EP0471625B1 - Device for obtaining of an adjustable d.c. voltage - Google Patents

Device for obtaining of an adjustable d.c. voltage Download PDF

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Publication number
EP0471625B1
EP0471625B1 EP91402248A EP91402248A EP0471625B1 EP 0471625 B1 EP0471625 B1 EP 0471625B1 EP 91402248 A EP91402248 A EP 91402248A EP 91402248 A EP91402248 A EP 91402248A EP 0471625 B1 EP0471625 B1 EP 0471625B1
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EP
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Prior art keywords
circuit
voltage
frequency
pulses
output
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EP91402248A
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German (de)
French (fr)
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EP0471625A1 (en
Inventor
Jacques Laeuffer
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General Electric CGR SA
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General Electric CGR SA
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    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05GX-RAY TECHNIQUE
    • H05G1/00X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08Electrical details
    • H05G1/26Measuring, controlling or protecting
    • H05G1/30Controlling
    • H05G1/32Supply voltage of the X-ray apparatus or tube
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05GX-RAY TECHNIQUE
    • H05G1/00X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08Electrical details
    • H05G1/10Power supply arrangements for feeding the X-ray tube
    • H05G1/20Power supply arrangements for feeding the X-ray tube with high-frequency ac; with pulse trains

Definitions

  • the present invention relates to devices for obtaining a DC voltage whose value is adjustable over a wide range, said devices being more particularly adapted to polarize a focus of an X-ray tube to a value chosen by the practitioner implementing a radiological installation.
  • Such devices are known from documents US-A-4, 541, 041 and GB-A-2,045,019.
  • a radiological tube is generally constituted as a diode, that is to say by two electrodes, one of which, 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 filament heated by an electric current which constitutes the source of electrons.
  • an electric current which constitutes the source of electrons.
  • a metal part, called a concentration part, supporting the filament is isolated from the latter and brought to a negative potential, called polarization, with respect to said filament.
  • polarization a negative potential
  • to modify the shape and therefore the concentration of the electron beam it is usual to modify this polarization potential over a wide range, for example between 300 and 3000 volts.
  • the cathode is itself brought to a voltage of the order of -20 to -75 kilovolts relative to the mass, which poses insulation problems to apply this potential or bias voltage.
  • the invention relates more particularly to a device for obtaining a bias voltage of a concentrating part of an X-ray tube cathode which is variable over a wide range of values.
  • Figure 1 gives the block diagram of a device of the prior art. It includes a supply circuit 10 which supplies a DC voltage E regulated and adjustable from an AC voltage supplied by the sector. The voltage E is applied to the terminals of an inverter circuit 11 which comprises a chopping circuit 12 and a control circuit 14.
  • the alternating signal supplied by the inverter circuit 11 is applied to a voltage step-up transformer 15, the secondary winding of which is connected to a rectification and filtering circuit 16.
  • This circuit 16 provides a direct voltage V s which is applied between the piece of concentration and filament of the x-ray tube.
  • the voltage V s being difficult to measure due to the high common mode potential (20 to 75 kilovolts), it is preferable to measure the voltage E which is substantially proportional to it and to regulate it.
  • the voltage E is measured by a resistive divider comprising the resistors R1 and R2 and the divided signal is applied to a voltage / frequency converter circuit 20 which receives, moreover, a signal V ref corresponding to the voltage that the it is desired to obtain between the concentration piece and the filament of the x-ray tube.
  • the chopper circuit 12 comprises, for example, two transistors 21 and 22, the openings and closings of which are controlled by the control circuit 14.
  • the control circuit 14 is also a voltage / frequency converter circuit similar to the circuit 20 but whose frequency is fixed.
  • the object of the present invention is therefore to provide a device for obtaining an adjustable direct voltage which does not have the above-mentioned drawbacks.
  • the means for undulating said voltage E comprise an oscillating circuit whose resonant frequency is greater than the frequency F.
  • the power circuit 33 comprises, in addition to the inverter circuit 35, a first rectification and filtering circuit 34 which, from an alternating voltage e, supplies a regulated direct voltage E supplying the switches T1 and T2.
  • the pulses supplied by the inverter circuit 35 are applied to the primary winding 36p of an isolation transformer 36 of the pulse type, the secondary winding 36s of which is connected to a rectification and filtering circuit 37 which supplies the required DC voltage V p .
  • the inverter circuit 35 comprises, as indicated above, at least two switches T1 and T2 produced by field effect transistors according to the metal-oxide technology more known by the English abbreviation of MOSFET transistors.
  • these transistors T1 and T2 each include in parallel a diode D1 for the transistor T1 and a diode D2 for the transistor T2, diodes including the anode is connected to the source S and the cathode connected to the drain D of the associated transistor.
  • the gate G of the transistor T1 is connected to the output 32-a of the control circuit 32 while the gate G of the transistor T2 is connected to the output 32-b of the control circuit 32.
  • the inverter circuit also includes a resonant circuit consisting of capacitors C1 and C2 and a coil L.
  • the capacitors C1 and C2 are connected in series between the drain D of the transistor T1 and the source S of the transistor T2 while the coil L is disposed in the primary circuit 36p of the transformer 36 and is connected on one side directly to the source of the transistor T1 and on the other side to the common point C of the capacitors C1 and C2 via the primary winding 36p of the transformer 36.
  • the inverter circuit may comprise only one capacitor, instead of the two capacitors C1 and C2, which would be connected for example to the negative terminal of the supply circuit 34.
  • the rectification and filtering circuit 37 is of the conventional type and has an output resistance R at the terminals of which the bias voltage V p is taken .
