DE1961621A1 - High voltage generator for X-ray diagnostic apparatus - Google Patents

Description

High voltage generator for X-ray diagnostic apparatus

The invention relates to a high-voltage generator for X-ray diagnostic apparatus, which has a high-voltage transformer with at least one primary winding connected to the network and at least one secondary winding that forms the X-ray tube feeds, and contains setting means for the high voltage on the X-ray tube.

High-voltage generators of this type are known in which the high-voltage transformer is used to set the high voltage designed as a variable transformer or a separate variable transformer is connected upstream of the high-voltage transformer. Because of the mechanical parts to be adjusted, the setting or regulation of the high voltage is at a certain level Delay connected, which is disruptive in certain operating modes, e.g. in initial load operation. In addition, the Variable transformer a complex component »

It is also already known, instead of a variable transformer in the primary circuit of the high-voltage transformer accordingly to switch on the desired high voltage resistors via contactors. For almost continuous adjustment or regulation the high voltage are relatively many contactors required, which one due to their mechanical contacts Are subject to wear and tear.

It is also already known to connect an intermediate transformer upstream of the high-voltage transformer, through which the primary voltage of the high voltage transformer is stepped up

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and a grid-controlled one in the secondary circuit of the intermediate transformer To turn on the electron tube in the course of a rectifier arrangement, through which the entire current in this Circle flows. The high voltage can be set or changed by changing the control voltage of this electron tube. be managed. Since the electron tube acts as a variable resistance, it may become a considerable one Power dissipation implemented, so that the thermal demands on this tube are high and this tube is therefore proportionate is expensive. In addition, the control of this tube must be done with a considerable control power, so that a great effort is required for the control means of this tube.

The object of the invention is to create a high-voltage generator of the type mentioned at the outset, in which the setting or regulation of the high voltage without mechanical parts, ie • takes place without delay, and in which the on the actuating means for the high voltage converted power is low, so that the effort for the adjusting means is small.

The object is achieved according to the invention in that in Primary circuit of the Hoefaspanmingstransformators in per se known Way a GleicJirichtergruppe is switched on in a bridge arrangement, in whose zero branch the setting means for the High voltage, consisting of a DC voltage source and electronic control means for setting the terminal voltage this DC voltage source is arranged such that the DC voltage source counteracts the rectifier voltage. The voltage across the primary winding of the high-voltage transformer corresponds to the difference between the supply voltage of the high-voltage transformer (mains voltage) and the voltage of the DC voltage source. Is the The voltage of the DC voltage source is zero, i.e. the DC

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The rectifier is short-circuited, so · the full supply voltage is present the primary winding. If the voltage of the DC voltage source is the same as the supply voltage, then there is none on the primary winding Tension. The high voltage can thus be set or regulated by changing the voltage of the DC voltage source will. The circuit complexity for this can be kept low.

An expedient embodiment of the invention consists in that the input of a sieve chain is connected to the rectifier, the output of which is connected to an electronic switch is connected, which by means of a control device with one of the desired size of the high voltage corresponding Duty cycle can be switched on and off. The power loss converted at the electronic switch is small because the electronic switch does not act as a variable resistor, so that the expense for the electronic switch and its control is little. If the high voltage is to be regulated, it is advisable to use the control device to control the automatic setting of the duty cycle from a setpoint / actual value comparison arrangement.

Further details of the invention emerge from the following Description of an embodiment based on the drawing.

The high-voltage generator shown in the drawing contains a three-phase high-voltage transformer with three primary windings 1, which are fed from the three-phase network and connected to a three-phase rectifier bridge 2. Of the The output of the rectifier bridge 2 is connected to the input of a filter chain 3, the output of which is connected to a thyristor 4 can be short-circuited. In parallel with the thyristor 4, the series connection of a capacitor 5 and a thyristor 6 is

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switches. The series circuit of a diode 7 is located between the cathode of the thyristor 4 and the anode of the thyristor 6 and an inductance 8. The control electrodes of the thyristors 4 and 6 are connected to a control generator 9.

The high-voltage transformer has two groups 10 and 11 of secondary windings, the three-phase rectifier bridges 12 and 13 dine. The rectifier bridges 12 and 13 are over

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an ammeter 18- connected in series with one another and supply the high voltage for an X-ray tube 14. A value corresponding to the actual value of the high voltage at the X-ray tube 14 Voltage is tapped off at a voltage divider 15, this one Voltage is a voltage corresponding to the setpoint value of the high voltage, which is applied to a voltage divider 16, which is fed by a DC voltage source 17 is tapped thus a voltage which corresponds to the deviation of the high voltage applied to the X-ray tube 14 from the nominal value.

