EP0471626A1 - Device for supplying and regulating the cathode filament current from an X-ray tube - Google Patents

Device for supplying and regulating the cathode filament current from an X-ray tube Download PDF

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Publication number
EP0471626A1
EP0471626A1 EP91402249A EP91402249A EP0471626A1 EP 0471626 A1 EP0471626 A1 EP 0471626A1 EP 91402249 A EP91402249 A EP 91402249A EP 91402249 A EP91402249 A EP 91402249A EP 0471626 A1 EP0471626 A1 EP 0471626A1
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EP
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Prior art keywords
circuit
current
filament
output
signal
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EP91402249A
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German (de)
French (fr)
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EP0471626B1 (en
Inventor
Jacques Laeufffer
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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
    • H05G1/20—Power supply arrangements for feeding the X-ray tube with high-frequency ac; with pulse trains
    • 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
    • H05G1/26—Measuring, controlling or protecting
    • H05G1/30—Controlling
    • H05G1/34—Anode current, heater current or heater voltage of X-ray tube

Definitions

  • the invention relates to a device for supplying current to a filament of a cathode of an X-ray tube and for regulating said current to a selected value.
  • An X-ray tube is generally made up like a diode, that is to say by two electrodes of which one, called cathode, emits electrons while the other, called anode, receives these electrons on a small surface which constitutes the X-ray source.
  • the cathode has a heated filament which is the source of electrons.
  • a so-called anodic current is established through the generator and crosses the space between the cathode and the anode in the form of an electron beam whose intensity depends on the temperature of the filament, this temperature being a function of the power dissipated in the filament, that is to say of the current, called the heating current, flowing through the filament.
  • the quantity of X-rays emitted by the anode depends mainly on the intensity of the anode current and therefore on the heating current of the filament. Also, the filament heating current constitutes one of the important parameters which must be determined for each exposure of radiography or radioscopy during an X-ray examination of a patient.
  • the parameters of the pose are determined according to the nature of the examination. Generally, these parameters are predetermined by an operator who displays the values on a control desk through which controlled the operation of the various organs of a radiology installation such as, for example, the high voltage generator and the generator of the filament heating current. More and more often, the values of these parameters are determined using a microprocessor device which calculates and programs the optimal values of these parameters according to, for example, the type of examination desired by the practitioner and the specific characteristics of the installation.
  • the parameters which are calculated and programmed are, for example, the duration of the exposure time, the energy of the X-ray by the choice of the value of the high voltage applied between the cathode and the anode and the intensity of the anode current. by the choice, in particular, of a value of the intensity of the heating current of the filament.
  • the intensity of the heating current must be able to be modified significantly, from one pose to the next, for example from 1.5 amperes to 5.5 amperes but also during the same pose.
  • these current values must be obtained quickly and automatically and be maintained for the required time.
  • the power supply circuit 11 comprises a DC voltage source 13 represented by a battery 13 ′ and an inverter circuit 14.
  • the inverter circuit 14 comprises a chopper circuit 31 comprising switches 20 and 21 controlled by a control circuit 19 and diodes 22 and 23, and a resonant circuit 10 comprising the capacitors 24 and 25 and the coil 26.
  • the resonant circuit 10 is connected to a primary winding 28 of an isolation transformer 9 of which the secondary circuit 27 comprises the filament 15 of the cathode of the X-ray tube 30.
  • the filament 15 is optionally supplied via a rectifier circuit 29 which is for example of the type with diodes and filtering capacitor.
  • the regulating circuit 12 comprises a circuit 8 for detecting the heating current of the filament and a circuit 16 for measuring this heating current of the filament, a comparator circuit 17 for the current measured with a predetermined value, called the reference value, a converter circuit 18 variable voltage-frequency which is applied to the inverter circuit 14 so as to modify the frequency and thus obtain a heating current whose value is equal to a set value Ic.
  • the device which has just been described succinctly has the following drawbacks.
  • the sudden blockage of the transistors of the switches 20 and 21 of the inverter circuit 14 gives rise to rapid variations in the current which create parasitic signals, the latter disturbing the surrounding circuits and, in particular, the primary circuit 28 of the transformer which includes the detection circuit. 8 of the heating current.
  • the measurement signals therefore contain parasites which create an error in the regulation circuit 12. When this error is reproducible, it can be corrected by calibrating the device.
  • the sudden blockage of the transistors of the inverter circuit 14 also has the effect that the current flowing in the filament 15 has a shape that changes between the sinusoid and the sawtooth when the voltage E of the source varies.
  • the regulation circuit 12 provision is made to calculate the effective current which characterizes the temperature of the filament by bringing the measurement made to the square.
  • the heating current approaches the sawtooth, its squared value has peaks which correspond to high-ranking harmonics that the RMS measurement circuit cannot reproduce because its bandwidth is insufficient. To avoid such a phenomenon, it is known to regulate the voltage E of the voltage source 13.
  • An object of the present invention is therefore to provide a supply circuit in which the operating phases of the inverter circuit do not include a sudden blockage of the current in the semiconductors, nor a waveform of filament current having high harmonics.
  • the invention proposes an inverter circuit of the hyporesonant type with discontinuous operation in which the switching frequency of the semiconductor of the inverter circuit is lower than the resonance frequency of the resonant circuit and in which the switching of the semiconductor is performed when the current in them is zero.
  • any filtering in the measurement chain is equivalent to a derivation in the direct chain, derivation which is source of instability.
  • the direct chain includes filtering which greatly limits the bandwidth of the servo loop, which results in the delay indicated above.
  • Another object of the present invention is therefore to produce a regulation circuit which does not include a filtering circuit in the measurement chain.
  • the measurement signal is raised from the square and is compared to the squared value of a setpoint and it is therefore not necessary to use a circuit for calculating the square root which would include a circuit for filtering.
  • FIG. 1 The diagram of FIG. 1 has been described succinctly in the preamble to show certain drawbacks of the devices for feeding and regulating the filament current of X-ray tubes according to the prior art.
  • the device for supplying and regulating the current of a cathode filament 40 of an X-ray tube 41 comprising an anode 42 comprises a current supply circuit 43 and a circuit 44 for regulating the current flowing in the filament 40.
  • the supply circuit 43 comprises a DC voltage source 45, an inverter circuit 46 and an isolation transformer 50.
  • the DC voltage source 45 can be of any known type without voltage regulation. It includes, for example, a source 47 of alternating voltage which is connected to diodes D1 to D4 mounted as a full-wave rectifier bridge. The output terminals of the rectifier bridge are connected to the inverter circuit 46 via a filter cell which mainly consists of an electrolytic capacitor C1.
  • the inverter circuit 46 comprises a chopping circuit 48 and a resonant circuit 49.
  • the chopping circuit 48 comprises, for example, two field effect transistors T1 and T2 which are connected in series on the output terminals of the supply circuit 45 and two diodes D5 and D6 which are respectively connected in parallel between the drain and the source of transistors T1 and T2, the outputs of which are each connected to the control gate of transistor T1 or T2 so that their anode is connected to the source of the corresponding transistor. It also includes a control circuit 51 of the transistors T1 and T2.
