Design Of High Efficiency Buck Converter Based On Burst Mode

The development of intelligent products is promoted by industry 4.0.Sensors,as the eyes of various intelligent devices of the internet of things,such as building automation,medical care and intelligent metering,play an important role in product intelligence.Product scalability is further improved by wired and wireless connections.But at the same time,the more strict power supply equipment of industrial sensor system is required which is high conversion efficiency and wide input range,to ensure the effective available power of the sensor and the transient anti-interference ability.The loss of Buck converter working in discontinuous conduction mode is deduced in this thesis.In order to improve the conversion efficiency,a hysteresis control Buck converter working in Burst mode is designed,which effectively reduces the quiescent current of the Buck converter.Based on the loss model,the relationship between the loss of Buck converter and the peak inductor current was deduced,and an off-chip adjustable peak inductor current circuit was designed to adjust the peak inductor current by changing the off-chip resistance.According to the characteristics of the control circuit,a dynamic sleep circuit is proposed,which can selectively turn off the sub-circuits in different working stages of the system,further reduce the quiescent current,and improve the conversion efficiency.Aiming at the disadvantage that the traditional zero current detector is easy to be affected by process and temperature,an adaptive zero crossing comparator is designed to improve the accuracy of low-side power switch MN by adjusting the offset resistance.A current limit soft start circuit is designed in the peak current comparator.In the power-on stage,the peak value of the inductor current rises slowly,limiting the energy transferred to the output end of each switching action,making the output voltage follow the soft start of the peak inductor current,and realizing the soft start function without increasing additional circuit.Based on 0.35μm BCD process,the circuit design and layout are completed,and the designed Buck converter is simulated.The simulation results show that the Buck converter can work normally at the input voltage of 5V～36V,and the output voltage ripple is 12 m V at the output voltage of 1.2V.The maximum output current of the Buck converter is 100 m A,and the overall efficiency curve is relatively smooth.The static current of the Buck converter is 16μA under no load.Under the condition of 12 V input voltage and 3.3V output voltage which is typical application conditions,the efficiency is 83% at 1m A and87% at 100 mA.