High Voltage Transformer

1. Field of the Invention

The present invention relates to a high voltage transformer, and more particularly to a planar transformer having a sandwich structure with high voltage ratio and tolerance with high breakdown voltage.

2. Description of the Prior Art

In recent years, electronic devices of various types have been miniaturized. Magnetic elements like inductors and transformers are indispensable to the power-supply section of each electronic component. The inductors and transformers can neither be made smaller nor be integrated with the other circuit components, whereas the other circuit sections have successfully been made much smaller in the form of LSIs. Therefore the volume of the power-supply section is much greater than that of the other sections. Thus the combination of the both has an inevitable large volume.

Referring to FIG. 1, a conventional transformer applied in high voltage power supply is shown. The magnetic core 10 is composed of a plurality of I-cores or two U-cores. Two conductor windings, using respectively as a primary winding 12 and a secondary winding 14, are spiraled around a leg 10a and a leg 10b of the core 10, respectively. Although the transformer with such structure has a large voltage gain and a high voltage ratio, the size of the transformer can not be reduced, especially when the level of the required output voltage becomes large. In addition, the conventional transformer is hard to maintain a uniform quality control on the winding structure in the manufacturing process and thus influence the magnetic and electrical characteristics of the products.

To reduce the size of the magnetic elements and solve the quality control problem, small planar inductors and planar transformers have been designed. A conventional planar inductor includes a spiral planar coil, two insulation layers sandwiching the coil, and two magnetic plates sandwiching the coil and insulation layers. A conventional planar transformer includes two spiral planar coils, used as a primary winding and a secondary winding, respectively, three insulation layers sandwiching these coils, and two magnetic layers sandwiching the coils and the insulation layers. The spiral planar coils incorporated in the inductor and the transformer can be either of the two alternative types. The first type is formed by one spiral conductor. The second type is composed of an insulation layer and two spiral conductors that are mounted on the two major surfaces of the insulation layer. These planar elements are disclosed in K. Yamasawa et. al, High-Frequency of a Planar-Type Microtransformer and Its Application to Multilayered Switching Regulators, IEEE Trans.Mag., Vol. 26, No. 3, May 1990, pp. 1204-1209. Planar coils are used in planar inductors. Spiral coils are the most preferable due to their great inductance and their good Q coefficient.

In fact, planar inductors having spiral planar coils have been manufactured, one of which is schematically illustrated in FIG. 2. As FIG. 2 shows, the planar inductor includes a spiral planar coil 20 shaped like a squire plate, two polymid films 22a, 22b sandwiching the coil 20, and two Co-base amorphous alloy ribbons 24a, 24b sandwiching the coil 20 and the polymid films 22a, 22b are prepared by cutting a Co-based amorphous alloy foil made by rapidly quenching cooling the melted alloy.

Additionally, another planar magnetic element is disclosed also in U.S. Pat. No. 5,583,474. As FIG. 3 shows, this inductor has two insulation layers 32a and 32b, two magnetic layers 34a and 34b, and a spiral planar coil 30. The coil 30 is sandwiched between the insulation layers 32a and 32b. The unit consisting of the insulation layers 32a, 32b and the coil 30 is sandwiched between the magnetic layers 34a and 34b. The spiral planar coil 30 is square, each side having a length a.sub.0. The magnetic layers 34a and 34b are also square, each side having a length w. They have the same thickness t. They are spaced apart from each other by a distance g.

FIG. 4 is also an exploded view illustrating another type of a planar inductor. The planar inductor comprises three insulation layers 42a, 42b, 42c, two magnetic layers 44a, 44b, two spiral planar coils 40a, 40b, and a through-hole conductor 46. The insulation layer 42b is interposed between the coils 40a and 40b. The unit consisting of the insulation layer 42b and the coils 40a, 40b is sandwiched between the other insulation layers 42a and 42b. The unit consisting of the insulation layers 42a, 42b, 42c and the coils 40a, 40b is sandwiched between the magnetic layers 44a and 44b. The through-hole conductor 46 extends through the insulation layer 42b and electrically connects the spiral planar coils 40a and 40b. The spiral planar coils 40a and 40b shaped in a squares having a length a.sub.0 at each side. The magnetic layers 44a and 44b are also squares, each side having a length w, and have the same thickness t. The magnetic layers 44a and 44b are spaced apart from each other by a distance g.

Both planar inductors shown in FIG. 3 and FIG. 4, respectively, can be advantageous in the following two respects when appropriate values are selected for a.sub.0, w, t and g:

(1) They have an effective magnetic shield, and the leakage magnetic flux is therefore very small.

(2) They have a sufficiently high inductance.