  • the control circuit 32 comprises a first logic AND circuit 40 which has two inputs on one of which are applied the variable frequency pulses F supplied by the circuit 31 while the other input is connected to a first delay circuit 41 whose delay is ⁇ 1.
  • the output of the AND circuit 40 is connected, on the one hand, to a bistable circuit 43 and, on the other hand, to the first delay circuit 41 as well as to a second delay circuit 42 whose delay is ⁇ 2.
  • the output corresponding to state 1 of the bistable circuit 43 is connected to one of the two inputs of a second logic AND circuit 44 while the output corresponding to state 0 is connected to one of the two inputs of a third AND circuit logic 45.
  • the second input of AND circuits 44 and 45 is connected to the output of the second delay circuit 42.
  • the purpose of these pulses of frequency F is to alternately control the transistors T1 and T2 by means of circuit 32 so as to create current pulses whose rectification and filtering in circuit 37 leads to the desired voltage V p between terminals 33-a and 33-b.
  • This curve 81 takes account of the linearity faults of the system while the curve 80 is a theoretical curve.
  • a bias voltage V p desired by the practitioner or by the device for controlling the radiological device corresponds to a numerical code N p which, applied to counter 31, leads the latter to supply pulses 70 and 70 '(figure 4-a) at frequency F according to the correspondence given by curve 81 of figure 3-a.
  • the pulse 70 controls the delay circuit 41 to end the opening signal 71 (figure 4-c) so that the AND circuit 40 closes for a time ⁇ 1.
  • the pulse 70 also controls the delay circuit 42 so that it provides a signal T'1 of duration ⁇ 2 (figure 4-b) which makes passing the circuits AND 44 and 45. Only the circuit AND 44, which receives the signal state 1 of the bistable circuit 43, provides a signal T'1 making the transistor T1 conductive at time t o (FIG. 4-d).
  • This signal T'1 makes and keeps the transistor T1 conductive and a current i1 (figure 4-d) says positive, flows in the transistor T1, the coil L, the primary winding 36p of the transformer 36, the capacitors C1 and C2 and the supply circuit 34 (in fact i1 / 2 in each capacitor).
  • This current i1 gives rise to a voltage V (figure 4-e) of rectangular shape at the terminals of the primary winding 36p and this results in a current I (t) (figure 4-f) in the secondary winding 36s of the transformer 36, current of identical appearance to the current i1 flowing in the primary winding.
  • the current i1 charges the capacitor C2 and discharges the capacitor C1 and their charging voltage is opposed to the circulation of the current i1 so that the latter is canceled at time t1, that is to say before the end of signal T'1.
  • the capacitor C2 then discharges while the capacitor C1 charges and a current i2 (figure 4-d), said to be negative, flows in the capacitors C1 and C2, the primary winding 36p, the coil L, the diode D1 and the supply circuit 34 (in fact i2 / 2 in each capacitor).
  • the signal T'1 ends by the effect of the delay circuit 42 introducing a delay ⁇ 2 so that the AND circuits 44 and 45 are blocked.
  • the delay circuit 41 After the time t2 and more precisely after a delay ⁇ 1 from the end of the signal 71 (figure 4-c), the delay circuit 41 provides a signal 71 'which turns the AND circuit 40 on.
  • a pulse 70 ' is supplied by the circuit 31 and its front edge controls the change of state of the bistable circuit 43, which goes to state 0 , as well as the resetting of the delay circuits 41 and 42.
  • This reset has the effect of terminating the signal 71 'and of supplying the signal T'2 which opens the AND circuits 44 and 45.
  • the bistable circuit 43 is at state 0 , only the AND circuit 45 provides a signal output on terminal 32-b and a pulse is applied to the control electrode of transistor T2 at time t ' o to make it conductive.
  • a current i'1 said to be negative, then flows in the transistor T2, the circuit 34, the capacitors C1 and C2 (in fact i'1 / 2 in each condenser), the primary winding 36p of the transformer 36 and the coil L.
  • This negative current gives rise to a negative voltage V (figure 4-e) of rectangular shape across the terminals of the primary winding 36p and it results in a current I (t) negative (figure 4-f) in the secondary winding 36s of the transformer 36, current of identical appearance to the current i'1 circulating in the primary winding.
  • the negative current i'1 charges the capacitor C1 and discharges the capacitor C2 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 C1 then discharges while the capacitor C2 charges and a positive current i'2 flows in the capacitors C1 and C2 (in fact i'2 / 2 in each capacitor), the primary winding 36p, the coil L, the diode D2 and the supply circuit 34.
  • This positive current gives rise to a positive rectangular voltage (FIG. 4-e) at the terminals of the primary winding 36p and, consequently, to a positive current I (t) (figure 4-f) in the secondary winding 36s.
  • the pulses which are thus created by the inverter circuit 35 are applied to the transformer 36 and are rectified and filtered in the circuit 37 and it appears at the terminals of the load resistor R a voltage V p corresponding to the frequency F determined by calibration.
  • the curves 80 'and 81' of the figure 4-b show the variations of the ratio V p / F according to the frequency F in correspondence with the curves 80 and 81 respectively of the figure 4-a. These curves and in particular the real curve 81 ′ resulting from the calibration are linear throughout the range.
  • the rectangular shape of the signals of the figure 4-e is due to the fact of the presence of the rectifying and filtering circuit 37 including / understanding diodes which, while becoming conducting, realize short-circuits.

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

Description

La présente invention concerne les dispositifs pour obtenir une tension continue dont la valeur est réglable dans une large gamme, lesdits dispositifs étant plus particulièrement adaptés à polariser un foyer d'un tube radiologique à une valeur choisie par le praticien mettant en oeuvre une installation radiologique. De tels dispositifs sont connus des documents US-A- 4, 541, 041 et GB-A- 2.045.019.The present invention relates to devices for obtaining a DC voltage whose value is adjustable over a wide range, said devices being more particularly adapted to polarize a focus of an X-ray tube to a value chosen by the practitioner implementing a radiological installation. Such devices are known from documents US-A-4, 541, 041 and GB-A-2,045,019.

Un tube radiologique 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.A radiological tube is generally constituted as a diode, that is to say by two electrodes, one of which, 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 par un courant électrique qui constitue la source d'électrons. Quand une 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.The cathode has a filament heated by an electric current which constitutes the source of electrons. When a 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.

