GB2178202A - Arrangements for maintaining a substantially constant voltage between two points in a circuit - Google Patents

Abstract

An arrangement for maintaining a substantially constant voltage between two points in a circuit, where the voltage is derived from a non-constant voltage source in the form of a main capacitor 16, includes a plurality of further voltage sources in the form of auxiliary capacitors 25, 26, 27 and 28. When the voltage across a klystron 13 drops because the main capacitor 16 discharges, this is sensed by a potential divider 22 and an auxiliary capacitor is included in the circuit by triggering a thyratron 29, 30, 31 or 32 into conduction. Further voltage drops are compensated for by switching in further voltage sources. In another arrangement, the further voltage sources are arranged in parallel. <IMAGE>

Description

SPECIFICATION Arrangements for maintaining a substantially constant voltage between two points in a circuit This invention relates to arrangements for maintaining a substantially constant voltage between two points in a circuit and more particularly where the voltage is derived from a non-constant voltage source.

It is often desirable to have a known voltage between two points in a circuit, such as in the arrangement illustrated in Figure 1 where it is wished to maintain a substantially constant voltage between the cathode 1 and interaction section 2 of a klystron 3. The interaction section 2 is that part of the klystron 3 where a radio frequency signal to be amplified and the klystron electron beam are made to interact. The kylstron 3 also includes a modulating anode 4, the potential of which is controlled by a modulator 5, and a collector 6. The radio frequency signal to be amplified is applied at 7 and coupled out of the klystron at 8. A capacitor 9 is connected in parallel with the klystron 3, having one plate connected to the cathode 1, and the other Plate to the interaction section 2 and collector 6.

The capacitor 9 thus acts as a voltage source for the voltage between the cathode 1 and interaction section 2. The capacitor 9 is charged by a dc current derived from the mains supply via a power supply unit 10. A crowbar device 11 such as, for example, a double ended thyratron, is also included in the circuit and is connected across the capacitor 9. This provides means for dumping the energy stored by the capacitor 9 should arcing occur within the klystron 3.

One way of operating the klystron 3 is to pulse the electron beam current by applying an appropriate modulating signal to the modulating anode 4. Ideally this would result in a pulse as illustrated in Figure 1a. However, over a period of time the capacitor 9 discharges and hence the voltage across the klystron 3 between its cathode 1 and interaction section 2 drops. thus the actual pulse shape is that illustrated by Figure 1 b and distortion of the amplified radio frequency signal will occur. A very large capacitor may be used in the arrangement to ensure that any voltage drop across the klystron 3 is not of significance. However, such a capacitor must be very large and hence expensive, and also requires a crowbar device 12 which is capable of handling the amount of energy stored by the capacitor.

This invention seeks to provide an improved arrangement.

According to this invention there is provided an arrangement for maintaining a substantially constant voltage between two points in a circuit where the voltage is derived from a nonconstant voltage source comprising a further voltage source and means for arranging its inclusion in the circuit depending on the deviation of the actual voltage between the two points from a desired voltage, whereby compensation for changes in voltage derived from the non-constant voltage source is enabled.

The voltage may be arranged to be substantially constant, such that it remains within a tolerable deviation from the desired voltage.

Thus by employing the invention, it is possible to use a nonconstant voltage source but still achieve a substantially constant voltage between two points in a circuit. Where the nonconstant voltage source is a capacitor, a smal ler capacitor may be used than would otherwise be the case, this being cheaper and easier to manufacture. Also where a crowbar device is required it need only be capable of handling the energy stored by such a capacitor.

Preferably the means for arranging its inclusion comprises switching means for switching the further voltage source into the circuit when the deviation reaches a certain level, and advantageously the switching means includes a thyratron. Preferably, means are included for monitoring the actual voltage between the two points, and it is preferred that the means for monitoring comprises a potential divider.

The further voltage source is preferably a capacitor but other sources, such as for example voltaic cells, could be employed.

