提出了一种可片内集成的软启动电路,电路由斜坡电压产生电路和带软启动功能的误差放大器组成.斜坡电压产生电路采用脉冲吞咽和窄脉冲充电技术,以小电容实现了缓慢上升的斜坡电压信号,便于片内集成;软启动完成后斜坡电压产生电路自动关闭,节省了功耗.在传统误差放大器的基础上只增加两个晶体管便实现了软启动过程控制,启动阶段误差放大器输出电压跟随斜坡信号上升,控制转换器输出电压和电感电流缓慢上升;在软启动结束时自动平滑地过渡到稳定工作状态,避免了开关切换方法产生的电感电流扰动.该软启动电路集成到一款峰值电流模升压型DC-DC转换器电路中,采用CSMC 0.5 μm BCD工艺实现.仿真结果表明,软启动电路有效地消除了浪涌电流,实现了输出电压平稳上升无过冲,并能自动平滑地过渡到稳定工作状态.电路简单易实现,便于片内集成.%An on-chip soft-start circuit consisting of a ramp-up voltage generator and an error amplifier with soft-start function is presented. The ramp-up voltage with slow ramp rate is achieved with small capacitors by using techniques of pulse swallowing and pulse current charging. The ramp-up voltage generator shuts down automatically to save power after the start-up has finished. The controlling scheme of start-up is realized by just adding two extra transistors to the conventional error amplifier circuit. In the start-up period, the output voltage of the converter and the current of the inductor rise are slowly controlled by the error amplifier output voltage which follows the ramp-up voltage. When the start-up finishes, a smooth transition from start-up to the steady states is achieved without disturbance to the current of the inductor, which always happens in the conventional method by using transferring switch. The soft-start circuit is applied to a peak-current mode boost DC-DC converter implemented with CSMC 0.5 μm BCD process. Simulation results show that the inrush current during start-up is eliminated effectively, and the output voltage rises smoothly without overshoot. Moreover, a smooth transition to the steady states without disturbance is achieved. The soft-start circuit is compact and suitable for on-chip implementation.
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