Pour concentrer le faisceau d'électrons, une pièce métallique, appelée pièce de concentration, supportant le filament est isolée de ce dernier et portée à un potentiel négatif, dit de polarisation, par rapport audit filament. En outre, pour modifier la forme et donc la concentration du faisceau d'électrons, il est habituel de modifier ce potentiel de polarisation dans une large gamme, par exemple entre 300 et 3000 volts. Par ailleurs, il est à noter que la cathode est elle-même portée à une tension de l'ordre de -20 à -75 kilovolts par rapport à la masse, ce qui pose des problèmes d'isolement pour appliquer ce potentiel ou tension de polarisation.To concentrate the electron beam, a metal part, called a concentration part, supporting the filament is isolated from the latter and brought to a negative potential, called polarization, with respect to said filament. In addition, to modify the shape and therefore the concentration of the electron beam, it is usual to modify this polarization potential over a wide range, for example between 300 and 3000 volts. In addition, it should be noted that the cathode is itself brought to a voltage of the order of -20 to -75 kilovolts relative to the mass, which poses insulation problems to apply this potential or bias voltage.

L'invention concerne plus particulièrement un dispositif pour obtenir une tension de polarisation d'une pièce de concentration d'une cathode de tube à rayons X qui soit variable dans une large gamme de valeurs.The invention relates more particularly to a device for obtaining a bias voltage of a concentrating part of an X-ray tube cathode which is variable over a wide range of values.

De tels dispositifs sont connus et, à titre indicatif, la figure 1 donne le schéma de principe d'un dispositif de l'art antérieur. Il comprend un circuit d'alimentation 10 qui fournit une tension continue E régulée et réglable à partir d'une tension alternative fournie par le secteur. La tension E est appliquée aux bornes d'un circuit onduleur 11 qui comprend un circuit hâcheur 12 et un circuit de commande 14.Such devices are known and, for information, Figure 1 gives the block diagram of a device of the prior art. It includes a supply circuit 10 which supplies a DC voltage E regulated and adjustable from an AC voltage supplied by the sector. The voltage E is applied to the terminals of an inverter circuit 11 which comprises a chopping circuit 12 and a control circuit 14.

Le signal alternatif fourni par le circuit onduleur 11 est appliqué à un transformateur élévateur de tension 15 dont l'enroulement secondaire est connecté à un circuit de redressement et filtrage 16. Ce circuit 16 fournit une tension continue Vs qui est appliquée entre la pièce de concentration et le filament du tube à rayons X.The alternating signal supplied by the inverter circuit 11 is applied to a voltage step-up transformer 15, the secondary winding of which is connected to a rectification and filtering circuit 16. This circuit 16 provides a direct voltage V s which is applied between the piece of concentration and filament of the x-ray tube.

Il est à remarquer que la tension Vs étant difficile à mesurer du fait du fort potentiel de mode commun (20 à 75 kilovolts), il est préférable de mesurer la tension E qui lui est sensiblement proportionnelle et de la réguler. A cet effet, la tension E est mesurée par un diviseur résistif comportant les résistances R1 et R2 et le signal divisé est appliqué à un circuit convertisseur tension/fréquence 20 qui reçoit, par ailleurs, un signal Vref correspondant à la tension que l'on souhaite obtenir entre la pièce de concentration et le filament du tube à rayons X. Le circuit convertisseur 20 fournit des impulsions de fréquence variable et/ou de durée variable qui commandent les commutateurs du circuit d'alimentation 10 de manière à modifier la tension de sortie E et donc modifier la tension Vs pour obtenir Vs = Vref.It should be noted that the voltage V s being difficult to measure due to the high common mode potential (20 to 75 kilovolts), it is preferable to measure the voltage E which is substantially proportional to it and to regulate it. For this purpose, the voltage E is measured by a resistive divider comprising the resistors R1 and R2 and the divided signal is applied to a voltage / frequency converter circuit 20 which receives, moreover, a signal V ref corresponding to the voltage that the it is desired to obtain between the concentration piece and the filament of the x-ray tube. The converter circuit 20 supplies pulses of variable frequency and / or of variable duration which control the switches of the supply circuit 10 so as to modify the voltage of output E and therefore modify the voltage V s to obtain V s = V ref .

De manière classique, le circuit hâcheur 12 comporte, par exemple, deux transistors 21 et 22 dont les ouvertures et fermetures sont commandées par le circuit de commande 14.Conventionally, the chopper circuit 12 comprises, for example, two transistors 21 and 22, the openings and closings of which are controlled by the control circuit 14.

Le circuit de commande 14 est également un circuit convertisseur tension/fréquence semblable au circuit 20 mais dont la fréquence est fixe.The control circuit 14 is also a voltage / frequency converter circuit similar to the circuit 20 but whose frequency is fixed.

Les inconvénients de ce dispositif de l'art antérieur qui vient d'être décrit sont :

  • de nécessiter deux convertisseurs de puissance : le premier 20 pour réguler la tension E et le deuxième 14 pour l'onduler,
  • de commuter brutalement le courant dans les semiconducteurs, ce qui est source de parasites,
  • d'avoir une faible gamme de tensions de sortie car la tension E que l'on règle ne peut pas tendre vers zéro à cause des limitations en rapport cyclique du circuit hâcheur.
The disadvantages of this device of the prior art which has just been described are:
  • to require two power converters: the first 20 to regulate the voltage E and the second 14 to undulate it,
  • suddenly switching the current in the semiconductors, which is a source of noise,
  • to have a low range of output voltages because the voltage E which is regulated cannot tend towards zero because of the limitations in cyclic relation of the chopper circuit.

Le but de la présente invention est donc de réaliser un dispositif d'obtention d'une tension continue réglable quine présente pas les inconvénients précités.The object of the present invention is therefore to provide a device for obtaining an adjustable direct voltage which does not have the above-mentioned drawbacks.

