Design And Research Of Core Circuits For Switching Power Supply Chip

Power supplies are widely used in scientific research,economic construction,defense facilities,and all aspects of daily life,so the role of high-performance power ICs becomes more and more important.The power supply is moving toward high integrationn,high conversion efficiency,and low power consumption.The flyback switching power supply has replaced the linear regulator due to its excellent performance.At present,the flyback switching power supply chip is the main research direction.Combined with the company's project,core circuits of a flyback switching power supply chip based on pulse width modulation is designed through system design,circuit design and simulation verification,which is mainly used in chargers and adapters.This research mainly includes the chip's under voltage lock out circuit,internal voltage generation circuit,power-on reset circuit,bandgap reference circuit,error amplifier and other modules.Aiming at the problems of slow response,large power consumption and large area of traditional under voltage lock out circuit,a new under voltage lock out circuit is designed,which can achieve the various indexes of under voltage lock out without using additional reference voltage source,comparator and complex digital logic,the turn-on voltage of the under voltage lock out circuit is 7.6V,and the turn-off voltage of the under voltage lock out circuit is 14,8V;Aiming at the problems that the traditional bandgap reference circuit has a complicated structure,high power consumption,and low output voltage accuracy,the new bandgap reference circuit uses cascode current mirror to clamp each branch current,at the same time,the new bandgap reference circuit generates a reference voltage directly on the branch with a positive temperature coefficient current,which simplifies the circuit structure and reduces chip manufacturing costs and static power consumption,the temperature coefficient is 64 ppm/? from-40? to 150?;Aiming at the problem that single-stage amplifier cannot meet the requirements of high gain and high swing in high-precision systems,the error amplifier uses a two-stage operational amplifier.The first stage circuit chooses a folded cascode structure to obtain the high gain required.The second stage uses a common source structure to expand the output signal swing.The circuit simulation is used to ensure that the phase margin,and unity-gain bandwidth of the amplifier circuit meet the design index requirements under different process conditions.Based on the 0.25?m BCD process,the design and simulation of core circuits are completed,and the chip and package are carried out.Finally,the physical test is carried out in the actual flyback conversion system.Test results show that the chip can work in a flyback circuit,and achieve 5V/3A output,and the efficiency can reach 86.2%.Compared with similar chips at home and abroad,the chip in this research has the advantages of stable output current,high efficiency,simple design,etc.,and has great market application prospects.