Research And Design Of Efficient Synchronous Rectification Psm Converter

PSM (Pulse Skip Modulation) is a novel modulation. PSM has many merits such as high efficiency at light load, high response speed, robustness and ease of implementation for circuit design. However, PSM also has some disadvantages, for example, the output voltage ripple is large at light load and the system may produce audio frequency noise. Synchronous uses low resistance power MOSFET instead of diode in DC-DC convector. The comparison with SBD proves that synchronous has many merits such as the positive voltage is low, negative voltage is high, negative current is low, efficiency is high. But the dead time reduces the efficiency.The dissertation based on the dead time control methods, proposes an adaptive dead-time optimization control circuit which based on the length of dead-time in current cycle to adjust the next cycle of dead time. The comparison with a fixed dead time circuit proves that the adaptive dead time circuit can improve the efficiency.In this thesis, based on the optimized PSM modulation model, introduced two kinds of duty-cycle, a synchronous boost converter is designed. The chip input voltage range of 4 ~ 4.5V, output voltage is 5V, the operating frequency is 300KHZ, the load current range of 1mA ~ 60mA. The dissertation mainly introduces the design and simulation of PowerMOS, Voltage Reference, Zero crossing comparator, Sequence check circuit, finally completes the layout of the chip and test. Zero-crossing comparator circuit can avoid the reverse flow of current in the synchronous rectifier caused by powerMOS, and improves the efficiency. Sequence Check circuit can keep system from entering the audio frequency range.The dissertation designs the efficient synchronous Boost converter control circuit, based on optimized PSM, which improves the efficiency of power converter system, besides optimizing the dead time, depressing the output voltage ripple and avoiding the audio noise.