L'invention concerne un dispositif d'obtention d'une tension continue réglable Vp caractérisé en ce qu'il comprend :

  • des moyens d'alimentation pour élaborer une tension continue E constante,
  • des moyens pour onduler ladite tension continue E de manière à obtenir des impulsions alternatives de fréquence F correspondant chacune à une quantité d'électricité constante d'une impulsion à la suivante,
  • un transformateur pour éléver la tension des impulsions alternatives,
  • des moyens pour redresser et filtrer lesdites impulsions alternatives élévées de manière à obtenir ladite tension continue Vp.
  • des moyens pour modifier la fréquence F desdites impulsions alternatives en fonction de la tension continue Vp que l'on souhaite obtenir.
The invention relates to a device for obtaining an adjustable direct voltage V p characterized in that it comprises:
  • supply means for developing a constant DC voltage E,
  • means for undulating said direct voltage E so as to obtain alternating pulses of frequency F each corresponding to a constant quantity of electricity from one pulse to the next,
  • a transformer to raise the voltage of the alternating pulses,
  • means for rectifying and filtering said high alternating pulses so as to obtain said direct voltage V p .
  • means for modifying the frequency F of said alternating pulses as a function of the DC voltage V p which it is desired to obtain.

Les moyens pour onduler ladite tension E comportent un circuit oscillant dont la fréquence de résonance est supérieure à la fréquence F.The means for undulating said voltage E comprise an oscillating circuit whose resonant frequency is greater than the frequency F.

La fréquence F est déterminée par étalonnage du dispositif en relevant la courbe Vp = f(F), courbe dont les caractéristiques sont enregistrées par un microprocesseur.The frequency F is determined by calibrating the device by taking the curve V p = f (F), curve whose characteristics are recorded by a microprocessor.

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 de principe d'un dispositif d'obtention d'une tension continue réglable selon l'art antérieur,
  • la figure 2 est un schéma de principe d'un dispositif d'obtention d'une tension continue réglable selon l'invention,
  • les figures 3-a et 3-b sont des diagrammes montrant d'une part une courbe d'étalonnage du dispositif et, d'autre part, la linéarité du dispositif selon l'invention.
  • les figures 4-a à 4-f sont des diagrammes permettant de comprendre le fonctionnement du dispositif selon l'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 block diagram of a device for obtaining an adjustable direct voltage according to the prior art,
  • FIG. 2 is a block diagram of a device for obtaining an adjustable direct voltage according to the invention,
  • the figures 3-a and 3-b are diagrams showing on the one hand a calibration curve of the device and, on the other hand, the linearity of the device according to the invention.
  • FIGS. 4-a to 4-f are diagrams making it possible to understand the operation of the device according to the invention,

Conformément au schéma fonctionnel de principe de la figure 2, le dispositif d'obtention d'une tension continue réglable selon l'invention comprend :

  • un microprocesseur 30 auquel est appliqué un signal de commande indiquant la valeur d'une tension continue Vp à obtenir et qui fournit un signal numérique Np indiquant une fréquence F caractéristique de la tension continue Vp à obtenir,
  • un compteur programmable 31 auquel est appliqué le signal numérique Np correspondant au signal Vp fourni par le microprocesseur 30 et qui fournit des impulsions de fréquence variable F selon la valeur de Np et donc de Vp,
  • un circuit de commande 32 auquel sont appliquées les impulsions de fréquence variable F et qui fournit sur ses sorties 32-a et 32-b des impulsions de commande des interrupteurs T1 et T2 d'un circuit onduleur 35, et
  • un circuit dit de puissance 33, comprenant le circuit onduleur 35, qui fournit sur ses bornes de sortie 33-a et 33-b la tension continue Vp.
In accordance with the functional block diagram of FIG. 2, the device for obtaining an adjustable direct voltage according to the invention comprises:
  • a microprocessor 30 to which a control signal is applied indicating the value of a direct voltage V p to be obtained and which supplies a digital signal N p indicating a frequency F characteristic of the direct voltage V p to be obtained,
  • a programmable counter 31 to which the digital signal N p corresponding to the signal V p supplied by the microprocessor 30 is applied and which supplies pulses of variable frequency F according to the value of N p and therefore of V p ,
  • a control circuit 32 to which the variable frequency pulses F are applied and which supplies on its outputs 32-a and 32-b control pulses for the switches T1 and T2 of an inverter circuit 35, and
  • a so-called power circuit 33, comprising the inverter circuit 35, which supplies on its output terminals 33-a and 33-b the direct voltage V p .

Le circuit de puissance 33 comprend, outre le circuit onduleur 35, un premier circuit de redressement et de filtrage 34 qui, à partir d'une tension alternative e, fournit une tension continue régulée E alimentant les interrupteurs T1 et T2. Les impulsions fournies par le circuit onduleur 35 sont appliquées à l'enroulement primaire 36p d'un transformateur d'isolement 36 de type impulsionnel dont l'enroulement secondaire 36s est connecté à un circuit de redressement et filtrage 37 qui fournit la tension continue requise Vp.The power circuit 33 comprises, in addition to the inverter circuit 35, a first rectification and filtering circuit 34 which, from an alternating voltage e, supplies a regulated direct voltage E supplying the switches T1 and T2. The pulses supplied by the inverter circuit 35 are applied to the primary winding 36p of an isolation transformer 36 of the pulse type, the secondary winding 36s of which is connected to a rectification and filtering circuit 37 which supplies the required DC voltage V p .

