Patent ID: 12191131

DETAILED DESCRIPTION

The present disclosure provides methods and systems for reducing noise coupling between two high-voltage power supplies in an electrically floated configuration with applications to mass spectrometry. In such a configuration, one power supply return is referenced to electric ground and a second power supply uses the output of the other power supply as a return reference. It is commonly known that connecting two power supplies in such a way can have undesired effects, such as ripple or noise coupling from the floated power supply to the ground referenced power supply. Such ripple or noise can result in performance degradation in mass spectrometry systems. As discussed in detail below, the methods and systems of the present disclosure can significantly reduce such ripple or noise coupling and hence improve the performance of a high-voltage power supply system, for example, when used in a mass spectrometry system.

FIGS.1and2schematically depict a power supply system10according to an embodiment of the present disclosure, which includes a ground referenced voltage power supply100(herein also referred to as the ground-referenced power supply or liner power supply) and a floated voltage bias power supply200(herein also referred to as the bias power supply), which is electrically coupled to the ground referenced power supply100so as to apply a bias voltage thereto in a manner discussed in more detail below. The floated bias voltage power supply200can apply a bias voltage to an ion detector406of a mass spectrometer400and the liner power supply100can apply a voltage to liner elements408of the mass spectrometer, as discussed in more detail below.

The floated bias voltage power supply200includes a transformer202, which includes a primary winding202aand a secondary winding202b. The primary winding202areceives an AC (alternating current) voltage from an AC power source204via a capacitor C1. In this embodiment, the primary winding202aof the transformer is coupled to the AC voltage source204. The secondary winding of the transformer can step up the AC voltage applied by the AC source to the primary winding and apply the stepped-up voltage to downstream components of the floated bias voltage power supply, as discussed below.

In this embodiment, a Faraday shield210is disposed in the transformer of the floated bias voltage power supply between its primary and secondary windings to inhibit parasitic coupling between the primary and the secondary windings.

Further, a floating metal shield220is disposed around the bias voltage supply200. As discussed in more detail below, the floating metal shield220provides a low-impedance path between one terminal of the secondary winding of the transformer of the floated bias voltage power supply to its other terminal, which can help inhibit noise current from returning to the second terminal via a path through the liner voltage supply.

The liner voltage power supply100also includes a transformer102that includes a primary winding102athat receives an AC voltage from an AC voltage source104and a secondary winding102bthat steps up the voltage of the primary winding and applies the stepped up voltage to downstream components of the liner voltage power supply. In this embodiment, the primary winding102ais coupled to the AC voltage source104via a capacitor C16.

With continued reference toFIGS.1and2, an electrical connecting path110electrically connects the bias voltage power supply200to the ground referenced voltage power supply100to allow application of a bias voltage by the floated bias voltage supply to the ground referenced voltage power supply. In this embodiment, the electrical connecting path110includes a return electrical path222of the floated bias voltage power supply, which is herein referred to as “a return electrical path.”

The electrical connecting path110extends from terminal A of the secondary winding202bof the transformer of the floated bias voltage power supply200via parasitic capacitor C9to electrical ground, and through electrical ground to terminal D of a capacitor C21associated with the liner power supply. The connecting path110further extends from terminal C of the capacitor C21via the return electrical path222of the floated bias voltage power supply to terminal B of the secondary winding of the transformer of the floated bias voltage power supply.

In this embodiment, two resistive elements R5and R7are disposed in the return electrical path of the floated bias voltage power supply to mitigate the noise injected from the floated bias voltage power supply into the liner power supply. Although in this embodiment two resistive elements are depicted, in other embodiments, one or more than two resistive elements may be employed. In some embodiments, the resistance of the combination of the resistive elements R5and R7can be, for example, in a range of about 10 kΩ to about 1 MΩ, e.g., in a range of about 100 kΩ to about 500 kΩ, or in range of about 200 kΩ to about 400 kΩ.

