Design Of A Multi-mode Controlled 700V Buck AC-DC Power Supply Chip

The innovation of electronic and electrical equipment has marked the technological progress of human society.In recent years,the volume of the electronic equipment market has continued to grow up and high-efficiency energy-saving equipment is more favored by people and recognized by the market.The power management chip of the electronic equipment plays an important role in the conversion and distribution of electric energy.And switching power supply chips have been widely used in fields such as home furnishing and communications and they are moving towards higher efficiency,lower cost and smaller size.Under this background,the thesis designed a multi-mode controlled buck AC-DC switching power supply chip with integrated 700 V power tube which can output constant voltage.Firstly,based on the learning of the basic topological structures of switching power supplies and under the premise of deep understanding of them,the thesis focuses on analyzing the principle of the buck topology and voltage and current characteristics and the internal control mode of it.Secondly,in order to effectively control cost and volume,and weaken static power consumption,the chip periphery adopts a non-isolated structure,eliminating the need for transformers.The 700 V power tube is integrated internally and a unique high-voltage start-up power supply module is designed,which can achieve stable power supply to internal modules under the full voltage range of 85Vac～265Vac.By changing the ratio of the external feedback resistance,the output voltage of the system can be adjusted.The bandgap reference circuit and inductor current sampling circuit are designed without operational amplifier,which can reduce power consumption.In order to improve the accuracy of the reference voltage,the chip adds a modifiable voltage regulator module.The system designs a combination of pulse width modulation(PWM)and pulse frequency modulation(PFM).The system adopts PWM mode control under heavy load,and adopts PFM mode control under light load which can improve the conversion efficiency.Under the control of PFM mode,the switching frequency is changed by changing the frequency of the relaxation oscillator.And the relaxation oscillator is designed with a special high and low threshold comparator to complete the comparison,and a frequency jitter circuit is added to reduce EMI.The system is also designed with protection circuits,such as: over-temperature protection,under-voltage lockout and over-current protection circuits to ensure that the chip works in a safe and reliable environment.The soft start circuit is also added to the system to effectively avoid voltage overshoot.In addition,this paper explores the stability of the constant voltage control loop.Finally,this paper explains the design principles and simulation verification of some sub-modules and builds the overall circuit of the system to simulate.The results show that the design performance meets the research requirements.The design and verification of the circuit are based on the EDA software under the Cadence platform,mainly including Spectre and Hspice and tested with 0.8um 700 V BCD process.The simulation results show that the performance of each sub-module is good,the circuit parameter indicators meet the design requirements during the overall simulation,and the expected results are achieved.And then the layout design work is carried out.