Le circuit onduleur 35 comprend, comme on l'a indiqué ci-dessus, au moins deux interrupteurs T1 et T2 réalisés par des transistors à effet de champ selon la technologie métal-oxyde plus connus sous l'abréviation anglo-saxonne de transistors MOSFET. De par construction, ces transistors T1 et T2 comportent en parallèle chacun une diode D1 pour le transistor T1 et une diode D2 pour le transistor T2, diodes dont l'anode est connectée à la source S et la cathode connectée au drain D du transistor associé. La grille G du transistor T1 est connectée à la sortie 32-a du circuit de commande 32 tandis que la grille G du transistor T2 est connectée à la sortie 32-b du circuit de commande 32.The inverter circuit 35 comprises, as indicated above, at least two switches T1 and T2 produced by field effect transistors according to the metal-oxide technology more known by the English abbreviation of MOSFET transistors. By construction, these transistors T1 and T2 each include in parallel a diode D1 for the transistor T1 and a diode D2 for the transistor T2, diodes including the anode is connected to the source S and the cathode connected to the drain D of the associated transistor. The gate G of the transistor T1 is connected to the output 32-a of the control circuit 32 while the gate G of the transistor T2 is connected to the output 32-b of the control circuit 32.

Le circuit onduleur comprend également un circuit résonant constitué de condensateurs C1 et C2 et d'une bobine L. Les condensateurs C1 et C2 sont connectés en série entre le drain D du transistor T1 et la source S du transistor T2 tandis que la bobine L est disposée dans le circuit primaire 36p du transformateur 36 et est connectée d'un côté directement à la source du transistor T1 et de l'autre côté au point commun C des condensateurs C1 et C2 par l'intermédiaire de l'enroulement primaire 36p du transformateur 36.The inverter circuit also includes a resonant circuit consisting of capacitors C1 and C2 and a coil L. The capacitors C1 and C2 are connected in series between the drain D of the transistor T1 and the source S of the transistor T2 while the coil L is disposed in the primary circuit 36p of the transformer 36 and is connected on one side directly to the source of the transistor T1 and on the other side to the common point C of the capacitors C1 and C2 via the primary winding 36p of the transformer 36.

Dans une variante connue, le circuit onduleur peut ne comporter qu'un seul condensateur, au lieu des deux condensateurs C1 et C2, qui serait connecté par exemple à la borne négative du circuit d'alimentation 34.In a known variant, the inverter circuit may comprise only one capacitor, instead of the two capacitors C1 and C2, which would be connected for example to the negative terminal of the supply circuit 34.

Le circuit de redressement et de filtrage 37 est de type classique et présente une résistance de sortie R aux bornes de laquelle est prise la tension de polarisation Vp.The rectification and filtering circuit 37 is of the conventional type and has an output resistance R at the terminals of which the bias voltage V p is taken .

Le circuit de commande 32 comprend un premier circuit ET logique 40 qui comporte deux entrées sur l'une desquelles sont appliquées les impulsions de fréquence variable F fournies par le circuit 31 tandis que l'autre entrée est connectée à un premier circuit retardateur 41 dont le retard est Θ₁. La sortie du circuit ET 40 est connectée, d'une part, à un circuit bistable 43 et, d'autre part, au premier circuit retardateur 41 ainsi qu'à un deuxième circuit retardateur 42 dont le retard est Θ₂.The control circuit 32 comprises a first logic AND circuit 40 which has two inputs on one of which are applied the variable frequency pulses F supplied by the circuit 31 while the other input is connected to a first delay circuit 41 whose delay is Θ₁. The output of the AND circuit 40 is connected, on the one hand, to a bistable circuit 43 and, on the other hand, to the first delay circuit 41 as well as to a second delay circuit 42 whose delay is Θ₂.

La sortie correspondant à l'état 1 du circuit bistable 43 est connectée à une des deux entrées d'un deuxième circuit ET logique 44 tandis que la sortie correspondant à l'état 0 est connectée à une des deux entrées d'un troisième circuit ET logique 45. La deuxième entrée des circuits ET 44 et 45 est connectée à la sortie du deuxième circuit retardateur 42.The output corresponding to state 1 of the bistable circuit 43 is connected to one of the two inputs of a second logic AND circuit 44 while the output corresponding to state 0 is connected to one of the two inputs of a third AND circuit logic 45. The second input of AND circuits 44 and 45 is connected to the output of the second delay circuit 42.

Le microprocesseur 30 réalise la fonction : N p = f (V p )

Figure imgb0001

c'est-à-dire qu'il donne pour chaque valeur de la tension de polarisation Vp, souhaitée par le praticien ou par le dispositif de commande, un code numérique, par exemple à huit chiffres ou digits qui, appliqué au compteur 31, conduit ce dernier à fournir des impulsions de fréquence F. Ces impulsions de fréquence F ont pour but de commander alternativement les transistors T1 et T2 par l'intermédiaire du circuit 32 de manière à créer des impulsions de courant dont le redressement et le filtrage dans le circuit 37 conduisent à la tension Vp souhaitée entre les bornes 33-a et 33-b.The microprocessor 30 performs the function: NOT p = f (V p )
Figure imgb0001

that is to say that it gives for each value of the bias voltage V p , desired by the practitioner or by the control device, a digital code, for example with eight digits or digits which, applied to the counter 31 , leads the latter to supply pulses of frequency F. The purpose of these pulses of frequency F is to alternately control the transistors T1 and T2 by means of circuit 32 so as to create current pulses whose rectification and filtering in circuit 37 leads to the desired voltage V p between terminals 33-a and 33-b.

En d'autres termes, le microprocesseur 30 et le compteur 31 réalisent la fonction F = f' (Vp), fonction qui est obtenue par étalonnage et dont l'allure est donnée par la courbe 81 de la figure 3-a. Cette courbe 81 tient compte des défauts de linéarité du système tandis que la courbe 80 est une courbe théorique.In other words, the microprocessor 30 and the counter 31 carry out the function F = f '(V p ), function which is obtained by calibration and whose pace is given by the curve 81 of the figure 3-a. This curve 81 takes account of the linearity faults of the system while the curve 80 is a theoretical curve.

