The Desgin Of A Low Dissipation AC/DC Switching Power Supply Control Chip

Nowadays,the development of electronic technologies has been rapidly and actively promoted,and as the continuously innovation of concepts and improvement of manufacturing process has happened in this area,the connection between electronic products and people’s daily life has become increasingly closed.This connection however,will be deadly confined by the low level power-supply system since the longevity and development of electronic product is highly relied on the power system.Meanwhile,this inferior power system also has created mass waste of the power resource.Therefore,the invention of high quality power system is urgently required by this fact.This thesis will introduce the history and status of the AC/DC convertor and the working principles and control modes of several typical convertors.Thereafter,in order to reduce power dissipation and promote the conversion rate,an AC/DC power managing chip is designed,which also matches the companies’ expectation,on the basis of the fly-back structure.This chip uses the low-cost technique named bipolar,which adopts the working mode of the combination of PWM and PFM.And its main function modules include reference voltage source circuit,PWM generation circuit,oscillator circuit,frequency modulation module circuit,etc.In order to make the system safe and work stably,a variety of protection circuits are integrated in the chip,which include over-voltage protection circuit,under voltage clamping circuit,over-current protection circuit,thermal protection circuit and leading edge blanking circuit,etc.The chip will change automatically between the PWM mode and the PFM mode according to the actual need,thus reducing the switch power consumption of the power tube and making the chip achieve high efficiency within the entire load range.Also,the circuit structure of this chip is simple,which does not require a high technological level.This loop not only reduces the conduction loss of the power transistor,but also saves the chip space and cost.The input voltage range of this chip is 0V～265V,which can generate 12 V output voltage stably,while the rated output power is 12 W.CADENCE simulation tools are used to complete simulation and especially the analysis of each module,then the whole circuit of the chip is also verified through simulation,which including normal working situation of the chip,PFM mode function during light load,and the efficiency under different load conditions.The theoretical analysis and simulation results show that the functions of the chip are normal and meeting design specifications.