  • the resonant circuit 49 comprises, for example, two capacitors C2 and C3 which are connected in series on the output terminals of the inverter circuit 48 and a coil L1, one terminal of which is connected directly to the anode of the diode D5 and whose another terminal is connected, via a primary winding 52 of the transformer 50, to the common point C of the capacitors C2 and C3.
  • the isolation transformer 50 of the pulse type, comprises, in addition to the primary winding 52, a secondary winding 53 whose output terminals are connected directly to the filament 40 of the cathode of the X-ray tube 41. It should be noted that, with respect to the diagram in FIG. 1, there is no rectifier circuit in the secondary circuit so that the filament 40 is supplied with pulse current. However, the device according to the invention can be implemented in the case where a rectifier circuit is connected between the secondary winding 53 and the filament 40.
  • the inverter circuit 46 is of the hyporesonant type, that is to say that the switching frequency of the transistors T1 and T2, as defined by the control circuit 51, is less than the resonance frequency of the resonant circuit 49.
  • the regulation circuit 44 comprises a circuit 54 for detecting and measuring the heating current I (t) which is connected, for example, in the primary circuit 52 of the transformer 50.
  • the signal detected by this measurement circuit is applied to a multiplier circuit 55 which multiplies the input signal proportional to I (t) by itself so that the signal at the output is proportional to I2 (t).
  • the output signal proportional to I2 (t) is applied to an input of a differentiator circuit 56 which also receives, on its other input, a reference signal I2 ref corresponding to the current I ref which it is desired to obtain in the filament 40.
  • This signal I2 ref is supplied by a control device 59.
  • the signal error ⁇ I2 ref - I2 (t) is applied to an integrator circuit 57 whose output signal is applied to a comparator 58 whose reference potential is ground.
  • the comparator 58 supplies a pulse as soon as the integrated signal is, for example, greater than the ground potential and this pulse lasts until the moment when said integrated signal becomes lower than the ground potential.
  • This pulse supplied by the comparator 58, is applied to the control circuit 51 to trigger the conduction of one or the other transistor T1 or T2 depending on whether the transistor which was previously conductive was T2 or T1.
  • FIG. 3 is a simplified block diagram of the control circuit 51; the latter comprises an AND logic circuit 60 of which an input 60-a is connected to the output of the comparator circuit 58 and of which the other input 60-b is connected to a delay circuit 64.
  • the output of the AND circuit 60 is connected, d on the one hand, at an input of a bistable circuit 61 and, on the other hand, at the input of two delay circuits, one referenced 64 and the other referenced 65.
  • the bistable circuit 61 has two outputs 61- a and 61-b, the first corresponding to state 1 and the second to state 0 , which are respectively connected to one of the two inputs of AND logic circuits 62 and 63.
  • the other input of AND circuits 62 and 63 is connected to the output of the delay circuit 65.
  • the AND circuit 60 supplies a state change control pulse of the bistable circuit 61 each time circuit 58 supplies a pulse and a certain time or delay ⁇ 1 has elapsed since the last pulse. This delay ⁇ 1 is obtained using the delay circuit 64.
  • the bistable circuit 65 supplies the control signals of the transistors T1 and T2 via the AND circuits 62 and 63, the opening of which is controlled by the signal of the retarder circuit 65 which fixes the minimum duration of conduction ⁇ 2 of said transistors.
  • ⁇ 1 and ⁇ 2 can be respectively 50 microseconds and 37 microseconds in the case where the maximum switching frequency is 20 kilohertz.
  • a pulse T′1 (FIG. 4-g) is applied to the time t o to the control electrode of transistor T1.
  • This pulse T′1 turns on and keeps the transistor T1 conductive and a current i1 (figure 4-a) says positive, flows in the transistor T1, the coil L1, the primary winding 52 of the transformer 50, the capacitors C2 and C3 and the source 45 (in fact i1 / 2 in each capacitor).
  • This current i1 gives rise to a voltage V (figure 4-b) of sinusoidal shape at the terminals of the primary winding 52 and it results from it a current I (t) (figure 4-c) in the secondary winding 53 of the transformer 50, current of identical appearance to the current i1 flowing in the primary winding.
  • the current i1 charges the capacitor C3 and discharges the capacitor C2 from the resonant circuit and their charging voltage is opposed to the circulation of the current i1 so that the latter is canceled out at time t1.
  • Capacitor C3 then discharges while capacitor C2 discharges load and a current i2 (figure 4-a), said negative, circulates in the capacitors C2 and C3 (in fact i2 / 2 in each capacitor), the primary winding 52, the coil L1 the diode D5 and the source 45.
  • a pulse T′2 is applied to the control electrode of the transistor T2 at the time t ′ o to make it conductive.
  • a current i′1 said to be negative, then flows in the transistor T2, the source 45, the capacitors C2 and C3 (in fact i′1 / 2 in each capacitor), the primary winding 52 of the transformer 50 and the coil L1 .
  • This negative current gives rise to a negative voltage V (figure 4-b) at the terminals of the primary winding 52 and this results in a negative current I (t) (figure 4-c) in the secondary winding 53 of the transformer 50 , current of identical appearance to the current i′1 flowing in the primary winding.
  • the negative current i′1 charges the capacitor C2 and discharges the capacitor C3 and their charging voltage is opposed to the circulation of the current i′1 so that the latter is canceled out at time t′1.
  • the capacitor C2 then discharges while the capacitor C3 charges and a positive current i′2 flows in the capacitors C2 and C3 (in fact i′2 / 2 in each capacitor), the primary winding 52, the coil L1, the diode D6 and the source 45.
  • This positive current gives rise to a positive tension (figure 4-b) at the terminals of the primary winding 52 and, consequently, to a positive current I (t) (figure 4-c) in the secondary winding 53.
  • the control circuit 51 operates in the following manner, assuming that the transistor which has just been conductive is the transistor T2.
  • the circuit 58 provides the pulse 70 (figure 4-f)
  • its front edge commands the change of the state (setting to state 1) of the bistable circuit 61 via the AND circuit 60 provided that the second input of this AND circuit receives the authorization signal 71 (figure 4-h) given by the delay circuit 64.
  • the signal supplied by the AND circuit 60 resets the two delay circuits 64 and 65 to zero so that the AND circuit 60 closes during time ⁇ 1 (figure 4-h) and that the circuits ET 62 and 63 open during time ⁇ 2 (figure 4-g).
  • the AND circuit 62 which receives the status signal 1 from the bistable circuit 61, supplies a signal which makes the transistor T1 conductive.
  • the duration of this signal is determined by the duration ⁇ 2 of the signal T′1 supplied by the delay circuit 65, that is to say at least equal to the half-period of the maximum frequency switching, so that the transistor T1 (or T2) is maintained in the conductive state for the time ⁇ 2.
  • the signal T′1 (or T′2) therefore always ends after the instant t1 (or t′1).
  • the delay circuit 64 provides a signal 71 ′ for opening the AND circuit 60 so that the next pulse 70 ′ changes the state of the bistable circuit 61 which changes to state 0 , ends signal 71 ′ through the circuit retarder 64 and supplies the signal T′2 via the retarder circuit 65.
  • the AND circuit 63 then supplies a signal of duration ⁇ 2 which makes the transistor T2 conductive.
  • the transistor T1 will be conductive because the bistable circuit 61 will return to state 1.
  • the control circuit 51 described in relation to FIG. 3 comprises two delay circuits 64 and 65 but it is understood that they can be produced using a single delay circuit.
  • the regulation of the current value is obtained by alternating current pulses which are substantially identical but reverse at each cycle but whose frequency varies to obtain the desired value I ref .
  • I ref increases the difference ⁇ will increase and the slope (part 73-fig. 4-e) of the integrated signal will also increase so that the pulse 70 ′ will appear a little earlier and therefore trigger the transistor T2 earlier.

