EP0179680B1 - Power supply circuit for an x-ray source for use in radiology - Google Patents

Power supply circuit for an x-ray source for use in radiology Download PDF

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Publication number
EP0179680B1
EP0179680B1 EP85401754A EP85401754A EP0179680B1 EP 0179680 B1 EP0179680 B1 EP 0179680B1 EP 85401754 A EP85401754 A EP 85401754A EP 85401754 A EP85401754 A EP 85401754A EP 0179680 B1 EP0179680 B1 EP 0179680B1
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EP
European Patent Office
Prior art keywords
circuit
capacitor
thyristors
current
switch
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EP85401754A
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German (de)
French (fr)
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EP0179680A1 (en
Inventor
Roberto Rovacchi
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General Electric CGR SA
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General Electric CGR SA
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/10—Power supply arrangements for feeding the X-ray tube
    • H05G1/18—Power supply arrangements for feeding the X-ray tube with polyphase ac of low frequency rectified
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/10—Power supply arrangements for feeding the X-ray tube

Definitions

  • the present invention relates to a supply circuit for an X-ray emitter usable in radiology.
  • radiology it is necessary to power an X-ray emitter or source for a determined period. This duration corresponds to a duration of exposure or placement of a radio-sensitive plate.
  • radio cinema it is also necessary to modulate the activity of the X-ray emitting source as a function of the rate at which images are taken: in this way the dose of radiation received by a patient during such an examination is reduced.
  • the transmitter supply assembly includes a transformer, the primary circuit of which is connected to a three-phase AC electrical network, and the secondary circuit of which is connected to the transmitter.
  • the primary circuit mounted in a star comprises, in place of a nodal connection, a switch for connecting together at the nodal point the three supply strands. The duration of closure of this switch conditions the commissioning of the primary, therefore that of the transformer, and consequently fixes the duration of activity of the X-ray emitter.
  • the switch conventionally comprises a set of thyristors which are initiates upon desired power up. To obtain an opening of the switch, the thyristors are extinguished.
  • the reverse current which is established in the set of thyristors has a sinusoidal shape. That is, this current increases to a maximum and then decreases.
  • a sufficient reverse current must be established there for a period greater than their recovery time. This leads to choosing capacitors of significant value. Indeed, the useful life of the sufficient reverse current is greater the higher the maximum intensity of this reverse current. The latter is dependent on the capacitance of the capacitor. It follows that at the high point of the blocking operation the thyristors are traversed by an unnecessarily large current since it is primarily their recovery time which controls their blocking.
  • the object of the present invention is to remedy the drawbacks mentioned. It achieves a high rate using a circuit that does not require a special sequence to recharge the capacitor. Indeed, during blocking, the discharge of the capacitor causes its recharging in an opposite polarity. What the invention proposes is that for the following cycle the terminals of the capacitor are switched so that, without changing the polarity of this capacitor, the latter again becomes correctly connected.
  • the invention relates to a supply circuit for an X-ray emitter usable in radiology, of the type comprising a transformer whose primary circuit is connected to the three-phase electrical network and whose secondary circuit is connected to the emitter, in which the primary circuit is switched on and off by a controlled switch, said switch comprising a set of closing thyristors to close the primary circuit and thus activate the supply circuit, and a correctly charged capacity, connectable to this primary circuit, to reverse the direction of current flow in the set of closing thyristors, so as to open the switch and consequently stop the supply, characterized in that it also comprises a circuit for switching the connection of the capacitor to said circuit primary.
  • FIG. 1 shows a supply circuit according to the invention.
  • This circuit includes a transformer 1, the primary circuit 2, 3, 4 of which is connected to the three-phase electrical network 5.
  • the secondary circuit 6, 7, 8 of this transformer is connected to an emitter 9 of X-radiation.
  • the connection of this secondary circuit comprises a current rectifier 10.
  • the primary circuit is put into service by means of a switch 11 which receives its command on two access terminals 12, 13.
  • This switch comprises a set 14 of thyristors which ensure the closing of the switch coming almost short-circuited points A and B of this switch.
  • the switch 11 also includes a correctly charged capacitor 15 connectable to the primary circuit to reverse the direction of current flow in the set 14 of the thyristors.
  • the capacity 15 is connected to the set 14 of the thyristors by a switching circuit 50.
  • This switching circuit comprises the thyristors 16 to 19. These thyristors are controlled two by two (16-17 and 18-19) by common control terminals 20 and 21 respectively. By selecting one or the other of these terminals you can reverse the direction of connection of the capacity to the set 14.
  • Windings 2, 3 and 4 are the three primary windings of the three-phase transformers. They are magnetically coupled to the three secondary windings of the transformer 1. On the side opposite to the three-phase electrical network, the windings 2, 3 and 4 are connected to six diodes 22 to 27. Each end of each of the windings is connected to the midpoint respectively of the pairs of diodes 25-22, 26-23, 27-24 connected in series. The three pairs are mounted in parallel between points A and B of the switch. To put the primary into service, simply short circuit point A, connected in common to the three cathodes of diodes 22 to 24, at point B connected in common to the three anodes of diodes 25 to 27. When the circuit is open, the DC voltage V R between points A and B is equal to ⁇ 2 times the voltage distributed by the network 5. To prevent the commissioning of the primary from causing overvoltages at the secondary, the connection from point A to point B is done in two stages.
