DE1282800B - Electronic switching device for phase-independent shutdown of the high-voltage transformer of an X-ray diagnostic apparatus - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

H05g

German KL: 21g -19/01

Number: 1282 800

File number: P 12 82 800.1-33 (V 28566)

Filing date: May 28, 1965

Opening day: November 14, 1968

O O CO (N OO CSl -H

The invention relates to an electronic switching device for phase-independent shutdown of the high-voltage transformer of an X-ray diagnostic apparatus by means of one in the primary circuit of the Three-phase high-voltage transformer lying rectifier bridge circuit and two between the DC voltage outputs of the bridge circuit and coupled to a control unit controllable electronic switching elements.

Hard beam technology and highly sensitive X-ray films have created the conditions in which X-ray diagnostics work with very short exposure times.

The switch-off delay corresponds to this tendency on the device side the mechanical contactors, which are usually used to switch off the X-ray diagnostic equipment is made against. This is particularly useful when using an X-ray exposure machine noticeable because the switch-off delay of the contactor has a decisive influence on the lower switching time limit.

One is therefore forced to take measures for the low-delay control of contactors or to bypass the use of contactors entirely in order to counter the above disadvantage.

A circuit arrangement is already known which works with a mechanical contactor. The switch-off delay is reduced by using capacitive or inductive coupling of a current pulse into the excitation circuit of the holding current of the contactor is initially partially compensated and then interrupted.

Furthermore, a circuit arrangement is already known in which a mechanical contactor in a detuned DC bridge, the detuning of which is reversed at the moment of switching off and its contacts by switching resistors into the primary circuit of the high-voltage transformer switch off only part of the power to reduce arcing.

Another known arrangement uses gas discharge tubes in place of the contactor Primary circuit of the high-voltage transformer of the X-ray apparatus.

Finally, a circuit arrangement of the type mentioned is known in which a controllable Gas discharge tube or a controllable semiconductor rectifier via a full-wave rectifier set in the primary circuit of the high-voltage transformer Electronic switching device for phase-independent Switching off the high-voltage transformer of an X-ray diagnostic apparatus

Applicant:

VEB Vakutronik,

Scientific industrial company, Dresden,

Dresden, Dornblüthstr. 21

Named as inventor:
Dipl.-Ing. Christian Friedrich,
Dieter Rudolph, Dresden

is switched on and in which a phase-independent deletion of the controllable rectifier and thus Switching off the high voltage transformer is possible.

The arrangements with mechanical contactors are particularly characterized by their small size Effort. However, they have a lower switching time limit caused by the drop-out delay Hardly to fall below between 5 to 10 ms. Furthermore, there is a more or less great uncertainty factor due to arcing when the contactor contacts open, the load, the phase position and the circuitry Arrangement of contacts depends. The arrangement in which the mechanical contactor through Gas discharge tubes is replaced, although it works practically without delay, but is disadvantageous in that the gas discharge tubes after receiving the switch-off command only in the next zero crossing block and thus an uncertainty factor of a maximum of half a period, i.e. of 10 ms, is given is. The uncertainty factor can be reduced to a maximum of 5 ms, but this is an increased one Cost of an additional four rectifiers and a transformer.

The circuit arrangement with a controllable rectifier and a full-wave rectifier circuit Although it fulfills the two main requirements for phase-independent and low-inertia switch-off of the high-voltage transformer of the X-ray system, but the required full-wave rectifier set is required very expensive.

The invention is based on the object of addressing the disadvantages of the known circuit arrangements reduce or eliminate and a switching

809 637/857

Direction for low-inertia and phase-independent switch-off of the high-voltage transformer on the primary side to develop an X-ray diagnostic apparatus.

The purpose of the invention is to help with the advancing Development of X-ray technology, increasing demands for the shortest exposure times can be underlined by high-quality film material. Be that way the medical requirements in medical technology for X-ray diagnostics are also met.

In a switching device of the type mentioned at the outset, this is achieved according to the invention by that any two of the three star point connections the primary windings of the high voltage transformer with the AC voltage inputs of a Bridge arrangement consisting of four rectifiers are connected, while the third neutral point connection the transformer primary windings with the midpoint of a series connection of two controllable semiconductor lights or controllable gas discharge rectifiers is connected that further these controllable semiconductor or gas discharge rectifiers in their forward direction in the direct voltage diagonal branch the bridge rectifier arrangement are in series and that the control unit so designed and with the control electrodes of the controllable rectifier and the end points and the midpoint of the series connection of the controllable rectifier is connected in such a way that it is in Switch-off time both the control electrodes of the controllable rectifier a blocking control voltage supplies, as well as via the DC voltage diagonal branch of the bridge rectifier arrangement Applied counter voltage.

