3842占空比请教

我想用3842做52K宽电压输入,经计算其占空比Dmax为63%了.具体参数如下:
         IN AC 85-265 V
        OUT DC 18 V
        f=52K
        Po=55W
        效率为0.75
        Dmax为63%
        LP=1.1mH
        Np=88
        Ns=12
        Nf=17
        芯片供电为25V