Test Transistor Performance

G.H.R.I.E.M. JALGAON
1. INTRODUCTION
Transistor testers are instruments for testing the electrical behavior of transistors
and solid-state diodes circuit. This device is used to detect a faulty transistor, within an
assembled PCB. The testing can be carried out on the PCB's components, so that only the
faulty transistor needs to be removed and replaced
1.1 Types of tester
There are three types of transistor testers each performing a unique operation.
• Quick-check in-circuit checker
• Service type tester
• Laboratory-standard tester
In addition, curve tracers are reliable indicators of transistor performance
1.1.1 Circuit Tester
A circuit tester is used to check whether a transistor which has previously been
performing properly in a circuit is still operational. The transistor's ability to "amplify" is
taken as a rough index of its performance. This type of tester indicates to a technician
whether the transistor is dead or still operative. The advantage of this tester is that the
transistor does not have to be removed from the circuit.
1.1.2 Service type transistor testers
These devices usually perform three types of checks:
• Forward-current gain,or beta of transistor.
• Base-to-collector leakage current with emitter open(ico)
• Short circuits from collector to emitter and base.
Transistor Tester Page 1

Some service testers include a go/no-go feature, indicating a pass when a certain hfe is
exceeded. These are useful, but fail some functional but low hfe transistors.
Some also provide a means of identifying transistor elements, if these are unknown.
The tester has all these features and can check solid-state devices in and out of circuit.
Transistor hfe varies fairly widely with Ic, so measurements with the service type
tester give readings that can differ quite a bit from the hfe in the transistor's real life
application. Hence these testers are useful, but can't be regarded as giving accurate real-life
hfe values.
1.1.3 Laboratory-standard transistor tester or Analyser
This type of tester is used for measuring transistor parameters dynamically under
various operating conditions. The readings they give are absolute. Among the important
characteristics measured are:
• Icbo collector current with emitter open (Common base)
• ac beta (Common emitter)
• Rin (Input resistance)
Transistor testers have the necessary controls and switches for making the proper
voltage, current and signal settings. A meter with a calibrated "good" and "bad" scale is on
the front. In addition, these transistor testers are designed to check the solid-state diodes.
There are also testers for checking high transistor and rectifiers.

2.COMPONENT LIST
There are component which are used in making of the project circuit as given below
Table No 1 Componant Discription
Sr No Componant Name Value Quantity
1 Timer IC 555 -- 2
2 Timer IC Base -- 2
3 Resistor 220 Ώ 4
33K 2
39 K 2
4 Capacitor 10nf 2
10µf 2
5 PCB cu Plane 1
Hole Type 1
6 Battery Supply 9v DC 2
7 Connecting Wires 1m 1
8 Solder -- 1
9 Soldering Wire -- 1
10 Transisters -- 4
11 LED Red & Green 4
3. DISCRIPTION OF COMPONENTS
3.1 RESISTORS –

A Resistor is a heat-dissipating element and in the electronic circuits it is mostly
used for either controlling the current in the circuit or developing a voltage drop across it,
which could be utilized for many applications. There are various types of resistors, which
can be classified according to a number of factors depending upon:
(I) Material used for fabrication
(II) Wattage and physical size
(III) Intended application
(IV) Ambient temperature rating
(V) Cost
Basically the resistor can be split in to the following four parts from the construction
viewpoint.
(1) Base
(2) Resistance element
(3) Terminals
(4) Protective means.
The following characteristics are inherent in all resistors and may be controlled by
design considerations and choice of material i.e. Temperature co–efficient of resistance,
Voltage co–efficient of resistance, high frequency characteristics, power rating, tolerance &
voltage rating of resistors. Resistors may be classified as
(1) Fixed
(2) Semi variable
(3) Variable resistor.
In our project carbon resistors are being used.
3.2 CAPACITORS:
The fundamental relation for the capacitance between two flat plates separated by a
dielectric material is given by:-