If the two controllable rectifiers are deleted, the current flow in the diagonal is the Bridge rectifier arrangement and thus at the same time the current flow through the three primary windings of the high voltage transformer interrupted.

The deletion of the controllable rectifier is achieved independently of the phase position by using Using a special control device that z. B. the switch-off signal by an X-ray exposure machine receives, a voltage is applied to them at the moment of switch-off, which the controllable rectifier at 'anode voltage zero blocks. "At the same time, the series connection of the two controllable The rectifier briefly effects a voltage equal to that of the voltage in the diagonal branch of the bridge circuit is opposite.

Switching off the imaging radiation of the X-ray diagnostic apparatus can thus be purely electronic and phase-independent as well low inertia.

A comparison with the circuit arrangement described above, using a full wave rectifier set shows that in contrast to six Rectifiers and a controllable rectifier in the switching device according to the invention four Rectifiers and two controllable rectifiers are required.

The advantage of the invention is that the same mode of operation is achieved with less structural effort and, at the same time, there is an increase in operational safety and reliability. ¹ The invention is to be explained in more detail below using an exemplary embodiment.

In the accompanying drawing, the three primary windings 1, 2 and 3 of the high-voltage transformer are shown, of which one terminal JJ, V and W is connected to the three-phase network. The connections 4, 5 and 6 ″ are usually connected to one another in a star connection. In the arrangement according to the invention, the connections 4 and 6 are connected to the AC voltage input of a bridge _T rectifier arrangement consisting of the four rectifiers 7, 8, 9 and 10 The connection 5 of the primary winding 2 is led to the midpoint of the series connection of the two controllable rectifiers 12 and 12. The controllable rectifiers 11 and 12 are in the forward direction in the diagonal branch between the points 13 and 14 of the bridge rectifier arrangement interrupted in the bridge diagonal, ie between points 13 and 14, which at the same time results in an interruption of the current flow in the primary windings 1, 2 and 3.

The deletion of the controllable rectifier 11 and 12 is made with the help of the special control device 20 such that in the moment of switch-off on the Control lines 15 and 16 as well as 17 and 18 to the control electrodes of the rectifiers 11 and 12 one such a voltage is applied that the rectifiers 11 and 12 block at zero anode voltage. Simultaneously causes the control unit 20 that over the Diagonal branch, d. H. between the points 13 and 14, a voltage is briefly effective that the existing tension is opposed. The counter voltage is generated via the control lines 18 and 19 fed to the diagonal branch of the bridge rectifier arrangement.

For the circuit arrangement according to the invention, the connections to the bridge rectifier arrangement or placed at the center of the series connection of the two controllable rectifiers are freely selectable, since of course the connections 4, 5 and 6 compared to the one shown Arrangement can still be interchanged as desired.

Claims (1)

Claim; Electronic switching device for phase-independent shutdown of the high-voltage transformer an X-ray diagnostic apparatus by means of one in the primary circuit of the three-phase high-voltage transformer lying rectifier bridge circuit and two between the DC voltage outputs of the bridge circuit horizontal controllable electronic switching elements coupled with a control unit, characterized in that two (z. B. 4 and 6) of the three star point connections (4; 5; 6) of the primary windings (1; 2; 3) of the 'high voltage transformer with the AC voltage inputs of a bridge arrangement consisting of four rectifiers (7; 8; 9; 10) are connected, while the third star point connection (e.g. 5) of the transformer primary windings with the center of a series connection of two controllable semiconductor rectifiers or controllable gas discharge rectifiers (11; 12) is connected that further these controllable semiconductor or gas discharge rectifiers (11; 12) in their forward direction in the direct voltage diagonal branch (13; 14) of the bridge rectifier arrangement are in series and that the control device (20) is designed and connected to the control electrodes of the controllable rectifier (11; 12) and the end points (13; 14) and the midpoint of the series connection of the controllable rectifier is connected in such a way that it is both the control electrodes at the time of switch-off the controllable rectifier (11; 12) supplies a blocking control voltage as well as via the direct voltage diagonal branch (13; 14) of the bridge rectifier arrangement (7 to 10) Applied counter voltage. Considered publications:
German Patent Nos. 694120, 1024165; German exploratory documents No. 1156 899,
1191917. 1 sheet of drawings 809 637/857 11.68 © Bundesdruckelei Berlin