JPS60221993A - High voltage dividing circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

Relationship to Related Applications This invention is disclosed in pending U.S. patent application Ser. No. 564,538, Ser.
No. 3, No. 564,582, No. 564,622, and No. 564,621. BACKGROUND OF THE INVENTION This invention relates generally to high voltage generators for X-ray machines, and more specifically to voltage divider circuits containing typical low voltages for controlling X-ray generators. Zuru. When generating and utilizing X11, it is common to select specific voltage and current levels to suit the particular application or procedure at hand. For example, in the field of medical xm imaging, typical voltage levels used in common radiography are 50
For fluorography, the voltage is more often in the range 50 to 120 kV, and for X-rays used in mammography, 24 to 50 kV.
There is a stronger possibility that there is a range C of 0 kV. Similarly, the level of applied current is 0.1111A for fluorescence photography.
It can vary up to 1250 mA for radiographic procedures consisting of. Traditionally, these voltage and current levels have been controlled by a circuit arrangement 4 that allows the operator to set the desired kVp and IA settings. Because of equipment variations that may occur during exposure, such as changes in the square tube, line voltage changes, or filament temperature changes, the kVp and III
It was not possible to precisely maintain the value of A at the desired level. Manufacturers of X-ray generators have traditionally anticipated possible changes and determined kVp and! Efforts have been made to incorporate circuit design features that compensate for these variations in a manner sufficient to keep IIA within scheduled tolerances. Recent developments have proceeded along the lines of closed-loop return systems that seem to overcome the drawbacks of open-loop systems discussed above. One such scheme is for a closed loop feedback device to control the mA of the x-ray generator. Such a device is described in pending US patent application Ser. No. 375,088. In the field of kVp control, it is possible to achieve satisfactory results by sensing the output voltage and using the feedback signal to directly modulate the output voltage with a fast and effective response that maintains a predetermined voltage level. No closed loop method has been developed. A conventional approach to maintaining a substantially constant voltage level over possible variations in the line is to use a so-called volt pack, a variable input/output transformer driven by a motor to provide a variable output. The main disadvantage of bolt packs is that they are relatively slow in operation. That is, the bolt pack has a response time of about 1 second. For this reason, the volt pack control is only used to set the correct voltage at the start of the exposure and not adjusted afterwards except during long exposures (fluoroscopic exposures). In comparison, the desired response time for an X-ray generator is in the millisecond range, capable of delivering short, well-defined power pulses for a variety of procedures and applications. It is. For example, the rise time is very fast, i.e. short, say 1 millisecond,
It has a short flat peak for exposure such as 1 millisecond,
It is also desirable to obtain a high voltage pulse with a fast fall time. Therefore, correction needs to be made within less than 1 millisecond. It is known to use an inverter in an X-ray generation circuit to supply alternating current to the primary side of a high voltage transformer. However, transistors have generally not been used for this purpose, primarily because they are relatively difficult to control. Rather, it was the thyristor that was used as the switching element for this purpose. Although thyristors are generally considered robust and relatively easy to control, they have the inherent drawback of requiring the use of forced commutation circuits. Not only does this require extra components, but the added capacitance tends to substantially slow down the response time of the circuit. For example, when using thyristor inverters, it is difficult to obtain short high voltage pulses in the 1 millisecond range while maintaining a reasonable level of repeatability. When controlling the AC output from the inverter, there are many possible methods for controlling the supply of DC voltage to the inverter. To name a few, there are phase-controlled rectifiers, transistor series or parallel regulators, and semiconductor switching DC voltage controllers. Among these, the semiconductor switching device is commonly called a chopper, and can control DC voltage more efficiently and with faster response than other methods. However, since it requires significant P-wave action in a DC circuit, the response time is much slower when operating from a fully closed loop voltage regulated inverter power supply. Such indirect methods introduce more circuit losses due to forced commutation circuits that must be used to handle the large voltage and current fluctuations required during X-ray generator operation. Ru. Furthermore, it will be appreciated that in such an arrangement the power delivered by the inverter is processed twice, once by the DC voltage controller and once by the inverter. In addition to the inherent variations in sources and loads, accidental and unplanned conditions can occur on the high pressure side, such as arcing in an X-ray tube, which, if not controlled, can cause component damage. . Moreover, with any control circuit, there is a risk of malfunction or failure of the control circuit, which, if not detected and addressed, may lead to undesirable consequences on the output of the control circuit or within the control circuit itself. Therefore, no matter what control or performance-enhancing features are added to a conventional device, associated monitoring and adjustment functions must be provided to effectuate such improvements. For this reason, in the field of X-ray generators used in medical diagnostic equipment, there has been a reluctance to make significant changes to conventional systems. It has long been a desire of manufacturers of X-ray generators to have closed-loop voltage feedback devices, but the typical conditions of X-ray applications (i.e., 0.1 to 1250 mA17)
Due to the variable load in the range, the variable voltage in the range from 24 to 150 kV, and the low mΔ of 0.25, such a suitable device was difficult to make. Good ripple control, high reproducibility, good linearity and fast rise times to control the shape of the power waveform, short steady-state exposure times, and low fall. The task is made all the more difficult due to various performance requirements (such as short time). To obtain a representative signal on the high voltage side of an x-ray generator, it is common to use a voltage divider or shunt circuit. A common method of shunt is to use a series of resistors to reduce the voltage level. A problem with this method is that the effects of stray capacitance from the resistor to the walls of the transformer cell typically distort the measurements. This happens even when using a resistor with very low inductance. Because of these constraints, a more common method is to use parallel resistors and
However, this method requires a considerable number of components. The number of resistors and :I capacitors required to reduce the output of ,000 volts can be as high as 100 elements, which takes up space and increases the cost of the device. , a primary object of this invention is to provide an improved x-ray generator having means for controlling the output voltage applied to an x-ray tube via a closed loop circuit. Another aspect of the invention is to provide the x-ray generator with a closed-loop voltage feedback loop that responds quickly and accurately to input voltage and load variations to maintain the desired voltage output. The purpose of is to generate a voltage pulse with a fast rise time followed by a relatively short exposure time of nearly constant voltage, followed by a relatively fast fall time over a wide range of operating conditions. It is an object of the present invention to provide an X-ray generator with a control circuit that is sufficiently fast and responsive.Another object of the present invention is to provide an X-ray generator with a control circuit that has good transient response, is economically manufacturable, and is easy to use. The object of the present invention is to provide an effective high-voltage shunt circuit in an X-ray generating device. The above and other objects, features and advantages will be better understood from the following description of the drawings. Briefly, in one aspect of this invention, the xm light benshi station is
It has a high voltage feedback from the X-ray tube and has control circuitry responsive to this feedback to control the operation of the system's inverter in a manner that maintains a predetermined voltage level to the tube. In this way, the feedback signal is applied to directly control the output of the inverter, allowing the device to respond quickly and accurately to variations in line voltage and load. Cooperative components such as high voltage transformer, high voltage output filter and high voltage shunt circuit match the fast response characteristics of the device. Moreover, R1 is set so as to be 11 times larger than that. The resulting control circuit has a short rise time of 1 ms, low ripple, and

[It is possible to supply an Become a device that can. Another aspect of the invention is that relatively high frequencies (i.e.
