| The neutron tube is a controllable neutron source.Compared with other neutron sources,it is suitable for detection outside with low cost,light weight,simple operation and maintenance.The neutron tube can run in a DC state,a fast pulse state,and a fast-slow pulse state.To meet the practical requirements,the frequency and width of pulse can be controlled by digital high voltage pulse circuit.DC high voltage power supply of ion source of neutron tube adopts the cascade structure of flyback topology and Cockroft-Walton voltage multiplier to design.For realizing the stable and adjustable output voltage,ICM7555 produces driving signal to drive IGBT and op amp HA17358 is used to design the TYPEI type voltage feedback network to realize external voltage from 0V to 2.5V meeting output voltage of power supply from 0V to 2000 V.Parameters of capacitors between gate and source of MOSFET are designed to reduce the turn-on and turn-off voltage spikes at drain of the MOSFET,and solve the problem that the 2kV DC power supply generates abnormal noise from primary adjustable period.Transformer of high-frequency and high-voltage is wound with EI33 magnetic core of PC40 material.Its input voltage of primary coil is 24 V,maximum output voltage of secondary coil is 600 V,and the working frequency is 40 kHz.The 2kV output voltage is realized by the 2nd order 4times voltage rectification circuit.In order to further reduce ripple of power supply,the first-order low-pass filter of RC is employed to reduce the AC component of output voltage,which can improve the stability of the neutron yield.At the same time,the over-current protection of the power supply is achieved by current detection circuit and voltage reference circuit.So as to fulfill the neutron tube operating in the pulse mode,the 2kV DC voltage is chopped by the series IGBT of push-pull structure.Compared with the traditional chopping scheme of single-tube,the series structure reduces voltage stress and cost of IGBT.MAX4428 is used to convert single PWM into complementary PWM without dead time and rising edge of PWM is changed through RCD delay circuit and 74HC14 schmitt trigger is used to realize 3 channels complementary PWM with adjustable dead time.Delay of rising edge of upper and lower three PWM is within 100 ns,which can compensate the difference between IGBTs,decrease time of over-voltage of IGBT and enhance reliability of circuit operation.Due to differences in characteristics of IGBT,there will be an unequal voltage distribution in series IGBT.Therefore,a static and dynamic voltage equalization network that is composed of resistors,capacitors and transient suppression diodes is necessary to solve the problem of insufficiently tolerant voltage of IGBT.The method of selecting parameters of voltage equalization network is given.The software of Saber is carried out to analyse influence of distributed inductance on pulse spike voltage and the restrained function of parameters of capacitance of voltage-equalizing network and damping resistance on pulse voltage spikes.The correctness of principle analysis is verified by actual tests.Percentage of overshoot voltage is reduced from 33.1% to 14% below through the damping resistor and absorption network of spike voltage under the condition of satisfying time of rising edge of 2kV pulse voltage.The STM32F103ZET6 and TLV2374 are used to design the core control board and driving board circuit to complete collecting of voltage and current,and regulating of DC high voltage power supply.In order to heighten adjustable accuracy of output voltage of DC high-voltage power supply,a second-order passive low-pass filter is designed to finish the conversion from PWM to DC.LABVIEW is used to design PC software to complete the function of monitoring parameters of voltage and current on DC high voltage power supply and the adjustable function of frequency and pulse width of trigger signal.Ensuring the reliability of communication,a communication protocol is added to PC software by self-definition,and the control instrument of string matching of LABVIEW is used to implement the diagnosis work of communication data for preventing communication errors.Test results of high voltage pulse power supply developed by this paper are as follows : In DC mode,output voltage is continuously adjustable from 0 to 2000 V,the maximum output power is 40 W,the stability of output voltage is less than 0.2%,the overall ratio of ripple voltage is less than 0.01%,and the max efficiency is up to 78.96%,the acquiring accuracy of voltage and current is 1V and 5uA respectively.In pulse mode,the frequency of pulse power supply is continuously adjustable from 0 to 20 kHz.The minimum pulse width is 10?s,the time of rising edge and falling edge is less than 2?s,and the minimum percentage of overshooting voltage is 13.1%,which satisfies the requirement of elemental analysis.By testing,pulse power supply has good performance.The equipment is currently used in the project of waterproof pulse neutron generator of the China Institute of Atomic Energy,it runs well and meets the overall demands of project. |
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