| Neutron generator is an instrument and equipment that can continuously produce neutrons.It is mainly composed of control system,accelerator power supply,ion source power supply,storage power supply and neutron tube.It has the advantages of high neutron energy,good monochromaticity,stable and controllable yield,and is widely used in explosive detection,coal quality analysis,oil logging,industrial on-line analysis and other fields.The traditional neutron generator can only work in DC mode,and the ion source power supply is linear power supply.This power supply has the disadvantages of large volume,low efficiency and difficult maintenance.To solve the above problems,this paper redesigns the ion source power supply of neutron generator,which has two working modes: DC and pulse.In pulse mode,neutrons can conduct a variety of nuclear reactions with substances to produce characteristic gamma rays such as inelastic,capture and delayed emission,which can meet the detection needs of different substances.The work done in this paper mainly includes the following points:(1)The cascade topology of step-down voltage stabilizing circuit and half bridge inverter circuit is used to design the high-voltage DC power supply.According to the internal structure and working principle of step-down and voltage stabilizing chip LM2678,the negative feedback circuit of power supply is designed to realize the closed-loop control of high-voltage DC power supply.Ir2153 s chip is used to design self-excited oscillation half bridge circuit to generate driving signal to control the switch.LLC(logical link control)resonant transformation technology is used to optimize the half bridge inverter circuit,reduce the power loss of the switch in the process of on and off,and improve the conversion efficiency of the power supply.The high-frequency and high-voltage transformer and rectifier filter circuit are designed to realize the output of 2KV high-voltage DC power supply.(2)The STM32F103 chip is used to design the control signal of the high-voltage chopper circuit,which is used to switch the working mode of the neutron generator,detect the rising and falling edges of the control signal,and generate two complementary output PWM(pulse width modulation)drive signals.Compared with the analog circuit with reciprocating clutter,the design is more concise and efficient.After the drive signal is amplified by tps2812 chip,the isolation transformer is used to isolate the drive circuit and high-voltage chopper circuit,and the irf840 switch tube is used to form a self-locking circuit to control the chopper power tube according to different drive signals.(3)The insulation scheme of high voltage pulse power supply adopts the combination design of gas,liquid,epoxy resin and other insulating materials.According to the requirements of the actual working environment of the power supply,select the appropriate insulating gas through experiments,adjust the insulating gas pressure and set the corresponding gas replenishment strategy to make the power supply system work in a safe and stable gas insulation environment.The insulation performance of transformer oil under different temperature and pressure is studied,and the methods to improve the insulation of transformer oil are designed.Epoxy resin potting adhesive is used to pour the low-voltage circuit of power supply to enhance the electrical performance and insulation of the circuit and prolong the service life of electronic devices.The power supply printed board is hollowed out to reduce the electromagnetic interference in the circuit and improve the stability of the power supply.The test results of the ion source high voltage pulse power supply developed in this paper are as follows: in DC mode,the output voltage range is 0～2kV continuously adjustable,the ripple coefficient is less than 0.85%,the stability is less than 0.2%,the maximum output power is 20 W,and the power efficiency is up to 80%;In pulse mode,the working frequencies of the power supply are 500 Hz and 10 kHz respectively,and the minimum duty cycle is 10μs.The time of rising edge and falling edge of pulse output waveform is less than 2 μs。 The designed high-voltage pulse power supply can meet the application requirements of ion source power supply for micro neutron generator.The power supply has good performance and stable working state. |
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