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  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • X-Ray Techniques (AREA)

Abstract

The invention relates to the devices for supplying current to the cathode filaments of X-ray tubes. The invention lies in the fact that the filament 40 is supplied with high-frequency current pulses provided by an inverter circuit 46 of the subresonant type whose transistors T1 and T2 are controlled by a regulating circuit 44. The latter carries out high-frequency regulation. <IMAGE>

Description

L'invention concerne un dispositif pour alimenter en courant un filament d'une cathode d'un tube radiogène et pour réguler ledit courant à une valeur sélectionnée.The invention relates to a device for supplying current to a filament of a cathode of an X-ray tube and for regulating said current to a selected value.

Un tube radiogène est généralement constitué comme une diode, c'est-à-dire par deux électrodes dont l'une, appelée cathode, émet des électrons tandis que l'autre, appelée anode, reçoit ces électrons sur une petite surface qui constitue la source de rayonnement X.An X-ray tube is generally made up like a diode, that is to say by two electrodes of which one, called cathode, emits electrons while the other, called anode, receives these electrons on a small surface which constitutes the X-ray source.

La cathode comporte un filament chauffé qui constitue la source d'électrons. Quand la haute tension, fournie par un générateur, est appliquée aux bornes des deux électrodes, de façon que la cathode soit à un potentiel négatif, un courant dit anodique s'établit au travers du générateur et traverse l'espace entre la cathode et l'anode sous la forme d'un faisceau d'électrons dont l'intensité dépend de la température du filament, cette température étant fonction de la puissance dissipée dans le filament, c'est-à-dire du courant, appelé courant de chauffage, qui circule dans le filament.The cathode has a heated filament which is the source of electrons. When the high voltage, supplied by a generator, is applied across the two electrodes, so that the cathode is at a negative potential, a so-called anodic current is established through the generator and crosses the space between the cathode and the anode in the form of an electron beam whose intensity depends on the temperature of the filament, this temperature being a function of the power dissipated in the filament, that is to say of the current, called the heating current, flowing through the filament.

La quantité de rayons X émis par l'anode dépend principalement de l'intensité du courant anodique et donc du courant de chauffage du filament. Aussi, le courant de chauffage de filament constitue un des paramètres importants qui doivent être déterminés pour chaque pose de radiographie ou de radioscopie au cours d'un examen radiologique d'un patient.The quantity of X-rays emitted by the anode depends mainly on the intensity of the anode current and therefore on the heating current of the filament. Also, the filament heating current constitutes one of the important parameters which must be determined for each exposure of radiography or radioscopy during an X-ray examination of a patient.

Les paramètres de la pose sont déterminés en fonction de la nature de l'examen. Généralement, ces paramètres sont prédéterminés par un opérateur qui en affiche les valeurs sur un pupitre de commande par lequel est commandé le fonctionnement des différents organes d'une installation de radiologie tels que, par exemple, le générateur haute tension et le générateur du courant de chauffage du filament. De plus en plus souvent, les valeurs de ces paramètres sont déterminées à l'aide d'un dispositif à microprocesseur qui calcule et programme les valeurs optimales de ces paramètres en fonction, par exemple, du type d'examen désiré par le praticien et des caractéristiques spécifiques de l'installation.The parameters of the pose are determined according to the nature of the examination. Generally, these parameters are predetermined by an operator who displays the values on a control desk through which controlled the operation of the various organs of a radiology installation such as, for example, the high voltage generator and the generator of the filament heating current. More and more often, the values of these parameters are determined using a microprocessor device which calculates and programs the optimal values of these parameters according to, for example, the type of examination desired by the practitioner and the specific characteristics of the installation.

Les paramètres qui sont calculés et programmés sont, par exemple, la durée du temps de pose, l'énergie du rayonnement X par le choix de la valeur de la haute tension appliquée entre la cathode et l'anode et l'intensité du courant anodique par le choix, notamment, d'une valeur de l'intensité du courant de chauffage du filament.The parameters which are calculated and programmed are, for example, the duration of the exposure time, the energy of the X-ray by the choice of the value of the high voltage applied between the cathode and the anode and the intensity of the anode current. by the choice, in particular, of a value of the intensity of the heating current of the filament.

Il est à remarquer que l'intensité du courant de chauffage doit pouvoir être modifiée de manière importante, d'une pose à la suivante, par exemple de 1,5 ampère à 5,5 ampères mais aussi au cours d'une même pose. En outre, ces valeurs de courant doivent être obtenus rapidement et automatiquement et être maintenues pendant le temps requis.It should be noted that the intensity of the heating current must be able to be modified significantly, from one pose to the next, for example from 1.5 amperes to 5.5 amperes but also during the same pose. In addition, these current values must be obtained quickly and automatically and be maintained for the required time.

Il existe de nombreux dispositifs d'alimentation et de régulation du courant de chauffage de filament d'un tube radiogène et l'un d'entre eux est décrit dans le brevet français 2 597 285. Ce dispositif de l'art antérieur, dont le schéma de principe est donné par la figure 1, comprend un circuit d'alimentation en courant 11 et un circuit de régulation 12 (y compris un circuit 8).There are numerous devices for supplying and regulating the filament heating current of an X-ray tube, and one of them is described in French patent 2,597,285. This device of the prior art, including the block diagram is given in Figure 1, includes a current supply circuit 11 and a regulation circuit 12 (including a circuit 8).

Le circuit d'alimentation 11 comprend une source de tension continue 13 représentée par une pile 13′ et un circuit onduleur 14. Le circuit onduleur 14 comprend un circuit hâcheur 31 comportant des interrupteurs 20 et 21 commandés par un circuit de commande 19 et des diodes 22 et 23, et un circuit résonant 10 comportant les condensateurs 24 et 25 et la bobine 26. Le circuit résonant 10 est connecté à un enroulement primaire 28 d'un transformateur d'isolement 9 dont le circuit secondaire 27 comporte le filament 15 de la cathode du tube radiogène 30. Le filament 15 est éventuellement alimenté par l'intermédiaire d'un circuit redresseur 29 qui est par exemple du type à diodes et à condensateur de filtrage.The power supply circuit 11 comprises a DC voltage source 13 represented by a battery 13 ′ and an inverter circuit 14. The inverter circuit 14 comprises a chopper circuit 31 comprising switches 20 and 21 controlled by a control circuit 19 and diodes 22 and 23, and a resonant circuit 10 comprising the capacitors 24 and 25 and the coil 26. The resonant circuit 10 is connected to a primary winding 28 of an isolation transformer 9 of which the secondary circuit 27 comprises the filament 15 of the cathode of the X-ray tube 30. The filament 15 is optionally supplied via a rectifier circuit 29 which is for example of the type with diodes and filtering capacitor.

Le circuit de régulation 12 comprend un circuit de détection 8 du courant de chauffage du filament et un circuit de mesure 16 de ce courant de chauffage du filament, un circuit comparateur 17 du courant mesuré avec une valeur prédéterminée, dite de consigne, un circuit convertisseur 18 tension-fréquence variable qui est appliqué au circuit onduleur 14 de manière à en modifier la fréquence et ainsi obtenir un courant de chauffage dont la valeur est égale à une valeur de consigne Ic.The regulating circuit 12 comprises a circuit 8 for detecting the heating current of the filament and a circuit 16 for measuring this heating current of the filament, a comparator circuit 17 for the current measured with a predetermined value, called the reference value, a converter circuit 18 variable voltage-frequency which is applied to the inverter circuit 14 so as to modify the frequency and thus obtain a heating current whose value is equal to a set value Ic.