A transistor inverter operating in the range of several kilohertz (kHz) is adapted to generate a square wave pulse width modulated output. The rectified output voltage level is controlled by selectively varying the frequency as well as the mark/spacing of the output waveform. The inverter is controlled in response to operator settings, output voltage feedback, and signals generated in accordance with the operating conditions of the device. Another aspect of the invention is the sensing of transformer core saturation conditions and responsively initiating corrective action to alleviate and reverse the problem. Means is provided for sensing the current in the Hg transformer and integrating the resulting signal to provide an indication that the core is approaching saturation. This signal is then applied to a sawtooth generator to generate a control signal. This control signal acts to selectively unbalance the two diagonal current flows in a manner that reduces saturation. A phase advance circuit is installed in the voltage feedback loop to dynamically change the gain of the device so that during the first stage a high gain is obtained and the rise time is short, and after that the gain is reduced to 1q. Decrease the kV(7) at the end of the rise time to clamp the 71-basute. In order to reduce this effect by 1q, the voltage low feedback signal is applied to the input voltage of the amplifier (before applying it to No. 8,
Applied to the phase advance circuit. The noise introduced by the phase-leading circuit is reduced by the phase-lag circuit installed in the feedback loop of the amplifier. A high-voltage shunt circuit is installed to display the output voltage and extract a low-voltage control signal for use in the control circuit. Instead of using a separate capacitor in the high voltage section of the voltage divider, a filtering capacitor is used for that purpose, thus serving a dual purpose. This results in a closed loop voltage feedback device with good transient response for use in the high frequency pulse width modulated output of the present invention without substantially reducing the number of components. To protect the equipment from undesirable conditions that may arise due to possible malfunctions, voltage spikes, flashovers, etc., a microblower sensor is incorporated to monitor the equipment and modulate the operation of the equipment based on the status signals it receives. or stop the operation of the equipment accordingly. Certain conditions for which the protective device will reduce, prevent, or stop the operation of the device are: The flow of current is an uncontrolled demand for excessive kilovolts. Timing of the x-ray exposure is started only after the output voltage level reaches 75% of the required value or device set point, thus ensuring improved performance and meeting the required conditioning conditions. ,+-1-to--beak->H-shape-arrow, ([comb 7,-. Preferred embodiments of the invention are shown in the drawings and will be described below, but various modifications may be made within the scope of the invention. It is appreciated that modifications may be made. Description of the Preferred Embodiment A conventional!lt! type x-ray generator is shown in FIG. It is connected to the three-phase transformer 13 through the tap of the autotransformer 12.
The secondary coil 16 can be selectively varied to change the connection of the primary to the input line, thus compensating for changing line conditions. The power transformer 13 typically has a primary winding 17 in a Y-connection and a secondary winding 1 in a Δ-Y connection.
It is typical to have 8 pulses, producing a 12 or 6 pulse output waveform. After this, the output is the double wave rectifier bridge 19
．． 21, from which a high voltage is supplied to the X-ray tube 22. The power level to XII tube 22 is varied by variable input/output transformer 13. Its primary winding 1
1 is selectively closed by a static contactor 23, usually S CH. Such conventional devices suffer from the various drawbacks mentioned above. The xm generator of the present invention is shown in FIG.
It consists of a DC to AC pulse width modulated inverter 27 operating at variable high frequency conditions, ie within a few kilohertz range. The output of inverter 21 is controlled by pulse width modulation by means of varying both mark-space ratio and frequency by means of a kV11 feedback controller, as will be explained in more detail below. The output of the PWM inverter 927 is sent to the high voltage transformer 28 and finally applied to the X-ray tube 31 via the single-phase rectifier 29. The x-ray tube 31 operates at voltage levels up to 150 kV, but can be loaded anywhere from 0.1 mA to 1250 mA, depending on the particular application and procedure.
In order to accommodate various radiographic applications, it must be possible to have a wide range of exposure times from 1 millisecond to several seconds. The present invention, as will now be described in detail, covers this wide range of operating conditions and performance parameters by providing fast and precise control of the x-ray output. Looking at FIG. 2, it can be seen that the main feature of this fast response system is the dead loop feedback control system. This feedback control device senses the voltage across the X-ray tube 31 using a voltage divider 32, and sends a signal representing it to a high voltage feedback control device 33.
This feedback controller generates a control signal for the PWM impark 27. Although the power supply has been described as having a three-phase input, it should be noted that it may also be a single-phase input. Since the device of the present invention is designed to operate at a much higher frequency than conventional generators, the problem of waveform ripple is greatly inverted. For this reason, even if conventional X-ray generators are not capable of single-phase operation, they can be practically achieved when the features of the present invention are incorporated and used. The square wave pulse width modulation inverter and controller of the present invention is shown schematically in FIGS. 3Δ and 3B, and includes a central control microprocessor kilovoltage demand controller 33 using a microprocessor 30, a mixing amplifier. and feedback controller 34, sawtooth generator and comparator 36, logic controller @ 31, power 1 to transistor controller 38, square wave pulse width modulated transistor inverter 21, power transistor inverter 27 to logic controller 37 An inverter monitor 40 with a dedicated microcomputer 41 that controls the interlock of safety signals to the inverter, a high voltage transformer 28, a high voltage rectifier 29, a high voltage shunt 32, a high voltage division feedback circuit 46, an error signal and a sawtooth wave generator. saturation prevention circuit 47 and current limit circuit 4 working together with the comparator and comparator 36;
8. Display console and operator control device 49 (with microprocessor) and image forming device 51
, which can be of any standard format. The entire apparatus shown in FIG. 3 will now be described generally, with the individual components being described in more detail thereafter. The operation of the entire control device is managed by a microcomputer 41 and a control microprocessor 1/30. The inverter microcomputer 41 is dedicated to continuously monitor and test the high voltage power transistor inverter 27 and is connected to the central control microprocessor 3.
0 acts to control the required value before and during exposure. The control microprocessor 130 also reads the kilovoltage coming from the return device and accurately controls what is happening on the high pressure side during exposure. Any of the numerous microprocessors and/or computers available on the market can be used with the present invention. For example, Intel's 8085-type microphone processor can be used for central control functions, and Intel's 874 can be used to monitor inverter operation.
A 9-inch microcomputer can be used. In response to signals from display console 49, central microprocessor 30 generates a kilovolt request value and sends this signal via D/A converter 52 to mixing amplifier and feedback controller 34. A kilovolt verification signal is sent to central microprocessor 30 via Δ/[) converter 53. In addition to being monitored by the central microprocessor 30 for that purpose, the kilovolt request signal and the kilovolt confirmation signal must be kept in close proximity to each other in the event of an arc on the high voltage side. Or it can also be used as an input for protective action if the component is damaged. In this case, the kilovoltage request signal is not followed by the kilovoltage confirmation signal, and the central microprocessor 3o therefore stops the operation f1 of the device. A central microprocessor 3o is connected via data link 54 to display console 49, via line 56.51 to inverter microcomputer 41, and via line 58 to high voltage feedback circuit 46. The operator enters the exposure time and other parameters at the console 49, and data processing and communication begins at this point. These are accomplished by a microprocessor in a device such as the Intel 8088 microprocessor and a processing unit such as the Intel 8081 which handles the calculations for the xi protection and exposure parameters. Parameters are analyzed and controlled. Communication between the console 49 and cabinets 1-33 or between the 8088 and 8o85 microprolets is via data link 54.
This is done by two data link protocol controllers 59.61. In one embodiment, these controllers are Intel 8213 chips. These controls are
NRZ with cyclic redundancy check words! The protection scheme ensures very high reliability of data transmission in both directions. Historically, the console 49 can communicate with a separate data link 62 to the imaging device 51, so that the communication is completely digital and provides high reliability during operation. Communication between the central microprocessor 30 and the inverter microcomputer 41 on the Internet side is also via line 5.
