High voltage circuit with arc protection

A high voltage circuit with arc protection comprises a circuit board, having a top surface and a bottom surface, and includes at least two electronic components in a circuit. An enclosure substantially surrounds the circuit board. A voltage differential of at least 5000 volts can exist between the enclosure and at least one of the electronic components. At least one electrically conductive plate is disposed between the top surface of the circuit board and the enclosure, disposed between the bottom surface of the circuit board and the enclosure, electrically insulated from the circuit board and the enclosure, and provides arc protection between at least one electronic component on the circuit board and the enclosure.

BACKGROUND

Unshielded, or insufficiently shielded, electronic components or electric circuits can be damaged due to arcing or short circuits. In very high voltage applications, it can be difficult to provide sufficient shielding to avoid such arcing or short circuits. For example, in a power supply for a small x-ray tube, a voltage differential of greater than 10 kV may exist between electronic components and a housing and the electronic components and housing may be separated by a distance of only about 1 cm. Potting may be used as an insulator, but such potting can break down, thus resulting in arcing or short circuits. Minor defects in the potting, including defects that cannot be visually observed, can allow such arcing or short circuits.

Shown inFIG. 7is a prior art circuit board11with traces62and electronic components13-14. Corners or sharp areas73on the components or connections to the components can have very high electric field strength if there is a large voltage difference between the corners or sharp areas73and a device77. The electric field strength at such corners or sharp areas73can be substantially higher than the electric field strength at broader areas74of the components.

SUMMARY

It has been recognized that it would be advantageous to have a circuit design which provides improved shielding of electronic components and which reduces the electric field strength.

In one embodiment, the present invention is directed to a circuit board configured to operate as a corona guard that satisfies the need of improved shielding of electronic components and which reduces the electric field strength. The circuit board comprises at least one conductive trace disposed on a first insulating substrate and at least one conductive trace disposed on a second insulating substrate. The conductive trace disposed on the first insulating substrate can face the conductive trace disposed on the second insulating substrate. At least one electronic component can be electrically connected between the traces. The first and second insulating substrates substantially can surround the electronic component on at least two sides.

In another embodiment, the present invention is directed to a high voltage circuit with arc protection that satisfies the need of improved shielding of electronic components. The high voltage circuit with arc protection comprises a circuit board, having a top surface and a bottom surface, and including at least two electronic components in a circuit. An enclosure substantially surrounds the circuit board. A voltage differential of at least 5000 volts exists between the enclosure and at least one of the electronic components. At least one electrically conductive plate is disposed between the top surface of the circuit board and the enclosure, disposed between the bottom surface of the circuit board and the enclosure, electrically insulated from the circuit board and the enclosure, and provides arc protection between at least one electronic component on the circuit board and the enclosure.

DEFINITIONS

As used herein, the term “arc protection” means a device that protects against undesirable arcing between two devices at different voltages.As used herein, the term “corona guard” can refer to a device that reduces a voltage gradient.As used in this description and in the appended claims, the word “electronic component” does not include conductive wires, conductive traces, or connectors which merely connect one circuit to another. “Electronic component” does include, without limitation, devices which amplify, control, or switch voltages or currents without mechanical or other nonelectrical commands. “Electronic component” includes devices such as capacitors, resistors, diodes, transistors, integrated circuits, semiconductors, transistors, amplifiers, and inductors.As used herein, the term “high voltage” or “higher voltage” refer to the DC absolute value of the voltage. For example, negative 1 kV and positive 1 kV would both be considered to be “high voltage” relative to positive or negative 1 V. As another example, negative 40 kV would be considered to be “higher voltage” than 0 V.As used herein, the term “low voltage” or “lower voltage” refer to the DC absolute value of the voltage. For example, negative 1 V and positive 1 V would both be considered to be “low voltage” relative to positive or negative 1 kV. As another example, positive 1 V would be considered to be “lower voltage” than 40 kV.As used herein, the terms “potting material” and “potting” mean insulating compounds, such as pourable insulating resins, that can be cast into cavities containing electronic components to insulate and protect the electronic components.As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result.

DETAILED DESCRIPTION

As illustrated inFIG. 1, a circuit board configured to operate as a corona guard10, includes at least one conductive trace12adisposed on a first insulating substrate11aand at least one conductive trace12bdisposed on a second insulating substrate11b. The conductive trace(s)12adisposed on the first insulating substrate11acan face the conductive trace(s)12bdisposed on the second insulating substrate11b. At least one electronic component13-15can be electrically connected between the two insulating substrates by electrical connection to the conductive traces. The first and second insulating substrates can substantially surround the electronic component(s) on at least two sides. In one embodiment, the conductive trace(s)12on each insulating substrate can comprise at least 3 electrically separate conductive traces. The first and second insulating substrates can be attached by insulating substrate material or there can be no insulating material connecting the two substrates. Insulating substrates11can be flexible or non-flexible material.