Le dispositif qui vient d'être décrit succinctement présente les inconvénients suivants. Le blocage brutal des transistors des interrupteurs 20 et 21 du circuit onduleur 14 donne naissance à des variations rapides du courant qui créent des signaux parasites, ces derniers perturbant les circuits environnants et, notamment, le circuit primaire 28 du transformateur qui comporte le circuit de détection 8 du courant de chauffage. Les signaux de mesure comportent donc des parasites qui créent une erreur dans le circuit de régulation 12. Lorsque cette erreur est reproductible, elle peut-être corrigée par étalonnage du dispositif.The device which has just been described succinctly has the following drawbacks. The sudden blockage of the transistors of the switches 20 and 21 of the inverter circuit 14 gives rise to rapid variations in the current which create parasitic signals, the latter disturbing the surrounding circuits and, in particular, the primary circuit 28 of the transformer which includes the detection circuit. 8 of the heating current. The measurement signals therefore contain parasites which create an error in the regulation circuit 12. When this error is reproducible, it can be corrected by calibrating the device.

Une telle reproductibilité n'est possible que si le régime de fonctionnement est stable, ce qui est obtenu par une régulation de la tension E de la source 13.Such reproducibility is only possible if the operating regime is stable, which is obtained by regulating the voltage E of the source 13.

Le blocage brutal des transistors du circuit onduleur 14 a aussi pour effet que le courant qui circule dans le filament 15 a une forme évoluant entre la sinusoïde et la dent de scie lorsque la tension E de la source varie. Or, dans le circuit de régulation 12, il est prévu de calculer le courant efficace qui caractérise la température du filament en portant au carré la mesure effectuée. Lorsque le courant de chauffage se rapproche de la dent de scie, sa valeur au carré présente des pointes qui correspondent à des harmoniques de rang élevé que le circuit de mesure de la valeur efficace ne peut reproduire car sa bande passante est insuffisante. Pour éviter un tel phénomène, il est connu de réguler la tension E de la source de tension 13.The sudden blockage of the transistors of the inverter circuit 14 also has the effect that the current flowing in the filament 15 has a shape that changes between the sinusoid and the sawtooth when the voltage E of the source varies. However, in the regulation circuit 12, provision is made to calculate the effective current which characterizes the temperature of the filament by bringing the measurement made to the square. When the heating current approaches the sawtooth, its squared value has peaks which correspond to high-ranking harmonics that the RMS measurement circuit cannot reproduce because its bandwidth is insufficient. To avoid such a phenomenon, it is known to regulate the voltage E of the voltage source 13.

Un but de la présente invention est donc de réaliser un circuit d'alimentation dans lequel les phases de fonctionnement du circuit onduleur ne comportent pas de blocage brutal du courant dans les semi-conducteurs, ni de forme d'onde de courant de filament présentant des harmoniques élevés.An object of the present invention is therefore to provide a supply circuit in which the operating phases of the inverter circuit do not include a sudden blockage of the current in the semiconductors, nor a waveform of filament current having high harmonics.

Pour atteindre ce but, l'invention propose un circuit onduleur du type hyporésonant à fonctionnement discontinu dans lequel la fréquence de commutation des semi-conducteurs du circuit onduleur est inférieure à la fréquence de résonance du circuit résonant et dans lequel la commutation des semi-conducteurs est effectuée lorsque le courant dans ces derniers est nul.To achieve this object, the invention proposes an inverter circuit of the hyporesonant type with discontinuous operation in which the switching frequency of the semiconductor of the inverter circuit is lower than the resonance frequency of the resonant circuit and in which the switching of the semiconductor is performed when the current in them is zero.

L'invention concerne donc un dispositif d'alimentation et de régulation du courant d'un filament d'une cathode d'un tube radiogène comportant un circuit d'alimentation en courant dudit filament et un circuit de régulation dudit courant, ledit circuit d'alimentation comprenant :

  • une source de tension continue,
  • un circuit onduleur pour obtenir des impulsions de courant à partir de la source de tension continue, et
  • un transformateur d'isolement dont l'enroulement primaire est connecté à la sortie du circuit onduleur, caractérisé en ce que :
    • le circuit onduleur est du type hyporésonant et fournit des impulsions de courant haute fréquence, et en ce que
    • le transformateur d'isolement, du type impulsionnel, a son enroulement secondaire qui est directement connecté audit filament de la cathode.
The invention therefore relates to a device for supplying and regulating the current of a filament of a cathode of an X-ray tube comprising a circuit for supplying current to said filament and a circuit for regulating said current, said circuit for food including:
  • a source of DC voltage,
  • an inverter circuit for obtaining current pulses from the DC voltage source, and
  • an isolation transformer whose primary winding is connected to the output of the inverter circuit, characterized in that:
    • the inverter circuit is of the hyporesonant type and supplies high frequency current pulses, and in that
    • the isolation transformer, of the pulse type, has its secondary winding which is directly connected to said filament of the cathode.

Le circuit de régulation de la figure 1, correspondant à l'art antérieur, présente un temps de retard important entre l'application d'une valeur de consigne et la réalisation de cette consigne au niveau du courant de filament. Ce temps de retard est dû au filtrage introduit par le circuit de calcul de la valeur efficace du courant de filament dans la chaîne de mesure. Or, tout filtrage dans la chaîne de mesure est équivalent à une dérivation dans la chaîne directe, dérivation qui est source d'instabilité. Pour éviter cette instabilité, la chaîne directe comporte un filtrage qui limite beaucoup la bande passante de la boucle d'asservissement, ce qui se traduit par le retard signalé ci-dessus.The regulation circuit of FIG. 1, corresponding to the prior art, has a significant delay time between the application of a setpoint and the achievement of this setpoint at the level of the filament current. This delay time is due to the filtering introduced by the circuit for calculating the effective value of the filament current in the measuring chain. However, any filtering in the measurement chain is equivalent to a derivation in the direct chain, derivation which is source of instability. To avoid this instability, the direct chain includes filtering which greatly limits the bandwidth of the servo loop, which results in the delay indicated above.

Un autre but de la présente invention est donc de réaliser un circuit de régulation qui ne comporte pas de circuit de filtrage dans la chaîne de mesure.Another object of the present invention is therefore to produce a regulation circuit which does not include a filtering circuit in the measurement chain.

Pour atteindre un tel but, le signal de mesure est élevé du carré et est comparé à la valeur au carré d'une consigne et il n'est donc pas nécessaire d'utiliser un circuit de calcul de la racine carrée qui comporterait un circuit de filtrage.To achieve such a goal, the measurement signal is raised from the square and is compared to the squared value of a setpoint and it is therefore not necessary to use a circuit for calculating the square root which would include a circuit for filtering.

Ainsi le circuit de régulation est caractérisé en ce qu'il comprend :

  • un circuit de mesure du courant I(t) dans le filament,
  • un circuit de calcul du carré I²(t) du courant I(t),
  • un circuit différentiateur pour obtenir la différence ε entre I²(t) et un signal I²ref représentant le carré du courant Iref à obtenir dans le filament,
  • un circuit intégrateur de la différence ε,
  • un circuit comparateur pour comparer le signal intégré à un seuil et obtenir un signal de sortie dès que le signal intégré dépasse ledit seuil,
  • un circuit de commande du circuit onduleur qui est commandé par le signal de sortie du deuxième circuit comparateur et fournit des signaux de commande des interrupteurs du circuit onduleur de manière à créer une impulsion de courant dans l'enroulement primaire du transformateur.
Thus the regulation circuit is characterized in that that he understands:
  • a circuit for measuring the current I (t) in the filament,
  • a circuit for calculating the square I² (t) of the current I (t),
  • a differentiating circuit to obtain the difference ε between I² (t) and a signal I² ref representing the square of the current I ref to be obtained in the filament,
  • an integrating circuit of the difference ε,
  • a comparator circuit for comparing the integrated signal with a threshold and obtaining an output signal as soon as the integrated signal exceeds said threshold,
  • an inverter circuit control circuit which is controlled by the output signal of the second comparator circuit and provides control signals for the switches of the inverter circuit so as to create a current pulse in the primary winding of the transformer.

