Basic Electronics Assignment: Characterization And Signal Amplification Of An NPN Transistor Using Biasing Techniques

How Does A Transistor Work. Understanding The Characteristics Of A Transistor ?

Introduction

In this experiment we constructed 3 different circuits to understand the characteristics and the functions of a transistor (NPN transistor). The 3 circuits are base biased, voltage biased and common-emitter amplifier. With this circuits we determined the quiescent operating conditions of the voltage-divider bias BJT configuration and measured the AC and DC voltages in a common-emitter amplifier.

Methodology: 

Equipments And Components:

1. Oscilloscope, Multi-meter, Signal Function Generator, DC Power Supply
2. Resistors: 1 kΩ (x1), 2.7 kΩ (x1), 3 kΩ (x1), 10 kΩ (x1), 33 kΩ (x1), 1MΩ (x1)
3. Capacitors: 15 µF (x2), 100 µF (x1)
4. Transistors: NPN (2N3904) Bipolar Junction Transistor (x1)

Discussion

Experiment 3.1:

The purpose of this experiment is to determine the b= of the circuit, it connects IC and IB. the values calculated are IB =1.93 x 10-5A , IC=4.03 x 10-3A and b=209.Therefore, a simple base bias circuit can be used to find the b value. We compare our b result with another groups and the percentage difference is 2.36%.

Experiment 3.2:

The objective of the experiment has been achieved in building stable dc operating condition for npn transistor. Calculations yield VB=2.3V ,VE=1.6V , VC=5.2V ,VBE=0.7V ,VCE=3.6V ,IE=1.6mA and IC=1.6mA, thus, confirming the active operation region (Vc>Vb). The bias stability was ensured by the voltage divider formed by R1 and R2. This experiment showcased DC biasing on a voltage divider bias circuit, which is an ideal way of identifying and setting the quiescent points.

Experiment 3.3:

The circuit was transformed into a common emitter amplifier by adding capacitors to the previous circuit. The capacitors ensured minimal loss of input and output signals. The VIN=30mVpp and the VOUT=5vpp. The values that we calculated are re = 15.8W, Av calculated from the amplifier voltage gain for a fully bypassed emitter is and the AV=189.87 and the calculated AV from vin and vout from the oscilloscope is AV=183.33. The percentage difference between both Av is 3.5%. Therefore, a common-emitter amplifier circuit is suitable for applications that process signals because it enables AC amplification while maintaining DC bias stability, amplifying the signal across the circuit.

Conclusion:

To sum up everything that has been stated so far, the voltage divides recircuit formalize a stable Dc operating point for npn transistor, yielding VB=2.3V ,VE=1.6V , VC=5.2V ,VBE=0.7V ,VCE=3.6V ,IE=1.6mA and IC=1.6mA, thus, making certain the active region points. The circuit without the capacitors actively maintained a consistent quiescent points but lack in amplifying AC signal. When the capacitors were added the circuits turned into a common emitter amplifier. This circuit ensured effective signal coupling and emitter bypassing, preserving DC stability and enhancing AC performance, this is all possible because of the low reactants of the capacitors. It demonstrated versatility between stable biasing and clear signal amplification in practical application.