Before the X-ray tube 14 is switched on, the Thyristor 6 ignited by a control pulse from the control generator 9. This charges the capacitor 5 until the Current through the thyristor 6 falls below the holding current. At this moment the thyristor 6 goes out and the charging of the capacitor 5 is terminated. The thyristor 4 is now ignited by a pulse from the control generator 9 and short-circuits the output of the sieve chain 3. As a result, high voltage is applied to the X-ray tube 14. The capacitor 5 discharges through the working section of the thyristor 4, the diode 7 and the inductance 8. When the maximum is reached of the discharge current causes the inductance 8 to charge the capacitor 5 with a voltage that corresponds to the voltage on Output of the sieve chain 3 is opposite. The diode 7 prevents oscillation back, so that the capacitor 5 with this voltage remains charged.

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After a time which corresponds to the setpoint value of the high voltage on the X-ray tube 14, the thyristor 6 is ignited again. As a result, the voltage of the capacitor 5 is applied to the working path of the thyristor 4. Since this tension is the Output voltage of the sieve chain 3 is opposite, is this causes the thyristor 4 to be extinguished. The condenser 5, after it has discharged via the thyristor 4, is again with one of the output voltage via the thyristor 6 the sieve chain 3 charged until the holding current of the thyristor 6 and the thyristor 6 is deleted. After a time which corresponds to the setpoint value for the high voltage on the X-ray tube 14, the Thyristor 4 from the control generator 9 again an ignition pulse and the game described is repeated.

The switching elements 3 to 8 form a DC voltage source, whose terminal voltage is opposite to the voltage of the rectifier bridge 2. At the entrance of the sieve chain 3 arises a voltage, the level of which depends on the duty cycle of the thyristor controller connected to the output of the filter chain 3. By changing the duty cycle of the thyristor 4, i.e. by changing the ratio of the times in which the thyristor 4 is conductive, at the times when it is blocked, this voltage can be changed. Since the the primary windings 1 lying voltage from the difference between the mains voltage and the output voltage of the rectifier bridge 2 depends, thus by changing the duty cycle of the thyristor 4, the high voltage at the X-ray tube 14 can be changed. This duty cycle is determined by the control generator 9, that of the control electrode the thyristor 4 to ignite an ignition pulse and the control electrode of the thyristor 6 to extinguish the thyristor 4 a ZUndimpuls supplies. The control generator 9 is based on the difference between the actual value and the setpoint value of the high voltage of the X-ray tube 14 in the sense of regulating the high voltage

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The load current in the primary circuit of the high voltage transformer flows through the thyristor 4, Since this thyristor acts as an electronic switch, the power dissipated on it is low, so that the effort for its control is low. The arrangement works practically inertia, so that the high voltage at the x-ray tube 14 is regulated with little delay.

Should only one setting instead of regulating the high voltage take place, the control generator 9 can be actuated according to the high voltage desired in each case Control means for changing the duty cycle of the thyristor 4 can be influenced. The voltage divider 15 is in superfluous in this case.

The frequency of the control pulses supplied by the control generator 9 is expediently chosen so high that the ripple the voltage at the input of the sieve chain 3, which is caused by the periodic ignition and extinction of the thyristor 4 is practically irrelevant.

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Claims (5)

- 7 claims yU high voltage generator for X-ray diagnostic apparatus, the one high-voltage transformer with at least one primary winding connected to the network and at least one secondary winding, which feeds the X-ray tube and contains setting means for the high voltage, characterized that in the primary circuit of the high-voltage transformer in a known manner a rectifier group (2) is switched on in a bridge arrangement, in whose zero branch the setting means for the high voltage, consisting from a DC voltage source (3 to 8) and electronic control means (9) for setting the terminal voltage this DC voltage source is arranged such that the DC voltage source counteracts the rectifier voltage . 2. High voltage generator according to claim 1, characterized in that that the input of a sieve chain (3) is connected to the rectifier, the output of which is connected to an electronic Switch (4) -connected, by means of a control device (5 to 9) with one of the desired sizes High voltage corresponding duty cycle can be switched on or off. 3. High-voltage generator according to claim 2, characterized in that daes the control device for the automatic setting of the pulse duty factor of a setpoint / actual value comparison arrangement (15 to 17) is controlled, 4. High-voltage generator according to claim 2 or 3, characterized in that the electronic switch (4) an electronic extinguishing switch (6) is connected in parallel, when - 8 109824/0945 Closure, an extinguishing voltage source (5) can be connected to the working path of the electronic switch and a Control generator (9) is connected to the control electrode of the electronic switch (4) and the extinguishing switch (6), which supplies these switches with ignition or extinguishing pulses, the spacing of which corresponds to the desired high voltage level » 5. High voltage generator according to claim 4, characterized in that that a capacitor (5) is used as the quenching voltage source, which is used when the electronic switch is closed (4) Chargeable via coupling means (7, 8) to a voltage suitable for erasing the electronic switch and via the LÖach switch (6) to delete the electronic switch with this voltage can be connected to the working section. 109824/0945