Patent ID: 12193135

DEFINITIONS

The following definitions, including plurals of the same, apply throughout this patent application.

As used herein, the terms “on”, “located on”, “located at”, and “located over” mean located directly on or located over with some other solid material between. The terms “located directly on”, “adjoin”, “adjoins”, and “adjoining” mean direct and immediate contact.

As used herein, the term “parallel” means exactly parallel; parallel within normal manufacturing tolerances; or almost exactly parallel, such that any deviation from exactly parallel would have negligible effect for ordinary use of the device.

As used herein, the term “x-ray tube” is not limited to tubular/cylindrical shaped devices. The term “tube” is used because this is the standard term used for x-ray emitting devices.

DETAILED DESCRIPTION

In an x-ray source, an isolation circuit can isolate bias voltage at a cathode from a bias voltage at an alternating current source, and can transfer the alternating current from the alternating current source to the cathode. An isolation circuit is described in U.S. Pat. No. 7,839,254.

Prior art isolation circuits suffer from variation in manufacturing. Such variation can result in failure of some units. For example, the prior art isolation circuits are typically made by manually winding a wire onto a transformer core. This is costly and error prone. During manufacturing, insulation on manually-wound wires can be accidently cut, resulting in failure of the isolation circuit. Accidental selection of incorrect insulation can also result in failure. Prior art isolation circuits can also be large and heavy.

The invention herein can include an isolation circuit24that can be made repeatedly with minimal variation or failed parts. Reduced manufacturing failures (a) can save cost; and (b) can reduce wasted materials, thus resulting in less adverse impact on the environment.

The isolation circuit24herein can be light weight. Therefore, user fatigue is reduced. This is particularly useful for portable x-ray sources. For example, the inventor achieved an 86% reduction in weight of the isolation circuit24through use of the invention herein (from 1.46 g to 0.20 g).

The isolation circuit24herein can be small. This is especially useful if the x-ray source needs to be inserted into tiny cavities for x-ray analysis, imaging, or electrostatic dissipation. For example, the inventor achieved a 74% reduction in size of the isolation circuit24through use of the invention herein (from 411 mm3to 107 mm3).

As illustrated inFIGS.1-2, x-ray sources10and20can include an x-ray tube29and a power supply25. The x-ray tube29can include a cathode15configured to emit electrons to a target17at an anode16. The target17can include a material that will emit x-rays out of the x-ray tube10or20in response to impinging electrons from the cathode15. The invention herein is applicable to both transmission target anodes and to reflective target, side-window x-ray tubes.

The power supply25can include (a) a voltage multiplier14configured to generate a bias voltage for the cathode15, (b) an alternating current source13(AC source13) configured to provide alternating current to the cathode15, and (c) an isolation circuit24electrically coupled between the AC source13and the cathode15.

The isolation circuit24can isolate the bias voltage at the cathode15from a bias voltage at the AC source13. The bias voltage at the AC source13can be at or near ground voltage, or can be a large positive voltage. The isolation circuit24can transfer the alternating current from the AC source13, at one bias voltage, to the cathode15, at a different bias voltage. There can be tens of kilovolts of voltage differential between the bias voltage at the AC source13and the bias voltage at the cathode15.

The isolation circuit24can include planar transformer(s)26, each with a primary trace11and a secondary trace12on circuit board(s)31(seeFIGS.3-9). A preferred material for the circuit board(s) is polyimide. The primary trace11can be located in close proximity to the secondary trace12such that alternating electrical current through the primary trace11will induce alternating electrical current through the secondary trace12. The primary trace11and the secondary trace12can be separated from each other solely by circuit board(s). A minimum distance D (FIG.4) between the primary trace11and the secondary trace12can be ≥0.3 mm, ≥0.5 mm, or ≥1 mm, and ≤1.7 mm, ≤3.5 mm, or ≤5 mm.