  • a thyristor 28 is first opened, at an instant t i (FIG. 2a), by sending a short-duration pulse on its trigger by the control terminal 12.
  • a resistor 29 connected in series with this thyristor 28 causes a voltage drop A V.
  • the drop A V is also shown in Figure 2a.
  • a main thyristor 30 is started by a short pulse applied to its control terminal 13.
  • the two thyristors 28 and 30 are mounted in parallel between points A and B, the first via resistor 29 in series, the second via an inductor 31 in series.
  • the inductance 31 limits the variation in current so that the voltage V AB then tends towards 0 exponentially (Fig. 2a).
  • the transformer is then energized. In radiology it is the beginning of the exhibition. In view of the fact that the thyristor 30 is on, the thyristor 28 placed in series with the resistor 29 is naturally blocked: the current which is likely to pass there is less than its holding current.
  • the thyristor 30 is forced to extinguish. For this, the electrical energy contained in the capacitor 15 is available.
  • This capacitor 15 in the invention is connected between the two midpoints 32 and 33 a switch bridge which has two branches in parallel.
  • a first branch comprises the thyristors 16 and 19 in series with one another and the second branch comprises the thyristors 18 and 17 also in series with one another.
  • the common ends of these two branches are connected in parallel to the terminals of the thyristor 30.
  • the capacitor 15 is in the electrical state shown in FIG. 1, namely that its armature close to terminal 33 is positively charged with respect to its other armature.
  • thyristors 16 and 17 are started at a date ta by a short pulse applied to their common control terminal 20.
  • Thyristors 18 and 19 remain blocked.
  • the capacitor 15 is discharged by passing through an inductor 34 connected in series with it between the points 32 and 33. The current crosses the inductor 34 and begins to flow in the opposite direction to the normal current in the thyristor 30.
  • I ch charge current of intensity I ch in the thyristor 30.
  • the reverse current follows a circuit passing through the thyristor 16, the capacitor 15, the inductance 34, the thyristor 17 and the thyristor 30.
  • the tail of discharge current of the capacitance passes through the circuit of the diodes 22 to 27 to close on the capacity 15.
  • the reverse current Towards the end of the half-wave the reverse current is canceled, it cannot become negative due to the presence of the thyristors 16 and 17 and the diodes 22 to 27.
  • the discharge current recharges the capacity 15 in reverse.
  • the circuit is open between points A and B, and the capacitor 15 is found charged, in reverse, at a voltage greater than the peak value of the network voltage due to the presence transformer leakage inductors.
  • the energy contained in the leakage inductors, at the time of blocking, is applied to the capacitor 15. This is the reason why the voltage V AB in FIG. 2a takes on blocking, on date t 5 , a value greater than the voltage Vn found in steady state between points A and B. At terminals A and B this overvoltage relapses to return to the normal value in steady state when switch 11 is open. On the other hand, at the terminals of the capacitor 15 the overvoltage could not decrease, within the limits of the leakage time of the capacitor 15. In fact the thyristor 16 then finds itself reverse biased and does not allow the discharge of the capacity 15.
  • the charging polarity of the capacitor 15 is therefore now the reverse of that shown in FIG. 1.
  • the thyristors 16 and 17 are no longer accessible via terminal 20 except the '' we will solicit but rather thyristors 18 and 19 by sending an impulse short-term electrical power on their common control terminal 21.
  • the capacitor which has been charged in reverse by the current which has been used to extinguish the thyristor 30, will then keep the polarity in which it is find.
  • the terminals 32 and 33 of this capacitor will be switched so that their connections to the thyristor 30 are the reverse of those they were previously. In other words, in the invention it is not necessary to provide a special sequence to restore the capacity to a single initial state.
  • the capacity 15 When the supply circuit is put into service for the first time, or else after too long a time between two successive commissionings, the capacity 15 is generally discharged. It must therefore be given a good starting charge.
  • the thyristors 18 and 19 are primed beforehand.
  • the voltage V R is applied to the terminals of the capacitor 15. The latter is charged as in the case presented in FIG. 1.
  • opening is controlled by switching on thyristors 16 and 17.
  • opening is controlled by switching on thyristors 18 and 19; so on as successive commissionings. If these successive commissionings are sufficiently close in time, in particular in the case of radiocinema, the capacitor 15 does not have time to discharge and the switching circuit operates normally. Therefore, the invention does indeed provide the two expected advantages, namely the saving of time by eliminating the recharging sequence of the capacitor and the technological gain by eliminating the source intended to provide additional energy to the capacitors.
  • the invention also has another characteristic. To obtain defusing of the thyristor 30, it is necessary to send it in reverse a current greater than its direct charge current for a time greater than its recovery time tq. This reverse current is supplied by the discharge of the capacitor 15.
  • the discharge circuit comprises a single inductor 34 as indicated in FIG. 1, the shape of the discharge current is that shown in FIG. 2b.
  • the above condition can lead to a large reverse lic peak current.
  • the capacitance / inductance pair 15-34 is replaced by a set of LC cells represented for example in FIG. 4, a discharge pulse having the form represented in FIG. 3 is obtained.
  • Each of cells 35 or 36 of the assembly 37 includes an inductor 38 in parallel with a capacitor 39.
  • the inductors of the different cells are slightly magnetically coupled together. We know how to calculate these cells and their number to obtain a desired pulse shape. What is important here is the duration during which this pulse lets pass a current whose intensity is greater than the charge intensity l eh .
  • this improvement brings a gain on the energy dissipated unnecessarily by the thyristor 30.
  • the energy dissipated unnecessarily corresponds approximately to the surface separating the curves l eh and li. These areas are hatched in FIGS. 2b and 3. As, ultimately, this useless energy had to be stored in the capacity 15, this makes it possible to significantly reduce the values of the cells capacities.