6.57 in both directions. For this reason, the state of the operator's control is supplied to the central control microprocessor 30 and from there to the inverter microcomputer 41, which determines the output voltage during exposure and the operation of the inverter. During the X-ray exposure, three microprocessors control the exposure time (i.e., the central control microprocessor 30 and the inverter microcomputer 41 on the cabinet side, and the (The display console microprocessor type 8088). This combination provides redundant protection against excessive radiation doses during exposure. One advantage of using closed-loop feedback and kilovoltage request and kilovoltage confirmation signals as shown is that in long-term exposures, such as in fluoroscopy operations, high-voltage feedback devices or any associated electronic If a deviation occurs in the component, the closed loop feedback will automatically compensate for it. Furthermore,
Communication via lines 56, 57 between the inverter microcomputer 41 and the cabinet side microprocessor 30 is such that the central control microprocessor 3o sends kilovoltage, exposure start commands and exposure time commands to the microphone 1'' computer 41. The microcomputer 41 continuously monitors the output status and sends status and confirmation signals back to the central microprocessor 3(). This allows a very simple communication link, with several levels of redundancy, to detect any possible problem in the power circuit and shut down the high power inverter within a few microseconds, or if necessary. It becomes possible to open the lifting platform and the safety contactor 63. A mixing amplifier and feedback controller 34 generates a narrow signal that is the difference between the kilovolt number request signal and the kilovolt number confirmation signal or feedback signal. The resulting kV
The error signal is amplified and processed by phase advance and phase delay circuits, which will be explained in detail later, to stabilize the device. The kV error signal is
The signal from the anti-saturation circuit 47 is sent to the sawtooth generator and comparator 36. A signal from anti-saturation circuit 47 controls the slope of the sawtooth generator to prevent high voltage transformer 28 from reaching saturation, as will be explained in more detail below. The kV error signal is provided to a sawtooth generator and comparator 36 to generate a PWM pulse train with a variable mark/space ratio that controls the output voltage and automatically adjusts the output voltage through closed-loop kilovolt feedback operation. It is applied to adjust the The sawtooth generator and comparator 36 and the logic controller 37 include:
The kV error signal from the mixer 34 is sent to the sawtooth generator once every half cycle under the control of a reset signal or synchronization signal that enters every half cycle from a dedicated microprocessor 41 via line 64. Avoid the multiple crossings that occur when the waveform crosses, which can lead to problems in the power stage circuitry. Logic controller 37, which handles all protection and timing for the device, provides an output on optical 1 line 66 which controls power transistor inverter 27 via power 1 line 6111-. . Logical control device 31
also handles the output of the current limit circuit 48. Current limit circuit 48 is responsive to the inverter current level sensed by current transformer 67 in series with the primary of high voltage transformer 28 . The sensed current level is connected to the current limit circuit 48.
If a circuit overload condition occurs, the output of the current limit circuit 48 is compared to a predetermined safety level.
is applied to dynamically interrupt the mark-space ratio. The output of current transformer 67 is also fed back to anti-saturation circuit 41, the output of which is applied via line 74 to a sawtooth generator to electronically compensate for transformer saturation. Dynamically change the slope. In addition to generating signals that directly control the power transistor inverter 27, the power transistor controller 38 also sends signals representing the state of the controller's power supply as well as the state of the transistors to the inverter microcontroller via line 68. This information is fed back to the computer 41 and this microcomputer uses this information to control the logic controller 37 so that if any transistor or power supply fails, the information coming from the transistor controller 38 is used to control the logic controller 37 in real time. The logic controller 37 first shuts off the inverter and secondly switches on the appropriate safety contactor 63. The pulse width modulated inverter 27 consists of a plurality of transistors, generally designated T+-1-4 in FIG. 3, arranged in the form of a double-wave bridge, with diagonal lines T1-1-4 and T2
1-3 alternately pass current through the primary side 28 of the transformer. Transistors may be used as shown or in parallel if required by power conditions. One type of 1-run sister found useful in this invention is WT-
5752, which is commercially available from Westinghouse Brake (Westcord) Ltd., UK. Pulse width modulation is performed by selectively turning ON and OFF only the upper transistors T+ and T2. High voltage transformer 28 is described in pending US Patent Application Serial No. 564,612, filed on the same date as this application. In this case, the rectangular waveform generated by the PWM inverter has very good waveform reproducibility and is sent to the secondary side of the transformer in a pulse form, so that the transformer 28 has a very small leakage inductance. It is said that it is designed to
It is enough. This minimizes pulse dropout, minimizes post-rectification ripple, and limits the size of the output filter. This facilitates high reproducibility of operation at low mA settings. The rectifier 29 is a normal single-phase type. The high voltage voltage divider or flow divider 32 consists of elements 69.71.107
Contains unique resistive and capacitive electronic circuitry, shown at 108, to improve the response of transformer 28 to dynamic load or source fluctuations or other transient conditions, minimizing rise and fall times. It's Nishide. The output of the high voltage shunt 32 is a kilovolt output and is supplied to the high voltage divider feedback circuit 46 in voltage step-down form via @72. That is, since the output of the shunt 32 is higher than the voltage that can be applied directly to the control circuit, it avoids transmitting high voltage transients from the high voltage area that could damage the control circuit. Therefore, the voltage is divided into several stages using different surge arresters and overvoltage protection methods.

[It is necessary to descend. This circuit will be explained in detail later. The operation of the closed loop kV feedback system relies primarily on a mixing amplifier and feedback controller 34 that generates a kilovolt demand signal and an error signal equal to the difference between kilopol1~output. Controller 34 is conditioned to the level of the electronic circuit through a high voltage divider feedback circuit such that: (1) the error signal generates a mark/space shaped pulse train having a specific ratio depending on the kilovoltage requirement; and (2) the three main variables that can disturb and distort the operation of the equipment during exposure: (a) the fixed DC rail, which changes with the line and the adjustment action of the line, and (b) the impedance of the x-ray tube. There is a need to compensate for variations that occur, particularly during long-term exposures such as electrocooling phenomena, and (c) variations in the offset that the electronic circuitry itself has with respect to the overall device. Saturation Prevention Circuit and Sawtooth Generator and Comparator Referring to FIG. 4, a circuit diagram of the combination of saturation prevention circuit 47 (FIG. 3) and sawtooth generator and comparator 36 is shown. As shown in FIG. 3, the sawtooth generator and comparator 36 includes (1) a synchronization signal coming from line 64 to reset the range of the sawtooth every half cycle; (2) saturation prevention. Line 13 from circuit 47
(3) a kilovolt error signal E from the mixing amplifier 34; Anti-saturation circuit 47 is responsive to the inverter current output received on line 74. Referring to FIG. 4, the inverter connects transistor T+-T4 and associated flywheel diode D.
