EP0241373A1 - Current supply device for an X-ray tube filament - Google Patents

Current supply device for an X-ray tube filament Download PDF

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Publication number
EP0241373A1
EP0241373A1 EP87400774A EP87400774A EP0241373A1 EP 0241373 A1 EP0241373 A1 EP 0241373A1 EP 87400774 A EP87400774 A EP 87400774A EP 87400774 A EP87400774 A EP 87400774A EP 0241373 A1 EP0241373 A1 EP 0241373A1
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EP
European Patent Office
Prior art keywords
current
filament
circuit
frequency
supply device
Prior art date
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Granted
Application number
EP87400774A
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German (de)
French (fr)
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EP0241373B1 (en
Inventor
Jacques Salesses
Arthur Baghdiguian
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General Electric CGR SA
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General Electric CGR SA
Thomson CGR
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Publication of EP0241373A1 publication Critical patent/EP0241373A1/en
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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
    • H05G1/26—Measuring, controlling or protecting
    • H05G1/30—Controlling
    • H05G1/34—Anode current, heater current or heater voltage of X-ray tube
    • 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

Definitions

  • the invention relates to a device for supplying current to a filament, in particular to an X-ray tube as used in radiodiagnostic installations.
  • the invention is particularly applicable in cases where it is necessary to successively supply filaments of very different resistances, with high current dynamics.
  • X-ray tubes for medical diagnosis are generally constituted as a diode, that is to say by two electrodes of which one called cathode emits electrons, and the other is called anode and receives these electrons on a small surface which is the source of X-rays.
  • the cathode has a heated filament which is the source of electrons.
  • a so-called anodic current is established in the circuit, 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 the current, called heating current, which circulates in the filament.
  • the quantity of X-ray emitted by the anode depends mainly on the intensity of the anode current, and therefore on the intensity of the heating current of the filament.
  • the filament heating current constitutes one of the important parameters which must be determined for each exposure of radiography or radioscopy, during a radiological 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 console control, by which is controlled the operation of the various organs of a radiodiagnostic installation, such as for example, high voltage generator and generator of the filament heating current. It is also common in certain installations for the values of these parameters to be predetermined using a microprocessor device incorporated or not in the control console, and which calculates and programs the optimum values of these parameters, depending for example on the type of examination desired by the practitioner, and according to the specific characteristics of the installation.
  • this operation consists in particular in programming different values, such as for example: duration of the exposure time, energy of the X-ray by the choice of the value of the high voltage applied between the anode and the cathode, and intensity of the anodic current by the choice in particular of a value of the intensity of the filament heating current.
  • the intensity of the heating current can be modified significantly, from one pose to a next pose, for example from 1.5 amperes to 5.5 amperes.
  • radiodiagnostic installations may comprise several X-ray tubes, having different characteristics, which are put into operation successively, sometimes during the same examination; these X-ray tubes may include filaments whose value of the ohmic resistance can vary considerably from one tube to another, from 0.6 Ohms to 4.5 Ohms for example.
  • a heating current generator making it possible to quickly obtain, that is to say automatically, a value of the heating current included in the range of values previously mentioned, and this regardless of the value of the resistance of the supplied filament.
  • the generator which produces the heating current must supply the latter in a very wide power range. It must also, in this power range, ensure sufficient quality to regulate the heating current, and allow the desired intensity value to be obtained quickly and automatically, as defined for example by a set value; this set value being able to vary from one pose to a next pose.
  • the heating current generators according to the prior art do not make it possible to obtain these conditions satisfactorily: either they require manual adjustments as a function of the intensity of the heating current and of the resistance value of the filament; either they allow power dynamics to the detriment of the quality of regulation; or that the conditions of power dynamics, automation and regulatory qualities lead to the design of complex generators, that is to say fragile, unreliable, or bulky and bulky and of a high price.
  • the regulation of the filament heating current is further complicated by the fact that the cathode, and the filament of the X-ray tube, are brought to the negative potential of high voltage; also, the problems of electrical insulation generally lead to applying to the filament the heating energy by means of an isolation transformer, the primary winding of which represents the load of the filament. Therefore the heating current is produced according to an alternating current whose measurement of the effective value can also present problems.
  • the supply device according to the invention does not have the above-mentioned drawbacks, thanks to a new arrangement which makes it a device which is simple to produce and simple to implement.
  • the present invention relates to a device for supplying current to a filament of an X-ray tube, making it possible to automatically obtain a heating current whose intensity corresponds to a set value, this intensity being included in the range of intensities which can be applied to a filament, and this for all the current ohmic resistance values of the filament.
  • a device for supplying current to a filament of at least one X-ray tube comprising, a generator supplying control pulses, an inverter receiving the control pulses and producing a current in a load circuit of alternative heating from a direct voltage, a regulation circuit regulating the heating current as a function of a set value, the load circuit comprising a primary winding of a transformer through which the heating current is applied to the filament, the heating current having the same frequency as the frequency of the control pulses, is characterized in that it comprises an oscillating circuit arranged in the load circuit, and in that the regulation circuit delivers a signal of error applied to the generator to modify the frequency of the control pulses, so as to modify the impedance of the oscillating circuit until a value of the current of the heating corresponding to the set value.
  • Figure 1 shows a supply device 1 according to the invention allowing, in the non-limiting example described, to ali by running the filament of an X-ray tube, for example selected from several X-ray tubes, of which only two tubes 26, 27 are shown in the example described.
  • the X-ray tubes are of a conventional type each comprising an anode, 28, 29 and a cathode 23, 24 represented by the filament which it contains.
  • the tubes 26, 27 are supplied with high voltage by conventional means (not shown).
  • the filament 23.24 of the tube 26.27 selected is brought to the negative potential - HT of the high voltage, and the problems of electrical insulation impose to apply to the filament 23.24 the electrical energy necessary for its heating. , via an isolation transformer 30.
  • the selection of the first or second tube 26, 27 is made by connecting the corresponding filament 23, 24, to the secondary winding 31 of the transformer 30, by means of a switching device. 35, comprising switches (not shown) constituted for example by electromechanical relays; the transformer 30 comprising a primary winding 12 to which is applied a heating current I delivered by an inverter 2.
  • the control of the switching device 35 can take place either by manual control, or automatically in the context of programmed sequences controlled for example by a control console 40; the latter being connected to the switching device 35 by a first and a second link CT1, CT2 by which it can select the first or the second tube 26,27, the first tube 26 for example, so as to apply to the filament 23 of this last a current I ⁇ for its heating.
  • a tube 26, 27 can be carried out in a different way, such as for example by switching at the level of the primary of the isolation transformer.
  • an isolation transformer in this case being associated with each filament.
  • the supply device 1 also comprises a source of regulated DC voltage 3, delivering via terminals 27, 28 respectively the positive polarity + and the negative polarity - of a DC voltage V1, regulated, having for example a value of 200 Volts.
  • the voltage source 3 is constituted in a conventional manner and develops the direct voltage V1 from, for example, a single-phase voltage (not shown) of 220 V.
  • the inverter 2 is supplied by the DC voltage V1, from which it produces an AC voltage.
  • the inverter 2 comprises two electronic switching means 4,5 arranged in series between the positive pole + and the negative pole - of the DC voltage V1.
  • the two switching means 4,5 are constituted by field effect transistors.
  • the source S of the first transistor 4 is connected to the positive pole + of the DC voltage V1 and its drain D is connected to the source S of the second transistor 5, whose drain D is connected to the negative pole - of the DC voltage V1.
  • a first and a second diode d1, d2 are respectively connected in parallel on the first and the second transistor 4,5; the first diode d1 having its cathode connected to the + pole of the voltage V1 and its anode connected on the one hand, to the junction 6 between the drain of the first transistor 4 and the source of the second transitor 5, and connected on the other hand to the cathode of the second diode d2, the anode of which is connected to the negative pole - of the DC voltage V1.
  • the junction 6 is also connected to the first end 7 of a current sensor means 9, the second end 10 of which is connected to the first end 11 of the primary winding 12 of the isolation transformer 30.
  • the second end 14 of the primary winding 12 is connected to the first end 15 of an inductor 16 whose second end 17 is connected to a capacitive midpoint 18.
