Semiconductor Transistors

worshiprelaxedElectronics - Devices

Nov 2, 2013 (3 years and 7 months ago)

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Semiconductor
Transistors

Edited 7/17/13 by Stephen Albright &

DGH


PURPOSE OF EXPERIMENT: S
tudy the characteristics of a semiconductor transistor.


REFERENCES: Tipler, Chapter 9 (esp. p. 340
-
342); Enge, Wehr and Richards, Chapter 11;
Horowtiz &

Hill, p. 11, 35, 192; Eisberg & Resnick, Chapter 13.


APPARATUS:
Power
Transistor,
Instek
D.C. Power Supply,
HP 3435A Mul
t
imeter
, HP
3468A
M
ultimeter,
11
k

Decade Resistance Box

and
12V
Indicator

Lamp.


OVERVIEW: A
transistor

is a semiconductor device commonly used to amplify or switch
electronic signals.

Common transistors come in two varieties
, PNP & NPN
. Two diodes connected
cathode to cathode (PNP) or anode to anode (NPN) approximate

a typical transistor
.

See below:














PNP Transistor

NPN Transistor




PROCEDURE:


1.

Construct the
following c
ircuit
.
The diode in the figure refers to a pair of contacts of the
transistor (as seen above, the device between any two adjacent contacts of a transistor is
equivalent to a diode).
Note, unlike the procedures we used to study diodes, in this lab the
sam
e circuit will be used to test for forward and reverse bias
, the grounded terminal of the


2

power supply
will

not be changed and no electrometers will be used


the accuracy is not
needed
.




Circuit for measuring I & V across

each pair of transistor contacts


2.

Set the decade resistance box to 5
k
Ω
, the ammeter to
0.00000 A & the Voltmeter to 60 V.


3.

Identify the transistors “Base”
by applying ~1V (as
read

on
Agilent
) across each
of
the three
pairs
of contacts. Apply

the voltage in both polarities.


4.

D
etermine if the transistor is PNP or NPN

by observing
the polarity of the forward and
reve
rse bias relative to the Base.



5.

Identify the transistor’s “Em
itter” and “Collector”

by applying ~12V in both polarities
across the

two remaining contacts
. Note
: The

current will be much higher when the polarity
of the Collector is forward biased relative the Base than when the polarity of the Emitter is
forward biased relative to the base.

Note: the Base is not connected in this a
rrangement
.



6.

Construct the following circuit
. Note: t
he
polarity of the Collector
-

Base connection is
reverse bias
. That is, the Base is
positive (
less negative
) relative to
the Collector
:




3



Circuit for measuring
I
B

&
I
C


7.

Set the

power supply to
~
11V, the
I
C

Ammeter to

6A
, the
I
B

Ammeter to
0.00000A

and the fine dial on the Resistance Box to 1
k
Ω (Full CW). Record
I
B

&
I
C
. Decrease the resistance one click at a time and record
I
B

&
I
C

for each
step.

Warning: Do not leave
I
C

set at maximum (
0
resistance) for
very
long,
the transistor could overheat and be destroyed.


8.

Plot
I
B

vs.
I
C
.


F
rom the graph find the saturation current
(
I
C
)
s

and

β.




9.

How does

the
saturation current

-

I
C

-

impact the performance of an amplifier?


I
C

I
B

(I
C
)
s

(I
B
)
s



4

10.

Leaving the base connected as shown, reverse the collect
or and the emitter
connections on

the transistor
. Can you still control

I
C

&
the
lamp

with

I
B
?
Why or why not?