lab 7 darlington

Related Concepts: Darlington Pair | Lab 6 complement power analysis | jfet lab report

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING SESSIONAL REPORT

Name of the Experiment: Experimental study on Darlington pair.

Objectives:

1. To study the current gain of a single transistor configuration.
2. To measure and verify the high current gain of a Darlington pair configuration.
3. To study the current gain of a parallel transistor connection.

Theory: A Darlington connection is a two-transistor circuit that operates as a single “super-beta” transistor. The main feature of this configuration is that the composite transistor acts as a single unit with a current gain that is the product of the current gains of the individual transistors (${\beta }_D={\beta }_1{\beta }_2$). This provides an extremely high current gain and a high input impedance, making it highly effective for applications requiring significant current amplification.

Apparatus Required:

Sl No.	Name of Apparatus	Rating	Quantity
1	DC Power Supply	(0 - 24)V	01
2	Function Generator	230V, 50Hz, 25W	01
3	Transistor	2N2219A	02
4	Resistor	$1k\Omega ,100\Omega ,47\Omega$	03
5	Variable Resistor	(0 - 500)$k\Omega$	01
6	Multimeter	(0 - 5)A, (0 - 600)V	01
7	Connecting wires	-	As required

(Source: Table 01)

Experimental Data:

Table 1: Objective 01 - Single Transistor Connection

$I_B$	$V_E$ (mV)	$I_{E(measured)}$ (mA)	$I_{E(calculated)}$ (mA)
$4\mu A$	35	0.34	0.35
$8\mu A$	72.6	0.74	0.762

Current Gain = $\frac{\Delta I_E}{\Delta I_B}=\frac{0.422\text{ mA}}{4\mu A}=105.5$

Table 2: Objective 02 - Darlington Pair Connection

$I_B$	$V_E$ (V)	$I_{E(measured)}$ (mA)	$I_{E(calculated)}$ (mA)
$1\mu A$	1.7	16.0	17.0
$2\mu A$	3.1	31.0	29.0

Current Gain = $\frac{\Delta I_E}{\Delta I_B}=\frac{15\text{ mA}}{1\mu A}=15,000$

Table 3: Objective 03 - Parallel Transistor Connection

$I_B$	$V_E$ (mV)	$I_{E(measured)}$ (mA)	$I_{E(calculated)}$ (mA)
$2\mu A$	24	0.21	0.240
$4\mu A$	46	0.428	0.460

Current Gain = $\frac{\Delta I_E}{\Delta I_B}=\frac{0.21\text{ mA}}{2\mu A}=105$

Result Analysis: The experimental data confirms the operational differences between the three configurations. For the single transistor and the parallel transistor connections, the calculated current gain ($\frac{\Delta I_E}{\Delta I_B}$) was measured at 105.5 and 105 respectively. However, for the Darlington pair, an input base current shift of just $1\mu A$ resulted in an immense emitter current shift of $15\text{ mA}$. This yielded an effective current gain of 15,000 for the Darlington setup.

Discussion: The experiment successfully verified the operation and the “super-beta” characteristics of the Darlington pair. The single transistor produced a standard $\beta$ value ($\approx 105$), but connecting two 2N2219A transistors in a Darlington configuration multiplied their individual gains (${\beta }_D\approx {\beta }_1{\beta }_2$), producing a massive overall gain of 15,000. The calculated emitter currents derived from the voltage drops closely matched the directly measured multimeter values across all tables. The parallel configuration showed a current gain nearly identical to the single transistor, demonstrating that paralleling primarily divides current handling rather than multiplying gain like Darlington pair.

Conclusion: From this experiment, it can be concluded that the Darlington pair configuration efficiently provides an extremely high current amplification compared to standard single or parallel transistor setups. The experimental findings are highly consistent with theoretical expectations, making the Darlington pair highly suitable for applications requiring significant current driving capability from minimal input currents.