  • the capacitive midpoint 18 is formed by the junction of a first and a second capacitor 19.20 connected in series between the positive and negative terminals +, - of the DC voltage V1; the first capacitor 19 being connected to the positive pole +, and the second capacitor 20 being connected to the negative pole -.
  • the two capacitors 19 and 20 form a capacitor which is placed in series with the inductor 16, to form an oscillating circuit 13 arranged in series with the primary winding 12 of the transformer 13, with which it constitutes a charging circuit 12-13 .
  • the primary winding 12 represents the filament 23 whose ohmic resistance R is reported in the charging circuit 12-13.
  • the filament 23 is of a conventional type, its resistance R can have any value included in the current value range, for example between 0.6 Ohms and 4.5 Ohms.
  • the current I ⁇ in the secondary circuit of the transformer 30, where the filament 23 is disposed being proportional to the current I flowing in the circuit of the primary winding or load circuit 12-13, according to a known ratio, and the resistance R of the filament 23 being reported in the charging circuit 12-13, it is the current I which flows in the charging circuit 12-13 which is called heating current for the sake of clarity of the description.
  • the current sensor 9 is placed in the charging circuit 12-13 and delivers by an output 59 a signal S1 proportional to the pseudo-sinusoidal heating current I; the current sensor 9 is of a conventional type, such as for example constituted by an intensity transformer.
  • the signal S1 proportional to the heating current I, is applied to the input 61 of a converter device 25, which conventionally processes the values of the signal S1, to provide by an output 62, a second signal S2 corresponding to the effective value of the heating current I.
  • These effective values are used to regulate the current I in the primary circuit or load circuit 12-13 which allows, thanks in particular to the isolation transformer 30 with low leakage, to carry out a control rigorous current I ⁇ passing through the filament 23 ensuring better proportionality between the current I 'in the filament 23 and the current I in the charging circuit 12-13.
  • the second signal S2 is applied to the first input 41 of an error processor 42, constituted for example by a differential amplifier.
  • the second input 43 of the error processor 42 receives a setpoint value VC corresponding to the desired value of the heating current I; this setpoint being for example delivered by the control console 40 which, for this purpose, is connected by a link 63 to the second input 43 of the error processor 42.
  • the error processor 42 delivers to its output 44 an error signal SE proportional to the difference between the second signal S2 and the set value VC.
  • the error signal SE is applied to a means for producing pulses at a given frequency F and for modifying this frequency F more or less depending on the sign and the amplitude of the error signal SE. In the nonlimiting example described, this means for producing pulses consists of a voltage-frequency converter 46, the input 45 of which is connected to the output 44 of the error generator 42.
  • An output 47 of the voltage-frequency converter 46 delivers a fourth signal S4 consisting of pulses delivered at frequency F, which frequency F constitutes the initial frequency at which the inverter 2 operates.
  • the signal S4 is applied to input 49 d 'A switching device 50 whose function is to produce first and second control pulses SC1, SC2, delivered at the same frequency F as the fourth signal S4, and intended respectively to control the first transistor 4 and the second transistor 5.
  • the first and second control pulses SC1, SC2 (not shown) have a width or duration t substantially equal to or less than half the time between the front edges of two pulses of the same type, that is to say half of the period P corresponding to the frequency F (t ⁇ 1 / 2F).
  • the switching device 50 delivers the first control pulses SC1 by a first output 51 which is connected to the cathode of a third diode d3 and, at the first end 53 of a resistor R1 whose second end 54 is connected to the anode of the third diode d3 and at the control input G1 of the first transistor 4.
  • the switching device 50 delivers the second control pulses SC2 by a second output 52 connected to the cathode of a fourth diode d4 and at the first end 55 of a second resistor R2; the second end 56 of the second resistor R2 is connected to the anode of the fourth diode d4 and to the control input G2 of the second transistor 5.
  • the general operation of the supply device 1 according to the invention is as follows.
  • these pulses SC1, SC2 are applied respectively the first and second transistor 4,5, via the networks formed on the one hand, by the third diode d3 and the resistor R1 and, on the other hand by the fourth diode d4 and the second resistor R2; the simultaneous non-conduction of the two transistors 4,5 being prohibited by a simple asymmetry in the conduction and blocking of each transistor 4,5.
  • the control pulses SC1, SC2 have a frequency F corresponding to an initial operating frequency of the inverter 2.
  • the control pulses SC1, SC2 being for example positive, the first pulses SC1 cause the first transistor 4 to conduct so that with the exception of the relatively low voltage drop across the terminals of the first transistor 4, the positive polarity + of the DC voltage V1 is applied to the junction 6, and the capacitor 19, which was charged at an intermediate voltage V2, tends to discharge in the charging circuit 12-13, i.e. in the inductor 16 and in the primary winding 12 which represents the filament 23; the heating current I then being established in the direction represented by the arrow marked I C1 ; the second capacitor 20 itself tending to charge at the value of the positive polarity + of the DC voltage V1.
  • the protection of the transistors 4,5 is thus ensured in an efficient and much simpler way than that of the switching means which, in the prior art, have the function of chopping a DC voltage. This is possible in particular because the transistors 4,5 are of the field effect type and are fast in switching.
  • the regulation circuit constituted by the current sensor 9, the converter device 25, the error generator 42 and the voltage-frequency converter 46, carry out a regulation of the heating current I on the effective value of the latter, corresponding to the setpoint VC delivered by the control panel 40.
  • a non-zero error signal SE applied to the voltage frequency converter 46 generates a modification of the frequency F of the pulses (signal S4) which the latter applies to the switching device 50, and consequently generates a modification of the frequency of the pulses SC1, SC2 that the switching device 50 applies to the transistors 4,5; whence there results a variation of the operating frequency of the inverter 2, so as to modify the value of the impedance Z, presented by the oscillating circuit 13 constituted by the inductor 16 in series with the capacitors 19, 20 .
  • the oscillating circuit 13 being in series with the load constituted by the resistance R of the filament 23, the value of the heating current I is directly linked to the impedance Z of the oscillating circuit LC, and decreases or increases as this impedance decreases or increases .
  • the inverter 2 operates in a relatively high frequency range, from 18 KHZ to 35 KHZ for example, which allows on the one hand, a significant reduction in the volume of the elements, in particular the magnetic elements and in particular of the isolation transformer 30; and on the other hand allows a quick response of the regulation circuit, as well as a quick stop if necessary for safety needs.
  • the inductor 16 and the capacitors 19, 20 are chosen so that the resonant frequency Fo of the oscillating circuit 13 is a little lower than the minimum operating frequency of the inverter 2, at 15 KHz pa example, so that in the load circuit 12-13 the current is ahead of the voltage; this arrangement being favorable for the switching of transistors 4,5.
  • the oscillating circuit 13 consists of the inductance 16 and a capacitance in series formed by the capacitors 19 and 20: it can be noted that the capacitors 19 and 20, in addition to constituting the capacitance of the oscillating circuit 13, are arranged in series in the DC voltage V1, and thus ensure efficient decoupling of the charging circuit 12-13 at the capacitive point 18; these two capacitors 19, 20 having to be considered as being connected in parallel to constitute the capacity of the oscillating circuit 13.
  • - inductance 16 to a value of 325 microhenry
  • the capacitors 19, 20 each have a value of 0.1 microfarad, and form a capacity of 0.2 microfarad
  • - the resonance frequency F o of the oscillating circuit 13 is approximately 15 KHZ
  • - the transformer self-leakage 30 is of the order of 250 microhenry - the DC voltage V1 at a value of 200 volts.
  • the supply device 1 makes it possible to successively supply several filaments 23, 24 having different resistances, as illustrated in FIG. 2.
  • FIG. 2 is a graph which represents, by a first and a second curve 65, 66, the variations of the heating current I as a function of the frequency F; the frequency F being plotted on the abscissa and expressed in KHZ, and the heating current I being plotted on the ordinate and expressed in amps.
  • the resonant frequency F o of the oscillating circuit 13 is 15 KHZ, and the operating frequency range F is between 18 and 35 KHZ.
  • the first and second curves 65, 66 correspond respectively to the supply of a first and a second filament 23, 24; the first filament 23 having a resistance of 4.5 ohms, and the second filament 24 having a resistance of 1 ohm.
  • first and second curves 65, 66 illustrate the possible values of the current I in the frequency range between 18 and 35 KHZ. It is observed that the same values of the current I are obtained with different frequencies F, depending on whether it is a question of feeding a filament 23 of 4.5 ohms (first curve 65) or a filament 24 of 1 ohm (second curve 66): - for 4.5 ohms, the values of 5.5 amps and 2.2 amps are obtained respectively at 18 KHZ and 30.5 KHZ; - for 1 ohm, the values of 5.5 amps and 2.2 amps are obtained respectively at 20.5 KHZ and 32.5 KHZ.
  • a limit to the maximum value of the heating current is achieved by means of a frequency stop device (not shown), in itself conventional.
  • the frequency stop device makes it possible, when approaching the resonant frequency F o , to limit the operating frequency range to a value greater than F o ; this limit being situated at approximately 15.7 KHZ in the nonlimiting example described.
  • This description constitutes a nonlimiting example, showing that the operating principle of the supply device 1 according to the invention makes it possible not only to supply a filament of an X-ray tube with a heating current regulated with great precision, but also allows in addition to automatically, supplying successively several heating filaments of different resistances, in a wide power range, while retaining great precision in the definition of the heating current.