C=0.08854KA/D
Where: -
C= capacitance in pf.
K= dielectric constant
A=Area per plate in square cm.
D=Distance between two plates in cm
Design of capacitor depends on the proper dielectric material with particular type of
application. The dielectric material used for capacitors may be grouped in various classes
like Mica, Glass, air, ceramic, paper, Aluminum, electrolyte etc. The value of capacitance
never remains constant. It changes with temperature, frequency and aging. The capacitance
value marked on the capacitor strictly applies only at specified temperature and at low
frequencies.
3.3 LED (Light Emitting Diodes):
As its name implies it is a diode, which emits light when forward biased. Charge
carrier recombination takes place when electrons from the N-side cross the junction and
recombine with the holes on the P side. Electrons are in the higher conduction band on the
N side whereas holes are in the lower valence band on the P side. During recombination,
some of the energy is given up in the form of heat and light. In the case of semiconductor
materials like Gallium arsenide (GaAs), Gallium phoshide (Gap) and Gallium arsenide
phoshide (GaAsP) a greater percentage of energy is released during recombination and is
given out in the form of light. LED emits no light when junction is reverse biased.
3.4 Timer Ic 555
The 555 is an integrated circuit (chip) implementing a variety of timer and
multivibrator applications. The IC was designed and invented by Hans R. Camenzind. It
was designed in 1970 and introduced in 1971 by Signetics (later acquired by Philips). The

original name was the SE555/NE555 and was called "The IC Time Machine". It is still in
wide use, thanks to its ease of use, low price and good stability. As of 2006, 1.5 billion units
are manufactured every year.
The 555 timer is one of the most popular and versatile integrated circuits ever
produced. It includes 23 transistors, 2 diodes and 16 resistors on a silicon chip installed in
an 8-pin mini dual-in-line package (DIP-8). The 556 is a 14-pin DIP that combines two
555s on a single chip. The 558 is a 16-pin DIP that combines four, slightly modified, 555s
on a single chip (DIS & THR are connected internally; TR is falling edge sensitive instead
of level sensitive). Also available are ultra-low power versions of the 555 such as the 7555
and TLC555. The 7555 requires slightly different wiring using fewer external components
and less power.
3.4.1 Operating modes:
Monostable mode:
In this mode, the 555 functions as a "one-shot". Applications include timers,
missing pulse detection, bouncefree switches, touch switches, Frequency
Divider,Capacitance Measurement, Pulse Width Modulation (PWM) etc.
Astable mode :
Free Running mode: the 555 can operate as an oscillator. Uses include LED and
lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse
position modulation, etc.
Bistable mode:
The 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor
is used. Uses include bouncefree latched switches, etc.
3.4.2 The connection of the pins is as follows:
Table No 1 Pin Discription
Pin No Pin Name Discription

1 Ground Ground, low level
2 Trigger 555 timer triggers when this pin transitions from
voltage at Vcc to 33% v voltage at Vcc. Output pin
goes high when triggered
3 Output Output pin of 555 timer
4 Reset Resets 555 timer when low
5 Control Voltage Used to change Threshold and Trigger set point
voltages and is rarely used
6 Threshold Used to detect when the capacitor has charged. The
Output pin goes low w when capacitor has charged to
66.6% of Vcc.
7 Discharge Used to discharge a capacitor
8 Vcc 5V to 15 V supply input
3.4.3 Schematic diagram
Fig.3.4.3 A) Functional Pin Diagram Of Timer IC (555)
Real picture

Fig.3.4.3 B) Real Picture Of Timer IC (555)
3.5.Transister
A transistor is a semiconductor device used to amplify and switch electronic
signals and electrical power. It is composed of semiconductor material with at least three
terminals for connection to an external circuit. A voltage or current applied to one pair of
the transistor's terminals changes the current through another pair of terminals. Because the
controlled (output) power can be higher than the controlling (input) power, a transistor can
amplify a signal. Today, some transistors are packaged individually, but many more are
found embedded in integrated circuits.
The transistor is the fundamental building block of modern electronic devices,
and is ubiquitous in modern electronic systems. Following its development in the early
1950s, the transistor revolutionized the field of electronics, and paved the way for smaller
and cheaper radios, calculators, and computers, among other things.
3.5.1 Bipolar junction transistor (BJT)
Bipolar transistors are so named because they conduct by using both majority and
minority carriers. The bipolar junction transistor, the first type of transistor to be mass-
produced, is a combination of two junction diodes, and is formed of either a thin layer of p-
type semiconductor sandwiched between two n-type semiconductors (an n-p-n transistor),
or a thin layer of n-type semiconductor sandwiched between two p-type semiconductors (a
p-n-p transistor). This construction produces two p-n junctions: a base–emitter junction and