+-D4. The current of the inverter or the current of the primary side of the transformer 28 is sensed by the current transformer 67,
via line 74 to an integrator 76. The output of this integrator is Ii! 77 to an amplifier 78 whose output is applied to two comparators 79.81. These comparators each have positive and negative reference levels, which are usually very low values, ie close to zero, and determine what is called the permissible saturation level of the transformer. The respective outputs of the comparators 79.81 are connected to NAND gates G1. It can be seen that the signal is applied to G2, and its output is applied to Nando Goo 1 to G3. The output of NAND gate G3 is connected to one diagonal -1-+, 1-a or the other diagonal T'2 . of the power inverter. It acts to close the FET switch F1 for T3. When FET switch F1 closes, an error amplifier output signal proportional to the sensed current becomes available to precision rectifier 82. This rectifier operates on first and fourth slopes and provides a linear horn to the sawtooth generator or compensator via FET switch F1. It is preset by a synchronization signal from 64 and generates a sawtooth wave. The slope of the sawtooth wave is, at zero saturation level,
As shown in Figures 5A and 5B, it is constant and limited by the range of a portion of the overall closed loop feedback system. The Nabeyama waveform signal is then applied along with the kV error signal E to a comparator 85 which responsively generates a PWM pulse train to control the inverter. For example, saturation begins to occur in the direction of the diagonal line T+, -ra and 1=
In this case, error amplifier 78 provides a DC level input to precision rectifier 82, with the output of the rectifier being linearly proportional to this input. Precision rectifier 82 is responsive to either a positive or negative DC input from error amplifier I8. Its sign is related to the direction of the relevant current in the power transistor inverter. As a result, the magnitude of a particular DC saturation level determines the output of the precision rectifier 82, and if this saturation level becomes higher than a preset reference level to correct the condition, this output is "
Pass through 1. For example, diagonal drill 1. When saturation occurs in King 4, the sawtooth generator generates one of the waveforms: ]1. By increasing the slope of the part where the diagonal of the 4th wave leads, as shown in Figure 58, increasing the slope in this way increases the mark/space ratio for a given return error signal. This leads to a decrease in J, so that with alternate recycles, the mark/space ratio of this diagonal is reduced to dynamically compensate for unbalances due to, for example, hysteresis rib differences in transistors or local saturation of the iron core. . If there is such a 'J saturation condition in FIG. r-+, Ta sentence/1 square wire on time and same 1uJ
, Therefore, when the T+ and T4 diagonal transistors turn on, the waveform of the sawtooth generator automatically becomes steeper and the mark/space ratio becomes smaller. The saturation level is thus dynamically and electronically compensated by closed-loop proportional control. That is, the mark period X becomes shorter and the period Y becomes longer. The advantage of this electronic [E-[compensation] is that once the current level in current transformer 67 exceeds a preset reference saturation level;
When the inverter operates continuously and the diagonal of the inverter approaches saturation,
By appropriately reducing the mark/space ratio, a logic controller 31 acts in conjunction with a microcombicoater 41 to compensate in a proportionally controlled manner. The analog and digital functions are explained below.The analog function is shown in Figure 6 and the logic signal flow is shown in Figure 7.The signal processing, whether analog or digital, is The output obtained by the circuit is fed to a microcomputer 41 which controls the overall inverter operation, protection and performance. On the right side, a series of output signals 01 to 06 are shown.These input and output signals are applied to or derived from a protection circuit within the device, and are Controls the operation of the overall device.First, the ground anode and cathode signals In, I+2 are
As can be seen from Figure B and Figure 8, the voltage divider or flow divider 3
1 coming from 2, these m numbers are added by an operational amplifier 84, and its output represents a high voltage output. This output is the main 1
Main or central microphone in 1 position 1) 3
(Feed back to 1, and as shown in Figure 3, the key [
] Pol 1 ~ Inspect the number. The output of the operational amplifier 84 is fed to the positive side of the operational amplifier 86, which then outputs the output from the central microprocessor 30 in the vignette as shown in FIG.
1]/Δ converter 52 and is compared with the poll number request signal 12. The operational amplifier 86 generates an error signal of 4 volts period, and that signal is sent to the comparator 8.
5 marked 1) 11 and shown in Figure 4 and Figure 5 below?
I is compared with the output of the sawtooth generator to generate output 01. Output 01 is a pulse width modulated pulse train that controls the inverter z+. FIG. 6 shows a protection circuit that protects not only the high voltage side including the transformer 28, but also the power transistor inverter 27, which normally originates from the high voltage side, and in all X-ray equipment! There are several types of related control circuits that are affected by flashovers or transients that occur in a lti-type manner. The output 02 of comparator 88 provides overvoltage protection that (1) is very fast in operation and (2) responds to small transients that may occur on the high voltage side. Referring to FIG. 6, the billing signal 12 from the cabinet's central processing unit is applied to the positive input of an operational amplifier 89 and is augmented to a reference signal which is considered to be the maximum allowable overvoltage, e.g. 10 kV. The output of operational amplifier 89 is a signal equal to the required value kV plus 10 kV, and comparator 88 converts this signal into high voltage kV which is sent from operational amplifier 84 to the negative input of comparator 88.
The return signal is subtracted from or compared to the return signal. The output 02 of the comparator 88 must be a logic 1 or a logic O, and a change from a logic O to a logic 1 is an indication of an overvoltage and is controlled by the software by a dedicated inverter microcombicoater.
Force the device to stop operating through a subroutine. The characteristic of this overvoltage is that once it is detected, 1
The inverter is tripped or stopped within a short time of 0 microseconds. This is 1000 to 2000 times faster than the filtration voltage response in conventional equipment. This feature thus protects the x-ray tube, high voltage rectifier 29 and high voltage transformer 28, extending their lifespan. For this reason, these components must be able to withstand overvoltage for only a few microseconds. Another feature of the protection shown in Figure 6 is that
This is for the unbalance of the difference between the anode voltage to ground and the cathode voltage to ground. This is done through an operational amplifier 91 with power 111,112. Reduce these inputs to
The output is applied to comparator 92 and compared with a 5kV reference signal. The unbalance between the anode voltage to earth and the cathode voltage to earth is 51
(If it is greater than v, the comparator 92 is turned off and the output 03 is immediately transferred to the inverter microcomputer 41.
to stop the device from operating. This protection circuit can detect manufacturing defects occurring in the secondary coil. That is, if the number of turns on the secondary side is incorrect and a difference of more than 5 kV occurs, this error will be detected during testing with the circuit just described. Furthermore, in the dynamic performance and operation of the X-ray generator, if there are problematic deviations in the anode or cathode sources, or due to a failure of one of the high-voltage diodes or, for example, a partial failure of the secondary coil. If another unbalance occurs due to a short circuit, the output difference will be greater than 5 kV, and this anomaly can be said to be a fault condition, but it will be detected by the output of the window comparator 92 and a logic signal representing it will be generated. Sent to operator console via data link. The protective action of comparator 92 thus detects possible faults, damage or deviations in either the secondary coil of the transformer, the high voltage rectifier, the output filter or the x-ray tube itself. Another protection circuit relates to the fact that when the film is exposed to X-rays, most exposures occur when the energy level is greater than 75% of the claimed level. Comparator 93
is provided to receive the kVIliJ far signal at its positive input and a signal representing the 75% kV next desired level at its negative input. This 15% signal is sent to the operational amplifier 90 and the voltage divider 9.