Description

La présente invention a pour objet un circuit d'alimentation pour émetteur de rayons X utilisable en radiologie. En radiologie il est nécessaire d'alimenter un émetteur ou source de rayons X pendant une durée déterminée. Cette durée correspond à une durée d'exposition ou de pose d'une plaque radio- sensible. En radio cinéma il est également nécessaire de moduler l'activité de la source émettrice de rayons X en fonction du rythme de prise d'images: de cette manière on réduit la dose de radiations que reçoit un patient au cours d'un tel examen.The present invention relates to a supply circuit for an X-ray emitter usable in radiology. In radiology it is necessary to power an X-ray emitter or source for a determined period. This duration corresponds to a duration of exposure or placement of a radio-sensitive plate. In radio cinema, it is also necessary to modulate the activity of the X-ray emitting source as a function of the rate at which images are taken: in this way the dose of radiation received by a patient during such an examination is reduced.

Classiquement le montage d'alimentation de l'émetteur comporte un transformateur dont le circuit primaire est relié à un réseau électrique alternatif triphasé, et dont le circuit secondaire est relié à l'émetteur. Le circuit primaire monté en étoile comporte, en lieu et place d'une connexion nodale, un interrupteur pour connecter ensemble au point nodal les trois brins d'alimentation. La durée de fermeture de cet interrupteur conditionne la mise en service du primaire, donc celle du transformateur, et en conséquence fixe la durée d'activité de l'émetteur de rayons X. L'interrupteur comporte classiquement un jeu de thyristors que l'on amorce lors de la mise sous tension désirée. Pour obtenir une ouverture de l'interrupteur, on provoque l'extinction des thyristors. Pour cela on dispose d'une quantité d'énergie électrique contenue dans un condensateur préalablement chargé et que l'on fait se décharger en inverse dans les thyristors. Lorsque la valeur de ce courant inverse dépasse la valeur du courant de charge des thyristors ceux-ci se désamorcent et se bloquent.Conventionally, the transmitter supply assembly includes a transformer, the primary circuit of which is connected to a three-phase AC electrical network, and the secondary circuit of which is connected to the transmitter. The primary circuit mounted in a star comprises, in place of a nodal connection, a switch for connecting together at the nodal point the three supply strands. The duration of closure of this switch conditions the commissioning of the primary, therefore that of the transformer, and consequently fixes the duration of activity of the X-ray emitter. The switch conventionally comprises a set of thyristors which are initiates upon desired power up. To obtain an opening of the switch, the thyristors are extinguished. For this we have a quantity of electrical energy contained in a capacitor previously charged and which is made to discharge in reverse in the thyristors. When the value of this reverse current exceeds the value of the load current of the thyristors, they are defused and blocked.

Avant d'entamer un autre cycle d'allumage- extinction de ce jeu de thyristors il est nécessaire de recharger le condensateur de blocage. La durée de cette séquence supplémentaire empêche la répétition du cycle de fonctionnement à une cadence élevée: par exemple 50 cycles par seconde comme cela est pratiqué en radiocinéma. En outre la recharge du condensateur nécessite de prévoir une alimentation électrique supplémentaire. Enfin, lors de la décharge du condensateur de blocage le courant inverse qui s'établit dans le jeu des thyristors a une allure sinusoïdale. C'est-à-dire que ce courant croît jusqu'à un maximum puis décroît. Pour bloquer les thyristors un courant inverse suffisant doit y être établi pendant une durée supérieure à leur temps de recouvrement. Ceci amène à choisir des condensateurs de valeur importante. En effet la durée utile du courant inverse suffisant est d'autant plus grande que l'intensité maximum de ce courant inverse est élevée. Ce dernier est dépendant de la capacité du condensateur. Il en résulte qu'au moment fort de l'opération du blocage les thyristors sont parcourus par un courant inutilement important puisque c'est en premier lieu leur durée de recouvrement qui commande leur blocage.Before starting another ignition-off cycle of this set of thyristors, it is necessary to recharge the blocking capacitor. The duration of this additional sequence prevents the repetition of the operating cycle at a high rate: for example 50 cycles per second as is practiced in radiocinema. In addition, recharging the capacitor requires the provision of an additional power supply. Finally, during the discharge of the blocking capacitor, the reverse current which is established in the set of thyristors has a sinusoidal shape. That is, this current increases to a maximum and then decreases. To block the thyristors a sufficient reverse current must be established there for a period greater than their recovery time. This leads to choosing capacitors of significant value. Indeed, the useful life of the sufficient reverse current is greater the higher the maximum intensity of this reverse current. The latter is dependent on the capacitance of the capacitor. It follows that at the high point of the blocking operation the thyristors are traversed by an unnecessarily large current since it is primarily their recovery time which controls their blocking.

La présente invention a pour objet de remédier aux inconvénients cités. Elle permet d'atteindre une cadence élevée en utilisant un circuit ne nécessitant pas une séquence spéciale pour recharger le condensateur. En effet, lors du blocage, la décharge du condensateur provoque sa recharge dans une polarité inverse. Ce que l'invention propose c'est que pour le cycle suivant les bornes du condensateur soient commutées de manière à ce que, sans changer la polarité de ce condensateur, celui- ci redevienne correctement connecté.The object of the present invention is to remedy the drawbacks mentioned. It achieves a high rate using a circuit that does not require a special sequence to recharge the capacitor. Indeed, during blocking, the discharge of the capacitor causes its recharging in an opposite polarity. What the invention proposes is that for the following cycle the terminals of the capacitor are switched so that, without changing the polarity of this capacitor, the latter again becomes correctly connected.