Le fonctionnement du dispositif selon l'invention sera maintenant expliqué à l'aide de la figure 2 et des diagrammes des figures 3 et 4. A une tension de polarisation Vp souhaitée par le praticien ou par le dispositif de commande de l'appareil radiologique correspond un code numérique Np qui, appliqué au compteur 31, conduit ce dernier à fournir des impulsions 70 et 70' (figure 4-a) à la fréquence F selon la correspondance donnée par la courbe 81 de la figure 3-a. Ces impulsions ont par exemple, une fréquence de 30 kilohertz pour obtenir Vp = 3000 volts et une durée d'une microseconde environ. Si l'on suppose que le circuit retardateur 41 fournit un signal d'ouverture 71, l'impulsion 70 commande le changement d'état du circuit bistable 43 qui passe, par exemple, à l'état 1. L'impulsion 70 commande le circuit retardateur 41 pour terminer le signal d'ouverture 71 (figure 4-c) de sorte que le circuit ET 40 se ferme pendant un temps Θ₁. L'impulsion 70 commande également le circuit retardateur 42 pour qu'il fournisse un signal T'1 de durée Θ₂ (figure 4-b) qui rend passant les circuits ET 44 et 45. Seul le circuit ET 44, qui reçoit le signal de l'état 1 du circuit bistable 43, fournit un signal T'1 rendant conducteur le transistor T1 au temps to (figure 4-d).The operation of the device according to the invention will now be explained using FIG. 2 and the diagrams of FIGS. 3 and 4. At a bias voltage V p desired by the practitioner or by the device for controlling the radiological device corresponds to a numerical code N p which, applied to counter 31, leads the latter to supply pulses 70 and 70 '(figure 4-a) at frequency F according to the correspondence given by curve 81 of figure 3-a. These pulses have for example a frequency of 30 kilohertz to obtain V p = 3000 volts and a duration of about one microsecond. If it is assumed that the delay circuit 41 provides an opening signal 71, the pulse 70 controls the change of state of the bistable circuit 43 which passes, for example, to state 1. The pulse 70 controls the delay circuit 41 to end the opening signal 71 (figure 4-c) so that the AND circuit 40 closes for a time Θ₁. The pulse 70 also controls the delay circuit 42 so that it provides a signal T'1 of duration Θ₂ (figure 4-b) which makes passing the circuits AND 44 and 45. Only the circuit AND 44, which receives the signal state 1 of the bistable circuit 43, provides a signal T'1 making the transistor T1 conductive at time t o (FIG. 4-d).

Ce signal T'1 rend et maintient conducteur le transistor T1 et un courant i₁ (figure 4-d) dit positif, circule dans le transistor T1, la bobine L, l'enroulement primaire 36p du transformateur 36, les condensateurs C1 et C2 et le circuit d'alimentation 34 (en fait i₁/2 dans chaque condensateur).This signal T'1 makes and keeps the transistor T1 conductive and a current i₁ (figure 4-d) says positive, flows in the transistor T1, the coil L, the primary winding 36p of the transformer 36, the capacitors C1 and C2 and the supply circuit 34 (in fact i₁ / 2 in each capacitor).

Ce courant i₁ donne naissance à une tension V (figure 4-e) de forme rectangulaire aux bornes de l'enroulement primaire 36p et il en résulte un courant I(t) (figure 4-f) dans l'enroulement secondaire 36s du transformateur 36, courant d'allure identique au courant i₁ circulant dans l'enroulement primaire.This current i₁ gives rise to a voltage V (figure 4-e) of rectangular shape at the terminals of the primary winding 36p and this results in a current I (t) (figure 4-f) in the secondary winding 36s of the transformer 36, current of identical appearance to the current i₁ flowing in the primary winding.

Le courant i₁ charge le condensateur C2 et décharge le condensateur C1 et leur tension de charge s'oppose à la circulation du courant i₁ de sorte que ce dernier s'annule au temps t₁, c'est-à-dire avant la fin du signal T'1. Le condensateur C2 se décharge ensuite tandis que le condensateur C1 se charge et un courant i₂ (figure 4-d), dit négatif, circule dans les condensateurs C1 et C2, l'enroulement primaire 36p, la bobine L, la diode D1 et le circuit d'alimentation 34 (en fait i₂/2 dans chaque condensateur).The current i₁ charges the capacitor C2 and discharges the capacitor C1 and their charging voltage is opposed to the circulation of the current i₁ so that the latter is canceled at time t₁, that is to say before the end of signal T'1. The capacitor C2 then discharges while the capacitor C1 charges and a current i₂ (figure 4-d), said to be negative, flows in the capacitors C1 and C2, the primary winding 36p, the coil L, the diode D1 and the supply circuit 34 (in fact i₂ / 2 in each capacitor).

Ce courant négatif donne naissance à une tension rectangulaire négative (figure 4-e) aux bornes de l'enroulement primaire 36p et, par voie de conséquence, à un courant I(t) (figure 4-f) négatif dans l'enroulement secondaire 53. Lorsque le courant i₂ s'annule, l'impulsion est terminée.This negative current gives rise to a negative rectangular tension (figure 4-e) at the terminals of the primary winding 36p and, consequently, to a negative current I (t) (figure 4-f) in the secondary winding 53. When the current i₂ is canceled, the pulse is ended.

Avant le temps t₂, le signal T'1 prend fin par l'effet du circuit retardateur 42 introduisant un retard Θ₂ de sorte que les circuits ET 44 et 45 sont bloqués.Before time t₂, the signal T'1 ends by the effect of the delay circuit 42 introducing a delay Θ₂ so that the AND circuits 44 and 45 are blocked.

Après le temps t₂ et plus précisément après un retard Θ₁ à compter de la fin du signal 71 (figure 4-c), le circuit retardateur 41 fournit un signal 71' qui rend passant le circuit ET 40.After the time t₂ and more precisely after a delay Θ₁ from the end of the signal 71 (figure 4-c), the delay circuit 41 provides a signal 71 'which turns the AND circuit 40 on.

Après un temps variable défini par la fréquence F, une impulsion 70' est fournie par le circuit 31 et son front avant commande le changement d'état du circuit bistable 43, qui passe à l'état 0, ainsi que la remise à zéro des circuits retardateurs 41 et 42.After a variable time defined by the frequency F, a pulse 70 'is supplied by the circuit 31 and its front edge controls the change of state of the bistable circuit 43, which goes to state 0 , as well as the resetting of the delay circuits 41 and 42.

