| X-ray tube has experienced three stages, the ion X-ray tube, the electronic X-ray tube, the rotating anode X-ray tube. Along with the electric & electronic technology and the microcomputer technology's development, the X-ray machine toward the high performance, low cost's direction is developing. Power-frequency (50Hz) transformer has been taken over in whole or in part by intermediate frequency, high frequency invertor in the high voltage circuit, which can reduce the bulb volume; MCU technology has used in the control circuit to realize the high accuracy closed loop control for the tube electric current, the tube voltage and X-ray exposure time; High frequency invertor can output DC high voltage for the X-ray tube, that reduces the soft X-ray to human body's injury.Based on microchip MC34067, One kind of IGBT full bridge circuit topology with Series and Parallel Quasi-resonant Zero-Voltage Swith (ZVS) is proposed in this paper.IGBT converter and Pulse Frequency Modulation (PFM) have been utilized in the high voltage DC circiut, in which the stable current convert in the wide range of load could be completely realized by Series and Parallel Quasi-resonant Zero Voltage Switch.one kind method of fast compensation space-charge effect is propsed to accurately control the tube current. This way uses the TL494 dead time control pattern to compensate the anode high voltage to the anode current influence. After the error amplification between the feedback signal of anode current and the hypothesis electric current, the comparison value is then sent to the PWM comparator of the integrated microchip TL494, the closed loop control of tube electric current is achieved by the filament current control. The experimental result indicates that this kind of IGBT series and parallel quasi-resonant VZS-PFW is suitable to X machine wide range load request, and the control policy is practical and feasible.High frequency DC dental X-ray machine has independently been developed, in which invertor frequency 20 KHz, instantaneous power more than 1600W, the tube voltage may be adjusted in the 50-100kV scope, the tube electric current may be adjusted in the 3-8mA scope, the power factor is not smaller than 0.92, the complete machine efficiency is more than 90% slightly, the bulb size (50X120X125mm).This dental X-ray machine adopts IGBT component as high frequency switch, serires and parallel quasi-resonant technology, outputs the DC tube voltage. So the efficiency and the reliability is extremely high, the anode high voltage is stable. Pulse Frequency Modulation is realized by microprocessor to control tube current, tube voltage. The protective measures are perfect, includes input voltage, tube current, filament current and overpower protection; The diagnosis system can detect connection condition of the various parts, then display these status. The man-machine contact surface is friendly, uses the ultra big Chinese character or English liquid crystal display. The multi-spot pressed keys of X-ray exposure, short-distance bulb exposure key, long-distance wired exposure key, long-distance infrared exposure key, maximumly assures operator's personal safety and convenient.2 sets of dental X-ray prototypes has been manufactured, carried on the electric circuit degradation testing, the antijamming experiment, the dielectrical strength experiment. The experimental result indicates that the performance is fine. After 100 hour continual experiment which one time exposures per 3 minutes, the prototypes still good work. The approximately 20 micron wide integrated circuit interior line, or tooth medulla cavity can clearly be recorded by CCD imaging system. Tooth medulla cavity may also clearly be recorded by dental film.The high frequency contravariant and microcomputer control technology is introducted to domestic dental X-ray machine, which very greatly impetus the technology progresses.Author:Yang Wei-JunDirected by Zhao Li-Hong, Chen Hai-Hui...
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