L'invention concerne un circuit d'alimentation pour émetteur de rayons X utilisable en radiologie, du type comportant un transformateur dont le circuit primaire est relié au réseau électrique triphasé et dont le circuit secondaire est relié à l'émetteur, dans lequel le circuit primaire est mis en et hors service par un interrupteur commandé, ledit interrupteur comportant un jeu de thyristors de fermeture pour fermer le circuit primaire et ainsi mettre en service le circuit d'alimentation, et une capacité correctement chargée, connectable à ce circuit primaire, pour renverser le sens de passage du courant dans le jeu de thyristors de fermeture, pour ouvrir ainsi l'interrupteur et faire cesser en conséquence l'alimentation, caractérisé en ce qu'il comporte en outre un circuit de commutation de la connexion de la capacité audit circuit primaire.The invention relates to a supply circuit for an X-ray emitter usable in radiology, of the type comprising a transformer whose primary circuit is connected to the three-phase electrical network and whose secondary circuit is connected to the emitter, in which the primary circuit is switched on and off by a controlled switch, said switch comprising a set of closing thyristors to close the primary circuit and thus activate the supply circuit, and a correctly charged capacity, connectable to this primary circuit, to reverse the direction of current flow in the set of closing thyristors, so as to open the switch and consequently stop the supply, characterized in that it also comprises a circuit for switching the connection of the capacitor to said circuit primary.

L'invention sera mieux comprise à la lecture de la description qui suit et à l'examen des figures qui l'accompagnent. Cette description est donnée à titre indicatif et nullement limitatif de l'invention.The invention will be better understood on reading the description which follows and on examining the figures which accompany it. This description is given for information and is in no way limitative of the invention.

Les figures représentent:

  • - figure 1, un schéma général d'un circuit d'alimentation conforme à l'invention;
  • - figure 2a et 2b, des formes d'ondes en différents endroits du circuit précédent;
  • - figure 3, une variante d'une forme d'onde précédente provoquée par un circuit de blocage particulier;
  • - figure 4, le circuit de blocage en question.
The figures represent:
  • - Figure 1, a general diagram of a supply circuit according to the invention;
  • - Figure 2a and 2b, waveforms in different places of the previous circuit;
  • - Figure 3, a variant of a previous waveform caused by a particular blocking circuit;
  • - Figure 4, the blocking circuit in question.

La figure 1 représente un circuit d'alimentation conforme à l'invention. Ce circuit comporte un transformateur 1 dont le circuit primaire 2, 3, 4 est relié au réseau électrique triphasé 5. Le circuit secondaire 6, 7, 8 de ce transformateur est relié à un émetteur 9 de rayonnement X. La liaison de ce circuit secondaire comporte un redresseur de courant 10. Le circuit primaire est mis en service au moyen d'un interrupteur 11 qui reçoit sa commande sur deux bornes d'accès 12, 13. Cet interrupteur comporte un jeu 14 de thyristors qui assurent la fermeture de l'interrupteur en venant quasiment courtcircuite les points A et B de cet interrupteur. L'interrupteur 11 comporte également une capacité 15 correctement chargée connectable au circuit primaire pour renverser le sens de passage du courant dans le jeu 14 des thyristors. Quand le courant dans les thyristors s'inverse, ils s'éteignent et rétablissent l'ouverture du circuit entre les points A et B de l'interrupteur. Dans ces conditions le primaire ne débite plus et l'émetteur 9 de rayons X ne peut plus émettre. Ce qui caractérise l'invention c'est que la capacité 15 est connectée au jeu 14 des thyristors par un circuit de commutation 50. Ce circuit de commutation comporte les thyristors 16 à 19. Ces thyristors sont commandés deux par deux (16-17 et 18-19) par des bornes communes de commande respectivement 20 et 21. En sélectionnant une ou l'autre de ces bornes on peut inverser le sens de raccordement de la capacité au jeu 14.Figure 1 shows a supply circuit according to the invention. This circuit includes a transformer 1, the primary circuit 2, 3, 4 of which is connected to the three-phase electrical network 5. The secondary circuit 6, 7, 8 of this transformer is connected to an emitter 9 of X-radiation. The connection of this secondary circuit comprises a current rectifier 10. The primary circuit is put into service by means of a switch 11 which receives its command on two access terminals 12, 13. This switch comprises a set 14 of thyristors which ensure the closing of the switch coming almost short-circuited points A and B of this switch. The switch 11 also includes a correctly charged capacitor 15 connectable to the primary circuit to reverse the direction of current flow in the set 14 of the thyristors. When the current in the thyristors reverses, they go out and restore the opening of the circuit between points A and B of the switch. Under these conditions the primary no longer debits and the X-ray emitter 9 can no longer emit. What characterizes the invention is that the capacity 15 is connected to the set 14 of the thyristors by a switching circuit 50. This switching circuit comprises the thyristors 16 to 19. These thyristors are controlled two by two (16-17 and 18-19) by common control terminals 20 and 21 respectively. By selecting one or the other of these terminals you can reverse the direction of connection of the capacity to the set 14.