In one aspect of the invention a plurality of further voltage sources are included, and are arranged in series. This enables one or more than one voltage source to be included in the circuit either simultaneously or at different times. In another aspect of the invention, a plurality of further voltage sources are included and arranged in parallel. This enables each further voltage source to be independently switchable into the circuit if desired. Preferably a plurality of switches is included, each being associated with the inclusion of a respective further voltage source. Advantageously means are provided for recharging the or a further voltage source when it is not included in the circuit. It is preferred that control means are included for controlling the inclusion of a further voltage source depending on the actual voltage monitored.

Preferably, an electric component is included in the arrangement and has terminals which are the said two points. The invention is particularly advantageous where the electrical com ponent is a klystron, its interaction section and its cathode being the said two points.

The invention is now further described with reference to Figures 2, 2a and 3 of the accompanying drawings in which; Figure 2 shows an arrangement in accor dance with the invention; Figure 2a is an explanatory diagram relating to Figure 2; Figure 3 shows schematically another arrangement in accordance with the invention, with like reference being used for like parts.

With reference to Figure 2, a klystron 13 has a voltage maintained between its interaction section 14 and cathode 15 which it is desired to maintain at substantially a constant value. the voltage across the klystron is derived from a main capacitor 16, one plate of which is connected to the cathode 15 and other to the interaction section 14 via a diode 17. The main capacitor 16 is a non-constant voltage source, the voltage derived from it reducing over the desired operating period. The capacitor 16 is charged by a dc current derived from the mains supply via a power supply unit 18. A crowbar device 19 is connected across the main capacitor 16 to divert stored energy if arcing occurs within the klystron 13. A modulator 20 is arranged to modulate the potential applied to a modulating anode 21 of the klystron 13 to enable pulsed operation of the klystron electron beam to be achieved.

A potential divider 22 is included to monitor the voltage between the interaction section 14 and cathode 15 of the klystron 13 and is connected via a line 23 to a control unit 24.

A plurality of further voltage sources in the form of auxiliary capacitors, only four of which 25, 26, 27 and 28 are shown, are connected in series between the interaction section 14 and the main capacitor 16. the auxiliary capacitors are isolated from the circuit by a plurality of thyratrons, four of which 29, 30, 31 and 32 are shown. Each thyratron is connected between an adjacent pair of auxiliary capacitors and the main capacitor 16. The control unit 24 has a plurality of output lines, 33, 34, 35 and 36 which are connected to control grids of thyratrons 29, 30, 31 and 32 respectively. An auxiliary power supply unit 37 is included in the arrangement for charging of the auxilliary capacitors 25, 26, 27 and 28, each of them being charged by the same amount. An auxilliary crowbar device 38 is connected across all of the auxiliary capacitors 25, 26, 27 and 28.

During operation of the arrangement, initially the thyratrons 29, 30, 31 and 32 are nonconducting and the main capacitor 16 is charged to its operating value. In this arrangement the klystron electron beam current is required to operate in a pulsed mode and thus charging is arranged to occur during the interpulse period. It is desired to obtain a pulsed electron beam current of a shape similar to that illustrated in Figure 1a, i.e, that the voltage between the interaction structure 14 and the cathode 15 is substantially constant. the auxiliary capacitors 25, 26 27 and 28 are also charged during the inter-pulse period.

At the beginning of a pulse, the voltage, as illustrated in Figure 2a, is at the required value. However, the capacitor 16 discharges and the voltage between the two points begins to fall. the potential divider 22 monitors the voltage between the interaction structure 14 and cathode 15 and transmits a signal representing the voltage along lines 23 to the control unit 24. When the voltage has dropped by a certain amount, the control unit 24 transmitsa trigger pulse along its output line 33 to a first thyratron 29, causing it to become conducting. Thus a first auxiliary capacitor 25 is switched into the circuit via an LR circuit 39 which aids a smooth switching in of the additional voltage derived from the auxiliary capacitor 25. The voltage across the klystron 13 is thus increased to the desired value again.After a further period of time, the voltage drops again and the control unit transmits a trigger pulse along its output line 34 to a second thyratron 30. The second thyratron 30 becomes conducting, switching in a second auxiliary capacitor 26 into the circuit.

