4.1 Semiconductions - Transistors Characteristics Flashcards
what are the two types of characteristics regarding a transistor’s limitations?
static
dynamic
what is residual current/reverse leakage current?
the current that still flows to the p-n junction when a reverse bias voltage is applied
how is residual current affected by temperature?
it can lead to a shift in the operation point if appropriate switching measures are not implemented
delta of 10c = residual current doubles
what are used instead of absolute values?
levels (measured in decibels)
what happens when the temperature rises in a semi conductor?
additional charge carrier pairs become free in a semiconductor
increasing its intrinsic conductivity
how many times does the residual current increase when its temperature is raised from 25 to 150 degrees c?
2000 times
why is it important to modulate the temperature of a transistor?
temperature changes causes a shift in operating point, causing both half waves to be distored
what is the max permissible temp of a germanium transistor?
75 to 90 degrees c
what is the max permissible temp of a silicon transistor?
150 to 200 degrees c
what is the position of the operating point determined by?
the magnitude of the base-emitter voltage
how is the operating point shift prevented when there is a temperature change?
when the base-emitter voltage is decreased as the temperature increases
how is base current adjusted to temperature?
means of a base swamping resistor
if a resistor is added in the emitter circuit, what is created?
negative current feedback
how does a negative current feedback circuit work?
the voltage divider and additional resistor adjust the emitter current in such a way that it is almost independent of the rest
what else is used in a negative current feedback? why?
a capacitor connected in parallel,
to prevent the emitter from creating negative feedback and only stabilises the AC input voltage
in a voltage feedback circuit, where is the voltage divider?
at the collector
why is a voltage feedback circuit a good method of stabilising the operating point?
because it provides good stability with minimal circuitry
what other method can be used to stabilise the operating point?
temperature-sensitive base voltage divider
how does a temperature-sensitive voltage divider circuit work?
NTC resistors are connected in a series-parallel network with a resistor.
as temperature increases, the resistance of the NTC resistor decreases
what must be done to keep the transistor and NTC resistor at the same temperature to ensure correct function?
installing them both on the same heat sink
how many types and how are transistors classified into types?
2
bipolar junction transistors (BJT)
field effect transistors (FET)
how are BJT transistors split into different types?
NPN and PNP Junction
how are FET transistors split into different types?
FET to Junction FET and Metal Oxide Semiconductor FET
JFET to depletion mode, then to N and P channel
MOSFET to depletion mode and enhancement mode, then both into n and P channel
how are BJT transistors controlled?
by current.
small current at base = large current from emitter to colelctor