A Low-power Current-mode Switching Power Supply Circuit

Simple switching power supply management IC was popular used in computer, electronic equipment, communications equipment for its low power consumption, high efficiency, lowest component count switcher solution. Electronic equipment becomes smaller and lower cost, which has been making switching power supply light, small, thin and high efficiency.Based on CMOS technology and using Composer and Spectre tools of Cadence EDA, a type of single-chip controller is designed for the fly-back switching power supply of AC/DC. It works at 70KHz with current mode pulse width modulation (PWM); and the max duty is 75 percent. The power consumption is decrease greatly because Green-mode and power limiting is included in this single-chip controller. Green-mode which provides off-time modulation to linearly decrease the working frequency under light-load conditions and power limiting which will turn off the transistor when peak current of inductor reaches the threshold current.This paper introduces the basic theory of fly-back topography and current mode PWM firstly. Then the total structure of the single-chip controller is present according to the function requirement and the working theory and the working principle are showed based on its actual application. In chapter three, the all sub-circuits including UVLO, current bias, LDO, oscillator, green mode, slop compensation, power limiting, PWM, OVP, blanking time generator, logic controller are designed and simulated. As a result, all of the sub-circuits are satisfied the requirements. The synthetic circuit is also simulated about normal working, green mode working and so on; the results of simulation meet the function requirement.The single-chip designed in this paper is summarized and the development trend of switching power supply is introduced at last.