iwatt原边方案设计说明.doc

iwatt原边方案设计说明.doc1
New Times are Comi ng -
Digitally Operated Primary Con trol Tech nology for AC/DC SMPS
Abstract
This paper describes a whole new con trol tech nique and had bee n successfully being employed in off-li ne type adapter/charger applicati ons, which results in sig nifica nt reduct ion to exter nal comp onents and various performa nee improveme nts.
In troduct ion
A new digital control methodology has resulted in greater simplicity and design flexibility in low power SMPS topologies which conven ti onal an alog methods would find difficult if not impossible to achieve. By comb ining this new con trol scheme into an off-li ne type of adapter or charger applicati on, it could greatly reduce the nu mber of exter nal comp onents as well as enhance supply performa nee in many respects.
The controller has built-in digital control algorithms to quickly and smoothly transition betwee n differe nt operati ng modes for reduced switchi ng losses duri ng no-load operati on.
The full-load efficie ncy is enhan ced by the use of so-called “ emulated primary curre nt mo
control ” to eliminate the need for a primary sensing resistor. The full-load efficiency is also enhan ced in cellular charger applicati ons by the elim in ati on of sec on dary-side con sta nt current sense circuitry. Its unique digital control algorithm allows fast pulse-by-pulse an alysis of the switch ing waveform a