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+// Example 9.3
+// Analysis of a Relay Driver
+R_eq=10+15; // from figure 9.13(a)
+L=400*10^-3;
+tau=L/R_eq;
+V=5; // DC voltage source
+I_ss=5/25; // steady state value of current in the circuit
+t=0:10^-3:30*10^-3;
+i_L1=I_ss*(1-%e^(-t/tau)); // 0<t<=30*10^-3;
+// the relay closes at time t1 when i_L1(t1)=150*10^-3;
+// Solving equation 200*(1-%e^(-t1/16))=150;
+t1= -tau*log(1-150/200);
+i_L2_peak= I_ss*(1-exp(-30/16)); // Value of current at the end of the pulse
+// After the pulse is over,the exponential decay of the current becomes
+t3=0.030:0.001:0.05
+i_L2=i_L2_peak*exp(-(t3-30*10^-3)/tau);
+// the relay then opens at t2 when i_L2(t2)=40*10^-3;
+// solving equation 169*exp(-t2/16)=40;
+t2= (30*10^-3)-tau*log(40/169)
+t_int=t2-t1;
+plot(t,i_L1,t3,i_L2)
+xlabel('t')
+ylabel('i_L(t)')
+title('Current Waveform')
+disp(t_int,"Relay remains closed over the interval(sec)=");