Les enroulements 2, 3 et 4 sont les trois enroulements primaires du transformateurs triphasé. Ils sont couplés magnétiquement aux trois enroulements secondaires du transformateur 1. Du côté opposé au réseau électrique triphasé les enroulements 2, 3 et 4 sont raccordés à six diodes 22 à 27. Chaque extrémité de chacun des enroulements est connectée au point milieu respectivement des couples de diodes 25-22, 26-23, 27-24 mises en série. Les trois couples sont montés en parallèle entre les points A et B de l'interrupteur. Pour mettre en service le primaire il suffit de courtcircuiter le point A, raccordé en commun aux trois cathodes des diodes 22 à 24, au point B raccordé en commun aux trois anodes des diodes 25 à 27. Lorsque le circuit est ouvert la tension continue VR entre les points A et B est égale à √2 fois la tension distribuée par le réseau 5. Pour éviter que la mise en service du primaire ne provoque des surtensions au secondaire le raccordement du point A au point B se fait en deux temps.Windings 2, 3 and 4 are the three primary windings of the three-phase transformers. They are magnetically coupled to the three secondary windings of the transformer 1. On the side opposite to the three-phase electrical network, the windings 2, 3 and 4 are connected to six diodes 22 to 27. Each end of each of the windings is connected to the midpoint respectively of the pairs of diodes 25-22, 26-23, 27-24 connected in series. The three pairs are mounted in parallel between points A and B of the switch. To put the primary into service, simply short circuit point A, connected in common to the three cathodes of diodes 22 to 24, at point B connected in common to the three anodes of diodes 25 to 27. When the circuit is open, the DC voltage V R between points A and B is equal to √2 times the voltage distributed by the network 5. To prevent the commissioning of the primary from causing overvoltages at the secondary, the connection from point A to point B is done in two stages.

Dans le jeu de thyristors 14 on ouvre d'abord, à un instant ti (figure 2a), un thyristor 28 en envoyant une impulsion de courte durée sur sa gâchette par la borne de commande 12. Une résistance 29 connectée en série avec ce thyristor 28 provoque une chute de tension AV. La chute AV est par ailleurs représentée sur la figure 2a. Puis au bout d'un court instant (l'instant séparant une date t2 de la date ti) on amorce un thyristor principal 30 par une courte impulsion appliquée sur sa borne de commande 13. Les deux thyristors 28 et 30 sont montés en parallèle entre les points A et B, le premier par l'intermédiaire de la résistance 29 en série, le second par l'intermédiaire d'un inductance 31 en série. L'inductance 31 limite la variation de courant de telle façon que la tension VAB tend alors vers 0 exponen- tiellement (Fig. 2a). Le transformateur est alors sous tension. En radiologie c'est le début de l'exposition. Compte-tenu du fait que le thyristor 30 est passant le thyristor 28 mis en série avec la résistance 29 se bloque naturellement: le courant qui est susceptible d'y passer est inférieur à son courant de maintien.In the set of thyristors 14, a thyristor 28 is first opened, at an instant t i (FIG. 2a), by sending a short-duration pulse on its trigger by the control terminal 12. A resistor 29 connected in series with this thyristor 28 causes a voltage drop A V. The drop A V is also shown in Figure 2a. Then at the end of a short instant (the instant separating a date t 2 from the date t i ) a main thyristor 30 is started by a short pulse applied to its control terminal 13. The two thyristors 28 and 30 are mounted in parallel between points A and B, the first via resistor 29 in series, the second via an inductor 31 in series. The inductance 31 limits the variation in current so that the voltage V AB then tends towards 0 exponentially (Fig. 2a). The transformer is then energized. In radiology it is the beginning of the exhibition. In view of the fact that the thyristor 30 is on, the thyristor 28 placed in series with the resistor 29 is naturally blocked: the current which is likely to pass there is less than its holding current.

Pour obtenir la mise hors tension du transformateur on provoque l'extinction forcée du thyristor 30. Pour cela on dispose de l'énergie électrique contenue dans la capacité 15. Cette capacité 15 dans l'invention est raccordée entre les deux points milieu 32 et 33 d'un pont de commutateurs qui comporte deux branches en parallèle. Une première branche comporte les thyristors 16 et 19 en série l'un avec l'autre et la deuxième branche comporte les thyristors 18 et 17 également en série l'un avec l'autre. Les extrémités communes de ces deux branches sont raccordées en parallèle aux bornes du thyristor 30.To obtain the power off of the transformer, the thyristor 30 is forced to extinguish. For this, the electrical energy contained in the capacitor 15 is available. This capacitor 15 in the invention is connected between the two midpoints 32 and 33 a switch bridge which has two branches in parallel. A first branch comprises the thyristors 16 and 19 in series with one another and the second branch comprises the thyristors 18 and 17 also in series with one another. The common ends of these two branches are connected in parallel to the terminals of the thyristor 30.