Abstract

L'invention concerne un dispositif d'alimentation en courant, permettant d'alimenter en courant de chauffage (I) un filament (23) d'un tube radiogène (26), avec une grande dynamique de puissance. Le dispositif d'alimentation (1) comporte un onduleur (2) débitant dans un circuit de charge (12,13) dans lequel est disposé un circuit oscillant (13) dont ont fait varier l'impédance.The invention relates to a current supply device for supplying heating current (I) to a filament (23) of an X-ray tube (26), with high power dynamics. The supply device (1) comprises an inverter (2) supplying a load circuit (12,13) in which is arranged an oscillating circuit (13) whose impedance has varied.

Description

L'invention concerne un dispositif d'alimentation en courant d'un filament, notamment de tube radiogène tel qu'utilisé dans les installations de radiodiagnostic. L'invention est particulièrement applicable dans les cas ou il est nécessaire d'alimenter succes­sivement des filaments de résistances trés différentes, avec une grande dynamique en courant.The invention relates to a device for supplying current to a filament, in particular to an X-ray tube as used in radiodiagnostic installations. The invention is particularly applicable in cases where it is necessary to successively supply filaments of very different resistances, with high current dynamics.

Les tubes à rayons X pour diagnostic médical sont géné­ralement constitués comme une diode, c'est à dire par deux électrodes dont l'une appelée cathode est émettrice d'électrons, et l'autre est appelée anode et reçoit ces électrons sur une petite surface qui constitue la source du rayonnement X.X-ray tubes for medical diagnosis are generally constituted as a diode, that is to say by two electrodes of which one called cathode emits electrons, and the other is called anode and receives these electrons on a small surface which is the source of X-rays.

La cathode comporte un filament chauffé qui constitue la source d'électrons. Quand la haute tension fournie par un générateur est appliqué aux bornes des deux électrodes, de façon que la cathode soit au potentiel négatif, un courant dit anodique s'établit dans le circuit, 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 en fonction de la puissance dissipée dans le filament, c'est à dire du courant, appellé 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 negative potential, a so-called anodic current is established in the circuit, 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 the current, called heating current, which circulates in the filament.

La quantité de rayon X émis par l'anode dépend principalement de l'intensité du courant anodique, et donc de l'intensité du courant de chauffage du filament.The quantity of X-ray emitted by the anode depends mainly on the intensity of the anode current, and therefore on the intensity of the heating current of the 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.Also, the filament heating current constitutes one of the important parameters which must be determined for each exposure of radiography or radioscopy, during a radiological 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 radiodiagnostic, tels que par exemple, générateur haute tension et générateur du courant de chauffage filament. Il est courant également dans certaines instal­lations que les valeurs de ces paramètres soient prédéterminées à l'aide d'un dispositif à microprocesseur incorporé ou non au pupitre de commande, et qui calcule et programme les valeurs optimums de ces paramètres, en fonction par exemple du type d'examen désiré par le praticien, et en fonction 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 console control, by which is controlled the operation of the various organs of a radiodiagnostic installation, such as for example, high voltage generator and generator of the filament heating current. It is also common in certain installations for the values of these parameters to be predetermined using a microprocessor device incorporated or not in the control console, and which calculates and programs the optimum values of these parameters, depending for example on the type of examination desired by the practitioner, and according to the specific characteristics of the installation.

Dans tous les cas cette opération consiste notamment à programmer différentes valeurs, telles que par exemple: durée du temps de pose, énergie du rayonnement X par le choix de la valeur de la haute tension appliquée entre l'anode et la cathode, et intensité du courant anodique par le choix notamment d'une valeur de l'intensité du courant de chauffage filament.In all cases, this operation consists in particular in programming different values, such as for example: duration of the exposure time, energy of the X-ray by the choice of the value of the high voltage applied between the anode and the cathode, and intensity of the anodic current by the choice in particular of a value of the intensity of the filament heating current.

Il est à remarquer que l'intensité du courant de chauffage peut être modifiée de manière importante, d'une pose à une pose suivante, par exemple de 1,5 ampère à 5,5 ampères.It should be noted that the intensity of the heating current can be modified significantly, from one pose to a next pose, for example from 1.5 amperes to 5.5 amperes.

D'autre part, il est courant que des installations de radio­diagnostic comportent plusieurs tubes radiogènes, ayant des carac­téristiques différentes, qui sont mis en fonctionnement succes­sivement, parfois au cours d'un même examen; ces tubes radiogènes pouvant comporter des filaments dont la valeur de la résistance ohmique peut varier de manière considérable d'un tube à l'autre, de 0,6 Ohms à 4,5 Ohms par exemple. Dans de tels cas, il est particulièrement intéressant de disposer d'un générateur de courant de chauffage permettant d'obtenir rapidement, c'est à dire de manière automatique, une valeur du courant de chauffage comprise dans la gamme de valeurs précédement mentionnées, et ceci quelle que soit la valeur de la résistance du filament alimenté.On the other hand, it is common for radiodiagnostic installations to comprise several X-ray tubes, having different characteristics, which are put into operation successively, sometimes during the same examination; these X-ray tubes may include filaments whose value of the ohmic resistance can vary considerably from one tube to another, from 0.6 Ohms to 4.5 Ohms for example. In such cases, it is particularly advantageous to have a heating current generator making it possible to quickly obtain, that is to say automatically, a value of the heating current included in the range of values previously mentioned, and this regardless of the value of the resistance of the supplied filament.

Par conséquent, le générateur qui produit le courant de chauffage doit fournir ce dernier dans une gamme du puissance très étendue. Il doit en outre, dans cette gamme de puissance, assurer une qualité suffisante à la régulation de courant de chauffage, et permettre d'obtenir rapidement et automatiquement la valeur d' intensité désirée, telle que définie par exemple par une valeur de consigne; cette valeur de consigne étant susceptible de varier d'une pose à une pose suivante.Consequently, the generator which produces the heating current must supply the latter in a very wide power range. It must also, in this power range, ensure sufficient quality to regulate the heating current, and allow the desired intensity value to be obtained quickly and automatically, as defined for example by a set value; this set value being able to vary from one pose to a next pose.

Les générateurs de courant de chauffage selon l'art antérieur ne permettent pas d'obtenir ces conditions de manière satisfaisante: soit qu'ils exigent des réglages manuels en fonction de l'intensité du courant de chauffage et de la valeur de résistance du filament ; soit qu'ils permettent la dynamique de puissance au détriment de la qualité de la régulation ; soit que les conditions de dynamique de puissance, d'automatisme et de qualités de régulation conduisent à concevoir des générateurs complexes, c'est à dire fragiles, peu fiables, ou volumineux et encombrants et d'un prix élevé.The heating current generators according to the prior art do not make it possible to obtain these conditions satisfactorily: either they require manual adjustments as a function of the intensity of the heating current and of the resistance value of the filament; either they allow power dynamics to the detriment of the quality of regulation; or that the conditions of power dynamics, automation and regulatory qualities lead to the design of complex generators, that is to say fragile, unreliable, or bulky and bulky and of a high price.

Il est à noter également, que la régulation du courant de chauffage filament est encore compliquée par le fait que la cathode, et le filament du tube radiogène, sont portés au potentiel négatif de la haute Tension; aussi, les problèmes d'isolation éléctrique conduisent généralement à appliquer au filament l'énergie de chauffage par l'intermédiaire d'un transformateur d'isolement, dont l'enroulement primaire représente la charge du filament. De ce fait le courant de chauffage est produit selon un courant alternatif dont la mesure de la valeur efficace peut également présenter des problèmes.It should also be noted that the regulation of the filament heating current is further complicated by the fact that the cathode, and the filament of the X-ray tube, are brought to the negative potential of high voltage; also, the problems of electrical insulation generally lead to applying to the filament the heating energy by means of an isolation transformer, the primary winding of which represents the load of the filament. Therefore the heating current is produced according to an alternating current whose measurement of the effective value can also present problems.

Le dispositif d'alimentation selon l'invention ne présente pas les inconvénients ci-dessus cités, grâce à un agencement nouveau qui en fait un appareil simple à réaliser et simple à mettre en oeuvre.The supply device according to the invention does not have the above-mentioned drawbacks, thanks to a new arrangement which makes it a device which is simple to produce and simple to implement.

La présente invention concerne un dispositif d'alimentation en courant d'un filament de tube radiogène, permettant d'obtenir de manière automatique un courant de chauffage dont l'intensité correspond à une valeur de consigne, cette intensité étant comprise dans la gamme des intensités succeptibles d'être appliquées à un filament, et ceci pour toutes les valeurs courantes de résistance ohmique du filament.The present invention relates to a device for supplying current to a filament of an X-ray tube, making it possible to automatically obtain a heating current whose intensity corresponds to a set value, this intensity being included in the range of intensities which can be applied to a filament, and this for all the current ohmic resistance values of the filament.