5. When the power transistor inverter 27 is turned on,
When the kV specific power begins to rise and reaches 75% of the billed value, comparator 93 is turned on and off, producing an output O4, thus reaching a level of 15% of the billed value, and at this time the exposure time The dedicated microcomputer 41 is informed that it is counted to the power of 1. An associated protection feature of this circuit is to detect any defects in either the power transistor inverter 27 or the integrator circuit during the kilovolt rise time, and to After that, 1 of kV return distance voltage required value
When it does not reach 5%, the power transistor inverter 27
It is assumed that there is a problem with the peripheral circuits, the high voltage transformer 28, the rectifier 29, the >P-wave device, or the feedback circuit. At this time, use this signal to move the device to A) for safety. The three protection circuits mentioned above are all concerned with sensing deviations in voltage levels. Excessive current level has occurred! We also need to sense this and protect against it. For this purpose, two identical circuits are provided at the bottom of Figure 6, called the first current limit and the second current limit, which are provided for redundancy but with the same settings. have a level. The reason for using redundant circuits is that in the event of an overload, the inverter 27 will try to generate even more current, so some method must be used to prevent the inverter from doing so. It is from. Such overloads may be caused by flashing of the x-ray tube, or by arcing in the transformer or shorting of the output diode, for example. Furthermore, the saturation prevention circuit 4
1 fails and transformer 2B tends to saturation, the current increases and this increase in current tends to lower the rail voltage, potentially leading to problems with the output. For this reason, the current limit circuit is
It consists of two redundant circuits with the same set level to ensure that the device is protected even in the event of a failure of one of the current limiting channels. In operation, current limiting action is initiated by a pair of current transformers 94,96 having ferrite cores and connected in series with the primary side of transformer 28 at the output of the inverter. The respective outputs are provided to differential amplifiers 97,98. These amplifiers have very strong common mode rejection to avoid possible N@ due to inverters, radiation, etc. Output Is. l6 is applied to each precision rectifier 99, 101 which generates a DC level signal proportional to the respective current with little delay. This is in contrast to traditional R(1') waveform schemes, which are accustomed to long delays that make the device unsafe enough to fully respond to the current limit action. The outputs of rectifiers 99 and 101 are applied to the positive inputs of comparators 102 and 103, respectively.2
Two current limit levels are applied to the negative inputs of the respective comparators 102.103 +J1. I will be treated. In operation, when the current exceeds the set level of either comparator 102 or 103, output 05 or 06 is turned off and applied to logic controller 37, as shown in FIG. is controlled such that the transistor is selectively turned off, so that the current is automatically reduced and delayed until it is turned back on in the next half cycle. In this case, the current limit is stored in the transformer windings and energy circulates through the lower diode and its diagonal lower transistor complementary to the previously conducting upper transistor. It must be noted that this works by blocking only the upper transistors ``100'' and ``2'' (see Figure 4) so that the Ms current is inductive. It ensures that the energy +Lτ is attenuated in the loop consisting of the lower flywheel diode, the transformer winding, and the lower transistor. , is more effective. If the four transistors turn off, the inductive energy must be dissipated from the lower flywheel diode through the transformer to the diagonally upper flywheel diode. In this loop, energy is fed back to the DC rail and decays much faster, allowing the lower flywheel diode and lower transistor to conduct.The diagonal lower and upper diodes This fast decay of the circulating energy returned to the fixed DC rail through For this reason, experiments have shown that the procedure of shutting off only the upper transistor leads to better performance and operation of the device. The decay time of the current as it circulates through the lower side 1 to the transistors and diodes is made longer, thus avoiding spurious operation of the inverter at high frequencies. Next, as shown in FIG. To explain the digital operation of a protective device, the core of this device is a dedicated inverter.
This is a microcomputer 41. This microcomputer prevents the upward slope of the sawtooth generator, synchronizes it with the error signal, controls the output 1 to transistors, ensures the detection of possible faults, if any, and assembles the output circuit. Communication is made to the central control microprocessor 30 to record whatever type of error is detected, thereby providing synchronization of the entire system. There are several signals sent from the Microproletz+J30 to the microcomputer 41. First, there is an exposure command signal generated within the microbutton 4 30 that signals the microcomputer to begin exposure. Before that occurs, the microcomputer 41 checks that (1) the state of the power supply as well as the four transistors are in the correct state, and (2) that the power transistor controller 38 is in the correct state before starting the exposure. To ensure this, the overall status of the device is checked using different signals. The microcomputer 41 is the microprocessor 30
In addition to the exposure command signal from the controller, it also receives an exposure time signal and a phase voltage control signal. The exposure time signal determines the length of the exposure time, and the phase voltage control signal determines the length of the exposure time for low energy exposures.
It is used to generate an output pulse with a very small pulse width for compensation at the output. Thus, pulse widths can be reduced to a few microseconds in duration to ensure tight control through closed-loop feedback operation. A well-known phase voltage control scheme synchronizes the lower diagonal transistor with the upper transistor, thus ensuring that the RC buffer circuit is fully discharged before turning off the output transistor. If the pulse width of the - or higher side transistor is fixed to a minimum time of, typically 20 microseconds, then both transistors on the same diagonal will pulse for a length of time determined by closed loop feedback action. Telephone. Therefore, if the energy required for exposure is at a low level, the phase mill controller generates a very small pulse width at the diagonal edge of the power transistor inverter, producing a precise low-1 energy exposure time. Achieve. The 75% output 10 volt signal comes from the protection circuit of FIG. Notify computer 41. For this purpose, the microcombicoater 41 sends a signal called exposure start back to the central microprocessor 3. At this time, the microprocessor 3 starts the exposure process. For redundancy, this is also done by the console's Micro Combi coater via the cabinet/console data link. If an overvoltage or unbalance condition occurs during exposure, the microcomputer 41 issues a signal to stop the output to the inverter transistors T+-1-4. In addition to the protection features described above, by driving the power transistor controller 38, the output A set of logic and gates hG4. controlling transistors T+-T4. G5. G6. G7
There is. Generally speaking, G4 controls the upper transistor '1, G5 controls T2, G6 controls T3, and G7 controls -14.The main signal coming into G4 is related to T1. This is the drive signal from the microcomputer 41 which is marked G4 so that the modulation signal can modulate the output of G4 to the transistor 1-1. .G6.G7, T2.'T-3.T
A driving signal related to 1-4 is supplied. Goo 1-G4. G5. G6. There are two other inputs to G7, the absence of which can stop modulation. One example where this signal (state 1] S) is absent is:
This is caused by a failure in the transistor drive power supply. If it is absent ゛C] - run sister T+ - operation of T4 lJ? The other signal, which acts like a n, knee 4I and 1q, is a signal called short-circuit protection or shoot-through protection, which is used to protect the optical fiber between one transistor, e.g. T+, and its complementary transistor ``3''. It is an interlock, and if transistor T3 malfunctions and is turned on, it is impossible to switch transistor 1 to bxn. This is because, if such a thing were to occur, vertical throughput would occur and damage the second transistor. This protection feature is bidirectional: if transistor [3 breaks down, T1 cannot be switched on. Conversely, if T1 yields, the interlock will switch on before T3 is switched on.