Supposons que la capacité 15 se trouve dans l'état électrique représenté sur la figure 1, à savoir que son armature proche de la borne 33 est chargée positivement par rapport à son autre armature. Pour obtenir la mise hors tension du circuit d'alimentation on amorce, à une date ta, les thyristors 16 et 17 par une courte impulsion appliquée sur leur borne commune de commande 20. Les thyristors 18 et 19 restent bloqués. Lors de cet armorçage la capacité 15 se décharge en passant au travers d'une inductance 34 raccordée en série avec elle entre les points 32 et 33. Le courant traverse l'inductance 34 et commence à passer en sens inverse du courant normal dans le thyristor 30. Pendant la durée de l'exposition il passe un courant de charge d'intensité Ich dans le thyristor 30. A l'instant ts un courant inverse de valeur Il commence à passer dans le thyristor 30. L'allure de ce courant en fonction du temps est représentée en figure 2b. Du fait de la présence de l'inductance 34 le courant Il à une allure sinusoïdale: mais une seule alternance (l'alternance positive) peut passer à cause des thyristors 16 et 17. Dès que le courant ll devient supérieur, en valeur absolue, au courant Ich le thyristor 30 commence à se bloquer. Pour que le blocage du thyristor 30 soit effectif il faut que le courant inverse soit supérieur au courant de charge pendant une durée t supérieure à un temps de recouvrement tq caractéristique du thyristor 30 utilisé.Suppose that the capacitor 15 is in the electrical state shown in FIG. 1, namely that its armature close to terminal 33 is positively charged with respect to its other armature. To get the power supply system switched off, thyristors 16 and 17 are started at a date ta by a short pulse applied to their common control terminal 20. Thyristors 18 and 19 remain blocked. During this ignition the capacitor 15 is discharged by passing through an inductor 34 connected in series with it between the points 32 and 33. The current crosses the inductor 34 and begins to flow in the opposite direction to the normal current in the thyristor 30. During the duration of the exposure, it passes a charge current of intensity I ch in the thyristor 30. At the instant ts an inverse current of value It begins to pass in the thyristor 30. The shape of this current as a function of time is shown in Figure 2b. Due to the presence of inductance 34 the current Il has a sinusoidal shape: but only one alternation (the positive alternation) can pass because of thyristors 16 and 17. As soon as the current l l becomes higher, in absolute value , at current I ch the thyristor 30 begins to block. For the blocking of the thyristor 30 to be effective, the reverse current must be greater than the load current for a period t greater than a recovery time tq characteristic of the thyristor 30 used.

Le courant inverse emprunte un circuit passant par le thyristor 16, la capacité 15, l'inductance 34, le thyristor 17 et le thyristor 30. Après le temps tq la queue de courant de décharge de la capacité passe par le circuit des diodes 22 à 27 pour se refermer sur la capacité 15. Vers la fin de la demi alternance le courant inverse s'annule, il ne peut pas devenir négatif du fait de la présence des thyristors 16 et 17 et des diodes 22 à 27. Pendant toute la phase d'ouverture, le courant de décharge vient recharger la capacité 15 à l'envers. Finalement le courant de recharge s'annule, le circuit est ouvert entre les points A et B, et le condensateur 15 se retrouve chargé, en inverse, à une tension supérieure à la valeur de crête de la tension du réseau du fait de la présence des inductances de fuite du transformateur. En effet, et c'est un intérêt notable de l'invention, l'énergie contenue dans les inductances de fuite, au moment du blocage, vient s'appliquer sur le condensateur 15. C'est la raison pour laquelle la tension VAB sur la figure 2a prend lors du blocage, à la date t5, une valeur supérieure à la tension Vn trouvée en régime permanent entre les points A et B. Aux bornes A et B cette surtension rechute pour revenir à la valeur normale en régime permanent quand l'interrupteur 11 est ouvert. Par contre, aux bornes de la capacité 15 la surtension n'a pas pu décroître, dans les limites du temps de fuite de la capacité 15. En effet le thyristor 16 se retrouve alors polarisé en inverse et n'autorise pas la décharge de la capacité 15. Cette décroissance du potentiel VAB après la surtension est d'ailleurs la raison du blocage naturel des thyristors 16 et 17. Le blocage de ces thyristors est d'ailleurs renforcé par le fait qu'à cet instant là le courant T; est faible et donc est inférieur à leur courant de maintien.The reverse current follows a circuit passing through the thyristor 16, the capacitor 15, the inductance 34, the thyristor 17 and the thyristor 30. After the time tq the tail of discharge current of the capacitance passes through the circuit of the diodes 22 to 27 to close on the capacity 15. Towards the end of the half-wave the reverse current is canceled, it cannot become negative due to the presence of the thyristors 16 and 17 and the diodes 22 to 27. During all the phase opening, the discharge current recharges the capacity 15 in reverse. Finally the charging current is canceled, the circuit is open between points A and B, and the capacitor 15 is found charged, in reverse, at a voltage greater than the peak value of the network voltage due to the presence transformer leakage inductors. Indeed, and this is a notable interest of the invention, the energy contained in the leakage inductors, at the time of blocking, is applied to the capacitor 15. This is the reason why the voltage V AB in FIG. 2a takes on blocking, on date t 5 , a value greater than the voltage Vn found in steady state between points A and B. At terminals A and B this overvoltage relapses to return to the normal value in steady state when switch 11 is open. On the other hand, at the terminals of the capacitor 15 the overvoltage could not decrease, within the limits of the leakage time of the capacitor 15. In fact the thyristor 16 then finds itself reverse biased and does not allow the discharge of the capacity 15. This decrease in the potential V AB after the overvoltage is moreover the reason for the natural blocking of the thyristors 16 and 17. The blocking of these thyristors is moreover reinforced by the fact that at this instant the current T; is weak and therefore is less than their holding current.

