Report on the Bipolar Transistor

Abstract of the Bipolar Transistor

The lab report is about the “Bipolar transistor”, in this lab experiment first of all determine DC characteristics of transistor, and then find the parameters of the CE amplifier.  In this experiment the discussion is about the introduction of BJT, and also explained its DC characteristics, and the CE amplifier specifications. Then the detailed discussion of the calculation is also presented as shown in the below result section. All the result if verified and discussed in the below section of discussion. At the end of report the conclusion and reference is also provided according to the requirements. 

Aim and Objective of the Bipolar Transistor

1. The aim of the lab report is to become familiar with the characteristics of the Single transistors, which extract the performance parameters, and comparison with those values which is given in the datasheet.  

2. In the simple single stage switching and amplifier circuits to obtained the understanding if the transistors. 

3. By using the Multisim to obtain the instrumentation techniques as well as circuit simulations then compare these values with the experimental values. 

Introduction of the Bipolar Transistor

The objective of this lab experiment is too determined the characteristics of the Bipolar transistors, where transistors has three terminal devices and it is also allows to control the larger current therefore it obtained the current gain. While bipolar transistor Junction (BJT) has the loss of polarity for the design of integrated circuits which is really useful for the discrete circuit designs. In this lab experiment the aim is to measure and analyzed the Common Emitter Amplifier (CE) for the BJT amplifier and also determines the voltage gain, output resistance for every configuration of the transistors. For the modern digital system, the BJT is the highly versatile, and the basic composition of the BJT has the two diode which is also placed back to back, and either the PNP or NPN configurations. This lab experiment is used the transistors in saturation region, active region which aid for the analog amplifications.  DC characteristics of the Bipolar Transistor

The DC characteristic of Transistor output is I_c=(V_CE) which the well-known isothermal conditions are and it is also supposed and modified through the self-heating phenomena. In this experiment the DC output characteristics of the bipolar transistors in CE configuration is determined on the simple model for the self-heating (JANKE, 2007). There are four types of the DC characteristics which is defined for the every transistors in the operating configuration’s, and all these DC characteristics is defied the relationship between the DC voltage and DC current at the transistors output and input;  

Input characteristics U_IN (I_IN )for U_out=const

I_out (I_IN )for U_out=const; forward current gain 

U_in (U_out )for I_IN=const Reverse voltage gain 

I_out (U_out )for I_IN=const. ; Output characteristics 

The BJT characteristics for the CE configuration is shown in the below figure; 

 Figure 1: BJT common-emitter configuration characteristics: (a) input characteristic, (b) Forward current gain characteristic, (c) reverse voltage gain characteristic, (d) Output characteristic

It is most important for the transistors characteristics which are used to determine the operating regions with respect to the operating region. These are the following regions; 

Cut-off region 

Saturation region 

Active region (DC characteristics, 2019)

The transistors operating region is shown in the below figure 2; 

Figure 2: Transistor output characteristics with different operating regions

CE amplifier of the Bipolar Transistor

The input signal is applied among the emitter and base in the Common emitter amplifier, where the output is taken among the emitter and collector as is shown in the below figure 3; this configuration is used for the transistors based amplifier and it is also shown normal method of the transistor connections. The CE configuration’s produced the power gain and higher current for the three bipolar transistor configurations (Electronics-tutorials, 2019). 

Figure 3: CE configuration 

Now the combination of the α and β shown the mathematical relationship among these parameters, thus the current gain of the transistors is given as;

α=I_C/I_E 

β=I_C/I_E 

I_C=αI_E= βI_B

β=α/(1-α)

I_E=I_C+I_B

Background of the Bipolar Transistor

In this lab experiment the equipment’s or component which is used are these; 

2N3904 Transistor

DC power supply

Oscilloscope

Digital-multimeter

Breadboard

Voltmeter

Capacitor

Resistors

The bipolar transistors, has the three BJT amplifiers which are, CE (Common emitter) CB (Common base), CC (common collector). All these three configuration are based on the biasing as shown in the below circuits; 

Figure 4: Biasing configuration 

Results of the Bipolar Transistor

In the result section, there is complete information about the three currents that is from the collector, emitter and base. 