Controls 1-3. Den Kadran Sister [2 and]-4
The same goes for the other vertical branch. The signal applied to the upper two transistors 1-1 and 1-2 is the line protection signal. The absence of this signal is caused by a failure of the kV output protector, which is supplied with three different signals to gate G10. This guard line is generated by ANDGIO. AND GIO1-GIO is switched by a second current limit level, overvoltage protection or unbalance protection, so that the output from GIO is protected signal C', via G1-G4 or G5, It can act to stop the driving of the 1 transistors T1 and 12. Any of the second current limits, overvoltages, or unbalanced circuits will disable the outputs of transistors T+ and T2 to avoid transmitting the underlying state to the power output stage. The lower transistors 1-3 and 14 are not as heavily taxed because they conduct across all four halves of the waveform from the eight-way transformer. These transistors are connected from the microprocessor's -13 and T4 terminals to the gate G6. Controlled by a signal applied to G7. The current limit characteristics represented by the 1-modulation signals for G1-G4 and G5 also act on the upper two transistors, T1 and T2. For this reason, the microphone [
. These nodes are connected to this synchronization signal and the secondary input,
That is, in the flip-flop 104, the second current limit signal,
In flip-flop 10G, gate G9 is controlled by both the output signal of AND gate G9 and
The OR gate G8 synchronizes with the pulse width modulated pulse train signal and a 20 microsecond monostable pulse generated from the output of the flip-flop 106. Receive a signal. The reason for this lowest pulse is that the series circuit at the output side of the transistor inverter (J, t Keep it from happening II
This is to prove my dismay. DESCRIPTION OF OPERATION In turn, assuming that the second current limit is turned off and -C, the output of flip-flop 104 acts synchronously with the second current limit, and flip-flop 106 acts synchronously with the second current limit. Monthly RC through current limit
A modulation pulse is generated in conjunction with the turn-on of a 20 microsecond monostable minimum pulse to ensure discharge. Thereafter, the microcomputer 41 generates the main frequency waveform of the transformer, which immediately transmits the lower transistor T 3 ,
It is applied to l'-4. This square wave is generated by gate G8. G
The upper transistor 11 and/or Apply to T2. At this time, ie at the end of every half cycle, the microcomputer 41 also generates a signal to switch from diagonal 1, ie transistors ]-1 and ]-4, to diagonal 2, ie transistors T2 and 13. This diagonal switching ensures successful complete off switching of the conducting diagonal transistors. Finally, the microcombicoater 41 also generates error and error codes for the faults, which are sent back to the control microblower 30 to determine when one of the possible faults has occurred and what type of fault it is. Let us know if it is. 2
The hex number is decoded and sent via the data link to the display console 49. The microcomputer 41 thus controls the power inverter, generates waveforms, communicates with the central microphone on the 1-side processor, receives commands, and, most likely, controls the power path. C1 has a very high degree of flexibility in providing information to the equipment to make decisions such as whether a failure has occurred or not. High voltage shunt and high voltage divider feedback circuit The high voltage shunt 44 and high voltage divider feedback circuit 46 of FIG. 3 are shown in more detail in FIG. The high voltage shunt 44 protects against overvoltage that occurs on the high EE side and affects the electronic control circuit. A unique feature is the use of the necessary output capacitor 11 from the DC side of the high-voltage rectifier 29 in a secondary role, instead of a large number of components of a conventional shunt. The only parts that need to be added are the lower capacitor 107 and the lower resistor 108 shown in Figure 8, which greatly reduces the physical q-factor of the shunt and makes it difficult to use a normal shunt ( The inherent inaccuracies and lost heights of using a large number of elements as described above are avoided.Typically, in low energy generators (in the range of 0°25 mA S) ω must be minimized. For example, in the preferred embodiment of the invention, the capacitance of capacitor 71 is approximately 4.5 nanofarads from the anode to ground. There is a capacitor and an identical shunt.The purpose of using the lower capacitor 107 is to
The problem that must be dealt with in this connection is to obtain an output signal in the range of 5 to 15 volts and to cover it in such a way that it can be fed back to the control circuit without adverse effects. , is a large voltage spike when an X-ray tube emits an arc. This is a phenomenon that can occur either between the anode and the ground, between the cathode and the ground, or between the anode and the cathode. Of course, some If protection is not in place, such overvoltages can damage the control circuitry. The circuit is provided with top-to-bottom voltage force scale filtering to ensure that during large voltage transients there are no overvoltages that could damage the equipment. To overcome this protective effect, the voltage divider conditions for a nominal maximum of 75 kV are such that the ratio of capacitor 107 to capacitor 71 is 2,
By multiplying by 000, Vx'c is determined. content 4no
The value of 107 is about 10 microfarads, and the voltage v
× equals 37.5 volts. At point vy in the voltage divider circuit applied to the input of differential amplifier 84, divided by resistors 109 and 111, voltage Vz is approximately half the value of vy, or 4.99 volts or For example, this results in a voltage close to 5 volts, which, when considered in relation to the voltage of the same cathode-to-ground voltage divider, at an output level of 150 kV, results in a total h4 signal of the voltage divider of 10 pol. When the partial pressure of Another element that has a contribution to A second lightning arrester SP2 is installed (c) to ensure complete protection. In addition to this cascading wave action, a second capacitor N3, 114, 116 and a resistor 117 are provided. There is another P-wave effect between resistor 117 and capacitor 114. Finally, V due to resistor 109 and capacitor 116
There is a filtering effect from y to Vz. Resistor 109 and capacitor 116 act in conjunction with the voltage dividing effect of resistor 109, 111 mentioned above. As a cumulative effect of this,
If the anode voltage is 75,000 pol 1-, the voltage V
The nominal value of z is 5 volts. There are also diodes 118,119 in the circuit of FIG. These diodes either redirect the spike to the 15 volt supply through diode 118 or redirect it from Vy to ground through diode 119, depending on the polarity of the spike. It! −
! Jru. Further, the driver amplifier 84 has a diode 121.1.
22 protects against overvoltage on its input terminals. (1) Lightning arrester SP1, coaxial cable 112, capacitor 113, air gap A1, lightning arrester SP2, and resistor 1 (19, 1
A single wave action of a combination of elements including 11,447 voltage dividers;
(2) One-wave action of the combination of resistor 117 and capacitor 114, (3) Filtering action of the combination of resistor 109 and capacitor 116, and energy is transferred to the power supply capacitor via diode 118 and 119. The effect combined with the ability to restore the voltage will cause damage to the electronic control circuit no matter what the level of the 12 spike that occurs on the high voltage side of C1.
1ii) so that no significant amount of energy is applied. Next, to explain the design of the high voltage shunt 44 in more detail, its transient response is related to the combined impedance of the capacitor 11, the resistor 69, and the capacitor 107 with the equivalent resistance at Vx. In steady state, its accuracy is related to the equivalent resistance of resistor 69 and Vx. A relatively small value damping resistor 124 is provided to dampen excess ripple oscillations to the resistor 71 that may be photoreduced by the series inductance. For this reason,
Preferably, high voltage capacitor 71 has a small inductance value, typically less than a nanohenry. resistance 6
9, and the equivalent resistance made up of resistors 117, 109, 111 in series and resistors 108 in parallel, and the relationship between capacitors 71 and 107 must be such that their time constants are the same, and The required voltage or ■
It is determined that the voltage should shift to about 0 volts. It should be noted that adjustment to the shunt setting is very simple and the only adjustment required is to adjust capacitor 101 to the tolerance of capacitor 51, typically around 5%. I would like to mention this. This single adjustment is in sharp contrast to traditional flow shunts, which typically require significantly more adjustments because they use a much larger number of components. Another advantage of the current shunt of this invention is that from the high voltage side to the 31.5 volt point Vz, the number of components is two resistors and two.
Since the number of errors is kept to a minimum, the cumulative error is minimized. The tolerances imposed on the resistors are not very tight. This is because the number of resistors is only two. Therefore, a current shunt with a fast transient response can be made very easily, at a low cost, and with high precision. Conventional current shunts using resistors usually do not have good transient response and fast rise, but they
The device of the present invention, which operates at high frequencies with low voltage, provides good transient response to enable closed-loop feedback voltage control. Furthermore, it is possible to operate with greater bandwidth, thus improving the response of the device. Mixing Amplifier and Feedback Controller A high voltage feedback controller is shown in FIG.
