第一阶段(t=0~20ms)电流过渡过程方程: f(t)=f(∞)+f(0)-f(∞)e T=RdC=2ms o)=2 3mA ImA R1+R2 i(t)=1+2e2mA 9/629    t f t f f f e − + ( ) = () + (0 ) − ()  ( ) 1 2 2 mA t i t e − = + (0 ) 3mA 1 = = + R E i ( ) 1mA 1 2 1 = +  = R R E i = R C = 2ms d  第一阶段（t = 0 ~ 20 ms）电流过渡过程方程： /62