In some embodiments, the resistive elements R5and R7disposed in the return path of the floated bias voltage power supply can reduce the noise injected by the floated bias voltage power supply to the liner power supply by a factor in a range of about 20 to about 100, e.g., in a range of about 30 to about 90, or in a range of about 40 to about 80, or in a range of about 50 to about 70. By way of example, the resistive elements R5and R7help reduce the noise injected from the floated bias voltage power supply to the liner power supply to a level less than about 60 mVpp (millivolts peak-to-peak).

The role of various elements according to the present disclosure for reducing noise coupling between the floated bias voltage power supply and the liner power supply can be further understood by considering that an inherent property of a voltage transformer is a parasitic coupling between its primary and secondary windings. Such a parasitic coupling between the primary and the secondary windings of the transformer of the floated bias voltage power supply is depicted herein as a capacitor C9, and a respective parasitic coupling between the primary and the secondary windings of the transformer of the liner power supply is herein represented by a capacitor C24. Further, an inherent side effect of placing the floated bias voltage power supply within the metal floating shield220, which is connected to return of bias transformer TX1terminal, is the presence of a parasitic capacitance between terminal A of the secondary winding of the transformer of the floated bias voltage power supply and the enclosure. Such a parasitic capacitance is herein represented by a capacitor C40and is in parallel to the secondary winding of transformer202.

A capacitive coupling between the secondary winding of the liner transformer and the ground is herein represented by a capacitor C41.

In the liner power supply, capacitors C24and C41are electrically connected in parallel with the inter-winding capacitor C17, which is significantly larger than C24and C41. These capacitors slightly increase the capacitive load on transformer TX2but do not produce any undesirable effects on the circuit's functionality.

In contrast, in the floated bias voltage power supply, the capacitor C9presents a path for a voltage signal present at terminal A of the secondary winding202bof the transformer202of the bias voltage power supply to the ground. Such a path allows AC currents through C9to flow to ground. If resistors R7and R5were not present, a current would return, via C9, to terminal B of the secondary winding of transformer202via capacitors C10and C21, which are connected in parallel (See,FIG.2). More specifically, most of such AC currents would return to terminal B of the secondary winding of the bias voltage transformer202via capacitor C21of the liner voltage power supply since C21has a much larger capacitance compared to C10. Such AC current can hence generate an AC voltage ripple across capacitor C21. In general, the impedance of capacitor C21is much lower than those of capacitors C9and C10. For example, typical impedances of C21, C10, and C9are as follows: C21is about 1400 Ohms, C10is about 10 kOhms and C9is greater than about 1 MOhms. Nonetheless, due to typical high amplitude signals present at terminal A of the secondary winding of the transformer of the floated bias voltage power supply, and the C9/C21divider configuration, the current that circulates along this path can generate an AC voltage ripple across C21of a magnitude that will undesirably appear at the output of the liner power supply.

In order to reduce the AC current circulating across C21, resistors R5and R7, which exhibit high resistances, are added in the return path222between C10and C21. By adding these resistors, most of the current via C9is forced to return to terminal B of transformer202via C10, which is the capacitance of the floating shielding box, to ground. The AC voltage on terminal A of transformer202can develop a ripple voltage on C10, which is attenuated by the ratio C10/C9and is further attenuated by the filtering action of network R7+R5and C21.

The use of the transformer Faraday shield210, the floating metal shield220, and the current reducing resistors R5and R7, can reduce the magnitude of the undesired current injected via the bias voltage supply into the liner power supply. In particular, in some embodiments, the transformer Faraday shield can reduce the capacitance of capacitor C9by a factor, e.g., in a range of about 5 to 10, which can in turn increase the impedance of C9and lower the magnitude of current returned through this capacitor, thus reducing magnitude of an undesired ripple at the output of the liner power supply.

The capacitance to ground (C10) of the floating metal shield220can in turn provide an alternate low impedance path from terminal B of the secondary winding of the floated bias voltage power supply for the current flowing through capacitor C9. Resistors R7and R4will advantageously reduce, and preferably inhibit, the current flowing through capacitor C21, therefore reducing the voltage ripple on the liner.

