Application of ionizing radiation is remaining widely in the daily lives of people such as scientific research, industry , medicine, military, and agriculture. Moreover , safely in work place is very important especially when it involves radioative materials. There are four major types of ionizing radiation from radioactive materials: alpha, beta, gamma and Xray,a part of the electromagnetic spectrum and ionizing radiation, specifically at its high frequency and short wavelengths.
VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF PHYSICS DUONG DINH QUY DESIGN AND FABRICATION OF HIGH VOLTAGE POWER SUPPLY FOR RADIATION DETECTOR Submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Nuclear Technology (Advanced Program) Hanoi - 2017 VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF PHYSICS DUONG DINH QUY DESIGN AND FABRICATION OF HIGH VOLTAGE POWER SUPPLY FOR RADIATION DETECTOR Submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Nuclear Technology (Advanced Program ) Supervisor: Dr NGUYEN THE NGHIA Hanoi - 2017 ACKNOWLEDGEMENT I have completed my thesis which is a partial fulfillment of requirement for the degree of Bachelor in Nuclear Technology On this opportunity, I would like to express my gratitude to the Department of Nuclear Physics, Faculty of Physics, VNU-University of Science generally and especially to my supervisor Dr Nguyen The Nghia for his help, advice and guidance throughout the process of collecting information, analyzing, experiment and completing the thesis I would also like to thank my teacher Bui Thi Hoa for her assistance and kind attitude in the process of doing this thesis To my family, I would like to express millions of thanks to them for their support and always understanding in everything Hence, I would like to thanks to all my friends for their great cooperation and supports either direct or indirect Student, Duong Dinh Quy i Contents ACKNOWLEDGEMENT i ACRONYMS iv LIST OF FIGURES v LIST OF TABLE vii PREFACE viii CHAPTER 1: INTRODUCTION TO HIGH VOLTAGE POWER SUPPLY 1.1 Principle of radiation detector 1.2 High voltage power supply CHAPTER 2: STRUCTURE OF HIGH VOLTAGE POWER SUPPLY 2.1 Oscillator 2.1.1 Requirement for common Oscillator 2.1.2.Phase-Shifting Oscillators 2.2 Inverse phase amplifier 2.3 Push-pull amplifier 12 2.4 Ferrite core transformer 15 2.5 Voltage multiplier 16 2.6 Stability voltage 17 2.7 Low voltage power 18 CHAPTER 3: CONSTRUCTION OF REALITYS HIGH VOLTAGE CIRCUIT BOARD 20 3.1 Low voltage DC power circuit 20 3.2 Calculation for Oscillator 20 3.3 Biasing for transistor in phase splitter stage 23 ii 3.4 Design for step-up transformer 24 3.5 Voltage divider and stability voltage stage 25 3.6 Reality high voltage power supply 26 CHAPTER 4: RESULTS AND DISCUSSIONS 30 CONCLUSIONS 34 REFERENCES 35 iii ACRONYMS List Acronym Definition AC Alternating Current BJT Bipolar Junction Transistor CW Cockcroft-Walton DC Direct Current G-M Geiger-Muller HUS Hanoi University of Science OP-AMP Operational Amplifier PCB Printed Circuit Board iv LIST OF FIGURES Figure 1.1.Nuclear instrument for radiation detection and measurement Figure 1.2.Gas-filled detector Figure 1.3.Scintillation detector Figure 1.4.High voltage level apply for gas-filled detector Figure 2.1: Block diagram of the typical radiation detector Figure 2.2.Conventional form of oscillator with feedback Figure 2.3.Phase-shifting oscillator’s principle Figure 2.4 All-pass network filter Figure 2.5.The phase angle of all-pass network Figure 2.6.Common emitter configuration 10 Figure 2.7.Common base configuration 10 Figure 2.8.Common collector configuration 11 Figure 2.9.Transistor with internal resistor 11 Figure 2.10.Class B output characteristics curves 13 Figure 2.11.Push-pull power amplifier 14 Figure 2.12.Ferrite core transformer 15 Figure 2.13.The typical Cockcroft-Walton Multiplier circuit 17 Figure 2.14.Configuration for stability high voltage 18 Figure 2.15.Low voltage DC source 19 Figure 2.16.AC current and DC current 19 Figure 2.17.Half-wave Rectifier RC-Filter 19 Figure 3.1.DC power ±15V 20 Figure 3.2.All-pass filter for sinusoidal oscillator 21 Figure 3.3.Circuit sinusoidal oscillator 21 Figure 3.4.Simulation of sine wave generator by Proteus 8.5 22 Figure 3.5.Phase splitter stage 23 v Figure 3.6.Stability voltage stage 25 Figure 3.7.Schematic diagram circuit for high voltage power supply 26 Figure 3.8.PCB in simulation 27 Figure 3.9.Printed circuit board in reality 27 Figure 3.10.High voltage power supply circuit board 28 Figure 3.11.High voltage power supply has been finally approved 28 Figure 