A traces12on the circuit can be separated from a device17and a substantial voltage differential may exist between at least one of the traces12and the device17. For example, in an x-ray source power supply, the circuit could be used to generate a high voltage differential across an x-ray tube. The device17could be a casing or shell to house the x-ray source. A voltage differential between the device17and at least one of the traces12could be at least 30 kilovolts (kV).

Various types of electronic components13-15could be used, such as capacitors, resistors, diodes, transistors, integrated circuits, semiconductors, transistors, amplifiers, and inductors. For example, electronic component13could be a capacitor with metallic ends16. Corners18on the ends16can be shielded from the device17by the trace12a, thus reducing the electric field strength at the corners18.

As illustrated inFIG. 2, an example of an electronic component23is shown. In one embodiment, a width Cw of the electronic component23can be at least as wide as a width Tw of the trace22. In another embodiment, a width Cw of the electronic component23can be at least 1.2 times wider than a width Tw of the trace22. In another embodiment, a width Cw of the electronic component23can be at least 1.5 times wider than a width Tw of the trace22. Wider traces can help shield the component and reduce the electric field strength thus helping to avoid arcing or short circuiting. Note that in a single plane of the trace, such plane parallel with a surface of the insulating substrate to which the trace is attached, there exists a “width” and a “length” of the trace. The length would be the longer of the two dimensions “width” and “length”. Width of a trace is a dimension perpendicular to the length. The electronic component23can be representative of any electronic component in any of the invention embodiments described herein. The trace22can be representative of any trace in any of the invention embodiments described herein.

In a circuit board configured to operate as a corona guard30shown inFIG. 3, an insulating substrate31can substantially surround at least one electronic component33on at least three sides. Traces12and electronic component(s)33can be disposed on the substrate31in a similar manner as was described previously for the circuit board10shown inFIG. 1. The insulating substrate31can comprise a flexible material. The conductive traces12on the insulating substrate31can act as a corona guard for the electronic component(s)33.

In a circuit board configured to operate as a corona guard50shown inFIG. 5, an insulating substrate31and traces52can substantially surround at least one electronic component33on at least three sides. For example, at least one trace52acan attach to the electronic component(s)33on one end of the component(s)33and can substantially surround the component33on at least two sides. At least one trace52bcan attach to the electronic component(s)33on an opposite end of the component(s)33and can substantially surround the electronic component(s)33on at least one side. Traces52and electronic component(s)33can be disposed on the substrate31in a similar manner as was described previously for the traces12and electronic component(s)13-15of the circuit board10shown inFIG. 1. The insulating substrate31can comprise a flexible material. The conductive traces52on the insulating substrate31can act as a corona guard for the at least one electronic component13.

As shown inFIG. 4, The various circuit board embodiments described herein45may be used in an x-ray source40. The x-ray source40can comprise an x-ray tube43including an anode41and a cathode42at opposing ends of the tube43and a voltage differential between the anode41and the cathode42. The voltage differential can be supplied by the circuit board45. In one embodiment, the voltage differential can be at least about 5 kilovolts. In another embodiment, the voltage differential can be at least about 30 kilovolts. The circuit board45and the x-ray tube43can be enclosed in a container44. The container44can be maintained at approximately zero volts. In one embodiment, a voltage differential between at least one component in the circuit45and the container can be at least about 5 kilovolts. In another embodiment, a voltage differential between at least one component in the circuit45and the container can be at least about 30 kilovolts.

Use of the various circuit board embodiments described herein can reduce electric field strength at or near the electronic components13-15or33or at or near traces12or52. For example, a device17can be disposed on an opposing side of the insulating substrate11or31from the conductive trace12or52. Between the device17and the trace12or52, there may be (1) a voltage differential of at least 1 kilovolt, at least 25 kilovolts, or at least 45 kilovolts, (2) a distance d of less than about 3 centimeters, and (3) a maximum electric field strength of less than about 240 kilovolts per centimeter.

Also, in this same embodiment there can be between the device17and at least one of the electronic components13-15or33(1) a voltage differential of at least 1 kilovolt, at least 25 kilovolts, or at least 45 kilovolts, (2) a distance d of less than about 3 centimeters, and (3) a maximum electric field strength of less than about 240 kilovolts per centimeter. In another embodiment, between the device17and the trace12or52and/or, at least one of the electronic components13-15or33there may be (1) a voltage differential of at least 25 kilovolts or at least 45 kilovolts, (2) a distance d of less than about 2 centimeters, and (3) a maximum electric field strength of less than about 200 kilovolts per centimeter.

