Transistors Flashcards
The various junctions in a transistor
1] Emitter
2]Base
3]Collector
Emitter junction
Is highly doped and medium sized junction
Base junction
Is lightly doped and very thin in size
Collector junction
Is moderately doped and large in size
r(input)
[/\V(BE)]/[/\I(B)]
Where :
/\ —> delta
A.C current gain( beta)
For common emitter configuration
Beta = |/\Ic| / |/\Ib|
Where /--> delta
Range of beta(A.C. Current gain) for common emitter configuration
20
AC current gain for common base configuration (alpha)
Alpha= |/\Ic| / |/\Ie|
Range of ac current gain for common Base configuration
0.95
Relationship between alpha and beta
Alpha = beta/(1+beta)
Beta= alpha/ (1-alpha)
Common emitter amplifier
1]current gain =
2]voltage gain =
3]power gain =
1] beta = |/\Ic| / |/\Ie|
2]Av = /\Vc / /\Vb = beta x (Rout/Rin)
3] Pout/Pin = beta^2 x (Rout/Rin)
Beta is always
Greater than 1
Oscillator always uses
Positive feedback
Condition to work as an oscillator
|A x beta| = 1
where beta is the feedback factor
Frequency determination of an oscillator
1/2||(LC)^1/2
For a transistor switch the active stage is achieved
At an intermediate input voltage
In transistor switch Value of output voltage
Decreases linearly till its value is less than 1V
In cut off region of transistor switch
Vi
Graph for transistor switch
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