It includes well-known means for generating a variable voltage command, which is a low level signal for electronic circuitry on the order of volts. In the present invention, this signal is generated by central microprocessor 30 via digital-to-analog converter 52. The kilovolt feedback signal returning from the output via line 72 is converted by an A-J digital converter 53 to
The same microprocessor 30 is supplied with real-time operation to verify that the device is operating correctly and that the feedback voltage follows the command voltage. Referring to FIG. 9, the preferred power stage first includes a power transistor inverter 39. This inverter has two fixed taps on the transformer and If Acts on one of the following. In Figure 9, the power transistor
At the output of the inverter 39, an equivalent circuit for the high voltage side, referred to as the primary side in this case, is shown. Its main components are:
Transformer leakage inductance, inductance and associated series inductance L-r, jJ wave'ndenna C
F and variable load R. This filtering capacitor is calculated for the primary side by multiplying the value at high voltage by the square of the turn ratio of the transformer, resulting in a very large value. The variable load on the primary side C can vary over a very wide range (typically 1.25(1+n△ to 0
．． 1 mA and 15.00 (with a 1:1 or possibly even larger negative power change). Also shown is the previously mentioned high voltage divider. This includes a mixer, amplification and controller 34 for voltage feedback and a central processing unit 30.
Generates a kilovolt feedback signal for operating μ. One of the main features of the closed loop feedback controller is that the resistor 126
, a mixed amplifier 1 obtained by the phase advance of the air-to-ground feedback performed by the combination of the resistor 127 and the capacitor 128, and the time constant of the feedback resistor 131 and the capacitor 132.
2 (), and a kV feedback difference signal is generated by the cooperative action of A, but this can be regarded as a DC signal in a steady state as the amount of the rise period changes) k1
It is compared with a sawtooth wave generator 36, and a pulse width modulated pulse train is generated at the output of the comparator 133. The saturation prevention circuit 47 mentioned above also has a closed loop feedback 40pol1
I would like to mention that it is part of the ~number loop. This is because when we dynamically change the slope of the waveform from the sawtooth generator, we are also changing the effective gain of the overall loop controller. Variations in the saturation prevention circuit 47 are small and vary dynamically according to the saturation level reached by the transformer itself, but the variable gain introduced into the loop is a consideration for stability as well as good performance operation of the device. This is another important feature that must be included. The purpose of the loop's lag circuit is to filter out noise in the error feedback signal. To achieve optimal performance, phase lag circuits must be minimized to improve device bandwidth, short pulse response, and feedback tracking. The delay circuit of this invention has a resistor of 13
1 and the time constant of the combination of capacitor 132, and the load determined by the values of RL and CF is determined in a particularly 1/l manner by the time constant of the P-wave device. However, the RL CF is variable and, as previously explained, is typically 15,000
Since the phase delay introduced into the mixing amplifier 129 by the resistor 131 and the capacitor 132 can vary by 0:1, the phase delay introduced into the mixing amplifier 129 by the resistor 131 and the capacitor 132 is considered to be a common problem in the X-ray generator in terms of control and stability. Do not compensate for the large load fluctuations that may occur. On the other hand, the resistor 131 and the capacitor () 13
The combination U of 2 must have the lowest time constant to ensure that the return device can respond to exposure times as short as 1 millisecond. In order to obtain a fast response of the device with the feedback of the mixing amplifier 129, a limiting circuit 135 of 1Q, which is available on the market, is provided. The effect of this circuit is to limit the maximum output of mixing amplifier 129 to a level of 10 polls. This level of 10pol1~ has the same amplitude as the output of the copper mine wave generator, and therefore,
The maximum output of charging amplifier 129 does not exceed the output level of the sawtooth generator. This relationship avoids saturation of the mixing amplifier which would cause the response to become slower, especially during the latter part of the rise period. The second action of the I-phase device is
The purpose is to compensate for the noise introduced by the phase-lead feature and, above the intended frequency, to ensure that the phase-lag device minimizes the effect of noise on the device. During the rise time, the phase-advancing effect of resistors 126, 127 and condenser 128 clamps the A-base at the predetermined level at the end of the rise time. This improves the system's response to dynamic changes in the load or to changes in other parameters, such as the DC rail voltage level, which may affect the kilovoltage. In this way, the phase advance circuit overshoes during the rise time]
is controlled and acts as a gradient function. From a control point of view, what it does is reduce the energy stored in the transformer and output DC filter during standstill time to control overshoe. The main disadvantage of using the phase advance feature is that there is an inherent increase in the noise signal to the output of the mixing operational amplifier, but as explained earlier, this is not the case at frequencies above the cutoff frequency. t
iltH, so that the increase in AC ripple caused by the phase advance is effectively offset by the aforementioned phase lag circuit and associated intermediate phase lag circuit. This circuit consists of a resistor 130 and a capacitor 140 connected in series.
C compensates for dynamic noise, thus making the noise level tolerable in the improved device with high gain and good stability. The bandwidth of the device is preferably in the range of 1 to 1.2 kHz, and the switching frequency of the transformer is typically on the order of 6 kl-12 or higher, thus supporting both leading as well as intermediate π phases. Both of the cutoff frequencies are 1-min lower than the switching frequency of the transformer to compensate for the increased AC ripple produced by the phase advance feature. The stability of the device is shown in FIG. 10 by a Nicol diagram. This figure shows an overall gain margin of about 20 dB and a phase margin of 70 degrees. Therefore, the linearity and control stability margins of the -C1 device are very good. The apparatus of the present invention may be better understood in consideration of its various design and performance features. For example, during the rise period, one condition is to increase the current flow in order to speed up the rise time, and the other is to increase the current flow to avoid A-basutes and to avoid the need for oversized components. It will be appreciated that there is a phase D, operating condition, in which there is a conflicting condition that seeks to restrict flow. During the rise time, current tends to flow very strongly to magnetize the transformer, charging the output filtering capacitor 69, but is limited by the transformer's leakage inductance. This leakage inductance is preferably kept to a minimum so that the reproducibility of the signal waveform between the primary side and the secondary side is very good. The size of the DC output filter of the X-ray generator depends on the desired switching frequency of the low l1lA1 inverter to be achieved,
and acceptable output voltage ripple. The feature of this invention is to increase the frequency during the rising period,
The goal is to reduce the current limiting effect and make the rise time faster, thus obtaining a waveform that is very close to a square wave. In addition to the conditions mentioned above, there is a need to limit current flow to a level that can be tolerated by power transistor inverter 27 and its associated control equipment. Furthermore, in order to avoid overshoeing at the end of the rise time, the current flow and associated overshooting rise time must be limited.
Must be J. For this reason, the current must not be controlled during the rise time, but at the same time
To obtain favorable results with the IA procedure, especially for short exposures,
The device is capable of providing L1 within a reasonable range of 0.5 to 1.5 milliseconds.
You have to achieve the required time. This kind of thing is
The effect of the increasingly variable mark/space ratio feature and operation at a higher frequency than steady state operation is achieved as previously described. Another aspect of the current level interaction phenomenon described above is that
During the rise time, the mixing amplifier 129 is in saturation;
During the saturation period, some control action must be taken to ensure that the equipment quickly recovers from saturation of the transformer core and that control action is maintained during this period. Must be. As explained earlier, in order to set this control effect, the output limiting circuit 1 is connected to the feedback of the mixing amplifier 129.