Another embodiment of the present invention is a high voltage circuit with arc protection60shown inFIG. 6. The high voltage circuit with arc protection60comprises a circuit board11, having a top surface62and a bottom surface63, and including at least two electronic components13in a circuit. The top surface62and the bottom surface63can be substantially parallel with each other. The electronic components11can be disposed on the top surface62or the bottom surface63. An enclosure61can substantially surround the circuit board11. The enclosure can be a case for holding power supply components. The power supply can be used to provide a high voltage bias of at least 10,000 volts between an anode and a cathode of an x-ray tube. The circuit board11and the enclosure61can be configured to have a voltage differential of at least 5000 volts between the enclosure61and at least one of the electronic components13. For example, the enclosure61can be at ground potential and the electronic components13can be part of a high voltage generation circuit or can be components disposed between the high voltage generation circuit and a high voltage device. In another embodiment, the circuit board11and the enclosure61can be configured to have a voltage differential of at least 15,000 volts between the enclosure61and at least one of the electronic components13. In another embodiment, the circuit board11and the enclosure61can be configured to have a voltage differential of at least 25,000 volts between the enclosure61and at least one of the electronic components13.

At least one electrically conductive plate64can be disposed between the top surface62of the circuit board11and the enclosure61, disposed between the bottom surface63of the circuit board11and the enclosure61, electrically insulated from the circuit board11and the enclosure61, and can provide arc protection between at least one electronic component13on the circuit board11and the enclosure61. Arc protection can be provided by the plate reducing electrical field gradients between the electronic component13and the enclosure61, thus reducing the chance of electronic component13failure due to arcing between the electronic component13and the enclosure61.

The high voltage circuit with arc protection60can be especially useful for separating very large voltages in small volumes. In one embodiment, the enclosure can have an internal volume of less than 200 cm3. In another embodiment, the enclosure can have an internal volume of less than 1000 cm3. In another embodiment, the enclosure can have an internal volume of less than 10,000 cm3. In one embodiment, a distance d between a component13on the circuit board11and the enclosure can be less than 1 cm and a voltage differential between this component and the enclosure can be at least 5000 volts. In another embodiment, a distance d between a component13on the circuit board11and the enclosure can be less than 2 cm and a voltage differential between this component and the enclosure can be at least 5000 volts. In another embodiment, a distance d between a component13on the circuit board11and the enclosure can be less than 4 cm and a voltage differential between this component and the enclosure can be at least 5000 volts.

In one embodiment, the at least one electrically conductive plate64can be a single plate wrapped around, and electrically insulated from, the circuit board11. In another embodiment, the at least one electrically conductive plate64can be at least two electrically conductive plates64a-b. One of the electrically conductive plates64acan be disposed between the top surface62of the circuit board11and the enclosure61and the other electrically conductive plate64bcan be disposed between the bottom surface63of the circuit board11and the enclosure61.

In one embodiment, the high voltage circuit60can be made with electrically conductive plates64comprised of metal sheets disposed on a rigid insulative substrate. The substrate can be standard circuit board substrate material. The electrically conductive plates64can be attached to the circuit board by insulative connectors66. This embodiment may be selected for ease of manufacturing. Electrically insulative potting material65can be disposed between the circuit board11and the electrically conductive plates64and between the electrically conductive plates64and the enclosure61.

In one embodiment, a surface area of one side of the at least one electrically conductive plate64can be between one-half to one times the surface area of the top surface62and bottom surface63of the circuit board11. In another embodiment, a surface area of one side of the at least one electrically conductive plate64can be approximately the same as the surface area of the top surface62and bottom surface63of the circuit board11. In another embodiment, a surface area of one side of the at least one electrically conductive plate64can be between the one to two times the surface area of the top surface62and bottom surface63of the circuit board11.

How to Make

For the circuit board10ofFIG. 1, components13-15can be soldered to traces12b. Opposing ends of the components can then have solder paste applied. Traces12acan be aligned with the components13-15and set in place on the components. The solder paste can then seal the components to traces12a, such as by high temperature in an oven.

For the circuit board30ofFIG. 3, component(s)33can be soldered to trace(s)12b. Opposing ends of the component(s) can then have solder paste applied. The insulating substrate31can then be wrapped around the component(s)33and trace(s)12acan be aligned with the component(s)33and set in place on the component(s). The solder paste can then seal the component(s)33to trace(s)12a, such as by high temperature in an oven.

For the circuit board50ofFIG. 5, component(s)33can be soldered to trace(s)52b(or52a). Opposing end(s) of the component(s) can then have solder paste applied. The insulating substrate31can then be wrapped around the component(s)33and trace(s)52a(or52b) can be aligned with the component(s)33and set in place on the component(s). The solder paste can then seal the component(s) to trace(s)52a(or52b), such as by high temperature in an oven. Trace(s)52acan be flexible so as to allow bending with the insulating substrate31.

The embodiments of the present invention may also be made by aligning components with traces then adhering components to traces by wave solder.