A Bipolar Cockcroft-Walton Voltage Multiplier for Gas Lasers

Rosli Besar,Shahid Iqbal

doi:10.3844/ajassp.2007.795.801

Abstract

A bipolar Cockcroft-Walton Voltage Multiplier (CWVM) is proposed as an attractive alternative to the symmetrical Cockcroft-Walton voltage multiplier for continuous wave gas lasers (e.g. carbon dioxide gas laser). The proposed CWVM formed by combining positive and negative voltage multipliers consisting of equal number of stages and driving in parallel by an ac voltage source. The proposed voltage multiplier needs only one ac power source, therefore there was no need of center taped high voltage transformer, unlike symmetrical voltage multiplier which require center-tape transformer. It possess inherit ability of cancellation of fundamental and higher order odd harmonics of ripple components, unlike the symmetrical CWVM which may generate odd harmonic of ripple in case of any asymmetry of driving voltage. In addition to this the proposed voltage multiplier has faster transient rise and less voltage drop as compared symmetrical CWVM. The experimental and simulation results are presented to show the effectiveness of proposed voltage multiplier.

Highlights

Cockcroft-Walton voltage multiplier (CWVM) circuit was developed long time ago in 1932, it is still widely used in many high-voltage low-current applications such as lasers, accelerators, ultra-high voltage electron microscopes, and x-ray power generators[1,2,3,4,5,6] etc
The fundamental harmonic component was found to be dominant in some lower load current application such as in some electron microscopes and accelerators where symmetrical CWVM is used as high voltage generator[12,13]
To overcome this problem of asymmetry of driving voltage and to get output voltage free from fundamental and higher order odd harmonics we have proposed a bipolar CWVM

Summary

INTRODUCTION

Cockcroft-Walton voltage multiplier (CWVM) circuit was developed long time ago in 1932, it is still widely used in many high-voltage low-current applications such as lasers, accelerators, ultra-high voltage electron microscopes, and x-ray power generators[1,2,3,4,5,6] etc. As a result the fundamental and higher order odd harmonic components of load current generated voltage ripple are cancelled and the dc output of proposed bipolar voltage multiplier contains only second and higher order even harmonics with second harmonic being the most significant. To estimate the total output ripple voltage let us suppose that Q = I ⋅T = I f is the charge transferred to load per cycle This charge is supplied by the series connected capacitors of smoothing column (C1, C2 ,− − − − C p ) and (C1, C2 ,− − − − Cq ) of positive and negative voltage multipliers. The change or ripple δVab in the dc output of positive voltage multiplier due to charging of smoothing column capacitor after being discharged by load current is given by; δVab pQ C p. Where, ∆Vbc and ∆Vbc is the voltage drop on load of positive and negative voltage multiplier respectively and is given by;

D 2 fC 3

D n3 fC 12

RESULTS AND DISCUSSION

CONCLUSION