35, so that the error signal does not go to the extreme point 1 that would prolong the time it takes for content 1 to recover, and the error signal is within the limits of the intersection of the sawtooth generator. , quickly bring the mixing amplifier out of saturation,
A good control effect is achieved at the end of the ramp-up period. At the end of this rise time, as well as during the rise time, anti-saturation circuit 47 must balance to ensure that transformer 28 comes out of saturation. This is because during this rise time, a dynamic asymmetry of the mark/space ratio or pol 1 fsec is imposed on the inverter 27 and the transformer 28. The increasing variable mark/space ratio during the rise time controls the slope of the voltage demand from the micro processor 30 through the D/A converter 52 so that a small pulse at the beginning of the rise time is applied to the power inverter. This can be achieved by limiting the current and also controlling the rise period, with a corresponding current limit. Figures 11A to 11F illustrate the performance of the apparatus of the present invention when operating the X-ray tube MX-1 (10) manufactured by General Electric Company using various parameters. is 55.60°70,80
．． 90 and 100 kV 17) Current to G40n+ at different kV levels t) Shows a typical four-dose exposure time of 32 milliseconds when using a load. First, the rise time is very fast; That is, it will be recognized that it is within 1 millisecond.Secondly, the linearity between the rising and falling times is very good;
J-bar shoe 1 at the end of the rise time for phase advance compensation.
~ is tightly controlled. It can be seen that during steady state operation, the output ripple decreases with the output voltage and the mark/space ratio increases with the voltage upper bound. However, in either case, ripples are extremely small. Figure 1113 shows people 12! One thing this diagram shows is that the effect of the feedback circuit is very fast. be. The flat top of the kV waveform demonstrates that the feedback is acting within 1 millisecond. This figure shows where current limiting action prevents A-basute by controlling the build-up of energy in the drain and transformer during the start-up period. It shows. The operating parameters are typical values when the X-ray generator operates with automatic exposure control at very low mA. For such very low mA, reproducibility is very difficult to achieve with conventional generators due to large variations in load. This invention is in such a state, there is no A-bashoot,
Good performance is achieved by controlling the kilopoles with a very fast closed-loop operation that ensures a flat top and fast response. Figure 11C is 1iokv, 400111A C+) R
(7) Indicates the exposure and current waveform of the inverter. This figure clearly shows two different time periods. The first period, the nonlinear rise period, indicates that the initial flow can flow at a much higher level than the steady state level, resulting in a faster rise time. Furthermore, both during rise time and during steady-state operation, the waveforms are shown to be highly symmetrical. This is the saturation prevention circuit 47
This indicates that there is no saturation phenomenon of the transformer due to the effect of Furthermore, the figure shows that the transition between the start-up period and the steady state occurs clearly and rapidly at the end of the phase advance operation and when the top of the kV number is reached. The kV step response is shown in FIG. 110, which shows a 200 mA, 70 kV waveform with 15 stages. As can be seen from this figure, there is no overshoot and the settling time is very fast (on the order of less than 1 millisecond). This appears to be the primary device, ie 1/(1+ST), in which the phase-in and phase-advance circuits are dominant. FIG. 11E shows the same waveform, but at a higher frequency, superimposed with a step of γ, 5 kVll, showing the kilovolt frequency response. The lower curve shows a clock generator that generates a variable intermediate demand value. Figure 11F is similar to Figure 11E, but 75kVl]
This is a case where y and 5ttvp are superimposed on the image. However, the time scale has changed and the frequency is now 5.5 kHz. From the performance data shown in FIGS. 10 and 11, the following conclusions can be drawn regarding voltage feedback controllers. (
1) Virtually no A-basicote across a wide range of systems used in X-ray generators. (2) Very good lagging from 1 to at least 5.5 kHz. (3) There is no instability, and rather the linearity and reproducibility are very good. (4) The behavior is the first
This is the behavior of the following device 1/(1-)-S-T'). Although the invention has been described with respect to specific embodiments and examples,
Various modifications will occur to those skilled in the art from the above description. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional X-ray generator, FIG. 2 is a schematic diagram of an X-ray generator of the present invention, and FIGS. 3A and 3B are circuit diagrams of the voltage feedback and control portion of a preferred embodiment of the present invention. ,
FIG. 4 is a circuit diagram of the saturation prevention circuit of the present invention, FIGS. 5A and 5B are simplified graphs showing typical pulses generated by the inverter control device of the present invention, and FIG. 6 is a circuit diagram of the saturation prevention circuit of the present invention. 7 is a circuit diagram showing the digital portion of the protection circuit of the invention; FIG. 8 is a circuit diagram of a voltage divider according to a preferred embodiment of the invention; FIG. 9 is a circuit diagram of a mixing amplifier and FIG. 10 is a circuit diagram of the feedback control portion of the present invention including associated phase advance circuits, FIG. 10 is a 1 Nicol diagram showing the kilovolt feedback of the present invention, and FIGS. Figure 2 is a graph showing traces obtained on an OssiO scope showing various characteristics of performance; Description of main symbols 23: 3-phase input 24: Rectifier 27: Inverter 28: High voltage transformer 29: Rectifier 37: Logic control T111 device 41: Saturation prevention uJ path 48: Current limit circuit 61 Two-current transformer Patent applicant General・I Lectric-Company-I
IIIllllIIIiIIIllIIIIL0 5
IQ Is 20 25 303540 hours (mm 4 father) FIG, llA 3 Io 15 20 25 'So 3540 45
FIG, 1 IC-″' seconds′ “'6′” ”-+1 example FIG, llF Commissioner of the Patent Office Manabu Shiga 2, Name of invention High-voltage voltage divider circuit Name General Electric Company Telephone (588) 5200-5207 April 10, 1985 (Delivery 1]: April 30, 1985) 6. As shown in Figure 10 of the drawings subject to amendment, 7, contents of amendment attached.

Claims (1)

[Scope of Claims] 1) In a high-voltage dividing circuit used in an X-ray generator having a high-voltage AC output and rectifying the AC output and applying it to an X-ray tube, on the output side of the rectifier. a single wave means including a capacitor connected in parallel and a voltage divider connected to the output of the filtering means, the voltage divider having a high voltage section and a low voltage section, the high voltage section 1. A high-voltage voltage divider circuit comprising a wave capacitor connected in parallel with a high-voltage resistance means, and the low-voltage portion comprising a low-voltage content connected in parallel with the low-voltage resistance means. 2. In the high voltage voltage dividing circuit according to claim 1), the high voltage voltage dividing circuit has means for applying the output of the low voltage section in order to control the high voltage. 3) In the high-voltage voltage divider circuit according to claim 2), a cascade filter is connected between the voltage divider and the applying means to eliminate the effects of voltage spikes that may occur in the circuit. A high voltage divider circuit that dampens the voltage. 4) The high voltage voltage dividing circuit according to claim 1, wherein the filtering capacitor has an inductance of less than 100 nanoHenries. 5) In a shunt circuit used in an X-ray generator having a high-voltage DC output and a control means responsive to the DC output, a single-wave means connected to receive the DC output and having a capacitor; connected to the output side of the means, high voltage R
A voltage divider made up of a C loop and a low voltage RC loop, and the high voltage RC loop connects the P wave capacitor and a high J
A shunt circuit consisting of iE Ili resistors. 6) In a shunt circuit that lowers the output voltage of a filtered DC output, one capacitor serves as both the filtering capacitor in the voltage divider [(0 loop) and the frequency compensation element].
A shunt circuit with heavy effects. 7) In the shunt circuit connected to the output side of the RCf wave generator,
It has a high pressure part and a low pressure part, and the high pressure part is the RCt.
A shunt circuit consisting of a capacitor in the P-wave device and a resistor connected in parallel with it.