3.12.Source ±15V DC 29 Figure 4.1.Operating of High Voltage circuit at 2000V 32 vi LIST OF TABLES Table 2.1.Comparision of three configuration operating BJT 12 Table 4.1.Determination of high voltage value at 2kV 30 Table 4.2.Measurement for four level voltage 31 Table 4.3 The dependence of the high voltage on the frequency of oscillator 32 vii PREFACE High Voltage Power Supply is essential for nuclear radiation detection or counting system A high voltage power supply unit that is suitable to use with Geiger Muller counter, scintillation detector and semi-conductor detector which are constructed with locally available components The constructed high voltage unit is based on push-pull topology driving high frequency transformer The desired voltage is rectified and multiplied by voltage multiplier unit provides kV-DC at approximately 1mA maximum output current In this study, I will describe how to make a High Voltage Power Supply from fundamental of theory to manufacture diagram schematic circuit and reality production I constructed a high voltage power supply based on the design, simulation and step by step fabrication stage of High Voltage Supply for G-M counter and Scintillation detector The content of the thesis is divided into four main chapters: Chapter 1: Introduction to High Voltage Power Supply Chapter 2: Structure of High Voltage Power Supply Chapter 3: Construction of High Voltage Circuit Board Chapter 4: Results and Discussions viii Design and Fabrication of High Voltage Power Supply for Radiation Detector In this circuit, the upper op-amp provides 180o of phase shift at low frequencies, while the two all-pass networks provide variable phase shift If the amplifiers are ideal, this circuit will oscillate at the frequency where the combined phase shift of the two all-pass networks is 180o, because at that frequency the phase shift around the entire loop is 360o and positive feedback occurs The dynamic resistances of diode D1, D2 are quite large when the voltage is low, so the gain of the inverting circuit composed of amplify gain is high make sure the starting of oscillation of the circuit The combined phase shift of the lower two circuits will be 180o at a frequency fo: 180o 2arctg 2 fo (R RV2 ) C1 180o 2arctg 2 f o (R10 RV3 ) C2 180o (10) The solution of this equation yields the oscillation frequency fo 2 C1C2 (R RV2 )(R10 RV3 ) (11) By the way using variable resistor RV2 and RV3, the frequency will change in winding range This design can generate sin wave form with adjustable frequency from 200Hz to 10000Hz By using the simulation software Proteus 8.5 find the appropriate values for the oscillator's operation with the best possible signal Figure 3.4.Simulation of sine wave generator by Proteus 8.5 22 Design and Fabrication of High Voltage Power Supply for Radiation Detector As shown in the figure, the output signal of the oscillator at point C is inverted phase with the input signal at point A and the phase delay of 90o with respect to point B This oscillator ensures two purposes: providing oscillator power for high voltage circuits and selecting the most suitable frequency for the operation of the pulse transformer 3.3 Biasing for transistor in phase splitter stage This amplifier stage uses configurations: Emitter common two and Collector common with a gain factor of and produces two reverse phase signals There is a complementary pair of transistors used here C828(NPN) and A564(PNP) A method of biasing a transistor for linear operation using a single source resistive voltage divider A DC bias voltage at the base of the transistor can be developed by a resistive voltage divider that consists of R1 and R2 VCC: the dc collector supply voltage Figure 3.5.Phase splitter stage With transistor NPN-C828 has a gain equal 100, assume that output voltage Uo=2V, transistor gain β=100, UE=2V, IC=1mA We have: RE UE UE 2k IE IC Select I P 12.I B 12 IC Therefore, R R1 R2 R2 120 A U cc 120k , IP U E U BE 0.6 21.6k R1 =120 -21.6 = 98.4 k IP 120.106 Select standard resistor: R1=100 k , R2= 27 k 23 Design and Fabrication of High Voltage Power Supply for Radiation Detector For the amplitude of output transistor equal to input signal in the B lead (leg) I choose RC = k The only functional difference between a PNP transistor and an NPN transistor is the proper biasing of the junctions when operating For any given state of operation, the current directions and voltage polarities for each type of transistor are exactly opposite each other Similar, biasing for PNP transistor-A564 with emitter common configuration have the same