先把开关左边电路做戴维南等效;
Us = -u1-2u1+I*R2;u1=-I*R1;
解得 I;那么端口开路电压 Uoc = Us + u1;
端口短路电流;
I1 = Us/R1;I2 = -2u1/R2 = - 2Us/R2;
Isc = I1 + I2;
那么,等效内阻 Rs=Uoc/Isc;
t=0,iL(0) = 0;
t=∞,i*R3 = iL*R4;
Uoc = (i + iL)*Rs + i*R3 -----(a) ;
iL(∞) =??
τ = L/(R4+Rs//R3);
代入全响应公式,得 iL(t);
根据(a)式,可得到 i(t);