As illustrated inFIG.1, the isolation circuit24can include a single planar transformer26. The AC source13can be electrically coupled to the primary trace11, and can provide alternating current to the primary trace11. The primary trace11can induce alternating current in the secondary trace12. The secondary trace12can be electrically coupled to the cathode15, and can provide alternating current to the cathode15. The secondary trace12can be electrically coupled to, and provide alternating current to, an electron emitter15E, such as a filament. The alternating current can heat the filament.

As illustrated inFIG.2, the isolation circuit24can comprise multiple planar transformers26, including an initial planar transformer26iand a final planar transformer26f. The primary trace11of each planar transformer26, except for the initial planar transformer26i, can be electrically coupled to the secondary trace12of an adjacent or proximate planar transformer26. The AC source13can be electrically coupled to the primary trace11of the initial planar transformer26i. The secondary trace12of the final planar transformer26fcan be electrically coupled to the cathode15. The secondary trace12can be electrically coupled to an electron emitter15E, such as a filament. The alternating current can heat the filament.

Also illustrated inFIG.2is a middle planar transformer26mbetween the initial planar transformer26iand the final planar transformer26f. The primary trace11of the middle planar transformer26mcan be electrically coupled to the secondary trace12of the initial planar transformer26i. The primary trace11of the final planar transformer26fcan be electrically coupled to the secondary trace12of the middle planar transformer26m.

If the isolation circuit24includes more than one middle planar transformer26m, then the secondary trace12of one middle planar transformer26mcan be electrically coupled to the primary trace11of another middle planar transformer26m.

In the isolation circuit24ofFIG.1orFIG.2, a primary capacitor27can be electrically-coupled in parallel with the primary trace11of the initial planar transformer26i. This primary capacitor27can be designed to resonate with the circuit for improved electrical power transfer. A secondary capacitor28can be electrically-coupled in parallel with the secondary trace12of the final planar transformer26f. This secondary capacitor28can be designed to resonate with the load (e.g. electron emitter15E) for improved electrical power transfer.

The isolation circuit24can transfer the alternating current with minimal or no change of voltage or current. Thus for example, 0.1≤Ai/Af≤10, 0.2≤Ai/Af≤5, or Ai=Af, where Ai is an amplitude of alternating electrical current through the primary trace11of the initial planar transformer26iand Af is an amplitude of alternating electrical current through the secondary trace12of the final planar transformer26f. As another example, 0.1≤Ap/As≤10, 0.2≤Ap/As≤5, or Ap=As, where Ap is an amplitude of alternating electrical current through the primary trace11and As is an amplitude of alternating electrical current through the secondary trace12of any specified stage26i,26m,26f, or combinations thereof.

A top-view of a planar transformer26for an isolation circuit24is illustrated inFIG.3. The secondary trace12can have or include a spiral shape, as shown inFIG.3. The primary trace11can also have or include a spiral shape. Each spiral shape can be located in a single plane. The spiral shapes can apply to any example described herein.

FIG.4is a cross-sectional side-view of the planar transformer26ofFIG.3. The primary trace11is on an opposite side of the circuit board31. Thus, the primary trace11and the secondary trace12can be on opposite sides of the same circuit board31.

FIG.5is a cross-sectional side-view of an isolation circuit24with multiple planar transformers26. A single circuit board31is used for the primary traces11and for the secondary traces12for all planar transformers26. Each primary trace11can be electrically coupled by wires51to a secondary trace12or to the AC source13(not shown inFIG.5). Each secondary trace12can be electrically coupled by wires51to a primary trace11or to the cathode11(not shown inFIG.5).

As illustrated in the planar transformers26ofFIGS.6aand6b, the primary trace11can be on a primary circuit board61and the secondary trace12can be on a secondary circuit board62. The primary circuit board61and the secondary circuit board62can be separate from each other, and spaced apart from each other.

The primary trace11can be sandwiched between the primary circuit board61and the secondary circuit board62(FIG.6a). The example ofFIG.6ais preferred if the primary trace11needs to be shielded.

