Design Of Multi-Mode Operation Green-Mode Switching Power Supply Controller

Efficient green mode power supplies are indispensable parts in active electronic systems. Integrated circuit with multi-mode control and protect functions is the kernel of the power supply system. Advanced PWM control integrated circuits can obviously reduce the size of today's power supplies and improve their efficiency and reliability.In this paper, we designed a highly efficient low-interference green mode switching power supply controller. Multi-mode operation which include Quasi- Resonant, PFM and Burst mode make it possible to achieve high conversion efficiency in a wide range of load. Burst mode ensures that power consumption in standby time is less than 0.3 watt. Quasi-resonant mode can improve the conversion efficiency and reduce the electromagnetic interference at the same time.In order to achieve reliable quasi-resonant operation, the design of an accurate valley detection circuit is very critical, Because opening the power MOSFET at time when the MOSFET drain voltage is lowest can minimize opening lose.In switching power supply was activated, the voltage between the two ends of the capacitor in load side is zero, which is equivalent to a very heavy load, may result in false overload or over-current protection. To resolve this problem we can shield the protection for a short time after the system starts, but that not only reduces the reliability of the chip, but also causes "inrush current" at input side, which debase the quality of power line, meanwhile it causes electromagnetic interference (EMI) and many other issues. So we designed a soft-start circuit to charge the load capacitor step by step after the system starts. The soft start process is over when the load capacitor voltage reaches the rated output voltage and the system automatically switches to normal mode.In addition, in order to enhance the stability and reliability of the chip, we designed advanced protection circuits, including overload protection, over-voltage protection, under-voltage lockout, over-current protection, over-temperature protection and so on, They can protect the power supply system and the chip itself in all foreseeable severe environments.To resolve the problem that voltage feed-forward characteristics are sacrificed to some extent in current mode quasi-resonant converters. The cause of the problem is analyzed and a solution is proposed in this paper. A voltage feed-forward compensation module was designed. With this module in chip, the voltage regulation can be reduced to 0.17% from 0.5% in the same power supply system. The improvement of voltage feedforward can not only improve the quality of power output, but also reduce the size of filter capacitors to save manufacturing costs. In small-capacity power supply with only passive power factor correction (PPFC) circuit, a small filter capacitor can also help the system improve power factor.