bjt cha_cc_cb_ce

8/6/2019 bjt cha_cc_cb_ce

http://slidepdf.com/reader/full/bjt-chacccbce 1/11

STUDY

OF

TRANSISTOR

CHARACTERISTICS

8-SHRIKANT KUNJ, M.N. PATANKAR MARG, KURLA(W)MUMBAI, 400070.PH- 09869112159

[email protected]

]



STUDY OF TRANSIST OR CHARACTERISTICS

Bipolar Junction Transistor - (BJT) Both holes and electrons participate in the conduction of current, hence the name bipolar.

Minority carrier –

In a p-type semiconductor electrons are the minority carrier type, in an n-type semiconductorholes are the minority carrier type.

Emitter –Emits minority carriers into the base region of a BJT. For example, in an NPN BJT the n-typeemitter, emits electrons into the p-type base. The emitter usually has the highest doping levelsof the three regions of a BJT.

Base - Thin region which is used to control the flow of minority carriers from the emitter to thecollector

Collector - Collects the minority carriers that make it through the base from the emitter. The

collector usually has the lightest doping concentrations of the three regions.

DC Beta (βdc ) – Large signal current gain (or hFE)

The ratio of the collector current to the base current. βdc = IC / IB

AC Beta (βac ) – Small signal current gain (or hfe) The ratio of the change in the collector current to the change in the base current. βac = D IC / DIB

Practical 1: AIM : To study Common Emitter (CE) of BJT.

In this lab, transistor current-voltage (I-V) characteristics of Common Emitter (CE)circuit will be investigated.

Material and Equipment : Matrix trainer kit, digital voltmeter

Theory : The bipolar junction transistor(BJT) can be modeled as a current controlled current source. Thecircuit symbol and the pin out for the actual device can be seen in Figure 1.

As an aid in visualizing the current/voltage relationships and transistor operation, a family of

static characteristics plots of collector current versus collector-emitter voltage for several values

of base current are plotted using circuit in Fig. 2.



Figure 2: CE configuration circuit using npn transistor

Figure 3-3: Characteristic curves for the BJT transistor.(CE)

These curves in Fig. 3-3 can be used to calculate the large signal current gain _DC (or hFE)

and the small signal current gain, _AC(or hfe). These values are in general calculated for a

given bias point ICQ, VCEQ using the following equations:

From this, one can see that a large signal gain depends only on the Q point and the small

signal gain depends only on small deviations around the Q point.Procedure

1) Transistor Common-Emitter Collector Characteristics using IV Measurement

2) Connect the MAINS Chord to AC mains put S5 To CE position to connected transistor in

COMMON EMITTER mode as circuit shown in Figure 4 below.

3) Put S1 to + position (R.H.S.) for +ve base to emitter supply & S4 to + position (R.H.S.) for

+ve collector to emitter supply.



Figure I-V Measurement Set-up

4) Put S6 to Down side to measure Ib (I1) in uA , Put S2 to 2nd middle position to get 10K

resistance & Set P1 for 10.0 on display for 100uA. (display shows divided by 10 reading for I1)

5) Put S6 to up position to measure Ic (I2) in mA Put S3 to 1st

position to get 470Ω resistance,

Put S7 to up position to measure Vce (V2) in volts and Set P1 in steps of 0.05V to plot

characteristics.

6) Measure (record) the collector current IC and the voltage across collector and emitter (VCE) .

7) Repeat the procedure for different values of Ib (vary Ib from 0-200µA in steps of 10µA).(

fallow step 4 for Ib setting)

8) Plot the V-I characteristics with IC on Y-axis and VCE on X-axis.

9) Calculate βDC and βAC from the curves.

10) Calculate transconductance parameter gm.

1) What is the average value of βDC and βAC for the BC548 transistor?

2) Give the expressions for βDC, βAC.

3) Determine the collector resistance at VCE = 6V, and IB = 50microamperes.

Use the following expression : ΔVce / Δ Ic Ib = constant



CE TEST READINGSIb = 100uA

Ic mA Vce V3.9 0.0510 0.1

15.9 0.15 20.3 0.2 22 0.25

23.3 0.3 24.3 0.3525.3 0.4 26.2 0.45 27 0.5 28 0.55

28.8 0.6 29.5 0.65 30.2 0.730.9 0.7531.6 0.8

32.2 0.85 32.7 0.9 33.2 0.95 33.7 0.134.7 0.11



Transistor Common-Emitter Base Characteristics:


resistance & Set P1 for 00.0 on display. (display shows divided by 10 reading for I1)

2) Put S3 to 1st position to get 470Ω resistance, Put S7 to up position to measure Vce (V2) in

volts and Set P1 in steps of 0 to plot input characteristics.

3) Put S7 to down position to measure Vbe (V2) - VBB in volts, Vary VBB from 0-2V insteps of

0.2V by P1, and measure (record ) the base current and the voltage across base and theemitter4) Repeat the procedure for different values of VCE. (0V, 0.1V, 1V, 2V )

5) Plot the V-I characteristics with IB(µA)on Y-axis and VBE on X-axis.6) Calculate the base spreading resistance rb.



Practical 2:

AIM : To study Common Collector (CC) of BJT.

In this lab, transistor current-voltage (I-V) characteristics of Common Emitter (CC) circuit will beinvestigated.

Material and Equipment : Matrix trainer kit , digital voltmeter

Procedure









5) Put S6 to up position to measure Ic (I2) in mA Put S3 to 1st position to get 470Ω resistance,


characteristics.









CC TEST READINGSIb = + 69uA

Ie mA Vec V- 7.5 -0.1-17.2 -0.2 -20.4 -0.3 -22.6 -0.4 -24.4 -0.5 -26.2 -0.6 -27.6 -0.7 -29 -0.8

-30.4 -0.9-31.3 -1.0



Practical 3: AIM : To study Common Base (CB) of BJT.

In this lab, transistor current-voltage (I-V) characteristics of Common Emitter (CB) circuit will beinvestigated.

Material and Equipment : Matrix trainer kit , digital voltmeter

Procedure









5) Put S6 to up position to measure Ic (I2) in mA Put S3 to 1st position to get 470Ω resistance,


characteristics.









CB TEST READINGSIe =- 8mA

Ic mA Vcb V1.8 -0.786.7 0.77.7 -0.6

8 -0.5

8 -0.4

8 -0.38 -0.2

8 -0.1

8 0

8 1

8 2

bjt cha_cc_cb_ce

Documents