a base–collector junction, separated by a thin region of semiconductor known as the base
region (two junction diodes wired together without sharing an intervening semiconducting
region will not make a transistor).
The BJT has three terminals, corresponding to the three layers of semiconductor
– an emitter, a base, and a collector. It is useful in amplifiers because the currents at the
emitter and collector are controllable by a relatively small base current."[25]
In an NPN
transistor operating in the active region, the emitter-base junction is forward biased
(electrons and electron holes recombine at the junction), and electrons are injected into the
base region. Because the base is narrow, most of these electrons will diffuse into the
reverse-biased (electrons and holes are formed at, and move away from the junction) base-
collector junction and be swept into the collector; perhaps one-hundredth of the electrons
will recombine in the base, which is the dominant mechanism in the base current. By
controlling the number of electrons that can leave the base, the number of electrons entering
the collector can be controlled.[25]
Collector current is approximately β (common-emitter
current gain) times the base current. It is typically greater than 100 for small-signal
transistors but can be smaller in transistors designed for high-power applications.
Bipolar transistors can be made to conduct by exposure to light, since
absorption of photons in the base region generates a photocurrent that acts as a base current;
the collector current is approximately β times the photocurrent. Devices designed for this
purpose have a transparent window in the package and are called phototransistors.
3.5.2 Field-effect transistor (FET)
The field-effect transistor, sometimes called a unipolar transistor, uses either
electrons (in N-channel FET) or holes (in P-channel FET) for conduction. The four
terminals of the FET are named source, gate, drain, and body (substrate). On most FETs,
the body is connected to the source inside the package, and this will be assumed for the
following description.
In a FET, the drain-to-source current flows via a conducting channel that connects
the source region to the drain region. The conductivity is varied by the electric field that is
produced when a voltage is applied between the gate and source terminals; hence the

current flowing between the drain and source is controlled by the voltage applied between
the gate and source.
For low noise at narrow bandwidth the higher input resistance of the FET is advantageous.
FETs are divided into two families: junction FET (JFET) and insulated gate FET
(IGFET). The IGFET is more commonly known as a metal–oxide–semiconductor FET
(MOSFET), reflecting its original construction from layers of metal (the gate), oxide (the
insulation), and semiconductor. Unlike IGFETs, the JFET gate forms a p-n diode with the
channel which lies between the source and drain. Functionally, this makes the N-channel
JFET the solid-state equivalent of the vacuum tube triode which, similarly, forms a diode
between its grid and cathode. Also, both devices operate in the depletion mode, they both
have a high input impedance, and they both conduct current under the control of an input
voltage.
Metal–semiconductor FETs (MESFETs) are JFETs in which the reverse biased p-n
junction is replaced by a metal–semiconductor junction. These, and the HEMTs (high
electron mobility transistors, or HFETs), in which a two-dimensional electron gas with very
high carrier mobility is used for charge transport, are especially suitable for use at very high
frequencies (microwave frequencies; several GHz).
Unlike bipolar transistors, FETs do not inherently amplify a photocurrent.
Nevertheless, there are ways to use them, especially JFETs, as light-sensitive devices, by
exploiting the photocurrents in channel–gate or channel–body junctions.
FETs are further divided into depletion-mode and enhancement-mode types,
depending on whether the channel is turned on or off with zero gate-to-source voltage. For
enhancement mode, the channel is off at zero bias, and a gate potential can "enhance" the
conduction. For depletion mode, the channel is on at zero bias, and a gate potential (of the
opposite polarity) can "deplete" the channel, reducing conduction. For either mode, a more
positive gate voltage corresponds to a higher current for N-channel devices and a lower
current for P-channel devices. Nearly all JFETs are depletion-mode as the diode junctions
would forward bias and conduct if they were enhancement mode devices; most IGFETs are
enhancement-mode types

4.OPERATING PRINCIPLE
Simple transistor tester is a transistor analyzer circuit which is suitable for testing
both NPN and PNP transistors. This is a very simple circuit as compared to other transistor
testers. This circuit is very useful for both technicians and students. This circuit can be
easily assembled on a general purpose PCB. A basic electronic component like resistors,
LED’s, diode and transformer is used for developing this circuit. Using this circuit, we can
check whether a transistor is in good condition or not, is it opened or shorted, and so on.
This circuit is locating a faulty transistor on a Circuit Board, crowded with soldered
in place components, can be a difficult proposition. With an In-Circuit TRANSISTOR
TESTER , however, the component's general quality can be determined, while avoiding
damage to other components and/or the foil pattern, due to excessive soldering iron heat.
The TESTER described here will indicate whether a suspect transistor is good or faulty and,
as a bonus, tell you the component's type (PNP or NPN).
A pair of flashing LED's indicate the transistor's condition. One LED flashes if the
transistor is a functional PNP type, while the other LED flashes if the transistor is a good
NPN type. If the transistor is faulty, either both LED's will flash or neither will flash,
depending on the type of failure.