amplitude with input signal and inversion phase 3.4 Design for step-up transformer In this part, I selected ERL-35 ferrite core transformer high frequency because it is used to apply in professional amplifiers features: High frequency, wide frequency, large transmission power, stable performance and low temperature rise Apply the equation (5) in chapter for calculating the number of required primary turns: V 10 N 4, 44 f B A in p max c During operation, the DC power voltage does not stay fixed at 15V With high loads, the voltage will be less than 15V So, I will take 12V as our lowest possible input voltage The switching frequency is selected 6000 Hz The value of maximum flux density Bmax is usually given in data sheet ferrite core We usually take value of Bmax between 1300G to 2000G This is usually a acceptable range for all ferrite core transformers[13,14] I will take 1600G for DCDC converter because high value of flux density will saturate the core and low value of flux density will lead to core under utilization The effective cross sectional area of ERL-35 core is AC = 0.95 cm2 From the values of all required parameters for calculation the number of required primary turns Np: Vin=12V, f=6000Hz, Bmax=1500G, AC=0.95 cm2 substitute to equation (5) we have Np= 31.6 turns In this case, I selected Np= 32 turns because it depend on unstable of maximum flux density Bmax ,I assumed that before Note that for push pull it will be half the primary number of turns 24 Design and Fabrication of High Voltage Power Supply for Radiation Detector Suppose that output secondary coil is 300V From equation (4) N N p s V V in , out and parameters found, we can find the number of secondary coil is Np= 640 turns 3.5 Voltage divider and stability voltage stage The device that consists of two input terminals, in which reference input signal is fed to one terminal and the actual value of the signal is fed to another terminal Then, an output signal is generated at the output terminal based on the difference between the two input signals fed to the two input terminals This generated output signal is either low or high The actual value come into negative terminal is the voltage from voltage divider I use two resistor 10 M and 10 k for this design: Input negative terminal = HV R24 =2V for 2kV high voltage, the R23 R24 reference value for positive terminal can be adjusted from to Vcc= 15V This is a adjusting the mechanical control Figure 3.6.Stability voltage stage In general, the output of an op-amp fluctuates positive and negative to extreme voltage that is approximately equal to the supply potentials In this case, op-amp µa741 is connected to a ±15V, then the maximum output voltage is given as 25 Design and Fabrication of High Voltage Power Supply for Radiation Detector ±11V (70% of Vcc) This is due to the extreme high open loop gain of the op amp (10,000 to million) Thus, if a hundred microvolts of voltage difference is created by any input, then it will be amplified approximately by one million times and output is driven into saturation Thus, the output remains at its maximum or minimum value 3.6 Reality high voltage power supply After a series of calculations and custom parameters we obtain the schematic diagram circuit as shown figure 3.7 Figure 3.7.Schematic diagram circuit for high voltage power supply After that, I convert schematic diagram circuit into a printed circuit board (PCB) layout using Proteus 8.5 software 26 Design and Fabrication of High Voltage Power Supply for Radiation Detector Figure 3.8.PCB in simulation PCB is very cost effective, it assembles the complex circuits in small space and eliminates the risk of loose connection, it has pre designed copper tracks to connect the components in effective and clean way Figure 3.9.Printed circuit board in reality From the printed circuit board, proceed to select the components according to the principle diagram was designed as shown in figure 3.6 After that I connect between the surface of the PCB and the electronic component and completed circuit as shown in figure 3.10 and figure 3.11 27 Design and Fabrication of High Voltage Power Supply for Radiation Detector Figure 3.10.High voltage power supply circuit board Figure 3.11.High voltage power supply has been finally approved 28 Design and Fabrication of High Voltage Power Supply for Radiation Detector Figure 3.12.Source ±15V DC This design is used two transformers: iron core transformer for low voltage circuit and ferrite core for high power voltage Three power transistor H1061 is selected for push-pull amplifier and stability