Analysis And Design Of Flyback Feedback From The Oirginal Edge Of A SMPS IC

Since switching power supply has been invented in1950s, its application has comegradually from space to people’s lives. It is at everywhere, such as Chargers, adapters, auxiliarypower supply, lamps, street lights and so on. With the switching power supply toward fourdirection of the development of high efficiency, small size and high frequency, EMI andswitching loss which restrict the development of switching power supply are becoming abottleneck. To reduce the impact of these issues, frequency shuffling, power factor correction,synchronous rectification which improve further the efficiency of the switching power supplychip are adopted. With the growing popularity of consumer electronics products, the marketdemand for the switching power supply is also increasing. Low-power and high efficiencyswitching power supply products can be widely applied.A primary-side flyback switching power supply chip which is based on1um40V ofHuahong high pressure technology library is designed. To reduce the circuit size, the primaryside feedback technology to replace feedback loop which is based on chip PC817and the TL431is adopted, but also put forward higher requirements for the flyback transformer. Except thebuilt-in overvoltage and overcurrent protection circuits, the chip also embedded in the frequencyshuffling module to reduce circuit EMI effect.This chip is different from other primary-side chipwhich sample stability of the feedback voltage after it was filtered, it directly sample thetransformer auxiliary winding voltage through resistor divider. So it makes chip’s built-insampling and holding circuit have higher requirements that it must accurately sample thestability of the voltage of a short time before the falling edge of output waveform.The design and simulation of various functional modules of the chip is completed.