5.CIRCUIT DESIGN
5.1 CIRCUIT DIAGRAM OF TRANSISTER TESTER
Fig.5.1 A) Circuit Diagram of Transister Tester
5.2 PCB LAYOUT :

Fig.5.1 A) Circuit Layout of Transister Tester
6.WORKING

The TESTER’s circuit (shown at the before of this section), is based on a 555 (IC1) timer
operating as a 12 Hz multivibrator. The output at pin 3 drives one flip-flop of IC2. This flip-flop
divides the input frequency by two, but more important, delivers complementary voltage outputs at
pins 15 of 1C 1 (Q) and 14 (not-Q).
These complementary outputs are connected to indicators LED1 and LED2 via current-
limiting resistor R3. The LED's are arranged so that when the polarity across the circuit is one way,
only one LED will glow, and when the polarity is the reverse of that, the other LED glows. Thus,
when no transistor is being tested, the LED's flash alternately. The IC2 complementary outputs are
also connected to resistor network R4 and R5. The junction of these two resistors is connected to the
base of the transistor being tested.
With a good transistor connected to the B, C and E (Base, Collector and Emitter) clips, when
the correct voltage is applied to the three connectors, the transistor will turn on. This produces a
short circuit across the LED pair. For example, when a PNP transistor is under test, during the
interval when the Q output is low and the Q (not-Q) output is high, the PNP device will turn on.
In this mode, LED1 is shorted, LED2 is reverse biased and, for that half cycle, neither LED
will glow. On the next half cycle, the conditions of Q and not-Q are reversed with Q high and not-Q
low. Under these conditions, LED1 is off because it is reverse biased, and since the PNP transistor is
cut off, it does not prevent LED2 from glowing.
Thus, when testing a good PNP transistor, LED2will flash, and when testing a good NPN
type, LED1will flash.
If the transistor under test is open circuit, both LED's will flash. If the transistor has an
internal collector-to-emitter short circuit, neither LEDwill flash.
To compensate for low-valued resistors that may be present in the circuit being tested, R4 is
selected to supply a large amount of base current to the transistor under test.
This makes it possible to overcome in-circuit resistances across the collector-base or base-
emitter junctions of as little as 40 ohms.
Diodes Dl through D4 become important if the transistor being tested has an internal short
between its collector-base or base-emitter junctions. In such a case, half of the transistor acts like a
diode and would normally conduct and indicate a good transistor.
To overcome the possibility of this type of problem occurring, diodes Dl through D4 are
added in series with the collector
7 .P.C.B. MANUFACTURING PROCESS

7.1 P.C.B.
It is an important process in the fabrication of electronic equipment. The design of
PCBs (Printed Circuit Boards) depends on circuit requirements like noise immunity,
working frequency and voltage levels etc. High power PCBs requires a special design
strategy.
The fabrication process to the printed circuit board will determine to a large
extent the price and reliability of the equipment. A common target aimed is the fabrication
of small series of highly reliable professional quality PCBs with low investment. The target
becomes especially important for customer tailored equipments in the area of industrial
electronics.
The layout of a PCB has to incorporate all the information of the board before one can go
on the artwork preparation. This means that a concept which clearly defines all the details of
the circuit and partly defines the final equipment, is prerequisite before the actual lay out
can start. The detailed circuit diagram is very important for the layout designer but he must
also be familiar with the design concept and with the philosophy behind the equipment.
7.2BOARD TYPES:
7.2.1 Single Sided Boards
The single sided PCBs are mostly used in entertainment electronics where
manufacturing costs have to be kept at a minimum. However in industrial electronics cost
factors cannot be neglected and single sided boards should be used wherever a particular
circuit can be accommodated on such boards.
7.2.2 Double Sided Boards
Double-sided PCBs can be made with or without plated through holes. The
production of boards with plated through holes is fairly expensive. Therefore plated through
hole boards are only chosen where the circuit complexities and density of components does
not leave any other choice.

