设计了一款带MPPT功能的太阳能充电器。输入由太阳能电池板提供20-25V的直流电，输出为12-15V的直流电，针对输入和输出都是直流的情况，提出了DC-DC变换的方案，将输入经Buck电路降压后输出。(A solar charger with MPPT function is designed. The input and output of direct current of 20-25V by solar panel is 12-15V. In view of the direct cur