Cette remise à zéro a pour effet de terminer le signal 71' et de fournir le signal T'2 qui ouvre les circuits ET 44 et 45. Comme le circuit bistable 43 est à l'état 0, seul le circuit ET 45 fournit un signal de sortie sur la borne 32-b et une impulsion 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, le circuit 34, les condensateurs C1 et C2 (en fait i'₁/2 dans chaque condensateur), l'enroulement primaire 36p du transformateur 36 et la bobine L. Ce courant négatif donne naissance à une tension V négative (figure 4-e) de forme rectangulaire aux bornes de l'enroulement primaire 36p et il en résulte un courant I(t) négatif (figure 4-f) dans l'enroulement secondaire 36s du transformateur 36, courant d'allure identique au courant i'₁ circulant dans l'enroulement primaire.This reset has the effect of terminating the signal 71 'and of supplying the signal T'2 which opens the AND circuits 44 and 45. As the bistable circuit 43 is at state 0 , only the AND circuit 45 provides a signal output on terminal 32-b and a pulse is applied to the control electrode of transistor T2 at time t ' o to make it conductive. A current i'₁, said to be negative, then flows in the transistor T2, the circuit 34, the capacitors C1 and C2 (in fact i'₁ / 2 in each condenser), the primary winding 36p of the transformer 36 and the coil L. This negative current gives rise to a negative voltage V (figure 4-e) of rectangular shape across the terminals of the primary winding 36p and it results in a current I (t) negative (figure 4-f) in the secondary winding 36s of the transformer 36, current of identical appearance to the current i'₁ circulating in the primary winding.

Le courant i'₁ négatif charge le condensateur C1 et décharge le condensateur C2 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 C1 se décharge ensuite tandis que le condensateur C2 se charge et un courant i'₂ positif circule dans les condensateurs C1 et C2 (en fait i'₂/2 dans chaque condensateur), l'enroulement primaire 36p, la bobine L, la diode D2 et le circuit d'alimentation 34. Ce courant positif donne naissance à une tension rectangulaire positive (figure 4-e) aux bornes de l'enroulement primaire 36p et, par voie de conséquence, à un courant I(t) positif (figure 4-f) dans l'enroulement secondaire 36s. Lorsque le courant i'₂ s'annule, l'impulsion est terminée.The negative current i'₁ charges the capacitor C1 and discharges the capacitor C2 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 C1 then discharges while the capacitor C2 charges and a positive current i'₂ flows in the capacitors C1 and C2 (in fact i'₂ / 2 in each capacitor), the primary winding 36p, the coil L, the diode D2 and the supply circuit 34. This positive current gives rise to a positive rectangular voltage (FIG. 4-e) at the terminals of the primary winding 36p and, consequently, to a positive current I (t) (figure 4-f) in the secondary winding 36s. When the current i'₂ is canceled, the pulse is ended.

Les impulsions qui sont ainsi créées par le circuit onduleur 35 sont appliquées au transformateur 36 et sont redressées et filtrées dans le circuit 37 et il apparaît aux bornes de la résistance de charge R une tension Vp correspondant à la fréquence F déterminée par étalonnage.The pulses which are thus created by the inverter circuit 35 are applied to the transformer 36 and are rectified and filtered in the circuit 37 and it appears at the terminals of the load resistor R a voltage V p corresponding to the frequency F determined by calibration.

Cette relation entre la fréquence F et la tension Vp résulte du fait que la charge électrique contenue dans chaque impulsion (figures 4-d et 4-f) est toujours la même quel que soit le point de fonctionnement à condition que la fréquence F soit inférieure à la fréquence du circuit résonant du circuit onduleur, ce qui signifie que le circuit onduleur est du type hyporésonant impulsionnel.This relation between the frequency F and the voltage V p results from the fact that the electric charge contained in each pulse (figures 4-d and 4-f) is always the same whatever the point of operation provided that the frequency F is less than the frequency of the resonant circuit of the inverter circuit, which means that the inverter circuit is of the pulse hyporesonance type.

En effet, la charge électrique Q d'une impulsion (figure 4-d) est donnée par :

Figure imgb0002

avec
   E la tension d'alimentation,
   V la tension aux bornes de l'enroulement primaire 36p,
Z= L/C
Figure imgb0003
l'impédance du circuit résonnant,
   avec C = C1 + C2,
T= 2 π LC
Figure imgb0004

on en déduit Q = 2 CE c'est-à-dire une constante si E et C sont constants, ce qui est le cas car le circuit d'alimentation 34 fournit une tension régulée et la capacité C est fixée par construction.Indeed, the electric charge Q of a pulse (figure 4-d) is given by:
Figure imgb0002

with
E the supply voltage,
V the voltage across the primary winding 36p,
Z = L / C
Figure imgb0003
the impedance of the resonant circuit,
with C = C1 + C2,
T = 2 π LC
Figure imgb0004

we deduce Q = 2 CE that is to say a constant if E and C are constant, which is the case because the supply circuit 34 provides a regulated voltage and the capacitance C is fixed by construction.

Or le courant Ir qui circule dans la résistance de charge R est donné par : I r = Q x F

Figure imgb0005

de sorte que la tension Vp = RIr = R x Q x F, ce qui signifie que Vp est proportionnel à F car R et Q sont des constantes. Ceci correspond à la courbe en pointillés 80 de la figure 4-a. Cependant, en pratique, le phénomène n'est pas parfaitement linéaire et la courbe réelle est celle référencée 81. Pour que le dispositif selon l'invention fonctionne selon la courbe 81, il est nécessaire de réaliser un étalonnage en utilisant au moins deux points de fonctionnement, par exemple ceux définis par A et B sur la courbe 81.However the current I r which circulates in the load resistance R is given by: I r = Q x F
Figure imgb0005

so that the voltage V p = RI r = R x Q x F, which means that V p is proportional to F because R and Q are constants. This corresponds to the dotted curve 80 of the figure 4-a. However, in practice, the phenomenon is not perfectly linear and the actual curve is that referenced 81. In order for the device according to the invention to operate according to curve 81, it is necessary to carry out a calibration using at least two points of operation, for example those defined by A and B on curve 81.