La polarité de charge de la capacité 15 est donc maintenant l'inverse de celle représentée sur la figure 1. A la prochaine mise sous tension que l'on désire faire ce ne sont plus les thyristors 16 et 17 accessibles par la borne 20 que l'on va solliciter mais plutôt les thyristors 18 et 19 en envoyant une impulsion électrique de courte durée sur leur borne commune de commande 21. Dans l'invention on constate que la capacité, qui a été chargée en inverse par le courant qui a servi à éteindre le thyristor 30, va garder alors la polarité dans laquelle elle se trouve. Tout simplement les bornes 32 et 33 de cette capacité vont être commutées pour que leurs connexions au thyristor 30 soient l'inverse de celles qu'elles étaient précédemment. Autrement dit dans l'invention il n'est pas nécessaire de prévoir une séquence spéciale pour remettre la capacité dans un état initial unique.The charging polarity of the capacitor 15 is therefore now the reverse of that shown in FIG. 1. At the next power-up that one wishes to make, the thyristors 16 and 17 are no longer accessible via terminal 20 except the '' we will solicit but rather thyristors 18 and 19 by sending an impulse short-term electrical power on their common control terminal 21. In the invention, it can be seen that the capacitor, which has been charged in reverse by the current which has been used to extinguish the thyristor 30, will then keep the polarity in which it is find. Quite simply the terminals 32 and 33 of this capacitor will be switched so that their connections to the thyristor 30 are the reverse of those they were previously. In other words, in the invention it is not necessary to provide a special sequence to restore the capacity to a single initial state.

Lors d'une première mise en service du circuit d'alimentation, ou bien après un temps trop long entre deux mises en service successives, la capacité 15 est en général déchargée. Il faut alors lui donner une bonne charge de départ. Dans ce but on amorce au préalable les thyristors 18 et 19. La tension VR vient s'appliquer aux bornes de la capacité 15. Celle-ci se retrouve chargée comme dans le cas présenté sur la figure 1. Après la première fermeture du circuit primaire, l'ouverture est commandée par l'allumage des thyristors 16 et 17. Après la fermeture suivante, l'ouverture est commandée par l'allumage des thyristors 18 et 19; ainsi de suite au fur et à mesure des mises en service successives. Si ces mises en service successives sont suffisamment rapprochées dans le temps, en particulier dans le cas du radiocinéma, la capacité 15 n'a pas le temps de se décharger et le circuit de commutation fonctionne normalement. Donc l'invention apporte bien les deux avantages attendus à savoir le gain de temps par suppression de la séquence de recharge du condensateur et le gain technologique par la suppression de la source destinée à apporter un complément d'énergie aux condensateurs.When the supply circuit is put into service for the first time, or else after too long a time between two successive commissionings, the capacity 15 is generally discharged. It must therefore be given a good starting charge. For this purpose, the thyristors 18 and 19 are primed beforehand. The voltage V R is applied to the terminals of the capacitor 15. The latter is charged as in the case presented in FIG. 1. After the first closing of the circuit primary, opening is controlled by switching on thyristors 16 and 17. After the next closing, opening is controlled by switching on thyristors 18 and 19; so on as successive commissionings. If these successive commissionings are sufficiently close in time, in particular in the case of radiocinema, the capacitor 15 does not have time to discharge and the switching circuit operates normally. Therefore, the invention does indeed provide the two expected advantages, namely the saving of time by eliminating the recharging sequence of the capacitor and the technological gain by eliminating the source intended to provide additional energy to the capacitors.

L'invention comporte également une autre caractéristique. Pour obtenir le désamorçage du thyristor 30 il est nécessaire de lui envoyer en inverse un courant supérieur à son courant direct de charge pendant un temps supérieur à son temps de recouvrement tq. Ce courant inverse est fourni par la décharge du condensateur 15. Lorsque le circuit de décharge comporte une simple inductance 34 comme indiqué sur la figure 1 la forme du courant de décharge est celle représentée sur la figure 2b. La condition indiquée ci-dessus peut conduire à un courant de crête inverse lic important. Par contre si l'on remplace le couple capacité/inductance 15-34 par un ensemble de cellules L-C représentées par exemple sur la figure 4 on obtient une impulsion de décharge ayant la forme représentée sur la figure 3. Chacune des cellules 35 ou 36 de l'ensemble 37 comporte une inductance 38 en parallèle avec une capacité 39. Les inductances des différentes cellules sont légèrement couplées magnétiquement entre elles. On sait calculer ces cellules ainsi que leur nombre pour obtenir une forme d'impulsion désirée. Ce qui est important ici c'est la durée pendant laquelle cette impulsion laisse passer un courant dont l'intensité est supérieure à l'intensité de charge leh. En comparant la figure 2b à la figure 3 on remarque que ce perfectionnement apporte un gain sur l'énergie dissipée inutilement par le thyristor 30. L'énergie dissipée inutilement correspond approximativement à la surface séparant les courbes leh et li. Ces surfaces sont hachurées sur les figures 2b et 3. Comme en définitive cette énergie inutile devait être stockée dans la capacité 15 ceci permet de réduire notablement les valeurs des capacités des cellules. Approximativement la valeur confondue des deux capacités 39 de la figure 4 est de l'ordre du quart de la capacité 15 utilisée dans les mêmes conditions sur la figure 1. Ceci provoque par ailleurs une économie sur les thyristors 16 à 19 du fait qu'ils doivent passer un courant maximum qui est bien inférieur au courant Iic vu précédemment.The invention also has another characteristic. To obtain defusing of the thyristor 30, it is necessary to send it in reverse a current greater than its direct charge current for a time greater than its recovery time tq. This reverse current is supplied by the discharge of the capacitor 15. When the discharge circuit comprises a single inductor 34 as indicated in FIG. 1, the shape of the discharge current is that shown in FIG. 2b. The above condition can lead to a large reverse lic peak current. On the other hand, if the capacitance / inductance pair 15-34 is replaced by a set of LC cells represented for example in FIG. 4, a discharge pulse having the form represented in FIG. 3 is obtained. Each of cells 35 or 36 of the assembly 37 includes an inductor 38 in parallel with a capacitor 39. The inductors of the different cells are slightly magnetically coupled together. We know how to calculate these cells and their number to obtain a desired pulse shape. What is important here is the duration during which this pulse lets pass a current whose intensity is greater than the charge intensity l eh . By comparing FIG. 2b to FIG. 3, it is noted that this improvement brings a gain on the energy dissipated unnecessarily by the thyristor 30. The energy dissipated unnecessarily corresponds approximately to the surface separating the curves l eh and li. These areas are hatched in FIGS. 2b and 3. As, ultimately, this useless energy had to be stored in the capacity 15, this makes it possible to significantly reduce the values of the cells capacities. Approximately the combined value of the two capacitors 39 in FIG. 4 is of the order of a quarter of the capacitor 15 used under the same conditions in FIG. 1. This also causes savings on the thyristors 16 to 19 because they must pass a maximum current which is much lower than the current I ic seen previously.

