KNL1262ANALOG AND DIGITAL APPLICATIONS

SEMICONDUCTOR-1

Lab 5 Transistor Characteristic

Name : AZMAN B SAMAT (29710) FARAH ATIQAH BT ALI YUSUP (30140) RATNADEWI TB SERBINI (32662)

Program : ELECTRONIC (TELECOMMUNICATION) ENGINEERING

Lecturer : DR. TAY KAI MING

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OBJECTIVES

Make current gain measurements on a bipolar junction

transistor (BJT) to calculate the forward current gain.

Measure collector current for a bipolar junction

transistor.

Recognize the range of readings to expect when testing

a transistor.

Determine bipolar junction transistor current gain from

given data.

Recognize characteristics of a bipolar junction

transistor.

Diagnose a fault in a bipolar junction transistor device.

REQUIRED EQUIPMENTS

Circuit #7 of D3000 – 2.1 Semiconductors1 Module.

Shorting links and connecting leads.

Digital multimeter with 50μA, 2.5mA, 25mA &

250mA DC ranges

Digital multimeter with 200μA, 2mA, 20mA & 20V

DC ranges, and diode test range.

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Exercise 5.1 Current Gain

Procedure

1. The 0-2V DC SUPPLY (upper right of Module) tuned

to MIN.

2. The digital multimeter on the 20V DC range connected

between sockets 7.11 (positive) and 7.12 (common).

3. The Module Power Supplies switched ON.

4. The 0-12V variable DC power supply tuned to 5V.

5. The digital multimeter disconnected from the circuit.

6. The digital multimeter on the 200μA DC range

connected to sockets 7.3 (positive) and 7.2 (common).

7. The analog multimeter on the 25mA DC range

connected to sockets 7.10 (positive) and 7.6 (common).

8. The 0-2V DC supply adjusted to give a base current (of

10μA using digital multimeter.

9. The value of the collector current was determined and

entered in Table below.

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Result

10. The 0-2V supply was reset back to give base current of

20μA and the reading of collector current was taken.

The readings entered in Table 5.1.

11. The adjustments and readings repeated from 10μA

through 80μA, the corresponding collector current

values entered in Table 5.1. The analog meter should be

switched to its 250mA range.

12. As a example is when Ib = 50μA. The value of the

static forward current gain (transfer ratio) hFE or β by

taking the ratio:

The value of static forward current gain =

= 352.6 mA.

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Base

Current µA

Collector

Current mA

Base

Current µA

Collector

Current mA

10 3.55 50 17.63

20 7.34 60 21.00

30 10.75 70 24.40

40 14.08 80 27.60

13. The transfer characteristic and collector current/base

current plotted on the axes provided.

14. As a example is the range Ib = 20μA to Ib = 70μA. The

change of base current (δIb) – where δ means “a change

of” – is given by (70μA - 20μA) = 50μA. The

corresponding values of collector current, Ic are read

from the table or graph. Then the δIc is calculated.

The dynamic value of the forward current gain hfe, β is

given by:

The dynamic value of β (hfe) from this characteristic

= = 343.57

The static value of forward current gain is lower than dynamic value.

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Exercise 5.2 Output Characteristic

Procedure

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1. The 0-2V DC Supply (upper right of Module) tuned to

MIN.

2. A shorting link linked between sockets 7.7 & 7.8 on

Circuit #7.

3. The digital multimeter on the 20V DC range connected

between sockets 7.11 (positive) and 7.12 (common).

4. The Module Power Supplies switched ON.

5. The 0-12V variable DC power supply tuned to 1V.

6. The digital multimeter disconnected from the circuit.

7. The digital multimeter on the 20mA DC range

connected between sockets 7.10 (positive) and 7.6

(common).

8. The digital multimeter on the 50μA DC range

connected between sockets 7.3 (positive) and

(common).

9. The 0-2V DC supply adjusted to give a base current

(analog meter) of 10μA.

10. The value of the collector current was determined and

entered in Table 5.2 under the 1V heading and against

10μA base current.

Result

Base

Current

Collector Voltage

1V 4V 7V 10V

10µA 3.53 mA 3.57 mA 3.69 mA 3.59 mA

20µA 6.91 mA 6.86 mA 7.23 mA 7.62 mA

30µA 9.90 mA 10.55 mA 10.92 mA 11.35 mA

40µA 13.04 mA 13.79 mA 14.62 mA 15.07 mA

50µA 15.96 mA 17.16 mA 18.22 mA 18.67 mA

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11. The 0-2V supply reset back to give a base current of

20μA and the reading of collector current was taken.

The values are entered in Table 5.2, still under 1V.

12. The adjustments and readings at steps of 10μA through

50μA are repeated and the corresponding collector

current values entered in Table 5.2 under 1V.

