter transformers T1 and T2 are controlled to be equal, and it becomes possible to have all cold cathode discharge tubes FL1-1 to FL2-2 emit evenly,

The inverter transformers T1 and T2 to be used in the cold cathode discharge tube drive circuit as shown in FIG. 2 employ such inverter transformer that uses two primary coils, two secondary coils and coils for balance transformer. However, a configuration of the inverter transformer, a relation between the inverter transformer and the discharge tubes, and a connecting relation to the coils for the balance transformer are not limited to those described above, and may be modified in a wide variety.

Embodiments 2 to 5

FIGS. 3A to 3D show configurations of core sections according to second to fifth embodiments of the present invention. The inverter transformer according to second embodiment uses two E-shaped cores 31 and 32 as shown in FIG. 3A. In this case, a through-hole 30 for coils for balance transformer is provided at the E-shaped core 32.

Further, the inverter transformer according to third embodiment uses one I-shaped core 33 and one E-shaped core 34 as shown in FIG. 3B. In this case, the through-hole 30 for coils of balance transformer is provided at the I-shaped core 34.

Still further, the inverter transformer according to fourth embodiment uses one I-shaped core 35 and one U-shaped core 36 as shown in FIG. 3C. In this case, the through-hole 30 for coils of balance transformer is provided at the U-shaped core 36.

In addition, the inverter transformer according to fifth embodiment uses one I-shaped core 37 and one E-shaped core 38 as shown in FIG. 3D. In this case, the through-hole 30 for coils of balance transformer is provided at the E-shaped core 38.

The above-mentioned embodiments 2 to 5 only show some of embodiments of the present invention, and it is possible to modify these embodiments with a similar manner.

In any of above mentioned embodiments shown in FIG. 3A to 3D, the position of the through-hole 30 is also set so that a magnetic flux generated by the primary coils T1-11 and T1-12 and the secondary coils T1-21 and T1-22 in the inverter transformer 1 and a magnetic flux generated by the coils CT1-1 and CT1-2 of the balance transformer do not interfere to each other. Accordingly, a core section where a through-hole is provided is made wider. In any of the embodiments, an entire core section where a through-hole is provided is made wider, however, it may be made wider only a portion where a through-hole is provided. For example, it is possible to reduce the amount of use of the core material by configuring the core portions as shown in FIGS. 3A, 3B, and 3D.

Embodiment 6

FIG. 4 is a perspective view showing one example of an inverter transformer assembled in a box shape according to sixth embodiment of the present invention. In this FIG. 4, an inverter transformer 40 uses both a lid section 41 and a base section 42 being made from magnetic material. In addition, there are provided a primary coil T40-1 and a secondary coil T40-2 for the inverter transformer 40. The secondary coil T40-2 is fit inside of the primary coil T40-1 when assembled.

In this case, an inner surface of the primary coil T40-1 is positioned by an outer surface of an arc-shaped guide 45, and an outer surface of the secondary coil T40-2 is positioned by an inner surface of the arc-shaped guide 45, respectively. Reference 40 is a mid-leg portion penetrating through the both coils T40-1 and T40-2. In this case, references 43 and 44 are auxiliary base section for extracting terminals and after being assembled, these are configured to be fit on both side portions of the base section 42. In this sixth embodiment, a through-hole 47 is provided at a corner of the lid section 41 for the coils of the balance transformer

In this sixth embodiment, a position of the through-hole 47 is also set so that a magnetic flux generated by the primary coils and the secondary coils and flow through the H-shaped core 2 and a magnetic flux generated by the coils of the balance transformer and flow through the H-shaped core do not interfere to each other. Accordingly, it is also possible to provide the through-hole 47 at any position of the lid section 41 or base section 42, if the fluxes do not interfere to each other.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An inverter transformer having core section made of magnetic material, and primary and secondary coils provided on said core section, comprising: a through-hole at the core section; andadditional coils wound through the through-hole.

2. The inverter transformer according to claim 1, wherein said additional coils configure a balance transformer.

3. The inverter transformer according to claim 1, wherein the through-hole is provided at a position of the core section and positioned apart from the primary and/or secondary coils at the core section.

4. The inverter transformer according to claim 1, wherein the core section is configured with an H-shaped core, and an I-shaped core, andsaid primary coil is wound on the H-shaped core, and said secondary coil is wound on the I-shaped core.

5. The inverter transformer according to claim 4, wherein the H-shaped core has two guards, andthe through-hole is provided at one of the two guards, which is longer in size than the other.

6. An inverter transformer having a core section configured with magnetic material for magnetically coupling primary coils and secondary coils, comprising: through-hole formed at an end portion of the core section; andcoils for a balance transformer wound through the through-hole.

7. The inverter transformer according to claim 6, wherein the through-hole is provided at a position of the core section and positioned apart from the primary and/or secondary coils at the core section.

8. The inverter transformer according to claim 6, wherein the core section is configured with an H-shaped core, and an I-shaped core, andsaid primary coils are wound on the H-shaped core, and said secondary coils are wound on the I-shaped core.

9. The inverter transformer according to claim 6, wherein the H-shaped core has two guards, andthe through-hole is provided at one of the two guards, which is longer in size than the other.

10. A discharge tube drive circuit comprising: at least two inverter transformers each cited in claim 6; anda switching circuit for supplying a switching pulses to at least two inverter transformers, whereinone primary coils of at least two inverter transformers and one secondary coil of the balance transformer are connected in series and connected to the switching circuit,each two primary coils of the balance transformer are connected in series and connected to the switching circuit.