D'autres buts, caractéristiques et avantages de la présente invention apparaîtront à la lecture de la description suivante d'un exemple particulier de réalisation, ladite description étant faite en relation avec les dessins joints dans lesquels :

  • la figure 1 est un schéma fonctionnel d'un dispositif d'alimentation et de régulation du courant de filament d'un tube radiogène selon l'art antérieur,
  • la figure 2 est un schéma fonctionnel d'un dispositif d'alimentation et de régulation du courant de filament d'un tube radiogène selon la présente invention.
  • la figure 3 est un schéma fonctionnel simplifié du circuit de commande 51 du schéma de la figure 2, et
  • les figures 4-a à 4-h sont des diagrammes de signaux en fonction du temps qui sont utiles pour la compréhension du fonctionnement du dispositif d'alimentation et de régulation selon la présente invention.
Other objects, characteristics and advantages of the present invention will appear on reading the following description of a particular embodiment, said description being made in relation to the accompanying drawings in which:
  • FIG. 1 is a functional diagram of a device for feeding and regulating the filament current of an X-ray tube according to the prior art,
  • Figure 2 is a block diagram of a device for supplying and regulating the filament current of an X-ray tube according to the present invention.
  • FIG. 3 is a simplified functional diagram of the control circuit 51 of the diagram of FIG. 2, and
  • FIGS. 4-a to 4-h are diagrams of signals as a function of time which are useful for understanding the operation of the supply and regulation device according to the present invention.

Le schéma de la figure 1 a été décrit succinctement dans le préambule pour montrer certains inconvénients des dispositifs d'alimentation et de régulation du courant de filament de tubes radiogènes selon l'art antérieur.The diagram of FIG. 1 has been described succinctly in the preamble to show certain drawbacks of the devices for feeding and regulating the filament current of X-ray tubes according to the prior art.

Le dispositif d'alimentation et de régulation du courant d'un filament 40 de cathode d'un tube radiogène 41 comportant une anode 42 comprend un circuit d'alimentation en courant 43 et un circuit de régulation 44 du courant circulant dans le filament 40.The device for supplying and regulating the current of a cathode filament 40 of an X-ray tube 41 comprising an anode 42 comprises a current supply circuit 43 and a circuit 44 for regulating the current flowing in the filament 40.

Le circuit d'alimentation 43 comprend une source de tension continue 45, un circuit onduleur 46 et un transformateur d'isolement 50.The supply circuit 43 comprises a DC voltage source 45, an inverter circuit 46 and an isolation transformer 50.

La source de tension continue 45 peut être de tous types connus sans régulation de tension. Elle comprend, par exemple, une source 47 de tension alternative qui est connectée à des diodes D1 à D4 montées en pont redresseur double alternance. Les bornes de sortie du pont redresseur sont connectées au circuit onduleur 46 par l'intermédiaire d'une cellule de filtrage qui est constituée principalement d'un condensateur électrolytique C1.The DC voltage source 45 can be of any known type without voltage regulation. It includes, for example, a source 47 of alternating voltage which is connected to diodes D1 to D4 mounted as a full-wave rectifier bridge. The output terminals of the rectifier bridge are connected to the inverter circuit 46 via a filter cell which mainly consists of an electrolytic capacitor C1.

Le circuit onduleur 46 comprend un circuit hâcheur 48 et un circuit résonant 49.The inverter circuit 46 comprises a chopping circuit 48 and a resonant circuit 49.

Le circuit hâcheur 48 comprend, par exemple, deux transistors à effet de champ T1 et T2 qui sont connectés en série sur les bornes de sortie du circuit d'alimentation 45 et deux diodes D5 et D6 qui sont connectées respectivement en parallèle entre le drain et la source des transistors T1 et T2 dont les sorties sont connectées chacune à la grille de commande du transistor T1 ou T2 de manière que leur anode soit connectée à la source du transistor correspondant. Il comprend également un circuit de commande 51 des transistors T1 et T2.The chopping circuit 48 comprises, for example, two field effect transistors T1 and T2 which are connected in series on the output terminals of the supply circuit 45 and two diodes D5 and D6 which are respectively connected in parallel between the drain and the source of transistors T1 and T2, the outputs of which are each connected to the control gate of transistor T1 or T2 so that their anode is connected to the source of the corresponding transistor. It also includes a control circuit 51 of the transistors T1 and T2.

Le circuit résonant 49 comprend, par exemple, deux condensateurs C2 et C3 qui sont connectés en série sur les bornes de sortie du circuit onduleur 48 et une bobine L1 dont une borne est connectée directement à l'anode de la diode D5 et dont l'autre borne est connectée, par l'intermédiaire d'un enroulement primaire 52 du transformateur 50, au point commun C des condensateurs C2 et C3.The resonant circuit 49 comprises, for example, two capacitors C2 and C3 which are connected in series on the output terminals of the inverter circuit 48 and a coil L1, one terminal of which is connected directly to the anode of the diode D5 and whose another terminal is connected, via a primary winding 52 of the transformer 50, to the common point C of the capacitors C2 and C3.

Le transformateur d'isolement 50, du type à impulsions, comporte, outre l'enroulement primaire 52, un enroulement secondaire 53 dont les bornes de sortie sont connectées directement au filament 40 de la cathode du tube radiogène 41. Il est à remarquer que, par rapport au schéma de la figure 1, il n'y a pas de circuit redresseur dans le circuit secondaire de sorte que le filament 40 est alimenté en courant impulsionnel. Cependant, le dispositif selon l'invention peut être mis en oeuvre dans le cas où un circuit redresseur est connecté entre l'enroulement secondaire 53 et le filament 40.The isolation transformer 50, of the pulse type, comprises, in addition to the primary winding 52, a secondary winding 53 whose output terminals are connected directly to the filament 40 of the cathode of the X-ray tube 41. It should be noted that, with respect to the diagram in FIG. 1, there is no rectifier circuit in the secondary circuit so that the filament 40 is supplied with pulse current. However, the device according to the invention can be implemented in the case where a rectifier circuit is connected between the secondary winding 53 and the filament 40.

Le circuit onduleur 46 est du type hyporésonant, c'est-à-dire que la fréquence de commutation des transistors T1 et T2, telle que définie par le circuit de commande 51, est inférieure à la fréquence de résonance du circuit résonant 49.The inverter circuit 46 is of the hyporesonant type, that is to say that the switching frequency of the transistors T1 and T2, as defined by the control circuit 51, is less than the resonance frequency of the resonant circuit 49.