Selon l'invention, un dispositif d'alimentation en courant d'un filament d'au moins un tube radiogène, comportant, un générateur fournissant des impulsions de commande, un onduleur recevant les impulsions de commande et produisant dans un circuit de charge un courant de chauffage alternatif à partir d'une tension continue, un circuit de régulation régulant le courant de chauffage en fonction d'une valeur de consigne, le circuit de charge comportant un enroulement primaire d'un transformateur par l'intermédiaire duquel le courant de chauffage est appliqué au filament, le courant de chauffage ayant une même fréquence que la fréquence des impulsions de commande, est caractérisé en ce qu'il comporte un circuit oscillant disposé dans le circuit de charge, et en ce que le circuit de régulation délivre un signal d'erreur appliqué au géné­rateur pour modifier la fréquence des impulsions de commande, de manière à modifier l'impédance du circuit oscillant jusqu'à obtenir une valeur du courant du chauffage correspondant à la valeur de consigne.According to the invention, a device for supplying current to a filament of at least one X-ray tube, comprising, a generator supplying control pulses, an inverter receiving the control pulses and producing a current in a load circuit of alternative heating from a direct voltage, a regulation circuit regulating the heating current as a function of a set value, the load circuit comprising a primary winding of a transformer through which the heating current is applied to the filament, the heating current having the same frequency as the frequency of the control pulses, is characterized in that it comprises an oscillating circuit arranged in the load circuit, and in that the regulation circuit delivers a signal of error applied to the generator to modify the frequency of the control pulses, so as to modify the impedance of the oscillating circuit until a value of the current of the heating corresponding to the set value.

Il est ainsi possible de contrôler la puissance transmise au transformateur qui relie le circuit de charge au filament, d'une manière souple et précise en faisant varier l'impédance du circuit oscillant par la fréquence des impulsions de commande, et d'obtenir une dynamique de puissance importante qui permet au dispositif de l'invention d'alimenter successivement, de manière automatique, des filaments ayant des resistances très différentes dans une large gamme de courant.It is thus possible to control the power transmitted to the transformer which connects the load circuit to the filament, in a flexible and precise manner by varying the impedance of the oscillating circuit by the frequency of the control pulses, and to obtain a dynamic of high power which allows the device of the invention to supply successively, automatically, filaments having very different resistances in a wide current range.

L'invention sera mieux comprise grâce à la description qui suit, faite à titre d'exemple non limitatif, et aux deux figures annexées, parmi lesquelles:

  • - la figure 1 représente shématiquement un dispositif d' alimentation conforme à l'invention;
  • - la figure 2 est un graphe qui illustre le fonctionnement du dispositif d'alimentation de l'invention.
The invention will be better understood thanks to the description which follows, given by way of nonlimiting example, and to the two appended figures, among which:
  • - Figure 1 shows schematically a feed device according to the invention;
  • - Figure 2 is a graph illustrating the operation of the supply device of the invention.

La figure 1 montre un dispositif d'alimentation 1 conforme à l'invention permettant, dans l'exemple non limitatif décrit, d'ali­ menter en courant le filament d'un tube radiogène, par exemple selectionné parmi plusieurs tubes radiogènes, dont seulement deux tubes 26,27 sont représentés dans l'exemple décrit.Figure 1 shows a supply device 1 according to the invention allowing, in the non-limiting example described, to ali by running the filament of an X-ray tube, for example selected from several X-ray tubes, of which only two tubes 26, 27 are shown in the example described.

Les tubes radiogènes sont d'un type conventionnel comportant chacun une anode, 28,29 et une cathode 23,24 représentée par le filament qu'elle contient. Les tubes 26,27 sont alimentés en haute tension par des moyens classiques (non représentés). En fonctionnement, le filament 23,24 du tube 26,27 sélectionné est porté au potentiel négatif - HT de la haute tension, et les problèmes d'isolation éléctrique imposent d' appliquer au filament 23,24 l'énergie électrique nécéssaire à son chauffage, par l'intermédiaire d'un transformateur d'isolement 30.The X-ray tubes are of a conventional type each comprising an anode, 28, 29 and a cathode 23, 24 represented by the filament which it contains. The tubes 26, 27 are supplied with high voltage by conventional means (not shown). In operation, the filament 23.24 of the tube 26.27 selected is brought to the negative potential - HT of the high voltage, and the problems of electrical insulation impose to apply to the filament 23.24 the electrical energy necessary for its heating. , via an isolation transformer 30.

Dans l'exemple non limitatif décrit, la sélection du premier ou du second tube 26,27 est opérée en connectant le filament 23,24 correspondant, à l'enroulement secondaire 31 du transformateur 30, par l'intermédiaire d'un dispositif de commutation 35, comportant des commutateurs (non représentés) constitués par exemple par des relais éléctromécaniques; le transformateur 30 comportant un enroulement primaire 12 auquel est appliqué un courant de chauffage I délivré par un onduleur 2.In the nonlimiting example described, the selection of the first or second tube 26, 27 is made by connecting the corresponding filament 23, 24, to the secondary winding 31 of the transformer 30, by means of a switching device. 35, comprising switches (not shown) constituted for example by electromechanical relays; the transformer 30 comprising a primary winding 12 to which is applied a heating current I delivered by an inverter 2.

La commmande du dispositif de commutation 35 peut s'opérer soit par commande manuelle, soit de manière automatique dans le cadre de séquences programmées et controlées par exemple par un pupitre de commande 40; ce dernier étant relié au dispositif de commutation 35 par une première et une seconde liaison CT1,CT2 par lesquelles il peut sélectionner le premier ou le second tube 26,27, le premier tube 26 par exemple, de manière à appliquer au filament 23 de ce dernier un courant Iʹ pour son chauffage.The control of the switching device 35 can take place either by manual control, or automatically in the context of programmed sequences controlled for example by a control console 40; the latter being connected to the switching device 35 by a first and a second link CT1, CT2 by which it can select the first or the second tube 26,27, the first tube 26 for example, so as to apply to the filament 23 of this last a current Iʹ for its heating.

Il est à remarquer que la sélection d'un tube 26,27 peut s'effectuer de manière différente, comme par exemple par commutation au niveau du primaire du transformateur d'isolement. un transformateur d'isolement étant dans ce cas associé à chaque filament.It should be noted that the selection of a tube 26, 27 can be carried out in a different way, such as for example by switching at the level of the primary of the isolation transformer. an isolation transformer in this case being associated with each filament.

Le dispositif d'alimentation 1 comporte en outre une source de tension 3 continue régulée, délivrant par des bornes 27, 28 respec­tivement la polarité positive + et la polarité négative - d'une tension continue V1, régulée, ayant par exemple une valeur de 200 Volts. La source de tension 3 est constituée de manière classique et élabore la tension continue V1 à partir, par exemple, d'une tension monophasée (non représentée) de 220 V.The supply device 1 also comprises a source of regulated DC voltage 3, delivering via terminals 27, 28 respectively the positive polarity + and the negative polarity - of a DC voltage V1, regulated, having for example a value of 200 Volts. The voltage source 3 is constituted in a conventional manner and develops the direct voltage V1 from, for example, a single-phase voltage (not shown) of 220 V.

L'onduleur 2 est alimenté par la tension continue V1, à partir de laquelle il réalise une tension alternative. L'ondoleur 2 comporte deux moyens de commutation éléctronique 4,5 disposés en série entre le pôle positif + et le pôle négatif - de la tension continue V1. Dans l'exemple non limitatif décrit, les deux moyens de com­mutation 4,5 sont constitués par des transistors à effet de champ. La source S du premier transistor 4 est reliée au pôle positif + de la tension continue V1 et son drain D est relié à la source S du second transistor 5, dont le drain D est relié au pôle négatif -de la tension continue V1. Une première et une seconde diode d1,d2 sont respec­tivement montées en parallèle sur le premier et le second transistor 4,5; la première diode d1 ayant sa cathode reliée au pôle + de la tension V1 et son anode reliée d'une part, à la jonction 6 entre le drain du premier transistor 4 et la source du second transitor 5, et reliée d'autre part à la cathode de la seconde diode d2 dont l'anode est reliée au pôle négatif - de la tension continue V1.The inverter 2 is supplied by the DC voltage V1, from which it produces an AC voltage. The inverter 2 comprises two electronic switching means 4,5 arranged in series between the positive pole + and the negative pole - of the DC voltage V1. In the nonlimiting example described, the two switching means 4,5 are constituted by field effect transistors. The source S of the first transistor 4 is connected to the positive pole + of the DC voltage V1 and its drain D is connected to the source S of the second transistor 5, whose drain D is connected to the negative pole - of the DC voltage V1. A first and a second diode d1, d2 are respectively connected in parallel on the first and the second transistor 4,5; the first diode d1 having its cathode connected to the + pole of the voltage V1 and its anode connected on the one hand, to the junction 6 between the drain of the first transistor 4 and the source of the second transitor 5, and connected on the other hand to the cathode of the second diode d2, the anode of which is connected to the negative pole - of the DC voltage V1.

