SWITCHING CHARACTERISTICS OF TRANSISTOR
AIM :- To verify the switching characteristics of a transistor.
APPARATUS :-
Sr.No. Item Range Remark
01. Ammeter
02. Ammeter
03. Voltmeter
04. Voltmeter
05. D.C.P.S.
THEORY:- Very often, bipolar junction transistor are used as electronic switches.
With the help of such a switch, a given can be turned ON or OFF by a small control
Signal. The power level of the control signal is usually very small and hence, it is in
-capable of switching the load directly. However such a control signal is certainly
capable of providing enough base drive to switch a transistor ON or OFF and hence,
the transistor is made to switch the load .
When using BJT as a switch, usually two levels of control signal are employed.
With one level, the transistor operates in the cutoff region(open) where as with the
Other level, it operates in the saturation region and acts as a short circuit.
While acting as open switch, the BE junction is reverse
Biased, means transistor is in cut-off region and it acts
As open switch.
Now, if Vi equals a positive voltage of sufficient
Magnitude to produce saturation i.e. if Vi=Vi,
The transistor acts as a closed switch.
PROCEDURE :
-
� Vcc applied equal to 10v.
� I/P to transistor, VBE is varied in steps.When VBE is less than 0.5 v transistor is in cut �off region.There fore IB =0 & I C =0 & VCE =VCC.
� As soon as VBE becomes more than 0.5v, base current flows also collector current flows and VCE reduces.
� VBE is increased to such an extent so that transistor goes into saturation.
� Note all the readings of IB, VCE, IC for various values of VBE.
CONCLUSION :-
(1) By performing the above experiment we can conclude that , when VBE (Input) is less than 0.5volts. This is called the cut-off region . At this value of
VBE, VCE~ VCC and IC=O . Thus, transistor is said to be in OFF condition.
(2) As VBE becomes greater as 0.5volt, VCE reaches approximately equal to zero value . IC becomes maximum and transistor is said to be in saturation and called as ON condition of transistor.
OBSERVATION TABLE :-
Sr.
No. IB
In A. IC
In mA. VBE
In volts . VCE
In volts.
01.
02.
03.
04.
05.
06.
07.
08.
09.
10.