Thus both the first and the second auxiliary capacitors 25 and 26 are now included in the circuit. The first thyratron 29 is switched off and no longer conducts since its anode voltage is reduced when the second thyratron 30 is triggered. Further voltage drops are compensated for in a similar manner. thus, a substantially constant voltage is achieved between the interaction structure 14 and cathode 15 of the klystron 13. When the pulse period ends the auxiliary capacitors 25, 26, 27 and 28 and the main capacitor 16 are recharged to ready them for the next pulse.

The power supply unit 18 may not have a constant output such the main capacitor 16 is not fully charged at the beginning of a pulse.

The potential divider 22 monitors this and enables more than one of the auxiliary capacitors to be initially switched into the circuit. For example, the control unit may send a trigger pulse along line 35 to trigger a thyratron 31 thus bringing three auxiliary capacitors 25, 26 and 27 into the circuit. This allows the circuit to compensate for mains supply voltage excursions and the consequent pulse-to-pulse amplitude variations which would result. In this arrangement, the auxiliary capacitors 25 26, 27 and 28 are of the same value but they could of course be chosen to have different values.

With reference to Figure 3 part of another arrangement is illustrated which is similar to that described with reference to Figure 2, but the arrangement of the further voltage sources is different.

In this arrangement, a plurality of auxiliary capacitors four of which 40 41, 42 and 43 are connected in parallel between the interaction section 14 of the klystron and main capacitor 16. Each auxiliary capacitor 40, 41, 42 and 43 is isolated from the circuit by an associated thyratron 44, 45, 46 and 47 respectively. Thus in this arrangement it is possible to switch any one of the auxiliary capacitors into the circuit at a particular time. For example, initially the auxiliary capacitor 40 may be switched into the ciruit and then a little time later another auxiliary capacitor 41 may be included in the circuit, its inclusion resulting in the thyratron 44 becoming nonconducting and the first auxiliary capacitor 40 being isolated from the circuit. The first auxiliary capacitor 40 may then be charged during the pulse period. To enable a substantially constant voltage to be maintained, capacitor 41 is charged to a higher voltage than capacitor 40 and capacitor 42 to a higher voltage than capacitor 41 and so on.

Claims (18)

1. An arrangement for maintaining a substantially constant voltage between two points in a circuit where the voltage is derived from a non-constant voltage source comprising a further voltage source and means for arranging its inclusion in the circuit depending on the deviation of the actual voltage between the two points from a desired voltage, whereby compensation for changes in voltage derived from the non-constant voltage source is enabled.

2. An arrangement as claimed in claim 1, and wherein the means for arranging its inclusion comprises switching means for switching the further voltage source into the circuit when the deviation reaches a certain level.

3. An arrangement as claimed in claim 2 and wherein the switching means includes a thyratron.

4. An arrangement as claimed in claim 1, 2 or 3 and including means for monitoring the actual voltage between the two points.

5. An arrangement as claimed in claim 4 and wherein the means for monitoring comprises a potential divider.

6. An arrangement as claimed in any preceding claim and wherein the non-constant voltage source is a capacitor.

7. An arrangement as claimed in any preceding claim and wherein the further voltage source is a capacitor.

8. An arrangement as claimed in any preceding claim and including a plurality of further voltage sources arranged in series.

9. An arrangement as claimed in any of claims 1 to 7 and including a plurality of further voltage sources arranged in parallel.

10. An arrangement as claimed in claim 9 and wherein each of the plurality is independently switchable into the circuit.

11. An arrangement as claimed in claim 8, 9 or 10 and including a plurality of switches each associated with the inclusion of a respective further voltage source.

12. An arrangement as claimed in claim 11 and wherein each of the switches is a thyratron.

13. An arrangement as claimed in any preceding claim and wherein means are provided for recharging the or a further voltage source when it is not included in the circuit.

14. An arrangment as claimed in any preceding claim and including control means for controlling the inclusion of a further voltage source depending on the actual voltage monitored.

15. An arrangement as claimed in any preceding claim and including an electrical component having terminals which are the said two points.

16. An arrangement as claimed in claim 14 and wherein the electrical component is a klystron its interaction section and its cathode being the said two points.

17. An arrangment substantially as illustrated in and described with reference to Figure 2 of the accompanying drawings.

18. An arrangement substantially as illustrated in and described with reference to Figure 3 of the accompanying drawings.