Le circuit de régulation 44 comprend un circuit 54 de détection et de mesure du courant de chauffage I(t) qui est connecté, par exemple, dans le circuit primaire 52 du transformateur 50. Le signal détecté par ce circuit de mesure est appliqué à un circuit multiplieur 55 qui effectue la multiplication du signal d'entrée proportionnel à I(t) par lui-même de sorte que le signal à la sortie est proportionnel à I²(t). Le signal sortie proportionnel à I²(t), est appliqué à une entrée d'un circuit différentiateur 56 qui reçoit par ailleurs, sur son autre entrée, un signal de référence I²ref correspondant au courant Iref que l'on souhaite obtenir dans le filament 40. Ce signal I²ref est fourni par un dispositif de commande 59. Le signal d'erreur ε = I²ref - I²(t) est appliqué à un circuit intégrateur 57 dont le signal de sortie est appliqué à un comparateur 58 dont le potentiel de référence est la masse. Le comparateur 58 fournit une impulsion dès que le signal intégré est, par exemple, supérieur au potentiel de la masse et cette impulsion dure jusqu'au moment où ledit signal intégré devient inférieur au potentiel de la masse. Cette impulsion, fournie par le comparateur 58, est appliqué au circuit de commande 51 pour déclencher la conduction de l'un ou l'autre transistor T1 ou T2 selon que le transistor qui a été précédemment conducteur a été T2 ou T1.The regulation circuit 44 comprises a circuit 54 for detecting and measuring the heating current I (t) which is connected, for example, in the primary circuit 52 of the transformer 50. The signal detected by this measurement circuit is applied to a multiplier circuit 55 which multiplies the input signal proportional to I (t) by itself so that the signal at the output is proportional to I² (t). The output signal proportional to I² (t), is applied to an input of a differentiator circuit 56 which also receives, on its other input, a reference signal I² ref corresponding to the current I ref which it is desired to obtain in the filament 40. This signal I² ref is supplied by a control device 59. The signal error ε = I² ref - I² (t) is applied to an integrator circuit 57 whose output signal is applied to a comparator 58 whose reference potential is ground. The comparator 58 supplies a pulse as soon as the integrated signal is, for example, greater than the ground potential and this pulse lasts until the moment when said integrated signal becomes lower than the ground potential. This pulse, supplied by the comparator 58, is applied to the control circuit 51 to trigger the conduction of one or the other transistor T1 or T2 depending on whether the transistor which was previously conductive was T2 or T1.

La figure 3 est un schéma fonctionnel simplifié du circuit de commande 51; ce dernier comprend un circuit logique ET 60 dont une entrée 60-a est connectée à la sortie du circuit comparateur 58 et dont l'autre entrée 60-b est connectée à un circuit retardateur 64. La sortie du circuit ET 60 est connectée, d'une part, à une entrée d'un circuit bistable 61 et, d'autre part, à l'entrée de deux circuits retardateurs, l'un référencé 64 et l'autre référencé 65. Le circuit bistable 61 comporte deux sorties 61-a et 61-b, correspondant la première à l'état 1 et la deuxième à l'état 0, qui sont connectées respectivement à une des deux entrées de circuits logiques ET 62 et 63. L'autre entrée des circuits ET 62 et 63 est connectée à la sortie du circuit retardateur 65.Figure 3 is a simplified block diagram of the control circuit 51; the latter comprises an AND logic circuit 60 of which an input 60-a is connected to the output of the comparator circuit 58 and of which the other input 60-b is connected to a delay circuit 64. The output of the AND circuit 60 is connected, d on the one hand, at an input of a bistable circuit 61 and, on the other hand, at the input of two delay circuits, one referenced 64 and the other referenced 65. The bistable circuit 61 has two outputs 61- a and 61-b, the first corresponding to state 1 and the second to state 0 , which are respectively connected to one of the two inputs of AND logic circuits 62 and 63. The other input of AND circuits 62 and 63 is connected to the output of the delay circuit 65.

Le circuit ET 60 fournit une impulsion de commande de changement d'état du circuit bistable 61 chaque fois que le circuit 58 fournit une impulsion et qu'un certain temps ou délai Θ₁ s'est écoulé depuis la dernière impulsion. Ce délai Θ₁ est obtenu à l'aide du circuit retardateur 64.The AND circuit 60 supplies a state change control pulse of the bistable circuit 61 each time circuit 58 supplies a pulse and a certain time or delay Θ₁ has elapsed since the last pulse. This delay Θ₁ is obtained using the delay circuit 64.

Le circuit bistable 65 fournit les signaux de commande des transistors T1 et T2 par l'intermédiaire des circuits ET 62 et 63 dont l'ouverture est commandée par le signal du circuit retardateur 65 qui fixe la durée minimale de conduction Θ₂ desdits transistors.The bistable circuit 65 supplies the control signals of the transistors T1 and T2 via the AND circuits 62 and 63, the opening of which is controlled by the signal of the retarder circuit 65 which fixes the minimum duration of conduction Θ₂ of said transistors.

Les valeurs de Θ₁ et Θ₂ peuvent être respectivement de 50 microsecondes et 37 microsecondes dans le cas où la fréquence maximale de commutation est de 20 kilohertz.The values of Θ₁ and Θ₂ can be respectively 50 microseconds and 37 microseconds in the case where the maximum switching frequency is 20 kilohertz.

Le fonctionnement du dispositif d'alimentation et de régulation selon l'invention sera maintenant expliqué à l'aide des figures 2, 3 et 4 en supposant qu'une impulsion T′1, (figure 4-g) est appliquée au temps to à l'électrode de commande du transistor T1. Cette impulsion T′1 rend et maintient conducteur le transistor T1 et un courant i₁ (figure 4-a) dit positif, circule dans le transistor T1, la bobine L1, l'enroulement primaire 52 du transformateur 50, les condensateurs C2 et C3 et la source 45 (en fait i₁/2 dans chaque condensateur).The operation of the supply and regulation device according to the invention will now be explained with the aid of FIGS. 2, 3 and 4 assuming that a pulse T′1, (FIG. 4-g) is applied to the time t o to the control electrode of transistor T1. This pulse T′1 turns on and keeps the transistor T1 conductive and a current i₁ (figure 4-a) says positive, flows in the transistor T1, the coil L1, the primary winding 52 of the transformer 50, the capacitors C2 and C3 and the source 45 (in fact i₁ / 2 in each capacitor).

Ce courant i₁ donne naissance à une tension V (figure 4-b) de forme sinusoïdale aux bornes de l'enroulement primaire 52 et il en résulte un courant I(t) (figure 4-c) dans l'enroulement secondaire 53 du transformateur 50, courant d'allure identique au courant i₁ circulant dans l'enroulement primaire.This current i₁ gives rise to a voltage V (figure 4-b) of sinusoidal shape at the terminals of the primary winding 52 and it results from it a current I (t) (figure 4-c) in the secondary winding 53 of the transformer 50, current of identical appearance to the current i₁ flowing in the primary winding.

Le courant i₁ charge le condensateur C3 et décharge le condensateur C2 du circuit résonant et leur tension de charge s'oppose à la circulation du courant i₁ de sorte que ce dernier s'annule au temps t₁. Le condensateur C3 se décharge ensuite alors que le condensateur C2 se charge et un courant i₂ (figure 4-a), dit négatif, circule dans les condensateurs C2 et C3 (en fait i₂/2 dans chaque condensateur), l'enroulement primaire 52, la bobine L1 la diode D5 et la source 45. Ce courant négatif donne naissance à une tension négative (figure 4-b) aux bornes de l'enroulement primaire 52 et, par voie de conséquence, à un courant I(t) (figure 4-c) négatif dans l'enroulement secondaire 53. Lorsque le courant i₂ s'annule, l'impulsion est terminée.The current i₁ charges the capacitor C3 and discharges the capacitor C2 from the resonant circuit and their charging voltage is opposed to the circulation of the current i₁ so that the latter is canceled out at time t₁. Capacitor C3 then discharges while capacitor C2 discharges load and a current i₂ (figure 4-a), said negative, circulates in the capacitors C2 and C3 (in fact i₂ / 2 in each capacitor), the primary winding 52, the coil L1 the diode D5 and the source 45. This negative current gives rise to a negative tension (figure 4-b) at the terminals of the primary winding 52 and, consequently, to a negative current I (t) (figure 4-c) in the secondary winding 53 When the current i₂ is canceled, the pulse is ended.