Claims (7)

1. A supply circuit for a source (9) of x-rays able to be used in radiology, of the type comprising a transformer (1) whose primary circuit (2 through 4) is connected with a three-phase electrical network (5) and whose secondary circuit (6 through 8) is connected with the source, in which the primary circuit is put into and out of operation by a controlled (12 and 13) switch (11), said switch comprising a set (14) of circuit closing thyristors (28 through 30) in order to complete the supply curcuit thus putting the supply circuit into operation, and an appropriately charged capacitor (15) able to be connected with this primary circuit in order to reverse (I;) the direction of flow of the current in the circuit closing set of thyristors, in order to thus open the switch and consequently cause the supply to be discontinued, said circuit comprising means (18, 19 and VR) in order to charge the capacitor with a given polarity, characterized in that it comprises furthermore a circuit (50) for the switching of the connection (32 and 33) of the capacitor with the said primary circuit, in order to invert the direction of this connection after each control signal applied to the switch.
2. The circuit as claimed in claim 1, characterized in that the switching circuit comprises a bridge made up of switches (16 through 19), and said bridge comprises two limbs (18, 17 and 16,19) connected in parallel at their ends with the terminals of the set of thyristors, the capacitor being inserted between the middle points (32 and 33) of these two limbs.
3. The circuit as claimed in claim 2, characterized in that each limb comprises two thyristors (18, 17 and 16, 19) connected in series.
4. The circuit as claimed in claim 2 or claim 3, characterized in that the switches (16 and 17) are situated in the two opposite limbs of the switching circuit and are simultaneously (20 and 21) operated (ts).
5. The circuit as claimed in any one of the claims 1 through 4, characterized in that the capacitor (15) is in series with an inductance (34).
6. The circuit as claimed in any one of the claims 1 through 6, characterized in that the capacitance comprises a group (figure 4) of inductance capacitor (38 and 39) cells (35 and 36) placed in cascade with each other.
7. The circuit as claimed in claim 6, characterized in that the group of the cells comprises two cells (figure 4).
EP85401754A 1984-09-14 1985-09-09 Power supply circuit for an x-ray source for use in radiology Expired EP0179680B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8414153 1984-09-14
FR8414153A FR2570569A1 (en) 1984-09-14 1984-09-14 POWER SUPPLY CIRCUIT FOR X-RAY EMITTER FOR USE IN RADIOLOGY

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EP0179680A1 EP0179680A1 (en) 1986-04-30
EP0179680B1 true EP0179680B1 (en) 1989-04-26

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EP85401754A Expired EP0179680B1 (en) 1984-09-14 1985-09-09 Power supply circuit for an x-ray source for use in radiology

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US (1) US4730352A (en)
EP (1) EP0179680B1 (en)
DE (1) DE3569865D1 (en)
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5077770A (en) * 1990-07-05 1991-12-31 Picker International, Inc. High voltage capacitance discharge system for x-ray tube control circuits
US5513093A (en) * 1994-03-11 1996-04-30 Miller Electric Mfg. Co. Reduced open circuit voltage power supply and method of producing therefor

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3720868A (en) * 1972-01-10 1973-03-13 Zenith Radio Corp Multiple input voltage source power supply
DE2608243A1 (en) * 1976-02-28 1977-09-01 Koch & Sterzel Kg X:ray appts. synchronised with AC mains - has variable attenuator and performs one exposure per cycle of mains supply
JPS5910557B2 (en) * 1976-11-15 1984-03-09 株式会社東芝 computer tomography device
DE2719373C2 (en) * 1977-04-30 1982-10-21 Philips Patentverwaltung Gmbh, 2000 Hamburg Circuit arrangement of an X-ray generator with an electronic switch controlled by a timing control element in the primary circuit of a high-voltage transformer
JPS58959Y2 (en) * 1977-05-18 1983-01-08 株式会社東芝 X-ray generator
DE2804591A1 (en) * 1978-02-03 1979-08-09 Koch & Sterzel Kg X=ray appts. for taking moving pictures - has gate turn-off thyristor(s) in prim. winding of HV transformer to switch radiation on and off
SU892612A1 (en) * 1980-03-28 1981-12-23 Предприятие П/Я В-2156 Dc voltage converter
DE3015039A1 (en) * 1980-04-18 1981-10-22 Siemens AG, 1000 Berlin und 8000 München X-RAY DIAGNOSTIC GENERATOR IN WHICH THE X-RAY TUBE VOLTAGE IS SET BY THE X-RAY TUBE CURRENT
SU957434A1 (en) * 1981-01-06 1982-09-07 Кемеровский государственный университет Direct current breaker

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US4730352A (en) 1988-03-08
FR2570569A1 (en) 1986-03-21
DE3569865D1 (en) 1989-06-01
EP0179680A1 (en) 1986-04-30

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