La jonction 6 est en outre reliée à la première extrémité 7 d'un moyen capteur de courant 9, dont la seconde extrémité 10 est reliée à la première extrémitée 11 de l'enroulement primaire 12 du transformateur d'isolement 30. La seconde extrémité 14 de l' enroulement primaire 12 est reliée à la première extrémité 15 d'une inductance 16 dont la seconde extrémité 17 est reliée à un point milieu capacitif 18. Le point milieu capacitif 18 est formé par la jonction d'un premier et d'un second condensateur 19,20 montés en série entre les bornes positives et négatives +,- de la tension continue V1; le premier condensateur 19 étant relié au pôle positif +, et le second condensateur 20 étant relié au pôle négatif -.The junction 6 is also connected to the first end 7 of a current sensor means 9, the second end 10 of which is connected to the first end 11 of the primary winding 12 of the isolation transformer 30. The second end 14 of the primary winding 12 is connected to the first end 15 of an inductor 16 whose second end 17 is connected to a capacitive midpoint 18. The capacitive midpoint 18 is formed by the junction of a first and a second capacitor 19.20 connected in series between the positive and negative terminals +, - of the DC voltage V1; the first capacitor 19 being connected to the positive pole +, and the second capacitor 20 being connected to the negative pole -.

Les deux condensateurs 19 et 20 forment une capacité qui est mise en série avec l'inductance 16, pour constituer un circuit oscillant 13 disposé en série avec l'enroulement primaire 12 du transformateur 13, avec lequel il constitue un circuit de charge 12-­13.The two capacitors 19 and 20 form a capacitor which is placed in series with the inductor 16, to form an oscillating circuit 13 arranged in series with the primary winding 12 of the transformer 13, with which it constitutes a charging circuit 12-13 .

Dans le circuit de charge 12-13, l'enroulement primaire 12 représente le filament 23 dont la résistance ohmique R est rapportée dans le circuit de charge 12-13. En suposant que le filament 23 soit d'un type classique, sa résitance R peut avoir une valeur quelconque comprise dans la gamme de valeur courante, par exemple entre 0,6 Ohms et 4,5 Ohms.In the charging circuit 12-13, the primary winding 12 represents the filament 23 whose ohmic resistance R is reported in the charging circuit 12-13. Assuming that the filament 23 is of a conventional type, its resistance R can have any value included in the current value range, for example between 0.6 Ohms and 4.5 Ohms.

Le courant Iʹdans le circuit secondaire du transformateur 30, où est disposé le filament 23, étant proportionnel au courant I circulant dans le circuit de l'enroulement primaire ou circuit de charge 12-13, selon un rapport connu, et la resistance R du filament 23 étant rapportée dans le circuit de charge 12-13, c'est le courant I qui circule dans le circuit de charge 12-13 qui est appelé courant de chauffage pour plus de clarté de la description.The current Iʹ in the secondary circuit of the transformer 30, where the filament 23 is disposed, being proportional to the current I flowing in the circuit of the primary winding or load circuit 12-13, according to a known ratio, and the resistance R of the filament 23 being reported in the charging circuit 12-13, it is the current I which flows in the charging circuit 12-13 which is called heating current for the sake of clarity of the description.

Le capteur de courant 9 est placé dans le circuit de charge 12-13 et délivre par une sortie 59 un signal S1 proportionnel au courant I de chauffage pseudo-sinusoïdal; le capteur de courant 9 est d'un type classique, tel que par exemple constitué par un trans­formateur d'intensité.The current sensor 9 is placed in the charging circuit 12-13 and delivers by an output 59 a signal S1 proportional to the pseudo-sinusoidal heating current I; the current sensor 9 is of a conventional type, such as for example constituted by an intensity transformer.

Le signal S1, proportionnel au courant de chauffage I, est appliqué à l'entrée 61 d'un dispositif convertisseur 25, qui traite de manière classique les valeurs du signal S1, pour fournir par une sortie 62, un second signal S2 correspondant à la valeur efficace du courant de chauffage I. Ces valeurs efficaces sont utilisées pour réaliser une régulation du courant I dans le circuit primaire ou circuit de charge 12-13 qui permet, grâce notamment au trans­formateur d'isolement 30 à faible fuite, de réaliser un contrôle rigoureux du courant Iʹ passant dans le filament 23 en assurant une meilleur proportionnalité entre le courant I' dans le filament 23 et le courant I dans le circuit de charge 12-13.The signal S1, proportional to the heating current I, is applied to the input 61 of a converter device 25, which conventionally processes the values of the signal S1, to provide by an output 62, a second signal S2 corresponding to the effective value of the heating current I. These effective values are used to regulate the current I in the primary circuit or load circuit 12-13 which allows, thanks in particular to the isolation transformer 30 with low leakage, to carry out a control rigorous current Iʹ passing through the filament 23 ensuring better proportionality between the current I 'in the filament 23 and the current I in the charging circuit 12-13.

Le second signal S2 est appliqué à la première entrée 41 d'un élaborateur d'erreur 42, constitué par exemple par un amplificateur différentiel. La seconde entrée 43 de l'élaborateur d'erreur 42 reçoit une valeur de consigne VC correspondant à la valeur désirée du courant de chauffage I; cette valeur de consigne étant par exemple délivrée par le pupitre de commande 40 qui, à cette fin, est relié par une liaison 63 à la seconde entrée 43 de l'élaborateur d'erreur 42. L'élaborateur d'erreur 42 délivre à sa sortie 44 un signal d'erreur SE proportionnel à la différence entre le second signal S2 et la valeur de consigne VC. Le signal d'erreur SE est appliqué à un moyen pour produire des impulsions à une fréquence F donnée et pour modifier cette fréquence F en plus ou en moins en fonction du signe et de l'amplitude du signal d'erreur SE. Dans l'exemple non limitatif décrit, ce moyen pour produire des impulsions est constitué par un convertisseur tension-fréquence 46 dont l'entrée 45 est reliée à la sortie 44 de l'élaborateur d'erreur 42.The second signal S2 is applied to the first input 41 of an error processor 42, constituted for example by a differential amplifier. The second input 43 of the error processor 42 receives a setpoint value VC corresponding to the desired value of the heating current I; this setpoint being for example delivered by the control console 40 which, for this purpose, is connected by a link 63 to the second input 43 of the error processor 42. The error processor 42 delivers to its output 44 an error signal SE proportional to the difference between the second signal S2 and the set value VC. The error signal SE is applied to a means for producing pulses at a given frequency F and for modifying this frequency F more or less depending on the sign and the amplitude of the error signal SE. In the nonlimiting example described, this means for producing pulses consists of a voltage-frequency converter 46, the input 45 of which is connected to the output 44 of the error generator 42.

Une sortie 47 du convertisseur tension-fréquence 46 délivre un quatrième signal S4 constitué par des impulsions délivrées à la fréquence F, laquelle fréquence F constitue la fréquence initiale à laquelle fonctionne l'onduleur 2. Le signal S4 est appliqué à l'entrée 49 d'un dispositif d'aiguillage 50 dont la fonction est de produire des premières et des secondes impulsions de commande SC1, SC2, délivrées à une même fréquence F que le quatrième signal S4, et destinées respectivement à commander le premier transistor 4 et le second transistor 5.An output 47 of the voltage-frequency converter 46 delivers a fourth signal S4 consisting of pulses delivered at frequency F, which frequency F constitutes the initial frequency at which the inverter 2 operates. The signal S4 is applied to input 49 d 'A switching device 50 whose function is to produce first and second control pulses SC1, SC2, delivered at the same frequency F as the fourth signal S4, and intended respectively to control the first transistor 4 and the second transistor 5.

Les premières et les secondes impulsions de commande SC1, SC2 (non représentées) ont une largeur ou durée t sensiblement égale ou inférieure à la moitié du temps qui sépare les fronts avant de deux impulsions de même type, c'est à dire à la moitié de la période P correspondant à la fréquence F(t≦ 1/2F). D'autre part les secondes impulsions de commande SC2 sont décalées dans le temps, par rapport aux premières impulsions de commande SC1, d'une demi période P/2 (P/2 = 1/2F) ,de manière que les premières et secondes impulsions de commande SC1 et SC2 soient respectivement appliquées au premier et second transistor, 4,5 en opposition de phase.The first and second control pulses SC1, SC2 (not shown) have a width or duration t substantially equal to or less than half the time between the front edges of two pulses of the same type, that is to say half of the period P corresponding to the frequency F (t ≦ 1 / 2F). On the other hand, the second control pulses SC2 are offset in time, with respect to the first control pulses SC1, by a half period P / 2 (P / 2 = 1 / 2F), so that the first and seconds control pulses SC1 and SC2 are respectively applied to the first and second transistor, 4.5 in phase opposition.

