Research And Design Of A Buck-Boost DC-DC Converter

As the rapid growth of consumer electronics market, battery-powered portable electronics products continue to become smaller, lighter, and this device battery capacity is also decreased. This requires such equipment as possible to improve the efficiency of power supply modules, reducing power consumption and enable a wide range of battery voltage to provide a stable output voltage to extend battery life.A low voltage power supply of the Buck/Boost DC/DC converters are described in this article. This converter can be used to convert the voltage of lithium battery to a stable voltage. And compared with conventional Buck/Boost topology, this converter can realize the output voltage and input voltage of the same direction. And using synchronous rectification to reduce power loss to improve efficiency and also reduces the size of the external circuit. When the system began to work, it will produce inrush current, so we designed a soft-start module to protect the conversion system.This article focuses on the design of the circuit module in the control loop, such as the error amplifier, RAMP module, PWM comparator circuit and so on. Using current-mode bandgap structure, to provide a stable reference voltage for the system. In addition, in order to make the system not received over voltage, over temperature and other conditions affecting, the system was designed over voltage, over temperature protection circuit to improve the stability of the system.In addition, the efficiency of traditional PWM modulation will fall dramatically with the decreasing of the load current. In this article, different modulation modes according to different load condition are use to improve the efficiency in light load condition, PWM modulation in heavy medium load condition and BURST modulation mode in light load condition.At last, all the circuit and the system are accomplished in chater.35 technology and simulated in Candence Spectre. The simulation results show all the circuits and the system works well, and almost realized all expected specifications.