Semester 2 Flashcards
weaknesses of an mechanical switch
wears out and limited speed
difference between latching and non-latching electrical switches
latching use a signal applied to an electrode and then remain switched on
for non latching the control signal must reamin on for the duration of the on period
advantages of electrical switches
- Lossless (ideal case)
- High frequency
- No moving parts
- Cheap
limittions of solid state switches
- Maximum current rating
- Maximum voltage rating
- Turn-on and turn-off switching transition times
- Maximum power dissipation
can arbitrarily decide to turn off a latching switch
no
what are most latching and non latching switches used for
latching - AC
non latching -DC
applications of latching switches
light dimming and motor control
what is the rough number of valence electrons of a semiconductor
3-5
what is n-type doping
the donor impuritie contributes free electrons
what is p-type doping
the cceptor impurity creates electron holes
what is the p-n junction
the area at which no current flows - widely the greater V needed
what are the 3 parts of a bipolar junction transsitor
collector, emitter, base
as Ib rises how does Ic rise
it rises linearly by Beta until it reaches the saturation current
at cut off how does the transistor behave
like an open switch
most common semiconductor
silicon
what happens when the electric field is connected in the same diection of the depletion zone
it grows the zone to behave like an insulator
why is a cureent put through the base
reducing the potential difference to the top reducing the depletion zone
can diode’s change current instantaneously
no
Icsat=
(Vcc-Vce)/Rl
Ibsat=
Icsat/Beta
advantages and disadvantages of overdriving
Speeds up the turn-on process and reduces switching losses
Slows down the turn-off process
why is overdriving done
to ensure saturation is acheived
reverse recovery tie is proportional to
base current
what happens in reverse recovery mode
a pulse of base current and the BJT remains on
what problems can happen with reverse recovery
liits the mximum switching frequency and electronic problems
what is the reverse recovery time in a diode
the time for the charge carriers to change
during the reverse recovery time how does the diode act
as a short circuit
forward recovery time
time taken for a diode to assume a low impedance state following a change from reverse bias to forward bias.
what is a switched mode power supply
chopped Dc signal - smoothed and transformed
purpose of protection
limit current to prevent power surges
how does a linear series regualtor work
it use BJT to drop the input to the output voltage
why may a heat sink be required by a regualtor
there ay be a small voltage drop that can result in a large power loss
what is required to improve the stability of a regulator
decoupling capacitors
what is a linear shunt regulator
BJT connected in parrallel to the load
what does a linear shunt regulator behave like
like a zener diode
how does overvoltage protection work
the protection will use a latching device that will blow once the current is removed
why are there so many components in an amplifier
to minimise distortion - very high loop gains
princple of class B amplifier
half of the period of the signal is used
what is cross over distortion
the transistor only conducts above 0.7V this results in distortion of results
how is cross over distortion prevented
ensure the transistor operate slightly above cut off using forward biased diodes
which is more efficient class A or B amplifiers
Class A
role of resistors in a class b amplifier
help set up desired q-point and prevent transistor thermal runaway
2 types of power amplifier
linear and digital
why is temperature anagement important
components stop workingat certain temperatures
forms of thermal management
heatsink
fans
liquid cooling
each component has thermal resistance and
coeffiecient of therml expansion
in a thermal equivalent what V, I and R
V- T
I - power
R- therml resistance
what is an SCR
a thyristor with 4 levels of semiconductor
what is required to activate the device
an external ulse current
is an SCR thyristor latching or non latching
latching
basic concept of a MOSFET
uses a chanel from a silicon diode
2 basic MOSFET types
ehancement and depletion
basic concept of an enhancement MOSFET
a positive voltage pulls the ions to create a chanel
what is required to turn a MOSFET on and off
turn on V around 12V
and turn off 0V
wht affects switching speed
parasitic capacitance
advantages and disadvantages of MOSFETS
small area of good capabilities
The switching times are short, the gate driver is simple and
requires very little power
how can a IGBT be thought of in comparison to a BJT
the same but with faster switching speeds
