00:01
Hello everyone here is the question and question is use the small signal model of the diode to find the value of r in b specify the value of i s of each of the diode and see when the current i and equal to 1 m is direct drawn from the regulator so here it is in a we can say that each diode has forward resistance so the diode is small signal equivalent circuit is the diode is replaced by a resistance rd.
00:35
So as a load current is 0, the change in output value i equal to the change in diode voltage del vd and the change in load current is equal to change in diode current del id.
00:49
So here we can say that determine the total diode resistance for rd, which is equal to the change in output voltage to the change in current.
01:46
Now we can say that rd equal to del vd divided by del i d.
01:59
Calculate the resistance rd.
02:02
So we can write here 4.
02:05
R d equal to del v d divided by del i d so 20 divided by 1 then we can write here r d equal to 5 om determine the diode current id using the following formula for for diodes connected in series we can write id equal to 4 vr divided by rd the thermal voltage is 25 mv so calculate the drain current equal to id equal to 25 multiply 10 to the power minus 3 divided by 5 now so we can read a 5m a the string of 4 diodes should provide an output voltage of v0 equal to 3v at no load so determine the nominal value of the current in the diode string is id equal to 15 minus 3 divided by r so we can write it 12 divided by r so equate the diode current to 5 m a so we can write here 12 divided by r equal to 5 multiply 10 to the power minus 3 so r equal to 2 decimal 4 k in b we can write that write the formula of the current saturation current i s so we can write here i s equal to i d e minus v divided by vr 4 output voltage v0 equal to 3 v so voltage so voltage drop cross each other diode is 3 divided by 4.
05:17
4 we can write here 0 decimal 75 volt now calculate the saturation current current i s equal to 5 multiply 10 to the power minus 3 e 0 decimal 75 divided by 25 multiplied 10 to the power minus 3 so we can write here i s equal to 4 decimal 7 multiply 10 to the power minus 16 a now in c, in c, the diode current id is equal to the difference between the current through the resistance are and the load current...