Les courbes 80' et 81' de la figure 4-b montrent les variations du rapport Vp/F en fonction de la fréquence F en correspondance avec les courbes 80 et 81 respectivement de la figure 4-a. Ces courbes et notamment la courbe réelle 81' résultant de l'étalonnage est linéaire dans toute la gamme.The curves 80 'and 81' of the figure 4-b show the variations of the ratio V p / F according to the frequency F in correspondence with the curves 80 and 81 respectively of the figure 4-a. These curves and in particular the real curve 81 ′ resulting from the calibration are linear throughout the range.

Dans la description du fonctionnement du circuit onduleur 35, on a indiqué que les courants i₁, i₂, i'₁ et i'₂ circulaient dans les condensateurs C1 et C2 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 C1 et l'autre moitié vers la branche contenant le condensateur C2.In the description of the operation of the inverter circuit 35, it was indicated that the currents i₁, i₂, i'₁ and i'₂ circulated in the capacitors C1 and C2 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 C1 and the other half towards the branch containing the capacitor C2.

La forme rectangulaire des signaux de la figure 4-e est due au fait de la présence du circuit de redressement et de filtrage 37 comportant des diodes qui, en devenant conductrices, réalisent des court-circuits.The rectangular shape of the signals of the figure 4-e is due to the fact of the presence of the rectifying and filtering circuit 37 including / understanding diodes which, while becoming conducting, realize short-circuits.

Claims (3)

  1. A device for producing a variable DC voltage Vp for the concentration member of the cathode of an x-ray tube, comprising:
    - supply means (33) for deriving a constant continuous voltage E,
    - means (35) for undulating said continuous voltage E in such a manner as to obtain alternating pulses with a frequency F each corresponding to a quantity of electricity which is constant from one pulse to the next one, said means (35) consisting of an oscillating circuit whose resonant frequency is greater than the frequency F,
    - a transformer (36) for increasing the voltage of the alternating pulses,
    - means (37) for rectifying and filtering the said increased alternating pulses in such a manner as to obtain the said continuous voltage Vp,
    - means for modifying of the frequency F of the said alternating pulses as a function of the continuous voltage Vp which it is desired to obtain,
    - means (31) for determining by calibration the frequency F of the said pulses as a function of the voltage Vp to be obtained,
    - means (32) for deriving control pulses at the frequency F from information as regards the value of the said frequency F, said pulses being applied to the said means for undulating said continuous voltage E.
  2. The device as claimed in claim 1, characterized in that the means for deriving control pulses at the frequency F comprise:
    - a count circuit (31) which furnishes pulses with the frequency F, and
    - a logic circuit (32) which furnishes signals for control of the means for undulating the voltage E whose duration is greater than half a cycle but less than the said resonance cycle and whose repetition cycle is at the most equal to the said resonance cycle.
  3. The device as claimed in claim 2, characterized in that the logic circuit (32) comprises:
    - a first AND circuit (40) of which one of the two inputs is connected with the output of the count circuit (31),
    - a bistable circuit (43) whose control input is connected with the output of the first AND circuit (40) in such a manner as to change in state responsive to each signal furnished by the latter,
    - a second AND circuit (44) of which one of the two inputs is connected with the output of the bistable circuit (43) corresponding to the 1 state
    - a third AND circuit (45) of which one of the two inputs is connected with the output of the bistable circuit (43) corresponding to the 0 state,
    - a first delay circuit (41) of which the input is connected with the output of the first AND circuit (40) and of which the output is connected with the second input of the first AND circuit (40), and
    - a second delay circuit (42) whose input is connected with the output of the first AND circuit (40) and whose output is connected with the other input of the second and third AND circuits (44 and 45).
EP91402248A 1990-08-14 1991-08-14 Device for obtaining of an adjustable d.c. voltage Expired - Lifetime EP0471625B1 (en)

Applications Claiming Priority (2)

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FR9010348 1990-08-14
FR9010348A FR2665999B1 (en) 1990-08-14 1990-08-14 DEVICE FOR OBTAINING AN ADJUSTABLE CONTINUOUS VOLTAGE.

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FR2768241B1 (en) * 1997-09-10 1999-12-03 Ge Medical Syst Sa DEVICE AND METHOD FOR OPTIMALLY CONTROLLED CONTROL OF A TRANSISTOR CONVERTER
JP3673075B2 (en) * 1998-03-09 2005-07-20 新電元工業株式会社 Switching power supply
JP3322217B2 (en) * 1998-07-21 2002-09-09 株式会社豊田自動織機 Inverter
EP1238195B1 (en) * 1999-12-17 2005-03-23 Carl Maria Prof. Dr. Fleck Controllable ignition circuit
JP5382139B2 (en) * 2009-12-28 2014-01-08 トヨタ自動車株式会社 Power supply
DE102020212085A1 (en) * 2020-09-25 2022-03-31 Siemens Healthcare Gmbh High voltage control system for x-ray applications, x-ray generation system and high voltage control method

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JPS5753100A (en) * 1980-09-13 1982-03-29 Toshiba Corp X-ray equipment
FR2507842A1 (en) * 1981-06-12 1982-12-17 Gen Equip Med Sa SEMICONDUCTOR VOLTAGE REGULATOR AND RADIOLOGY GENERATOR COMPRISING SUCH A REGULATOR
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JP2707465B2 (en) * 1989-06-29 1998-01-28 スタンレー電気株式会社 Inverter device

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FR2665999A1 (en) 1992-02-21
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US5243509A (en) 1993-09-07
EP0471625A1 (en) 1992-02-19
DE69101476T2 (en) 1994-08-11

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