Après un temps variable qui est déterminé par le circuit de régulation, une impulsion T′2 est appliquée à l'électrode de commande du transistor T2 au temps t′o pour le rendre conducteur. Un courant i′₁, dit négatif, circule alors dans le transistor T2, la source 45, les condensateurs C2 et C3 (en fait i′₁/2 dans chaque condensateur), l'enroulement primaire 52 du transformateur 50 et la bobine L1. Ce courant négatif donne naissance à une tension V négative (figure 4-b) aux bornes de l'enroulement primaire 52 et il en résulte un courant I(t) négatif (figure 4-c) dans l'enroulement secondaire 53 du transformateur 50, courant d'allure identique au courant i′₁ circulant dans l'enroulement primaire.After a variable time which is determined by the regulation circuit, a pulse T′2 is applied to the control electrode of the transistor T2 at the time t ′ o to make it conductive. A current i′₁, said to be negative, then flows in the transistor T2, the source 45, the capacitors C2 and C3 (in fact i′₁ / 2 in each capacitor), the primary winding 52 of the transformer 50 and the coil L1 . This negative current gives rise to a negative voltage V (figure 4-b) at the terminals of the primary winding 52 and this results in a negative current I (t) (figure 4-c) in the secondary winding 53 of the transformer 50 , current of identical appearance to the current i′₁ flowing in the primary winding.

Le courant i′₁ négatif charge le condensateur C2 et décharge le condensateur C3 et leur tension de charge s'oppose à la circulation du courant i′₁ de sorte que ce dernier s'annule au temps t′₁. Le condensateur C2 se décharge ensuite tandis que le condensateur C3 se charge et un courant i′₂ positif circule dans les condensateurs C2 et C3 (en fait i′₂/2 dans chaque condensateur), l'enroulement primaire 52, la bobine L1, la diode D6 et la source 45. Ce courant positif donne naissance à une tension positive (figure 4-b) aux bornes de l'enroulement primaire 52 et, par voie de conséquence, à un courant I(t) positif (figure 4-c) dans l'enroulement secondaire 53. Lorsque le courant i′₂ s'annule, l'impulsion est terminée.The negative current i′₁ charges the capacitor C2 and discharges the capacitor C3 and their charging voltage is opposed to the circulation of the current i′₁ so that the latter is canceled out at time t′₁. The capacitor C2 then discharges while the capacitor C3 charges and a positive current i′₂ flows in the capacitors C2 and C3 (in fact i′₂ / 2 in each capacitor), the primary winding 52, the coil L1, the diode D6 and the source 45. This positive current gives rise to a positive tension (figure 4-b) at the terminals of the primary winding 52 and, consequently, to a positive current I (t) (figure 4-c) in the secondary winding 53. When the current i′₂ is canceled, the impulse is ended.

Le circuit de commande 51, décrit en relation avec la figure 3, fonctionne de la manière suivante en supposant que le transistor qui vient d'être conducteur est le transistor T2. Lorsque le circuit 58 fournit l'impulsion 70 (figure 4-f), son front avant commande le changement l'état (mise à l'état 1) du circuit bistable 61 par l'intermédiaire du circuit ET 60 à condition que la deuxième entrée de ce circuit ET reçoive le signal d'autorisation 71 (figure 4-h) donnée par le circuit retardateur 64. Le signal fourni par le circuit ET 60 remet à zéro les deux circuits retardateurs 64 et 65 de manière que le circuit ET 60 se ferme pendant le temps Θ₁ (figure 4-h) et que les circuits ET 62 et 63 s'ouvrent pendant le temps Θ₂ (figure 4-g). Cependant, seul le circuit ET 62, qui reçoit le signal d'état 1 du circuit bistable 61, fournit un signal qui rend conducteur le transistor T1.The control circuit 51, described in relation to FIG. 3, operates in the following manner, assuming that the transistor which has just been conductive is the transistor T2. When the circuit 58 provides the pulse 70 (figure 4-f), its front edge commands the change of the state (setting to state 1) of the bistable circuit 61 via the AND circuit 60 provided that the second input of this AND circuit receives the authorization signal 71 (figure 4-h) given by the delay circuit 64. The signal supplied by the AND circuit 60 resets the two delay circuits 64 and 65 to zero so that the AND circuit 60 closes during time Θ₁ (figure 4-h) and that the circuits ET 62 and 63 open during time Θ₂ (figure 4-g). However, only the AND circuit 62, which receives the status signal 1 from the bistable circuit 61, supplies a signal which makes the transistor T1 conductive.

Comme on l'a indiqué précédemment, la durée de ce signal est déterminée par la durée Θ₂ du signal T′1 fourni par le circuit retardateur 65, c'est-à-dire au moins égale à la demi-période de la fréquence maximale de commutation, de manière que le transistor T1 (ou T2) soit maintenu dans l'état conducteur pendant le temps Θ₂. Le signal T′1 (ou T′2) se termine donc toujours après l'instant t₁ (ou t′₁).As previously indicated, the duration of this signal is determined by the duration Θ₂ of the signal T′1 supplied by the delay circuit 65, that is to say at least equal to the half-period of the maximum frequency switching, so that the transistor T1 (or T2) is maintained in the conductive state for the time Θ₂. The signal T′1 (or T′2) therefore always ends after the instant t₁ (or t′₁).

Un temps Θ₁ après l'impulsion 70, le circuit retardateur 64 fournit un signal 71′ d'ouverture du circuit ET 60 de sorte que l'impulsion suivante 70′ change l'état du circuit bistable 61 qui passe à l'état 0, termine le signal 71′ par l'intermédiaire du circuit retardateur 64 et fournit le signal T′2 par l'intermédiaire du circuit retardateur 65. Le circuit ET 63 fournit alors un signal de durée Θ₂ qui rend conducteur le transistor T2.A time Θ₁ after the pulse 70, the delay circuit 64 provides a signal 71 ′ for opening the AND circuit 60 so that the next pulse 70 ′ changes the state of the bistable circuit 61 which changes to state 0 , ends signal 71 ′ through the circuit retarder 64 and supplies the signal T′2 via the retarder circuit 65. The AND circuit 63 then supplies a signal of duration Θ₂ which makes the transistor T2 conductive.

Lors du cycle suivant, le transistor T1 sera conducteur car le circuit bistable 61 reviendra à l'état 1.During the following cycle, the transistor T1 will be conductive because the bistable circuit 61 will return to state 1.

Le circuit de commande 51 décrit en relation avec la figure 3 comporte deux circuits retardateurs 64 et 65 mais on comprend qu'ils peuvent être réalisés à l'aide d'un seul circuit retardateur.The control circuit 51 described in relation to FIG. 3 comprises two delay circuits 64 and 65 but it is understood that they can be produced using a single delay circuit.