The voltages at the collector end are given by 15 volts and the value of gain is about 100

V_cc=15 V

Now from the datasheet the collector current at the saturation point can be achieved easily 

I_(csat )=10 m A 

The value of beta will be β=325

The value of collector and emitter resistor will be about

R_c+R_e=V_cc/I_(csat ) =15/10=1.5 k ohm 

The ratio between the collector resistor and emitter resistor is given by 

R_c/R_e =100:1

For that case 

R_c=148.5 ohm  and R_e=15 ohm

Given data  voltage difference between collector and emitter

V_CE=7.5 Volts,〖   I〗_c=5 mA

The voltages at the emitter can be found through this 

V_e=I_c×R_e=5 ×15=0.075 volts 

Voltages at the base are given by 

V_b= V_e+0.7=0.775 volts 

The current at the base is calculated by 

I_b=I_c/β=5/325=1.5 μ A

The gain can be found through 

Gain=I_C/I_B 

collector current=20  mA

R_c=(V_cc-V_ce)/I_c =(5-2.2)/0.002=140 ohms 

β_avg=(200+450)/2=325

β_avg=I_c/I_B 

The base current will be about 

I_B=0.002/325=6.15×10^(-6)

The voltage across the red LED

V_(Red LED)=2.2

V_Rb=V_in-V_b=5-0.7=4.3

Multisim Results 

Current at collector Current at base

I_c1=4.3 mA I_B1=15 μA

I_C1=8.8 mA I_B2=30 μA

I_C3=13 mA I_B3=45 μA

The value of beta 

β_1=286.69

β_2=293.33

β_3=288.89

Total beta will be β_total=868.89

 The measurement of voltages and current 

Voltage of the Bipolar Transistor

Voltage across components On OFF

Voltage across transistors 0.52956 0.2059

Voltage across collector resistor 2.4989 0.002

Voltage across base resistor 4.2559 2.150

Current 

Current through the components On OFF

I_c 2.4484/140=0.0174 0.002/140=0.0000142

I_B 4.2559/69.9=0.6088 2.15/69.9=0.0306 

Power 

Power through components On OFF

P_transistor =0.52956×2.489/140=0.00941 =0.0259×0.002/140=0.00000037

P_LED =0.0344 =0.00001145

Discussion of the Bipolar Transistor

The results are found in the above section. In that section, we have found the value of voltages, currents, and power across the bipolar transistor. Now it can be seen from the value of voltages that are taken across the transistor, its collector and its base. The readings are taken by turning ON and OFF. When the transistor is on, the value across the transistor is about 0.52956, and when it is off, then it is about 0.2059. This value of voltage is due after off is due to the potential difference present between them. As it can be noted that, the voltage across the collector is about 2.4989 and across the base is about 4.2559 volts 

Conclusion of the Bipolar Transistor

Summing up all the discussion from above, it is concluded that the voltages across the base of the bipolar transistor are always high. The main reason is that at the base, the value of the current is low. At the start, there is complete information about the characteristics of such transistors and their types.  In that report, there is a complete analysis of the bipolar transistors and their voltages current and power. These values are calculated and then checked through the help of software. 

References of the Bipolar Transistor

DC characteristics. (2019). DC characteristics of Bipolar Junction Transistors (BJT). DEPARTMENT OF SEMICONDUCTOR AND OPTOELECTRONIC DEVICES.

Electronics-tutorials. (2019). Bipolar Transistor. Retrieved from https://www.electronics-tutorials.ws/transistor/tran_1.html

JANKE, W. (2007). Bipolar transistor d.c. output characteristics.Calculations including self-heating. International Journal of Electronics, 45(5), 475-479