| With the energy efficiency and environmental protection becoming very important, we need more green-energy power supply which has high efficiency and low-cost to meet the demand for portable electronics market.Nowadays, there are mainly three kinds of modulation modes using in switching mode power supply (SMPS), including pulse width modulation (PWM), pulse frequency modulation (PFM) and pulse skip modulation (PSM). PFM is rather difficult due to the random characteristic of the frequency spectrum distribution, that's why we usually use PWM. However, the efficiency of PWM is very low at light load, so we must take some ways to improve the efficiency. Pulse skip modulation (PSM) which bases on fixed pulse width and varying frequency is a good choice to reduce the switching frequency and decrease the power consumption at light load.A small-size and high performance green-energy offline power supply controller was designed in this thesis. It can achieve stable and adjustable output voltage during the input voltage range from 8.6V to 18.0V and maximum load current up to 400mA. The chip can switch automatically from pulse width modulation and pulse skip modulation to maintain high efficiency by detecting different load conditions. This power management IC could be used in most of portable applications, such as: Smart Phones, Personal Digital Assistants, Digital Cameras, MP4 Players, and Portable Media Players.In this thesis, fly-back optical coupling topology, feedback method and working principle of this chip were given firstly. After that the whole chip diagram was proposed according to the design specification and the whole chip operating principle was introduced. Then 4 sub-circuits, including band-gap reference circuit, under voltage lock and over-voltage protection circuit, oscillator and the slope compensation circuit and operating mode selection circuit were analyzed in details. These circuits were simulated and verified by SPECTRE and HSPICE. By contrasting the integrated system simulation and design parameters of the overall index, the design of the circuits can satisfy the pre-index requirements well.Finally, after the overall simulation of the design, the chip was laid out and taped out on CSMC0.5μm18VCMOS process. The test of the key performance parameters of the fabricated chip indicated that the chip met the original targets well. |
