Construction of the transfer characteristic curve between IB and IC of a transistor in common emitter configuration

When $I_C$ is plotted against $I_B$, a curve similar to the one shown in Figure 36.3 is obtained.

The gradient of the linear portion of the graph gives the direct current gain $\beta$ of the transistor.

$$\beta = \frac{\Delta I_C}{\Delta I_B}$$

1. Set up the circuit on the circuit board as shown in Figure 36.1.

2. Rotate both potential dividers $VR_1$ and $VR_2$ anticlockwise completely (middle terminal will reach close to the Earth terminal).

3. Connect the power supply to the circuit.

4. Rotate $VR_1$ slowly and clockwise until the voltmeter reading ($V_{RC}$) becomes 5 V.

5. Since this reading changes when $I_B$ is changed, $V_{RC}$ should be kept constant by adjusting $VR_2$.

6. Rotate $VR_1$ slowly clockwise and measure the values of $I_C$ starting from 0 to 10 μA each time.

7. Record all values of $I_C$ relevant to the values of $I_B$ in Table 36.1.

$I_B$ (μA)	0	5	10	15	20	25	30	35	40	50	60	70	80	90	100
$I_C$ (mA)

1. Plot $I_C$ against $I_B$.
2. Calculate the gradient of the linear portion.
3. Calculate $\beta$ using:

$$\beta = \frac{\Delta I_C}{\Delta I_B}$$

State the value of the current gain $\beta$ of the transistor.