Either planar inductor can be formed on a glass substrate, by means of thin-film process described above. Alternatively, it can be formed on any other insulated substrate (e.g., a substrate made of a high-molecular material such as polymid). The magnetic flux generated by one spiral planar coil or a plurality of spiral planar coils must be prevented from leaking from the planar inductors. Otherwise, the leakage magnetic fluxes of either inductor adversely influence the other electronic components arranged very close to the inductor and formed on the same chip, thus forming a hybrid integrated circuit. According to the above statement about both inductors, the ratio between the width w of either magnetic layer and the width a.sub.0 of the square planar coil or coils should be set at an optimum value so that the magnetic fluxes generated by the coil or coils are prevented from leaking.

As is known in the art, the characteristics of planar magnetic elements greatly depend on their structure parameters and the characteristics of the planar coils and magnetic layers. Additionally, as that has been pointed out, planar inductors and planar transformers have a limit of transformer breakdown voltage, especially depend on inserting the insulated material between planar coils, insulation layers and magnetic layers. Typically, the insulated material is ceramic around the spiral windings in the multi-layered planar inductors. This structure has an insufficient breakdown voltage such that the spark discharge will be generated. Therefore, the conventional transformer can hardly met the requirement of sufficient breakdown voltage, no leakage fluxes and sufficiently small integrated LC-circuit sections.

It is a first object of the present invention in providing a planar transformer with multi-layered spiral windings on printed circuit boards. The planar transformer can be manufactured with uniform quality control and can effectively increase the voltage gain with a high voltage output.

It is a second object of the present invention in providing a planar transformer having an appropriate breakdown distance to effectively improve the breakdown voltage.

It is a third object of the present invention to provide a planar transformer to reduce the leakage magnetic fluxes.

In accordance with the above objects, the present invention provides a high voltage transformer. A magnetic core is used as a medium that enables transfer of power. A plurality of coils served as a secondary winding is formed in a multi-layered printed circuit board (PCB), and the coils are spiraled around one leg of the magnetic core. A conductor windings using as a primary winding 12, is spiraled around another leg of the magnetic core. An anode doubling rectifier circuit and a cathode doubling rectifier circuit are respectively formed on different insulated boards. A voltage doubling rectifier circuit unit is composed of the anode doubling rectifier circuit and the cathode doubling rectifier circuit. By using the anode doubling rectifier circuit and the cathode doubling rectifier circuit sandwiching the multi-layer PCB, the voltage gain of the transformer can be increased. The voltage doubling rectifier circuit unit and multi-layer PCB are sandwiched by two magnetic caps, which results the reduction of the magnetic fluxes of the transformer. A plurality of supports are used to fix the multi-layered PCB, the voltage doubling rectifier circuit unit and two magnetic caps. Additionally, an appropriate breakdown distance can be provided by this way, and the breakdown voltage can be increased by using insulated oil.

FIG. 1 is a structural view of showing a conventional transformer applied in high voltage power supply;

FIG. 2 is a structural view of showing a first planar transformer according to the conventional method;

FIG. 3 is a structural view of showing a second planar transformer according to the conventional method;

FIG. 4 is a structural view of showing a third planar transformer according to the conventional method;

FIG. 5 is a structural view of showing a planar transformer according to the present invention;

FIG. 6 is a separated view of showing a planar transformer according to the present invention;

FIG. 7 is a view of showing the breakdown distance according to an embodiment of the present invention; and

FIG. 8 is a view of showing the breakdown distance according to an embodiment of the present invention.