Alternatively, the secondary trace12can be sandwiched between the primary circuit board61and the secondary circuit board62(FIG.6b). The example ofFIG.6bis preferred if the secondary trace12needs to be shielded. InFIGS.1-2, for each planar transformer26, the secondary trace12would have a higher voltage than the primary trace11across the circuit board31. Therefore, normally it would be more important to shield the secondary trace12, and the example ofFIG.6bis usually preferred.

FIG.7is a cross-sectional side-view of multiple planar transformers26for an isolation circuit24, including a first planar transformer26aand a second planar transformer26b. Each planar transformer26can comprise a stack74of three circuit boards31, including a middle circuit board31M sandwiched between an upper circuit board31U and a lower circuit board31L. Each of the three circuit boards31can be used for all of the multiple planar transformers26in this isolation circuit24.

Each primary trace11and each secondary trace12can be sandwiched between two of the three circuit boards31in the stack74. The primary traces11and the secondary traces12of the multiple planar transformers26can include spiral shapes, each of which can be embedded between two of the three circuit boards31of the stack74.

The isolation circuit24can include three connections71,72, and73along an outer face75of the stack74, and through an outer circuit board31L or31U to a primary trace11, to a secondary trace12, or both. Each of these three connections71,72, and73can be a trace along the outer face75.

A first connection71can extend from the AC source13, across the outer face75of the lower circuit board31L, then through the lower circuit board31L to the primary trace11of the first planar transformer26a.

A second connection72can extend (a) from the secondary trace12of the first planar transformer26a, (b) through the upper circuit board31U, (c) across the outer face75of the upper circuit board31U, and (d) then back through the upper circuit board31U to the primary trace11of the second planar transformer26b.

A third connection73can extend from the secondary trace12of the second planar transformer26b, through the lower circuit board31L, across the outer face75of the lower circuit board31L, then to the cathode15(not shown inFIG.7), or back through the lower circuit board31L to the primary trace12of another planar transformer (not shown inFIG.7).

The stack74of three circuit boards31can allow easier and more repeatable manufacturing. Electrical connections to a center of the spiral shape of the primary traces11and the secondary traces12can be traces through the circuit board31and along the outer faces75of the stack74. This can be more repeatable and less expensive than manually soldering wires.

FIGS.8and9are cross-sectional side-views of planar transformers26for isolation circuits24. The secondary trace12can be divided into two secondary trace parts12aand12b. The primary trace11can be sandwiched between the two secondary trace parts12aand12b. This can improve electromagnetic coupling between the primary trace11and the secondary trace12, and allow increased turns in the secondary trace12.

The secondary circuit board62can include two secondary circuit boards62aand62b. The two secondary circuit boards62aand62bcan be separate and spaced apart from each other. One of the two secondary trace parts12acan be on one of the two secondary circuit boards62aand the other of the two secondary trace parts12bcan be on the other of the two secondary circuit boards62b. The primary trace11can be sandwiched between the two secondary circuit boards62aand62b. The two secondary circuit boards62aand62bcan be parallel with respect to each other.

As illustrated inFIG.8, the primary circuit board61can be a different circuit board31than either of the two secondary circuit boards62aand62b. This can be easier for manufacturing. As illustrated inFIG.9, the primary circuit board61can be the same circuit board31as one of two secondary circuit boards62a. This can improve electromagnetic coupling between the primary trace11and the secondary trace12.

The two secondary trace parts12aand12bcan be connected at a center of the spiral shape, defining a secondary trace connection81. The secondary trace connection81can extend through, such as preferably through a center of, the primary circuit board61and the secondary circuit boards62aand62b.

The spiral shape of one of the two secondary trace parts12a(or12b) can spiral in and the spiral shape of the other of the two secondary trace parts12b(or12a) can spiral out. The spiral direction is defined as a direction of current flow at a single point in time.