As discussed above, the floating metal shield220will add a parasitic capacitor C10to the ground. This capacitor will create a new path for the current flowing through capacitor C9to return to terminal B of the secondary winding of the transformer of the floated bias voltage power supply via a path exhibiting much larger impedance (e.g., larger by a factor in a range of about 10 to about 20 times) than the impedance exhibited by the path extending from C9to C21. Consequently, the capacitor C10will not considerably increase the magnitude of voltage ripple across C21. Further, the resistive elements R5and R7increase the impedance of the return path222(e.g., from a few kΩ to about hundreds of kΩ) and hence result in reducing the magnitude of a voltage ripple across capacitor C21, e.g., by a 10 to 100 times, and in some cases more. In other words, in many embodiments, the current flowing through capacitor C9will use capacitor C10as the return path and hence most of any voltage ripple will occur across capacitor C10, which is not present at the output of the liner voltage supply.

Further, in some embodiments, the phases of the AC signals applied by the AC voltage sources104and204to the transformers102and202of the bias voltage supply and the ground-referenced voltage supply, respectively, can be synchronized such that a voltage ripple generated by the floated bias voltage power supply200will be subtracted from a voltage ripple generated by the liner power supply, thus resulting in an overall ripple reduction at the output of the liner power supply.

By way of example and with reference toFIG.1, a controller12in communication with the AC voltage sources104and204can synchronize the phases of the AC voltages generated by those voltage sources so as to ensure that a voltage ripple generated by the floated bias voltage power supply200will be subtracted from a voltage ripple generated by the liner voltage supply100. The controller12can be implemented in hardware, firmware and/or software using techniques known in the art informed by the present disclosure. By way of example,FIG.3schematically depicts an example of implementation of such a controller12, which includes a processor14, a random access memory (RAM)16, a read-only memory (ROM)18, and a communications bus20, which allows communication between the processor and the other components. The controller12can further include a communications module22that allows communication between the controller12and the AC voltage sources104and204. Instructions for synchronizing the phases of the AC voltages can be stored in the ROM18and be transferred by the processor at runtime to the RAM16for execution.

Referring again toFIG.1, in the floated bias voltage power supply, the capacitors C2and C6together with the diodes D1and D2form a conventional two-times voltage multiplier, which can reduce the demand on the transformer210of the floated bias voltage power supply for multiplying the AC voltage applied to its primary winding. The floated bias voltage power supply200further includes a filter, which is formed by resistors R1and R2as well as capacitors C7and C8. The filter is a differential filter that reduces a differential voltage at the output of the bias power supply.

With continued reference toFIG.1, the liner power supply100includes a four-times voltage multiplier that is formed by diodes D3, D4, D5, and D6and capacitors C39, C30, C11and C12, which collectively provide a conventional multiplier configuration. The four-times voltage multiplier reduces the demand on the transformer100of the liner power supply for amplifying the voltage applied to the primary winding of the transformer of the liner power supply by the AC voltage source104.

As noted above, a high-voltage power supply system according to the present disclosure can be employed in a variety of mass spectrometers, such as those having a time-of-flight mass analyzer, a quadrupole mass analyzer, among others. By way of example, such a high-voltage power supply system can be used to provide ion acceleration and/or to apply the requisite voltages to an ion detector of a mass spectrometer.

By way of illustration, with reference toFIG.4as well asFIG.1, a mass spectrometer400according to an embodiment of the present disclosure can include, among other elements, an ion source402for generating ions, a mass analyzer404for analyzing the ions and an ion detector406for detecting the ions. In this embodiment, the high-voltage power supply system100can apply a bias voltage to the ion detector of the mass spectrometer and a bias voltage to the liner elements of the mass spectrometer. More specifically, as depicted inFIG.1, in this embodiment, the output voltage of the floated bias voltage power supply is employed to bias the ion detector and the output voltage of the ground-referenced voltage power supply is employed to bias the liner elements of the mass spectrometer.

The mass analyzer404can be any suitable mass analyzer employed in mass spectrometry systems known in the art. By way of example, the mass analyzer404can be a time-of-flight mass analyzer, a quadrupole mass analyzer, a tandem quadrupole-quadrupole mass analyzer, among others.

Those having ordinary skill in the art will appreciate that various changes can be made to the above embodiments without departing from the scope of the invention.