一种基于自适应峰值电流检测的模式切换电路

在降压转换器中，为了在不同的负载情况下获得高效率，常采用的方法是在重载时使用脉冲宽度调制(PWM),在轻载时使用脉冲频率调制(PFM),因此需要模式切换信号去控制整个降压转换器的工作状态，同时模式切换信号也可以用于自适应改变功率级电路中的功率管栅宽，减小功率管的栅极电容，提高整体电路的效率。文章设计了一个自适应峰值电流模式切换电路，用于产生模式切换信号，其原理是监控峰值电流的变化，产生峰值电压，将峰值电压与参考电压进行比较，得到模式切换信号，以决定降压转换器是采用PFM模式还是PWM模式。仿真结果表明，在负载电流0.5～500 mA范围内，该电路可以在两种调制模式之间平稳切换，其峰值效率可提升到94%以上。

A Mode Switching Circuit Based on Adaptive Peak Current Detection for Buck Converter

In buck converter, in order to obtain high efficiency under different load conditions, pulse width modulation (PWM) is often used under heavy load, and pulse frequency modulation (PFM) is used under light load, so the mode switching signal is needed to control the working state of the whole buck converter. At the same time, the mode switching signal can also be used to adaptively change the grid width of the power stage circuit, which reducing the grid capacitance of the power tube and improving the efficiency of the whole circuit. An adaptive peak current mode switching circuit was designed to generate a mode switching signal. Its principle is to monitor the change of peak current and generate a peak voltage. After comparing the peak voltage with a reference voltage, the mode switching signal is obtained to decide whether the buck converter adopts PFM mode or PWM mode. The simulation results show that the circuit can switch smoothly between the two modulation modes in the range of load current from 0.5 mA to 500 mA, and its peak efficiency can be improved to over 94%.