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# Circuit Elements

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Find (a), (b) and (c) in the attached circuit.

https://brainmass.com/physics/circuits/circuit-elements-43506

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Dear Student,

The diagram given to you is a small signal circuit representation of a BJT ( May be common emitter, I am saying maybe because the terminals are not mentioned)

You are asked to calculate the io, i1, i2.

a) To find i0,

You are given gm = 5 x 10-3
gm = I0/Iin = Current gain. Note that the Iout and Iin are the DC currents and not the AC currents. You are asked the i0, which is the total current flowing out of the outout terminal. It's so to say the sum of all the AC and DC currents at the outout.

Iin = Input current = Input Voltage /Input resistance = 200 / (8 + 12) K = 10 m A
Iout = gm * I in = 5 x 10-3 * 10 x 10 -3 A = 5 x 10 -6 A

We will come back to calculating the final i0, after solving parts (b) and (c)

b) And c) To find i1 and i2

VA = voltage across 12k resistance = 12 K * 10 mA = 12 V

I1 = 12 V / 9 k = 1.33 mA
I2 = 12 V / 3 K = 4 mA

Now i0 = Iout + i1 + i2 = 5 x 10 -6 A + 1.33 x 10 -3 + 4 x 10 -3 = 5.335 mA

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