Le dispositif d'aiguillage 50 délivre les premières impulsions de commande SC1 par une première sortie 51 qui est reliée à la cathode d'une troisième diode d3 et, à la première extrémité 53 d'une résistance R1 dont la seconde extrémité 54 est reliée à l'anode de la troisième diode d3 et à l'entrée de commande G1 du premier transistor 4. Le dispositif d'aiguillage 50 délivre les secondes impulsions de commande SC2 par une seconde sortie 52 reliée à la cathode d'une quatrième diode d4 et à la première extrémité 55 d'une seconde resistance R2; la seconde extrémité 56 de la seconde résistance R2 est reliée à l'anode de la quatrième diode d4 et à l'entrée de commande G2 du second transistor 5.The switching device 50 delivers the first control pulses SC1 by a first output 51 which is connected to the cathode of a third diode d3 and, at the first end 53 of a resistor R1 whose second end 54 is connected to the anode of the third diode d3 and at the control input G1 of the first transistor 4. The switching device 50 delivers the second control pulses SC2 by a second output 52 connected to the cathode of a fourth diode d4 and at the first end 55 of a second resistor R2; the second end 56 of the second resistor R2 is connected to the anode of the fourth diode d4 and to the control input G2 of the second transistor 5.

Le fonctionnement général du dispositif d'alimentation 1 selon l'invention est le suivant.The general operation of the supply device 1 according to the invention is as follows.

A la mise en fonctionnement, commandée par exemple par le pupitre de commande 40, grâce à une liaison 60 entre ce dernier et le dispositif d'aiguillage 50, autorisant la sortie des impulsions de commande SC1,SC2, ces impulsions SC1, SC2 sont appliquées respectivement au premier et au second transistor 4,5, par l'inter­médiaire des réseaux formés d'une part, par la troisième diode d3 et la resistance R1 et, d'autre part par la quatrième diode d4 et la seconde résistance R2; la non conduction simultanée des deux transistors 4,5 étant interdite par une simple dissymétrie à la conduction et au blocage de chaque transistor 4,5.When it is put into operation, controlled for example by the control console 40, by virtue of a link 60 between the latter and the switching device 50, authorizing the output of the control pulses SC1, SC2, these pulses SC1, SC2 are applied respectively the first and second transistor 4,5, via the networks formed on the one hand, by the third diode d3 and the resistor R1 and, on the other hand by the fourth diode d4 and the second resistor R2; the simultaneous non-conduction of the two transistors 4,5 being prohibited by a simple asymmetry in the conduction and blocking of each transistor 4,5.

Les impulsions de commandes SC1,SC2 ont une fréquence F correspondant à une fréquence initiale de fonctionnement de l' onduleur 2. Les impulsions de commande SC1,SC2 étant par exemple positives, les premières impulsions SC1 provoquent la conduction du premier transistor 4 de sorte, qu'à l'exception de la chute de tension relativement faible aux bornes du premier transistor 4, la polarité positive + de la tension continue V1 est appliquée à la jonction 6, et le condensateur 19, qui était chargé à une tension intermédiaire V2, tend à se décharger dans le circuit de charge 12-13, c'est à dire dans l'inductance 16 et dans l'enroulement primaire 12 qui représente le filament 23; le courant de chauffage I étant alors établi dans le sens représenté par la flèche repérée IC1; le second condensateur 20 tendant lui-même à se charger à la valeur de la polarité positive + de la tension continue V1. A la fin de l'impulsion de commande SC1, la premier transistor 4 est bloqué et, le front avant d'une seconde impulsion de commande SC2 met en conduction le second transitor 5 qui applique, à la jonction 6, la polarité négative - de la tension continue V1. Le phénomène est alors à l'inverse du précédent, c'est à dire que le second condensateur 20 tend à se décharger dans le circuit de charge 12-13, et que le premier condensateur 19 tend à se charger; le courant de chauffage I ayant alors le sens montré par la seconde flèche IC2. Ce fonctionnement est répété pour chaques impulsions de commande SC1,SC2.The control pulses SC1, SC2 have a frequency F corresponding to an initial operating frequency of the inverter 2. The control pulses SC1, SC2 being for example positive, the first pulses SC1 cause the first transistor 4 to conduce so that with the exception of the relatively low voltage drop across the terminals of the first transistor 4, the positive polarity + of the DC voltage V1 is applied to the junction 6, and the capacitor 19, which was charged at an intermediate voltage V2, tends to discharge in the charging circuit 12-13, i.e. in the inductor 16 and in the primary winding 12 which represents the filament 23; the heating current I then being established in the direction represented by the arrow marked I C1 ; the second capacitor 20 itself tending to charge at the value of the positive polarity + of the DC voltage V1. At the end of the control pulse SC1, the first transistor 4 is blocked and, the leading edge of a second control pulse SC2 turns on the second transitor 5 which applies, at junction 6, the negative polarity - of the DC voltage V1. The phenomenon is then the reverse of the previous one, that is to say that the second capacitor 20 tends to discharge in the charging circuit 12-13, and that the first capacitor 19 tends to charge; the heating current I then having the direction shown by the second arrow I C2 . This operation is repeated for each control pulse SC1, SC2.

Les premières et seconde diode d1, d2 assurent chacune une double fonction :

  • 1 - la première et la seconde diodes d1, d2 assurent la protection respectivement du premier et du second transistor 4,5 contre les surtensions, soit une fonction ecrêtage réalisée par chaque diode d1, d2 fonctionnant en inverse.
  • 2 - Chaque doide d1, d2 a pour fonction de conduire, en direct, le courant réactif au blocage du transistor 4,5 opposé : la première diode d1 conduit au blocage du second transistor 5, pour conduire le courant réactif au pôle positif + de la tension V1; la seconde diode d₂ conduit au blocage du premier transistor 4, pour refermer le courant réactif au pôle négatif - de la tension V1. Ceci implique que les diodes d1, d2 sont rapides à la conduction.
The first and second diodes d1, d2 each perform a dual function:
  • 1 - the first and second diodes d1, d2 respectively protect the first and second transistor 4,5 against overvoltages, ie a clipping function performed by each diode d1, d2 operating in reverse.
  • 2 - Each doide d1, d2 has the function of conducting, directly, the reactive current to the blocking of the opposite transistor 4,5: the first diode d1 leads to the blocking of the second transistor 5, to conduct the reactive current to the positive pole + of the voltage V1; the second diode d₂ leads to the blocking of the first transistor 4, to close the reactive current to the negative pole - of the voltage V1. This implies that the diodes d1, d2 are fast at conduction.

La protection des transistors 4,5 est ainsi assurée d'une façon efficace et beaucoup plus simple que celle des moyens de com­mutation qui, dans l'art antérieur, ont pour fonction de hacher une tension continue. Ceci étant possible notamment du fait que les transistors 4,5 sont du type à effet de champ et sont rapides en commutation.The protection of the transistors 4,5 is thus ensured in an efficient and much simpler way than that of the switching means which, in the prior art, have the function of chopping a DC voltage. This is possible in particular because the transistors 4,5 are of the field effect type and are fast in switching.

Le circuit de régulation, constitué par le capteur de courant 9, le dispositif convertisseur 25, l'élaborateur d'erreur 42 et le con­vertisseur tension-fréquence 46, réalisent une régulation du courant de chauffage I sur la valeur éfficace de ce dernier, correspondant à la valeur de consigne VC délivrée par le pupitre de commande 40.The regulation circuit, constituted by the current sensor 9, the converter device 25, the error generator 42 and the voltage-frequency converter 46, carry out a regulation of the heating current I on the effective value of the latter, corresponding to the setpoint VC delivered by the control panel 40.

En supposant que la valeur de courant de chauffage I soit différente de celle imposée par la valeur de consigne VC, il en résulte un signal d'erreur SE non nul.Assuming that the heating current value I is different from that imposed by the setpoint value VC, this results in a non-zero error signal SE.

