Transistors

Question 1

How does a BJT work

Answer 1

-Consists of two pn type junctions (NPN or PNP)
-The NP junction is located between the Emitter and base
-The PN jct is between the base and collector
-Electrons flow from the emitter to the base and from the base to the collector.

Question 2

Define the depletion region

Answer 2

-An insulating region where mobile charge carries have been diffused away or forced away by an electric field.

Question 3

Which has a greater depletion region? np jct or pn jct and explain why

Answer 3

• np jct
  -the np jct is reversed biased so the flow of majority carriers will be 0
  -so the insulation is greater

Question 4

What is current in the emitter equal to

Answer 4

Ie = Ib + Ic

Question 5

In common emitter configuration, for the output characteristic, what is on the axis?

Answer 5

-Collector current is on the y axis and collector-emitter voltage is on the x axis

Question 6

define the constant beta

Answer 6

base forward current amplification factor
Has a range from 50-400

Question 7

define alpha

Answer 7

-dc: the ratio of Ic/Ie
-ac: the ratio of ∆Ic/∆Ie
- has a range from 0.9-0.99

Question 8

Which part of the transistor always has the largest current

Answer 8

the emitter

Question 9

What is the difference between unipolar and bipolar

Answer 9

-Bipolar uses holes and electrons as charge carriers(BJT)
-Unipolar only has one type of charge carrier(JFET)

Question 10

Which terminal in a bjt is the most doped?

Answer 10

Emitter

Question 11

Define the I(CO) current

Answer 11

The collector current measured with the emitter open
-leakage current

Question 12

What is the source of leakage current

Answer 12

The flow of minority charge carriers

Question 13

In common-base configuration, how can we determine emitter current?

Answer 13

On the output characteristic, emitter current is approximately collector current

Question 14

What is the voltage amplification factor and how do we find VL?

Answer 14

Av = VL/Vs
- IL is Ii so use ohms law

Question 15

Why is it best to stay within the active region?

Answer 15

-there are a range of different operating points
-The device could be destroyed

Question 16

How do we find VCE

Answer 16

Vce = Vc - Ve

Question 17

How can we find base current using KVL in the base-emitter loop?

Answer 17

KVL: Vcc -IbRb -Vbe = 0
therefore Ib = (Vcc - Vbe) / Rb

Question 18

Define Biasing in terms of transistor amplification and explain why it is necessary

Answer 18

Biasing: application of Dc voltages to establish fixed values for current and voltage.
In terms of transisitor amplification: establish an operating point for amplification
why: prevents the output from being distorted

Question 19

When trying to find the resistance of the base terminal, there is current (down), what do we assume?

Answer 19

The current Ip + Ib, where Ip > 10Ib, otherwise the bias will shift

Question 20

How can Vce be calculated with kvl?

Answer 20

Vce = Vcc - Ie(Re+Rc)