7.3 CHRONOLOGY
The following steps have been followed in carrying out the project.
1. Study the books on the relevant topic.
2. Understand the working of the circuit.
3. Prepare the circuit diagram.
4. Prepare the list of components along with their specification.
5. Estimate the cost and procure them after carrying out market survey.
6. Plan and prepare PCB for mounting all the components.
7. Fix the components on the PCB and solder them.
8. Test the circuit for the desired performance.
9. Trace and rectify faults if any.
10. Give good finish to the unit.
11. Prepare the project report
7.4DESIGN SPECIFICATION

7.4.1 PCB DESIGNING
The main purpose of printed circuit is in the routing of electric currents and signal
through a thin copper layer that is bounded firmly to an insulating base material sometimes
called the substrate. This base is manufactured with an integrally bounded layers of thin
copper foil which has to be partly etched or removed to arrive at a pre-designed pattern to
suit the circuit connections or other applications as required.
The term printed circuit board is derived from the original method where a printed
pattern is used as the mask over wanted areas of copper. The PCB provides an ideal
baseboard upon which to assemble and hold firmly most of the small components.
From the constructor’s point of view, the main attraction of using PCB is its role
as the mechanical support for small components. There is less need for complicated and
time consuming metal work of chassis contraception except perhaps in providing the final
enclosure. Most straight forward circuit designs can be easily converted in to printed wiring
layer the thought required to carry out the inversion cab footed high light an possible error
that would otherwise be missed in conventional point to point wiring .The finished project
is usually neater and truly a work of art.
Actual size PCB layout for the circuit shown is drawn on the copper board. The
board is then immersed in FeCl3 solution for 12 hours. In this process only the exposed
copper portion is etched out by the solution.
Now the petrol washes out the paint and the copper layout on PCB is rubbed
with a smooth sand paper slowly and lightly such that only the oxide layers over the Cu are
removed. Now the holes are drilled at the respective places according to component layout
as shown in figure.
7.4.2 LAYOUT DESIGN

When designing the layout one should observe the minimum size (component body
length and weight). Before starting to design the layout we need all the required
components in hand so that an accurate assessment of space can be made. Other space
considerations might also be included from case to case of mounted components over the
printed circuit board or to access path of present components.
It might be necessary to turn some components around to a different angular
position so that terminals are closer to the connections of the components. The scale can be
checked by positioning the components on the squared paper. If any connection crosses,
then one can reroute to avoid such condition.
All common or earth lines should ideally be connected to a common line routed
around the perimeter of the layout. This will act as the ground plane. If possible try to route
the outer supply line to the ground plane. If possible try to route the other supply lines
around the opposite edge of the layout through the center. The first set is tearing the circuit
to eliminate the crossover without altering the circuit detail in any way.
Plan the layout looking at the topside to this board. First this should be translated inversely,
later for the etching pattern large areas are recommended to maintain good copper adhesion.
It is important to bear in mind always that copper track width must be according to the
recommended minimum dimensions and allowance must be made for increased width
where termination holes are needed. From this aspect, it can become little tricky to negotiate
the route to connect small transistors.
There are basically two ways of copper interconnection patterns under side the
board. The first is the removal of only the amount of copper necessary to isolate the
junctions of the components to oneanother. The second is to make the interconnection
pattern looking more like conventional point wiring by routing uniform width of copper
from component to component.
7.4.3 ETCHING PROCESS

Etching process requires the use of chemicals. acid resistant dishes and running
water supply. Ferric chloride is mostly used solution but other etching materials such as
ammonium per sulphate can be used. Nitric acid can be used but in general it is not used
due to poisonous fumes.
The pattern prepared is glued to the copper surface of the board using a latex type of
adhesive that can be cubed after use. The pattern is laid firmly on the copper using a very
sharp knife to cut round the pattern carefully to remove the paper corresponding to the
required copper pattern areas. Then apply the resistant solution, which can be a kind of ink
solution for the purpose of maintaining smooth clean outlines as far as possible. While the
board is drying, test all the components.
Before going to next stage, check the whole pattern and cross check with the circuit
diagram. Check for any free metal on the copper. The etching bath should be in a glass
or enamel disc. If using crystal of ferric- chloride these should be thoroughly dissolved
in water to the proportion suggested. There should be 0.5 lt. of water for 125 gm of
crystal.
To prevent particles of copper hindering further etching, agitate the solutions carefully by
gently twisting or rocking the tray.
The board should not be left in the bath a moment longer than is needed to remove
just the right amount of copper. Inspite of there being a resistive coating there is no
protection against etching away through exposed copper edges. This leads to over etching.
Have running water ready so that etched board can be removed properly and rinsed. This
will halt etching immediately.
Drilling is one of those operations that calls for great care. For most purposes a
0.5mm drill is used. Drill all holes with this size first those that need to be larger can be
easily drilled again with the appropriate larger size.
7.4.4 COMPONENT ASSEMBLY