Selon une caractérisitique de l'invention, un signal d'erreur SE non nul appliqué au convertisseur tension fréquence 46, engendre une modification de la fréquence F des impulsions (signal S4) que ce dernier applique au dispositif d'aiguillage 50, et par suite engendre une modification de la fréquence des impulsions SC1, SC2 que le dispositif d'aiguillage 50 applique aux transistors 4,5; d'où il résulte une variation de la fréquence de fonctionnement de l'onduleur 2, de manière à modifier la valeur de l'impédance Z, présentée par la circuit oscillant 13 constitué par l'inductance 16 en série avec les condensateurs 19, 20.According to a characteristic of the invention, a non-zero error signal SE applied to the voltage frequency converter 46, generates a modification of the frequency F of the pulses (signal S4) which the latter applies to the switching device 50, and consequently generates a modification of the frequency of the pulses SC1, SC2 that the switching device 50 applies to the transistors 4,5; whence there results a variation of the operating frequency of the inverter 2, so as to modify the value of the impedance Z, presented by the oscillating circuit 13 constituted by the inductor 16 in series with the capacitors 19, 20 .

Le circuit oscillant 13 étant en série avec la charge que constitue la résistance R du filament 23, la valeur du courant de chauffage I est directement liée à l' impédance Z du circuit oscillant LC, et diminue ou augmente selon que cette impédance diminue ou augmente.The oscillating circuit 13 being in series with the load constituted by the resistance R of the filament 23, the value of the heating current I is directly linked to the impedance Z of the oscillating circuit LC, and decreases or increases as this impedance decreases or increases .

Dans l'exemple non limitatif décrit, l'onduleur 2 fonctionne dans une plage de fréquence relativement élevée, de 18 KHZ à 35 KHZ par exemple, ce qui permet d'une part, une réduction importante du volume des éléments, notamment des éléments magnétique et en particulier du transformateur d'isolement 30; et permet d'autre part une réponse rapide du circuit de régulation, ainsi qu'un arrêt rapide si nécessaire pour des besoins de sécurité.In the nonlimiting example described, the inverter 2 operates in a relatively high frequency range, from 18 KHZ to 35 KHZ for example, which allows on the one hand, a significant reduction in the volume of the elements, in particular the magnetic elements and in particular of the isolation transformer 30; and on the other hand allows a quick response of the regulation circuit, as well as a quick stop if necessary for safety needs.

Dans l'exemple non limitatif de la description, l'inductance 16 et les condensateurs 19, 20 sont choisis de manière que la fréquence de résonnance Fo du circuit oscillant 13 soient un peu inférieure à la fréquence minimum de fonctionnement de l'onduleur 2, à 15 KHz pa exemple, de manière que dans le circuit de charge 12-13 le courant soit en avance sur la tension; cette disposition étant favorable à la commutation des transistors 4,5.In the nonlimiting example of the description, the inductor 16 and the capacitors 19, 20 are chosen so that the resonant frequency Fo of the oscillating circuit 13 is a little lower than the minimum operating frequency of the inverter 2, at 15 KHz pa example, so that in the load circuit 12-13 the current is ahead of the voltage; this arrangement being favorable for the switching of transistors 4,5.

Le circuit oscillant 13 est constitué par l'inductance 16 et une capacité en série formée par les condensateurs 19 et 20 : on peut remarquer que les condensateurs 19 et 20, outre qu'il consituent la capacité du circuit oscillant 13 sont disposés en série dans la tension continue V1, et assurent ainsi un découplage efficace du circuit de charge 12-13 au point capacitif 18; ces deux condensateurs 19, 20 devant être considérés comme étant montés en parallèle pour constituer la capacité du circuit oscillant 13.The oscillating circuit 13 consists of the inductance 16 and a capacitance in series formed by the capacitors 19 and 20: it can be noted that the capacitors 19 and 20, in addition to constituting the capacitance of the oscillating circuit 13, are arranged in series in the DC voltage V1, and thus ensure efficient decoupling of the charging circuit 12-13 at the capacitive point 18; these two capacitors 19, 20 having to be considered as being connected in parallel to constitute the capacity of the oscillating circuit 13.

Dans un exemple de réalisation indiqué à titre d'exemple non limitatif :
- l'inductance 16 à une valeur de 325 microhenry;
- les condensateurs 19, 20 ont chacun une valeur de 0,1 microfarad, et forment une capacité de 0,2 microfarad;
- la fréquence de résonnance Fo du circuit oscillant 13 est de sensiblement 15 KHZ;
- la self de fuite du transformateur 30 est de l'ordre de 250 microhenry
- la tension continue V1 à une valeur de 200 volts.In an exemplary embodiment indicated by way of nonlimiting example:
- inductance 16 to a value of 325 microhenry;
- The capacitors 19, 20 each have a value of 0.1 microfarad, and form a capacity of 0.2 microfarad;
- the resonance frequency F o of the oscillating circuit 13 is approximately 15 KHZ;
- the transformer self-leakage 30 is of the order of 250 microhenry
- the DC voltage V1 at a value of 200 volts.

Dans ces conditions, le dispositif d'alimentation 1 selon l'invention permet d'alimenter successivement plusieurs filaments 23,24 ayant des résistances différentes, comme il est illustré par la figure 2.Under these conditions, the supply device 1 according to the invention makes it possible to successively supply several filaments 23, 24 having different resistances, as illustrated in FIG. 2.

La figure 2 est un graphe qui représente, par une première et une seconde courbe 65,66 les variations du courant de chauffage I en fonction de la fréquence F; la fréquence F étant portée en abscisse et exprimée en KHZ, et le courant de chauffage I étant porté en ordonnée et exprimé en ampères.FIG. 2 is a graph which represents, by a first and a second curve 65, 66, the variations of the heating current I as a function of the frequency F; the frequency F being plotted on the abscissa and expressed in KHZ, and the heating current I being plotted on the ordinate and expressed in amps.

Ainsi qu'il a été précédemment mentionné, la fréquence de résonnnance Fo du circuit oscillant 13 est à 15 KHZ, et la plage de fréquences F de fonctionement est comprise entre 18 et 35 KHZ.As previously mentioned, the resonant frequency F o of the oscillating circuit 13 is 15 KHZ, and the operating frequency range F is between 18 and 35 KHZ.

Dans l'exemple non limitatif décrit, la première et la seconde courbe 65, 66 correspondent respectivement à l'alimentation d'un premier et d'un second filament 23, 24; le premier filament 23 ayant une resistance de 4,5 ohms, et le second filament 24 ayant une résistance de 1 ohm.In the nonlimiting example described, the first and second curves 65, 66 correspond respectively to the supply of a first and a second filament 23, 24; the first filament 23 having a resistance of 4.5 ohms, and the second filament 24 having a resistance of 1 ohm.

Ces première et seconde courbe 65, 66 illustrent les valeurs possibles du courant I dans la plage de fréquences comprises entre 18 et 35 KHZ. On observe que des mêmes valeurs du courant I sont obtenues avec des fréquences F différentes, selon qu'il s'agit d'alimenter un filament 23 de 4,5 ohms (première courbe 65) ou un filament 24 de 1 ohm (seconde courbe 66) :
- pour 4,5 ohms, les valeurs de 5,5 ampères et 2,2 ampères sont obtenues respectivement à 18 KHZ et 30,5 KHZ;
- pour 1 ohm, les valeurs de 5,5 ampères et 2,2 ampères sont obtenues respectivement à 20,5 KHZ et 32,5 KHZ.These first and second curves 65, 66 illustrate the possible values of the current I in the frequency range between 18 and 35 KHZ. It is observed that the same values of the current I are obtained with different frequencies F, depending on whether it is a question of feeding a filament 23 of 4.5 ohms (first curve 65) or a filament 24 of 1 ohm (second curve 66):
- for 4.5 ohms, the values of 5.5 amps and 2.2 amps are obtained respectively at 18 KHZ and 30.5 KHZ;
- for 1 ohm, the values of 5.5 amps and 2.2 amps are obtained respectively at 20.5 KHZ and 32.5 KHZ.

Dans le but d'éviter des surcharges accidentelles, une limite à la valeur maximum du courant de chauffage est réalisée grâce à un dispositif de butée de fréquence (non représenté), en lui-même classique. Le dispositif de butée en fréquence permet, à l'approche de la fréquence de résonnance Fo, de limiter la plage de fréquence de fonctionnement à une valeur supérieure à Fo; cette limite étant située à environ 15,7 KHZ dans l'exemple non limitatif décrit.In order to avoid accidental overloads, a limit to the maximum value of the heating current is achieved by means of a frequency stop device (not shown), in itself conventional. The frequency stop device makes it possible, when approaching the resonant frequency F o , to limit the operating frequency range to a value greater than F o ; this limit being situated at approximately 15.7 KHZ in the nonlimiting example described.

