GB2206251A

GB2206251A - Power supply circuit for RF-energised load

Info

Publication number: GB2206251A
Application number: GB08813506A
Authority: GB
Inventors: John Alexander Smith
Original assignee: HIDEN ANALYTICAL Ltd
Current assignee: HIDEN ANALYTICAL Ltd
Priority date: 1987-06-17
Filing date: 1988-06-08
Publication date: 1988-12-29
Also published as: GB8813506D0; GB8714216D0

Abstract

A power supply circuit 10, for example for use with a quadrupole mass spectrometer, for connection between an RF source 40 and a load has primary tuned circuits 32, 33 coupled to secondary tuned circuits 28, 29 and having outputs 24, 25 to the load. Power semi-conductors 36, 37 connect the circuits 32, 33 to the source 40 and the outputs 24, 25 can be adjusted by first tuning the secondary circuits 28, 29, then adjusting the coupling K between the primary 27a and secondary coils 27b of transformer 27, then tuning the primary circuits 32, 33. The primary tuned circuits may typically be tuned to 2ROOT 2 of the frequency of the secondary tuned circuits. Only one primary tuned circuit and one secondary tuned circuit may alternatively be provided. The coupling factor K is low, preferably in the range 0.05 to 0.1. The transformer 27 may comprise a single layer secondary coil (60) (Figure 3), coaxially located within an electrically insulating tube (50) and wound on insulating rods (51). The primary coil (61) is wound on an insulating block (55) and is within and nominally coaxial with secondary (60). A knob (59) can be tuned so that the axis of coil (61) is skew to that of coil (60) in order to adjust the coupling K. <IMAGE>

Description

POKER SUPPLY CIRCUITS This invention relates to power supply circuits, one example being power supply circuits for an electric field device of a quadrupole mass spectrometer.

According to this invention a power supply circuit for connection between an RF source and a load comprises a transformer having primary and secondary coils, the primary coil forming part of a first tunable circuit and the secondary coil forming part of a secondary tunable circuit, and means for varying the coupling between the primary and secondary coils.

The primary coil may be connected to the source through power semi-conductors.

The primary coil may form part of two tunable circuits in parallel.

The primary tunable circuits may be connected to the RF source through power semi-conductors.

The secondary coil may form part of two tunable circuits in parallel whose outputs are for connection to the load.

The primary coil may be inside the secondary coil and adjustable relative thereto to vary the coupling.

The invention also includes a quadrupole mass spectrometer including means for producing an electric field having a power supply comprising a power supply circuit as above.

The invention may be performed in various ways and one specific embodiment with possible modifications will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of a quadrupole mass spectrometer; Fig. 2 is a power supply circuit; and Fig. 3 is a perspective view of a transformer.

Referring to Fig. 1, a quadrupole mass spectrometer 10, as is known, comprises a chamber 11 to which a gas is supplied through an inlet 12. In some cases a vaporiser 13 may be provided at the inlet region. The gas molecules then pass through a region 14, at which some receive an electric charge, typically by electron impact, and then through a device 16 which accelerates the charged ions, to an electric or separation'region 17 in which the charged ions are subjected to an electric field produced by device 9.

The path stability of a charged ion depends among other things on the atomic mass of the ion. A detector 18 has an inlet 19. As the electric field is progressively changed, ions of different mass are received at the inlet 19. The detector 18 provides an output on line 20 to receive and control equipment 21 which in known manner provides information on the relative amounts of the ions of differing mass and may include visual presentation of the information.

The electric field may be produced by device 9 having four angularly spaced parallel rods arranged in two orthogonal pairs of diametrially opposed rods with the rods in each pair receiving the same RF (radio frequency) input in anti-phase with the input to the other pair.

The present invention is concerned-with the power supply to the device 9 and in particular with increasing the power supply so as to enable the production of a stronger electric field and thus enabling the spectrometer to be used with ions of greater atomic mass. However the power supply circuit of the invention is not restricted to use with mass spectrometers but may be used to connect other RF sources to electrical loads.

Referring to Fig. 2, the device 9 has its anti-phase inputs 22, 23 respectively connected to output lines 2W, 25 of the circuit 26 of Fig. 2. The circuit 26 comprises a transformer 27 having a primary coil inductance and a secondary coil inductance. The primary inductance has a centre tap giving inductances 27a and the secondary inductance has a centre tap giving inductances 27b. The secondary coil forms tawable circuits 28, 29 tuned to the same frequency and respectively with adjustable capacitors 30a, 31a and adjustable capacitors 30b, 31b, the HF outputs of these two tuned circuits respectively forming outputs 2W, 25.

