A Blend Mode Offline Switching Power Supply Chip Design

Single-chip switching power supply management IC has many virtues such as high integration level, most cost effective, lowest component count switcher solution, and high performance. Making use of it can form high efficiency insulated switching power supply without using utility power transformer. The switching power IC is selected firstly in the design of high power switching power supply, precision switching power supply, application specific switching power supply and so on in the world, which has been making switching power supply short, small, light and thin.Based on CMOS technology, adopting hybrid modulation, an off-line switcher chip which has the same electronic parameters as TNYs is developed. A power MOSFET with breakdown voltage exceeding 700V is integrated on this chip, and the maximum output power is about 15W. The operational mode is controlled by the current limit state machine and auto-restart circuit, both of which are integrated in this chip. The current limit state machine can feel the weight of the load and defines it as different states. The output power is small in light state and becomes larger in heavier state, which makes the switcher have the best efficiency.The basic theory of SMPS, PWM and PFM are given first. The fly back converter and the function block diagram of the chip are introduced later. And then Chapter 3 explains the working of digital circuits such as state machine, auto-restart counter, bypass capacitor selector and so on. The principle and simulation results of voltage reference, jitter oscillator, protection circuits are introduced in Chapter 4. Finally, this paper introduces the chip's layout design, and the testing result and analysis are given.