Cette description constitue un exemple non limitatif, montrant que le principe de fonctionnement du dispositif d' alimen­tation 1 selon l'invention permet, non seulement d'alimenter un filament de tube radiogène par une courant de chauffage régulé avec une grande précision, mais permet en outre de manière automatique, d'alimenter en courant de chauffage successivement plusieurs filaments de résistances différentes, dans une large gamme de puissance, tout en conservant une grande précision dans la définition du courant de chauffage.This description constitutes a nonlimiting example, showing that the operating principle of the supply device 1 according to the invention makes it possible not only to supply a filament of an X-ray tube with a heating current regulated with great precision, but also allows in addition to automatically, supplying successively several heating filaments of different resistances, in a wide power range, while retaining great precision in the definition of the heating current.

Claims (9)

1- Dispositif d'alimentation en courant d'un filament d'au moins un tube radiogène, comportant un générateur (46,51) fournissant des impulsions de commande (SC1,SC2), un onduleur (2) recevant les impulsions de commande (SC1,SC2) et produisant dans un circuit de charge (12-13) un courant de chauffage (I) alternatif à partir d'une tension continue (VI), un circuit de régulation (9,41,46) régulant le courant de chauffage (I) en fonction d'une valeur de consigne (VC), le circuit de charge (12-13) comportant un enroulement primaire (12) d'un transformateur (30) par l'intermédiaire duquel le courant de chauffage (I) est appliqué au filament(23,24), le courant de chauffage (I) ayant une même fréquence que la fréquence des impulsions de commande (SC1,SC2), caractérisé en ce qu'il comporte un circuit oscillant (13) disposé dans le circuit de charge (12-13), et en ce que le circuit de régulation (9,41,42,46) délivre un signal d'erreur (SE) appliqué au générateur (46,51) pour modifier la fréquence F des impulsions de commande (SC1,SC2) de manière à modifier l'impédance du circuit oscillant (13) jusqu'à obtenir une valeur du courant de chauffage (I) correspondant à la valeur de consigne (VC).1- Device for supplying current to a filament of at least one X-ray tube, comprising a generator (46,51) supplying control pulses (SC1, SC2), an inverter (2) receiving the control pulses ( SC1, SC2) and producing in a load circuit (12-13) an alternating heating current (I) from a direct voltage (VI), a regulation circuit (9,41,46) regulating the current of heating (I) as a function of a set value (VC), the charging circuit (12-13) comprising a primary winding (12) of a transformer (30) through which the heating current (I ) is applied to the filament (23,24), the heating current (I) having the same frequency as the frequency of the control pulses (SC1, SC2), characterized in that it comprises an oscillating circuit (13) arranged in the charging circuit (12-13), and in that the regulation circuit (9,41,42,46) delivers an error signal (SE) applied to the generator (46,51) to modify the frequency e F of the control pulses (SC1, SC2) so as to modify the impedance of the oscillating circuit (13) until a value of the heating current (I) corresponding to the set value (VC) is obtained. 2 - Dispositif d'alimentation selon la revendication 1, caractérisé en ce que le circuit de régulation (9,41,46) comporte un capteur de courant (9) situé dans le circuit de charge (12-13).2 - Power device according to claim 1, characterized in that the regulation circuit (9,41,46) comprises a current sensor (9) located in the charging circuit (12-13). 3- Dispositif d'alimentation selon l'une des revendications précédentes, caractérisé en ce que l'onduleur (2) comporte entre les pôles (+,-) de la tension continue (V1), d'une part au moins deux commutateurs électroniques (4,5) en série, et d'autre part deux condensateurs (19,20) en série, une première extrémité du circuit de charge (12-13) étant reliée à la jonction (6) des deux moyens de commutation électronique (4,5), l'autre extrémité du circuit de charge (17) étant reliée à la jonction (18) des deux condensateurs (19,20).3- Power device according to one of the preceding claims, characterized in that the inverter (2) comprises between the poles (+, -) of the DC voltage (V1), on the one hand at least two electronic switches (4,5) in series, and on the other hand two capacitors (19,20) in series, a first end of the charging circuit (12-13) being connected to the junction (6) of the two electronic switching means ( 4,5), the other end of the charging circuit (17) being connected to the junction (18) of the two capacitors (19,20). 4- Dispositif d'alimentation selon la revendication précédente, caractérisé en ce que les deux condensateurs (19,20) constituent la capacité du circuit oscillant (13)4- Supply device according to the preceding claim, characterized in that the two capacitors (19,20) constitute the capacity of the oscillating circuit (13) 5- Dispositif d'alimentation selon la revendication 3, carac­térisé en ce que les deux moyens de commutation électronique (4,5) sont des transistors à effets de champ.5- supply device according to claim 3, characterized in that the two electronic switching means (4,5) are field effect transistors. 6- Dispositif d'alimentation selon l'une des revendications précédentes, caractérisé en ce que le circuit oscillant (13)est constitué d'une capacité (19,20) en série avec une inductance (16).6- Supply device according to one of the preceding claims, characterized in that the oscillating circuit (13) consists of a capacitor (19,20) in series with an inductor (16). 7- Dispositif d'alimentation selon l'une des revendications précédentes, caractérisé en ce que le circuit oscillant (13) à une fréquence de résonnance (Fo) inférieure à la fréquence F des impulsions de commande (SC1,SC2).7- Supply device according to one of the preceding claims, characterized in that the oscillating circuit (13) at a resonant frequency (F o ) lower than the frequency F of the control pulses (SC1, SC2). 8- Dispositif d'alimentation selon la revendication 3, carac­térisé en ce que les deux condensateurs (19,20) constituent un découplage du circuit de charge (12-13).8- Power device according to claim 3, characterized in that the two capacitors (19,20) constitute a decoupling of the charging circuit (12-13). 9- Dispositif d'alimentation selon l'une des revendications précédentes, caractérisé en ce qu'il comporte un dispositif de commutation (35) permettant de sélectionner un tube radiogène (26,27) dont le filament (23,24) est à alimenter en courant (I) de chauffage.9- supply device according to one of the preceding claims, characterized in that it comprises a switching device (35) for selecting an X-ray tube (26,27) whose filament (23,24) is to be supplied in heating current (I).
EP87400774A 1986-04-11 1987-04-07 Current supply device for an x-ray tube filament Expired - Lifetime EP0241373B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8605240A FR2597285B1 (en) 1986-04-11 1986-04-11 DEVICE FOR SUPPLYING CURRENT TUBE FILAMENT WITH CURRENT
FR8605240 1986-04-11

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EP0241373A1 true EP0241373A1 (en) 1987-10-14
EP0241373B1 EP0241373B1 (en) 1990-08-16

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US (1) US4809310A (en)
EP (1) EP0241373B1 (en)
DE (1) DE3764292D1 (en)
FR (1) FR2597285B1 (en)

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EP0471626A1 (en) * 1990-08-14 1992-02-19 General Electric Cgr S.A. Device for supplying and regulating the cathode filament current from an X-ray tube
US5950772A (en) * 1997-08-29 1999-09-14 Hayes Brake, Inc. Bicycle brake system having a flexible disk

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JP2677409B2 (en) * 1988-09-19 1997-11-17 勲 高橋 Inverter device
DE3927888A1 (en) * 1989-08-24 1991-02-28 Philips Patentverwaltung INVERTER ARRANGEMENT
MX9200368A (en) * 1991-01-29 1992-08-01 Dawari Datubo Dan Harry HIGH DENSITY AND HIGH FREQUENCY POWER CONVERSION SYSTEM.
US5301095A (en) * 1991-10-01 1994-04-05 Origin Electric Company, Limited High power factor AC/DC converter
US5272618A (en) * 1992-07-23 1993-12-21 General Electric Company Filament current regulator for an X-ray system
FR2782206B1 (en) * 1998-08-05 2000-09-29 Europ Agence Spatiale CONTINUOUS-CONTINUOUS VOLTAGE CONVERTER, LIKE SHORT-CIRCUIT PROTECTION
DE10228336C1 (en) * 2002-06-25 2003-11-27 Siemens Ag Voltage generation circuit for X-ray tube incorporates alternate voltage and current feedback regulation for HF voltage stage
CN113438785A (en) * 2021-06-18 2021-09-24 浙江国研智能电气有限公司 Power supply for bulb tube filament of high-voltage X-ray machine

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EP0471626A1 (en) * 1990-08-14 1992-02-19 General Electric Cgr S.A. Device for supplying and regulating the cathode filament current from an X-ray tube
FR2666000A1 (en) * 1990-08-14 1992-02-21 Gen Electric Cgr DEVICE FOR SUPPLYING AND REGULATING THE CURRENT OF A CATHODE FILAMENT OF A RADIOGENIC TUBE.
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Also Published As

Publication number Publication date
FR2597285A1 (en) 1987-10-16
EP0241373B1 (en) 1990-08-16
US4809310A (en) 1989-02-28
FR2597285B1 (en) 1988-06-17
DE3764292D1 (en) 1990-09-20

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