i will rate you at the same time 2. A Wilson current source drives a 10 KS2 load

Question

i will rate you at the same time

2. A Wilson current source drives a 10 KS2 load such that the output voltage is 5V. All transistors are matched with B -20, V 75V, and V 7 TV when Ic 50 LLA. Find: BE (a) the output current, lo. (b) the base-emi er voltages of all three transistors (assume V VBE2 VBE3) (c) the reference current REF, using the values of Ic2 and I (d) the current transfer ratio, REF (e) the value of the resistance R. 15V 15V 0 KS2 REF Q3 -15V 3. (a) Design a Wilson current source to give an output current of lo- 2.5 mA. The EN 9:01 PM 3/25/2014.

Explanation / Answer

let the reverse saturation current for the transistors is Is.

then we know that,

a)

Ic = Is*(exp(q*Vbe/KT) - 1)------------------1

where KT/q = 0.026 V where K is the boltzman constant and T is absolute temperature.

now as Vo = 5 V given so, Iout = (15 - 5)/10K = 1mA.------------2.----------------------------------ans

from equation 1 we can write,

50u = Is (exp(0.7/0.026) -1) or Is = 1.01490*10^-16 A-------------------------3.

now, for transistor 3 we can wire usig Is value above that,

b)

1m = Is(exp(q*Vbe/KT) - 1)) or Vbe = 0.7778 V

so Vbe1,2,3 = 0.7778 V ------------------------------------------ans.

c) Ic2 = 1mA as Vbe is constant and

Ib3 = Ic3/beta = Ic3/20 = 0.05 mA

so,

Iref = Ic2 + Ib3 = 1.05 mA---------------------------------------ans.

d) from the values wehave,

Io/Iref = 1/1.05 = 0.95238 ---------------------------------------ans

e)

the node voltage at the collector of M1 is Vbe1 + Vbe3

or,

Vc1 = 2*0.778 V = 1.556 V.

Iref = 1.05 mA

so, R = (15 - Vc1)/Iref = (15 - 1.556)/1.05m = 12.8038 K Ohm-----------------------------ans.

2.

to get Io = 2.5mA.

u just need to provide the perfect resister value for the Iref branch.

as we have seen Is = 1.0149*10^-16 A.

so, Vbe for Ic = 2.5 m A will be,

2.5 = Ic(exp(q*Vbe/KT) -1) or Vbe = 0.80171 V.

so, now Vc1 = 2*0.80171 = 1.60 V.

so, for approximately 2.5mA current.

R = (15 - 1.60)/2.5m = 5.358 KOhm.

so u just use R = 5.358 KOHm resister to get that current.

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