in order to improve the dynamic range and the signal-noise ratio of the image intensifier, keep the flux of the screen of image intensifier constant. in the article, introduced a design of the switching power supply and tested its performance. firstly, used a sampling amplifier amplify the feedback current signals. the feedback signals were converted into square wave signals through a digital circuit. then, using the mosfet in the post stage circuit produced high voltage and high speed adjustable square pulses. the frequency of the pulse is 1 khz, the speed of the cutting edge is 20ns and the amplitude is 200v. the photoelectron emission time of the photocathode is short when the width of the high speed pulse is narrow for strong illumination. on the contrary, the time is long when the width is wide for weak illumination. the number of photoelectron is a constant no matter what kind of the illumination. it keeps the flux reaching the phosphor screen constant. © 2017 spie.