voltage stage Multiple voltage circuit is design with increasing five times from output secondary pulse transformer to high voltage output Most of stage design is simulated in Proteus 8.5 and achieving good working 29 Design and Fabrication of High Voltage Power Supply for Radiation Detector CHAPTER RESULTS AND DISCUSSIONS An experimental prototype was fabricated in the Accelerator room-HUS using the above design and tested for its performance The experimental data is shown in Table 4.1 and 4.2 Table 4.1.Determination of high voltage value at 2kV Time(min) High Voltage (V) May, 16th May, 17th May, 20th May, 23rd 2000 2010 2010 2010 2001 2011 2012 2010 10 2001 2011 2012 2011 15 2001 2012 2012 2011 20 2001 2011 2012 2011 25 2001 2011 2012 2011 30 2001 2011 2011 2011 35 2001 2011 2012 2011 40 2001 2011 2012 2011 45 2001 2011 2012 2010 50 2001 2011 2012 2011 55 2000 2011 2013 2011 60 2000 2011 2012 2011 65 2000 2012 2012 2011 70 2001 2011 2013 2011 75 2001 2011 2013 2011 80 2001 2011 2013 2012 85 2001 2011 2013 2011 90 2001 2011 2013 2012 95 2001 2011 2013 2011 100 2001 2011 2013 2011 105 2001 2011 2013 2011 110 2001 2011 2013 2011 115 2002 2011 2013 2011 120 2001 2011 2013 2011 30 Design and Fabrication of High Voltage Power Supply for Radiation Detector Table 4.2.Measurement for four levels voltage Time (min) High Voltage (V) 2011 1502 1000 500 2012 1502 1000 501 10 2012 1502 1000 501 15 2012 1502 1000 501 20 2012 1503 1000 501 25 2012 1502 1000 501 30 2011 1503 1000 501 35 2012 1503 1000 501 40 2012 1503 1000 501 45 2012 1503 1000 501 50 2012 1503 1000 502 55 2013 1503 1000 501 60 2012 1503 1001 501 65 2012 1503 1000 501 70 2013 1503 1001 501 75 2013 1503 1000 501 80 2013 1504 1000 501 85 2013 1503 1000 501 90 2013 1503 1000 501 95 2013 1504 1000 501 100 2013 1504 1000 501 105 2013 1504 1000 501 110 2013 1504 1000 501 115 2013 1504 1000 501 120 2013 1504 1000 501 31 Design and Fabrication of High Voltage Power Supply for Radiation Detector Figure 4.1 Operating of High Voltage circuit at 2000V Table 4.3.The dependence of the high voltage on the frequency of oscillator Frequency (KHz) Voltage (V) 3.50 1997 3.60 2000 3.65 2001 3.68 2003 3.70 2002 3.75 2002 3.80 1994 3.85 1985 32 Design and Fabrication of High Voltage Power Supply for Radiation Detector The Table 4.1 as shown the stability of high voltage at 2kV is quite good The precision of the measurement system can be as high as 0.1% at 2kV This is probably caused by the gain factor of transistor depending on temperature The component in PCB can not be standard condition Because there is no the detector output of the high voltage power, so the delay will be smaller, and the stability will be higher However, If the high voltage power supply has 1% change, the magnification of the photomultiplier tubes will be a change of about 10%, so the stability demanding for high voltage power supply is very high As shown Table 4.2, high voltage can be change in the large range from 200V to 2000V We can see the range 500V-1000V almost non-fluctuation Therefore, this design is not only suitable for Geiger-Muller counter but also can be used for some scintillation detector requiring low requirements for high voltage In the last table show that the dependence of the high voltage on the frequency of oscillator During measurement, the resonant frequency at high voltage was found (3.68 KHz) In this frequency, my design can be got the highest efficiency 33 Design and Fabrication of High Voltage Power Supply for Radiation Detector CONCLUSIONS To complete the thesis, this thesis brings together the conclusions from throughout the work and arranges them under the different themes of the research This thesis has been illustrated basic principal of high voltage power supply for some of radiation detector A detailed step-by-step design process of a push-pull topology DC-DC converter is presented here The theoretical design is supported by simulation and experimental verification As further work, the design process can be extended to use for scintillation detector Based on the design that was done, there is a need for 15 volt to 2000 volt DC-DC converters, especially when being used with sine wave inverters For the design of a push pull topology seems to work best with rather high efficiency Based on schematics and simulations, the device should have worked Although the design might not work as expected, a lot was learned by myself in terms of researching existing products, finding components to give desired results, schematic and PCB layout 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