4.1 Semiconductions - Transistors Flashcards
what is the term used to describe how transistors work?
current flowing in the output circuit is determined by the current flowing in the input circuit
what two categories do transistors fall into?
bi polar
field-effect
how are bipolar transistors contructed?
NPN or PNP junctions of semiconductor material
what are the 3 electrodes called?
collector
base
emitter
what is the emitters role?
to emit charge carriers
what is the base’s role?
to regulate the emission of charge carriers
what is the collectors role?
to collect the charge carriers
what does the current have to be in a transistor?
Current out = current in
how can a transistor be tested?
same way as a diode, using an ohmmeter
between the base-emitter PN junction and Base-collector PN junction
how is it possible to identify the polarity of an unknown transistor?
using an ohmmeter, providing you can identify the emitter, base and collector leads
what should the voltage reading be of a base-emitter and base-collector transistor with the correct polarity known?
0.5-0.8 vDC
what should the meter show when reading a base-emitter and base-collector transistor in the reverse direction?
indicate open circuit
what should the resistance be when testing the transistor for emitter to collector?
open circuit in both directions
what are the typical current gains of a transistor?
100 to 600
what 3 characteristics curves are used for transistors?
input characteristics
output characteristics
current transfer characteristics
what is the input characteristics curve?
describe changes in input current with variation of input voltage whilst keeping output current constant
what is the output characteristic curve?
describes output current versus output voltages with constant input current
what is the current transfer characteristics curve?
describes the output current IAW the input current, keeping voltage constant
how are a transistors circuit designated?
according to the electrode where the AC signals are earthed, and which forms the common reference potential for the other two electrodes
if one electrode is where the AC signals come from, what role does the other electrodes have?
Form either control circuit or the operating circuit
which type of transistor circuit is the most widely used?
emitter circuit
what does an emitter circuit make it possible to do?
amplify both current and voltage, increasing power greatly
what other names are given to collector circuits?
emitter follower
impedance converter
what are the characteristics of an emitter circuit?
medium input and output impedance, medium current gain and voltage gain
what are the characteristics of a collector circuit?
extremely high input resistance and low output resistance
voltage gain less than 1 and large current gain
what are the characteristics of base circuits?
low input resistance and high output resistance
why is a base circuit particularly useful?
harmful capacitances between collector-base and emitter-base are connected to ground,
useful for high-frequency applications
what is the phase shift of an emitter circuit, compared to the other types?
180 degrees
what is the difference between the circuit types regarding input, output and current transfer characteristics?
input characteristics = CB and CE the same, CC different
output characteristics = all the same
current transfer characteristics = all the same
