Research Of Mixed Model PFC Chip

With the progress of technology, the functions of electric products becomes more and more completely, at the same time the power consumption becomes increasing too. Through the fine management of the power, the switching power supply achieves the purpose of saving energy. This paper designed a AC/DC switching power supply chip by mixed model control, basing on BCD process, with the EDA tool cadence.The main content of this topic includes principle analysis of this mixed model control PFC chip, designing of chip structure, simulation and verification of the circuit, designing and verification of layout for this chip, and taping out successful. This chip designed mainly for BOOST structure used for up voltage, and the typical application circuit has been simulated and verified by specture. When input AC220V voltage, the circuit can output DC385V voltage, and the rated power dissipation is250W.The mixed mode PFC chip uses average circuit mode control with heavy load. The core control module is multiplying unit, it can sampling voltage and current signals of front circuit, and at the same time referent the voltage signals of back circuit. With the help of error amplifier, it can get the average current control loop, and then the current loop signal compares with the oscillator signal, the signal output from the comparator through amplifying circuit to increase driver ability, finally getting the gate driver signal.The mixed mode PFC chip uses critical mode control with light load. The chip achieves mutual switching between average current mode and critical mode by ZCD circuit module. When the ZCD mode detects zero current signal of inductance, it will output signal to logic control circuit, and the output signal of logic mode will change, then inductance will enter into charging cycle ahead of schedule. So that the chip can get higher conversion efficiency under different load conditions.