13. The base current reduced to 10μA and the collector

voltage changed to 4V (0-12V variable DC supply).

14. All measurements of collector current repeated at 10μA

steps of base current, the results entered in Table 5.2

under the 4V heading.

15. All steps repeated again at collector voltages of 7V and

then 10V, the results entered in the table as before.

16. The variable reduced to zero when these readings are

completed, since the transistor may overheat if left for

some time at these high voltages and currents.

17. After that, the collector voltage set to 0.2V (0-12V

variable DC supply).

18. The base current set to 30μA using the 0-2V variable

supply.

19. The value of the collector current is read and entered in

Table 5.3 below.

20. The readings repeated at steps of 0.2V through 1.0v, the

results entered in Table below

Result .

Collector Voltage 0.2V 0.4V 0.6V 0.8V 1.0V

Collector Current 5.32mA 7.17mA 9.85mA 9.96mA 10.00mA

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21. The family of output characteristics, collector current

against collector voltage, and one for each value of base

current is plotted on the axes provided.

Exercise 5.3 Transistor Testing

Procedure.

1. All links are removed and the Module Power Supplied

switched ON.

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2. The positive lead of the multimeter connected to socket

7.1 and the common lead to socket 7.7, as shown in Fig

5.4, in order to test the base-emitter junction.

3. The digital multimeter set to the diode range.

4. The reading recorded in the first row of Table 5.4 for

the Base-Emitter Junction. (The reading in the format

of a resistance or a voltage depending on the type of

meter used)

Result

Base-Emitter Base-Collector Collector-Emitter

Forward 0.725 0.727 Out of range

Reversed Out of rage Out of range Out of range

Table 5.4

5. The common lead transferred to socket 7.6 to test the

base-collector junction. The reading recorded in the

first row of Table 5.4.

6. The meter lead connections reversed to the transistor

junctions and both junctions tested again, the readings

entered in the second row of Table 5.4.

7. The positive lead of the multimeter connected to socket

7.6 and the common lead connected to socket 7.7 to test

the collector-emitter junction. The reading recorded in

the last column of Table 5.4.

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8. The lead connections (7.6 common and 7.7 positive) are

reversed and the reading recorded in the last column of

Table 5.4.

When testing a known good NPN transistor with the

diode test range of a digital multimeter, a low value

reading will be measured when the meter leads are

connected positive to base, common to collector.

Worksheet W6

A fault has been inserted by the Management

Computer into Circuit #7.

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1. The circuit of Fig 5.5 constructed using the components

of Circuit #7.

2. The Module Power Supplies switched ON.

3. The 0-12V variable DC supply set to 9V.

4. The 0-2V DC supply adjusted to maximum voltage, in

order to saturate the transistor.

5. The voltage of the collector measured respected to the

ground line

Collector Voltage = 9.00 V

6. The fault has been deduced.

7. A diode test is carried out in conformation, the results

compared with those in Table 5.4.

Report

Since the fault exercise has been completed, the fault

has been removed by the Management Computer.

DISCUSSIONS

Exercise 5.1 Current Gain

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Circuit Faulty

Component

Nature

of Fault

Reason for Diagnosis

#7 Transistor

TR1

Open circuit Collector voltage is same with the

supply voltage.

The static forward current transfer ratio (ß or hFE) or

current gain can calculated from the ratio:

The dynamic forward current transfer ratio (ß or hfe) is

obtained from changes of base and collector currents.

The same symbol ß is used in both cases, but when

using “h parameter” the suffix is in lower-case letters

for the dynamic, and upper-case for the static ratio.

Exercise 5.2 Output Characteristic

At higher values of input (base) current there is an

increasing variation of output current with voltage.

At low values of collector voltage (Vce) the collector

no longer attracts the free charge carriers in the base

region and the collector current falls off very rapidly.

Exercise 5.3 Transistor Testing

Both of the base-emitter and base-collector junctions

give a forward bias reading when the positive lead is

connected to the base.

When reverse the meter lead connection to the

transistor junction, the result got with indicating a

reverse biased junction when the negative lead is

connected to the base.

After steps 7 and 8, there are no difference which way

round the leads are connected because of the two back-

to-back junctions, one or other of which will always be

reverse biased.

CONCLUSIONS

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The forward current gain has been calculated by

making current gain measurements on a bipolar

junction transistor (BJT) which is 278.2.

The collector current has been measured for a bipolar

junction transistor.

The range of readings is recognized to expect when

testing a transistor.

The bipolar junction transistor current gain determined

from given data.

The characteristics of a bipolar junction transistor have

been recognized.

A fault in a bipolar junction transistor device is

diagnosed.

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