4.1 Semiconductions - Transistors

Question 1

what is the term used to describe how transistors work?

Answer 1

current flowing in the output circuit is determined by the current flowing in the input circuit

Question 2

what two categories do transistors fall into?

Answer 2

bi polar
field-effect

Question 3

how are bipolar transistors contructed?

Answer 3

NPN or PNP junctions of semiconductor material

Question 4

what are the 3 electrodes called?

Answer 4

collector
base
emitter

Question 5

what is the emitters role?

Answer 5

to emit charge carriers

Question 6

what is the base’s role?

Answer 6

to regulate the emission of charge carriers

Question 7

what is the collectors role?

Answer 7

to collect the charge carriers

Question 8

what does the current have to be in a transistor?

Answer 8

Current out = current in

Question 9

how can a transistor be tested?

Answer 9

same way as a diode, using an ohmmeter

between the base-emitter PN junction and Base-collector PN junction

Question 10

how is it possible to identify the polarity of an unknown transistor?

Answer 10

using an ohmmeter, providing you can identify the emitter, base and collector leads

Question 11

what should the voltage reading be of a base-emitter and base-collector transistor with the correct polarity known?

Answer 11

0.5-0.8 vDC

Question 12

what should the meter show when reading a base-emitter and base-collector transistor in the reverse direction?

Answer 12

indicate open circuit

Question 13

what should the resistance be when testing the transistor for emitter to collector?

Answer 13

open circuit in both directions

Question 14

what are the typical current gains of a transistor?

Answer 14

100 to 600

Question 15

what 3 characteristics curves are used for transistors?

Answer 15

input characteristics
output characteristics
current transfer characteristics

Question 16

what is the input characteristics curve?

Answer 16

describe changes in input current with variation of input voltage whilst keeping output current constant

Question 17

what is the output characteristic curve?

Answer 17

describes output current versus output voltages with constant input current

Question 18

what is the current transfer characteristics curve?

Answer 18

describes the output current IAW the input current, keeping voltage constant

Question 19

how are a transistors circuit designated?

Answer 19

according to the electrode where the AC signals are earthed, and which forms the common reference potential for the other two electrodes

Question 20

if one electrode is where the AC signals come from, what role does the other electrodes have?

Answer 20

Form either control circuit or the operating circuit

Question 21

which type of transistor circuit is the most widely used?

Answer 21

emitter circuit

Question 22

what does an emitter circuit make it possible to do?

Answer 22

amplify both current and voltage, increasing power greatly

Question 23

what other names are given to collector circuits?

Answer 23

emitter follower
impedance converter

Question 24

what are the characteristics of an emitter circuit?

Answer 24

medium input and output impedance, medium current gain and voltage gain

Question 25

what are the characteristics of a collector circuit?

Answer 25

extremely high input resistance and low output resistance
voltage gain less than 1 and large current gain

Question 26

what are the characteristics of base circuits?

Answer 26

low input resistance and high output resistance

Question 27

why is a base circuit particularly useful?

Answer 27

harmful capacitances between collector-base and emitter-base are connected to ground,

useful for high-frequency applications

Question 28

what is the phase shift of an emitter circuit, compared to the other types?

Answer 28

180 degrees

Question 29

what is the difference between the circuit types regarding input, output and current transfer characteristics?

Answer 29

input characteristics = CB and CE the same, CC different
output characteristics = all the same
current transfer characteristics = all the same