The primary coil forms + b circuits 32, 33 respectively with adjustable capacitors 34, 35 and tuned to the same frequency. The two primary tuned circuits respectively receive anti-phase RF input signals on lines 36, 37 through respective power semi-conductors 38, 39 e.g.

VXOS transistors, the signals on lines 36, 37 coming from an RF source 40 including a crystal oscillator.

The transformer has a variable coupling factor K between the primary and secondary coils.

By tuning the resonant frequencies of circuits 28, 29, 32, 33 (by adjusting the appropriate capacitor) and adjusting the coupling factor K, the output characteristics of the semi-conductors 38, 39 can be matched to the voltage and current requirements of the load supplied by outputs 24, 25 i.e. the device 9. The tuned circuits 28, 29 are in parallel and the tuned circuits 32, 33 are in parallel.

Circuits 28, 29 are first tuned to the output frequency of the HF source 40. Then the coupling factor K is adjusted to give optimum output at lines 24, 25. Then the circuits 32, 33 are adjusted or tuned to give optimum outputs at lines 24, 25. The coupling K is low e.g. in the range up to 0.1 preferably in the range 0.05 to 0.1. The primary tuned circuits may typically be tuned to (2 of the frequency of the secondary tuned circuits.

It is possible to have only one primary tuned circuit, in this case using the whole primary inductance; and only one secondary tuned circuit, in this case using the whole secondary inductance.

The semi-conductors may be bipolar or field-effect, and may be replaced by thermionic valves.

One form of transformer 27 is shown in Fig. 3 and comprises an electrically insulating tube 50 in which are mounted four parallel insulating rods 51. The secondary coil 60 is coaxial with tube 50 and formed by a single layer 52 of wire wound on the rods 51 as a former and having connecting wires 53, 54 extending through insulating bosses in the tube 50. The primary coil 61 is wound on an insulating block 55. The block 55 has opposed insulating lateral supports 56, 57 respectively extending through the tube wall. Support 56 carries connecting wires 58 for coil 61. Support 57 is in threaded engagement with the tube wall and connected to an operating knob 59.

The coil 61 may be coaxial with tube 50 and coil 60 but the knob sq can be turned to rotate the supports 56, 67 and turn the coil 61 so that its axis is skew to the axis of coil 60, or transverse thereto, to an adjustable extent.

This changes the coupling factor K.

The electric field is changed by varying the strength of the RF signal on lines 36, 37 by adjusting control 40a of source 40.

The knob 58 is, for any given use of tne circuit 26, normally set at an appropriate position and would not be adjusted during use.

The use of power semi-conductors is preferred to valves and provides for simple construction, does not require high voltage high direct current supply, and enables higher power to be used and thus stronger magnetic fields produced.

With the arrangement of Fig. 2, if the outputs 24, 25 go open circuit or are shorted e.g. in a fault condition, the circuit 26 may still safely operate because the low coupling factor reduces electric reflections from the secondary to the primary circuits.

The full power supply circuit would include other features as understood by those skilled in the art. For example the supply would include a DC component for example on lines 70, 71 Fig. 2 with interposition of capacitor 72.

Claims

1. A power supply circuit for connection between an HF source and a load comprising a transformer having primary and secondary coils, the primary coil forming part of a first tunable circuit and the secondary coil forming part of a secondary tunable circuit, and means for varying the coupling between the primary and secondary coils.

2. A circuit as claimed in Claim 1, in which the first tunable circuit is connected to the source through power semi-conductors.

3. A circuit as claimed in Claim 1, in which the primary coil forms part of two tunable circuits in parallel.

4. A circuit as claimed in Claim 3, in which the two tunable circuits are respectively connected to the source through power semi-conductors.

5. A circuit as claimed in any preceding Claim, in which the secondary coil forms part of two tunabie circuits in parallel whose outputs are for connection to the load.

6. A circuit as claimed in any preceding Claim, in which the primary coil is inside the secondary coil and adjustable relative thereto to vary the coupling.

7. A power supply circuit for connection between an HF source and a load substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

8. A quadrupole mass spectrometer including means for producing an electric field having a power supply comprising a power supply circuit as claimed in any preceding Claim.

9. w mass spectrometer as claimed in Claim 8 in which the means for varying the coupling is substantially as hereinbefore described with reference to and as shown in Fig. 3 of the accompanying drawings.