Quasi-resonant Ac / Dc Controller Chip Design Based On The Primary Side Control, High Frequency, High Efficiency

Currently, the requirement for power supply is increasingly stringent with the rapid development of portable electronic devices. Multi-function, small size and green power have become the main characteristics in the field of the cell phone charger and the adapter, and it promotes the development of power management which adopts the high-frequency and high-efficiency controller chip. Meanwhile, in the AC/DC, the fly-back converter has become the main topology. But in the fly-back converter, switching losses and EMI noise will arise because of the high voltage stress of Vce of the power switch. What's worse, with the higher switching frequency, the situation becomes more badly. To satisfy the requirement of small size, high-frequency and high-efficiency, a high-frequency and high-efficiency quasi-resonant fly-back AC/DC converter controller chip based on the primary side control is presented in this dissertation, which is mainly used in the small-size lithium battery charger and adapter.The controller provides accurate constant current, constant voltage (CC/CV) regulation. For eliminating the opto-coupler and secondary control circuit, the said controller adopts primary side control technology. And it can also maintain system stability without loop compensation circuitry. Further, it has a smaller system size because of operating in high switch frequency. For resolving the conflicts between high-frequency and high-efficiency of the system, the controller adopts quasi-resonant (QR) control mode in the heavy load condition, which turns on the power transistor at the valley of Vce to reduce the switching losses and suppress the EMI interference. In light load condition, it works in PFM control mode to achieve high efficiency at full load range.The basic principles of switch power supply and the characteristics of each mode are analyzed in this dissertation. And the complete system architecture of a high-frequency and high-efficiency quasi-resonant AC/DC converter controller based on primary side control is also proposed. Based on detailed analysis of the operational principles of the controller, the circuits are designed and simulated, which include accurate constant current, constant voltage (CC/CV) regulation, built-in line compensation and output cable voltage drop compensation, quasi-resonant, complete protections and so on. The chip has been taped-out in 1.5um bcd process of BCD semiconductor. The test results show that the controller designed in this dissertation provides a 5V output in 0.55 A maximum load current, operates in quasi-resonant mode in heavy load conditions, and maintains stability at full load range. The average conversion efficiency comes to 70% or more, and the desired functions of system have been achieved.