BJT Characteristics

Load the PSPICE file bjt-dc2.sch, Figure 31.

**Figure 31:** Circuit for measuring BJT characteristics.
$\begin{figure} \begin{center} \epsfig{file=images/clab6img3.eps}\end{center}\end{figure}$

Exercise:

1.

Simulate the circuit for the given setup. Is the transistor Q₁ on or off? Why?

2.

We now want to obtain the family of characteristics, I_C vs V_CE for various values of I_B, (like Figure 32, which shows I_C as a function of V_CE; note that in this simulation V_CE=V_CC). We use the nested DC sweep feature:

V_CC is set as the main sweep variable, ranging from 0 V to 5 V in increments of 0.1 V. I_B is the nested sweep variable, ranging from 0 to 20 $\mu$ A in increments of 5 $\mu$ A.

Enable DC sweep and simulate again. Determine the correct value of I_B for each of the curves.

Lecture Notes : BJT Transistor Circuits : BJT Characteristics

3.

Find the saturation and active regions for a fixed value of I_B.

4.

Obtain a graphs of I_C versus I_B.

5.

What is the current gain $\beta$ ?

Use the graphs to determine the ratio I_C/I_B in the active region for several curves.

**Figure 32:** BJT characteristics (I_C versus V_CE for several values of I_B).
$\begin{figure} \begin{center} \epsfig{file=images/clab6img4.eps}\end{center}\end{figure}$

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