Research And Design For Flybcak Digital Power Critical Analog Circuits

With the rapid development of semiconductor and other related electronic technology,the consumption of electronic products,such as cell phone and desktop,has increased rapidly.People's consumption habits are constantly guiding the direction of technological breakthroughs.The variety and quantity of electronic products are increasing,and the market is getting bigger and bigger,which naturally stimulates the research and innovation of relevant designers.For all kinds of electronic products to work well,the power supply is of vital importance.The power supply of electronic equipment from linear voltage regulator to switching power supply to digital power supply has become an irreversible trend.The performance of the internal analog critical circuit plays a decisive role in the overall performance of digital power IC,but,some analog circuits inside switching power supply,such as linear voltage regulator,bandgap reference,can still apply in the digital power supply IC,however,oscillator circuit is a serious challenge for all designers because of its original limit.This article first summarizes and describes the power IC from linear regulators to the switching power supply and then to the digital power of the history and current research status,at the same time it made clear that digital power has become the inevitable trend of the future development of electronic equipment power supply.The emphasis is put on the Flyback type topology.Then,the detailed description and principle derivation of its modulation mode,primary side feedback technique(PSR)and constant current control mode are given.Aiming at the shortcomings of the present digital power simulation critical internal circuit,this article,integrating the characteristics of analog circuit and digital control,design a function of temperature calibration,high frequency,low temperature drift,without any external time unit of the on-chip oscillator;And a BJT power tube drive circuit which is suitable for the Flyback converter with low conduction and turn-off delay.Oscillator design with on-chip RC oscillator as the main body,an integrated temperature-sensitive ring oscillator output clock frequency as a reference,through the digital self-calibration to generate a calibration signal to adjust the capacitor charging current,the temperature used in the chip to achieve temperature Since the calibration function,the oscillator designed in this article still achieves high stability over a wide temperature range and very large voltage fluctuations;Drive circuit with digital control at the beginning of the conduction with maximum saturated base current acceleration power tube into conducting state,intelligent matching load change output during conduction,closer to the turn off with the minimum saturated base current to realize its "shut off" function,effectively reduce the BJT power tube conduction and shut off time delay,and reduce the system cost.The Cadence and HSPICE software are used to simulate the oscillator and driving circuit designed in this article.The simulation results show that under the typical process conditions,the center frequency of the oscillator is 10.1MHz and the duty cycle is 50%.The temperature coefficient of the output clock signal is 49.5ppm / ? within the range of-55 ?-155 ?.In the case of power supply voltage fluctuations,the maximum output clock frequency drift of 0.9%;The turn-on and turn-off delay of the driver circuit at light loads is 350.1ns,287.9ns,and the turn-on and turn-off delays at heavy loads are 326.9ns,326.7ns.All the indexes meet the design requirements.