Dans le dispositif d'alimentation et de régulation du courant de filament selon l'invention, la régulation de la valeur du courant est obtenue par des impulsions alternatives de courant qui sont sensiblement identiques mais inverses à chaque cycle mais dont la fréquence varie pour obtenir la valeur souhaitée Iref. Ainsi, dans le cas où Iref augmente la différence ε augmentera et la pente (partie 73-fig. 4-e) du signal intégré augmentera également de sorte que l'impulsion 70′ apparaîtra un peu plus tôt et déclenchera donc le transistor T2 plus tôt.In the filament current supply and regulation device according to the invention, the regulation of the current value is obtained by alternating current pulses which are substantially identical but reverse at each cycle but whose frequency varies to obtain the desired value I ref . Thus, in the case where I ref increases the difference ε will increase and the slope (part 73-fig. 4-e) of the integrated signal will also increase so that the pulse 70 ′ will appear a little earlier and therefore trigger the transistor T2 earlier.

Dans la description du fonctionnement du circuit onduleur, on a indiqué que les courants i₁, i₂, i′₁ et i′₂ circulaient dans les condensateurs C2 et C3 mais il est clair que chacun de ces courants se divise en deux parties égales au point C, une moitié vers la branche contenant le condensateur C2 et l'autre moitié vers la branche contenant le condensateur C3.In the description of the operation of the inverter circuit, it was indicated that the currents i₁, i₂, i′₁ and i′₂ circulated in the capacitors C2 and C3 but it is clear that each of these currents is divided into two parts equal to the point C, one half towards the branch containing the capacitor C2 and the other half towards the branch containing the capacitor C3.

Claims (3)

Dispositif d'alimentation et de régulation du courant d'un filament (40) d'une cathode d'un tube radiogène (41) comportant un circuit d'alimentation en courant (43) dudit filament comprenant : - une source de tension continue (45), - un circuit onduleur (46) pour obtenir des impulsions de courant à partir de la source de tension continue (45), et - un transformateur d'isolement (50) dont l'enroulement primaire (52) est connecté à la sortie du circuit onduleur (46), caractérisé en ce que : - le circuit onduleur (46) est du type hyporésonant et fournit des impulsions de courant audit transformateur d'isolement (50), - ledit circuit onduleur (46) est commandé par des impulsions haute fréquence qui sont fournies par un circuit de régulation, et - le transformateur d'isolement (50), du type impulsionnel, a son enroulement secondaire (53) directement connecté audit filament (40) de la cathode. Device for supplying and regulating the current of a filament (40) of a cathode of an X-ray tube (41) comprising a current supply circuit (43) of said filament comprising: - a DC voltage source (45), - an inverter circuit (46) for obtaining current pulses from the DC voltage source (45), and - an isolation transformer (50) whose primary winding (52) is connected to the output of the inverter circuit (46), characterized in that: the inverter circuit (46) is of the hyporesonant type and supplies current pulses to said isolation transformer (50), said inverter circuit (46) is controlled by high frequency pulses which are supplied by a regulation circuit, and - the isolation transformer (50), of the pulse type, has its secondary winding (53) directly connected to said filament (40) of the cathode. Dispositif selon la revendication 1, caractérisé en ce que le circuit de régulation (44) comprend : - un circuit de détection (54) du courant I(t) dans le filament (40), - un circuit de calcul (55) du carré I²(t) du courant I(t), - un circuit différenciateur (56) pour obtenir la différence ε entre I²(t) et un signal I²ref représentant le carré du courant Iref à obtenir dans le filament (40), - un circuit intégrateur (57) de la différence ε, - un circuit comparateur (58) pour comparer le signal intégré à un seuil et obtenir un signal de sortie dès que le signal intégré dépasse ledit seuil, - un circuit de commande (51) du circuit onduleur (46) qui est commandé par le signal de sortie dudit deuxième circuit comparateur (68) et fournit des signaux de commande des interrupteurs (T1,T2) du circuit onduleur (46) de manière à créer des impulsions de courant dans l'enroulement primaire (52) du transformateur. Device according to claim 1, characterized in that the regulation circuit (44) comprises: a detection circuit (54) of the current I (t) in the filament (40), - a circuit for calculating (55) the square I² (t) of the current I (t), - a differentiating circuit (56) to obtain the difference ε between I² (t) and a signal I² ref representing the square of the current I ref to be obtained in the filament (40), - an integrating circuit (57) of the difference ε, - a comparator circuit (58) for comparing the integrated signal with a threshold and obtaining an output signal as soon as the integrated signal exceeds said threshold, - a control circuit (51) of the inverter circuit (46) which is controlled by the output signal of said second comparator circuit (68) and supplies control signals of the switches (T1, T2) of the inverter circuit (46) creating pulses of current in the primary winding (52) of the transformer. Dispositif selon la revendication 2, caractérisé en ce que le circuit de commande (51) comprend : - un premier circuit ET (60) dont une des deux entrées est connectée à la sortie du deuxième circuit comparateur (58), - un circuit bistable (61) dont l'entrée de commande est connectée à la sortie du premier circuit ET (60) de manière à changer d'état à chaque signal fournit par ce dernier, - un deuxième circuit ET (62) dont une des deux entrées est connectée à la sortie du circuit bistable (61) correspondant à l'état 1, - un troisième circuit ET (63) dont une des deux entrées est connectée à la sortie du circuit bistable (61) correspondant à l'état 0, - un premier circuit retardateur (64) dont l'entrée est connectée à la sortie du premier circuit ET (60) et dont la sortie est connectée à la deuxième entrée du premier circuit ET (60), et - un deuxième circuit retardateur 65 dont l'entrée est connectée à la sortie du premier circuit ET (60) et dont la sortie est connectée à l'autre entrée des deuxième et troisième circuits ET (62,63). Device according to claim 2, characterized in that the control circuit (51) comprises: - a first AND circuit (60), one of the two inputs of which is connected to the output of the second comparator circuit (58), - a bistable circuit (61), the control input of which is connected to the output of the first AND circuit (60) so as to change state at each signal supplied by the latter, a second AND circuit (62), one of the two inputs of which is connected to the output of the bistable circuit (61) corresponding to state 1 , a third AND circuit (63), one of the two inputs of which is connected to the output of the bistable circuit (61) corresponding to the state 0 , a first delay circuit (64) whose input is connected to the output of the first AND circuit (60) and whose output is connected to the second input of the first AND circuit (60), and - A second delay circuit 65 whose input is connected to the output of the first AND circuit (60) and whose output is connected to the other input of the second and third AND circuits (62,63).
EP91402249A 1990-08-14 1991-08-14 Device for supplying and regulating the cathode filament current from an X-ray tube Expired - Lifetime EP0471626B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9010349A FR2666000B1 (en) 1990-08-14 1990-08-14 DEVICE FOR SUPPLYING AND REGULATING THE CURRENT OF A CATHODE FILAMENT OF A RADIOGENIC TUBE.
FR9010349 1990-08-14

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EP0471626A1 true EP0471626A1 (en) 1992-02-19
EP0471626B1 EP0471626B1 (en) 1994-12-28

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US (1) US5200984A (en)
EP (1) EP0471626B1 (en)
DE (1) DE69106273T2 (en)
FR (1) FR2666000B1 (en)

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Also Published As

Publication number Publication date
FR2666000A1 (en) 1992-02-21
DE69106273T2 (en) 1995-05-18
EP0471626B1 (en) 1994-12-28
US5200984A (en) 1993-04-06
DE69106273D1 (en) 1995-02-09
FR2666000B1 (en) 1996-09-13

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