From the greatest variety of electronic components available, which runs into
thousands of different types it is often a perplexing task to know which is right for a given
job.
There could be damage such as hairline crack on PCB. If there are, then they can be
repaired by soldering a short link of bare copper wire over the affected part.
The most popular method of holding all the items is to bring the wires far apart after
they have been inserted in the appropriate holes. This will hold the component in position
ready for soldering.
Some components will be considerably larger .So it is best to start mounting the
smallest first and progressing through to the largest. Before starting, be certain that no
further drilling is likely to be necessary because access may be impossible later.
Next will probably be the resistor, small signal diodes or other similar size
components. Some capacitors are also very small but it would be best to fit these
afterwards. When fitting each group of components mark off each one on the circuit as it is
fitted so that if we have to leave the job we know where to recommence.
Although transistors and integrated circuits are small items there are good reasons
for leaving the soldering of these until the last step. The main point is that these components
are very sensitive to heat and if subjected to prolonged application of the soldering iron,
they could be internally damaged.
All the components before mounting are rubbed with sand paper so that oxide
layer is removed from the tips. Now they are mounted according to the component layout.
7.4.5 SOLDERING: -

This is the operation of joining the components with PCB after this operation the
circuit will be ready to use to avoid any damage or fault during this operation following care
must be taken.
1. A longer duration contact between soldering iron bit & components lead can exceed the
temperature rating of device & cause partial or total damage of the device. Hence before
soldering we must carefully read the maximum soldering temperature & soldering time for
device.
2. The wattage of soldering iron should be selected as minimum as permissible for that
soldering place.
3 .To protect the devices by leakage current of iron its bit should be earthed properly.
4. We should select the soldering wire with proper ratio of Pb & Tn to provide the suitable
melting temperature.
5. Proper amount of good quality flux must be applied on the soldering point to avoid dry
soldering.
8 .ADAVANTAGES OF THE CIRCUIT

The key advantages that have allowed transistors to replace their vacuum tube predecessors
in most applications are
• Small size and minimal weight, allowing the development of miniaturized electronic
devices.
• Low operating voltages compatible with batteries of only a few cells.
• No warm-up period for cathode heaters required after power application.
• Lower power dissipation and generally greater energy efficiency.
• Higher reliability and greater physical ruggedness.
• Complementary devices available, facilitating the design of complementary-
symmetry circuits, something not possible with vacuum tubes.
9 .DISADAVANTAGES OF THE CIRCUIT

 Only detect whether Transistor is good or damage
 Does not show internal problem of the Transister
 At a time only one element can be tested

10.APPLICATION OF CIRCUIT
The circuit thus can be used to check:
 Used in Electronics store to check the Transistor
 Also used in College Practical labs ..
 etc

11.PRECAUTIONS
1. The soldering iron being used for soldering of semiconductors should be of low
voltage.
2. While soldering semiconductors heat sinks should be used.
3. While soldering solder should not spread over the entire circuit and solder tip should
be sharp and smooth.
4. While mounting components their values should be visible.
5. Semiconductors and other polarized components should be mounted with correct
polarity.
6. Time should be carefully observed while etching process takes place on the PCB.

12. REFERENCES
Referances List
 www.indiabix.com
 www.redcircuit.com
 http://www.talkingelectronics.com
 Datasheet for BC549, with A,B and C gain groupings
"http://www.fairchildsemi.com/ds/BC/BC549.pdf. Retrieved 2012-06-30.
 Vardalas, John, Twists and Turns in the Development of the Transistor IEEE-
USA Today's Engineer, May 2003

Test Transistor Performance

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