FIG. 5 and FIG. 6 are the structural views of the present invention. The planar transformer structure includes a magnetic core 50 that is used as a power transformation medium. A multi-layer printed circuit board (PCB) 52 has a plurality of spiral planar coils that are used as a secondary winding. The second winding spirals around a leg 50a of the core 50. A conductor windings using as a primary winding 53 is spiraled around another leg 50b of the core 50. The multi-layer printed circuit board (PCB) 52 has an opening 60c that the leg 50a of the core 50 is passed through, and a plurality of windings are spiraled around the leg 50a. A voltage doubling rectifier circuit unit is made of an anode voltage doubling rectifier circuit 54a and a cathode voltage doubling rectifier circuit 54b which are respectively formed on a first and a second insulated boards 54a, 54b. The multi-layer printed circuit board (PCB) 52 is sandwiched between the anode voltage doubling rectifier circuit 54a and the cathode voltage doubling rectifier circuit 54b. The voltage gain can be increased by the voltage doubling rectifier circuit unit. The compounded structure of the multi-layer printed circuit board (PCB) 52 and the anode/cathode voltage doubling rectifier circuit 54a, 54b are sandwiched between two magnetic caps 56a, 56b. The two magnetic caps 56a, 56b are used to reduce the magnetic fluxes. A plurality of supports 58 are used to fix the PCB 52, the anode/cathode voltage doubling rectifier circuit 54a, 54b and two magnetic caps 56a, 56b. The breakdown distance of separated device is kept by supports 58 to increase the durability of breakdown voltage. The top magnetic cap 56a has a plurality of fist fixed-holes 58a and a first opening 60a. The first insulated board 54a that the anode voltage doubling rectifier circuit 54a is formed on has a plurality of second fixed-holes 58b and a second opening 60b. The multi-layer printed circuit board (PCB) 52 comprises a plurality of third fixed-holes 58c and a third opening 60c. The second insulated board 54b that the cathode voltage doubling rectifier circuit 54b is formed on comprises a plurality of fourth fixed-holes 58d and a forth opening 60d. The bottom magnetic cap 56b comprises a plurality of fifth fixed-holes 58e and a fifth opening 60e. The magnetic core 50 is compounded of a plurality of I-cores or two U-cores. The appearance of the magnetic core 50 is a close rectangle frame. The one leg 50a of the core 50 is passed through the third opening 60c of the multi-layer printed circuit board (PCB) 52 and another leg 50b is set outside of the multi-layer PCB 52. The high voltage transformer with high voltage output is generated by the ratio of the second winding turns to the primary winding turns.

In the transformer structure, the gap of every device influences the breakdown voltage. Therefore, it becomes very important to concern the gap of every device in designing transformer. Referring to FIG. 7, it shows an embodiment of the present invention. A x-ray power supply is applied to provide a voltage about 150 KV. The breakdown distance 7a between the multi-layer PCB 52 and the one leg 50a of the magnetic core 50 in the third opening 60c of the multi-layer PCB 52 is about 10 mm. The breakdown distance 7b between the multi-layer PCB 52 and another leg 50b of the magnetic core 50 outside of the multi-layer PCB 52 is also about 10 mm. Also, referring to FIG. 8, the breakdown distance of every device in the transformer is shown. The breakdown distance 8a between the anode/cathode voltage doubling rectifier circuit 54a, 54b and the multi-layer PCB 52 is 15 mm. The breakdown distance 8b between the top/bottom magnetic caps 56a, 56b and the anode/cathode voltage doubling rectifier circuits 54a, 54b is about 40 mm. The anode/cathode voltage doubling rectifier circuits 54a, 54b are interposed between the top/bottom magnetic caps 56a, 56b. The multi-layer PCB 52 is sandwiched between the anode/cathode voltage doubling rectifier circuits 54a, 54b. A plurality of supports 58 are used to fix the multi-layer PCB 52, the anode/cathode voltage doubling rectifier circuits 54a, 54b and the top/bottom magnetic caps 56a, 56b. The supports 58 are composed of a plurality of supporting rods. The breakdown distance of every device is formed by using the supports 58 to increase the durability of breakdown voltage.

The combined structure is positioned into an oil tank with an insulated oil. The insulated oil is then flowed into the compounded structure. The transformer is oil packed by the insulated oil to improve the capability of insulated breakdown voltage.

Accordingly, the present invention provides a transformer structure applied in the high voltage power supply. The relevant breakdown distances, such as the distance between the spiral planar coils of the multi-layer PCB and the magnetic core, the distance between the multi-layer PCB and the anode/cathode voltage doubling rectifier circuits, the distance between the anode/cathode voltage doubling rectifier circuits and the top/bottom magnetic caps, are designed in an appropriate distance. The entire combined structure is oil packed by the insulated oil. This structure can be operated with a high voltage output without inducing abnormal spark discharge. For the conventional planar transformer, although the size of the transformer will be miniaturized by using a multi-layer sandwiching structure, the breakdown distance can not be remained in an appropriate distance. Therefore, the value of breakdown voltage is decreased. Additionally, a typical insulated material such as polymid or ceramic is applied in the insulated breakdown voltage. It is observed that the conventional transformers have the problem of an insufficient breakdown voltage in an x-ray power supply applied. Therefore, the present invention eliminates these disadvantages and provides a new structure. The breakdown distance can be designed in an appropriate distance by using supports. The sandwiching structure and the insulated oil are used to generate an optimal insulated breakdown voltage. The entire structure can be simply combined and fixed. Therefore, the cost can be reduced. Additionally, in the multi-layer PCB structure, the spiral planar coils that are used as secondary winding which can effectively increase the winding turns ratio. The employment of multi-layered printed circuit boards as a secondary winding can ensure a uniform quality in manufacturing process.

Although specific embodiments including the preferred embodiment have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from the spirit and scope of the present invention, which is intended to be limited solely by the appended claims.