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Electrical > Semester 2 > Flashcards

Semester 2 Flashcards

1
Q

weaknesses of an mechanical switch

A

wears out and limited speed

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2
Q

difference between latching and non-latching electrical switches

A

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

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3
Q

advantages of electrical switches

A
  • Lossless (ideal case)
  • High frequency
  • No moving parts
  • Cheap
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4
Q

limittions of solid state switches

A
  • Maximum current rating
  • Maximum voltage rating
  • Turn-on and turn-off switching transition times
  • Maximum power dissipation
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5
Q

can arbitrarily decide to turn off a latching switch

A

no

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6
Q

what are most latching and non latching switches used for

A

latching - AC

non latching -DC

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7
Q

applications of latching switches

A

light dimming and motor control

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8
Q

what is the rough number of valence electrons of a semiconductor

A

3-5

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9
Q

what is n-type doping

A

the donor impuritie contributes free electrons

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10
Q

what is p-type doping

A

the cceptor impurity creates electron holes

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11
Q

what is the p-n junction

A

the area at which no current flows - widely the greater V needed

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12
Q

what are the 3 parts of a bipolar junction transsitor

A

collector, emitter, base

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13
Q

as Ib rises how does Ic rise

A

it rises linearly by Beta until it reaches the saturation current

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14
Q

at cut off how does the transistor behave

A

like an open switch

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15
Q

most common semiconductor

A

silicon

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16
Q

what happens when the electric field is connected in the same diection of the depletion zone

A

it grows the zone to behave like an insulator

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17
Q

why is a cureent put through the base

A

reducing the potential difference to the top reducing the depletion zone

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18
Q

can diode’s change current instantaneously

A

no

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19
Q

Icsat=

A

(Vcc-Vce)/Rl

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20
Q

Ibsat=

A

Icsat/Beta

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21
Q

advantages and disadvantages of overdriving

A

Speeds up the turn-on process and reduces switching losses

Slows down the turn-off process

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22
Q

why is overdriving done

A

to ensure saturation is acheived

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23
Q

reverse recovery tie is proportional to

A

base current

24
Q

what happens in reverse recovery mode

A

a pulse of base current and the BJT remains on

25
Q

what problems can happen with reverse recovery

A

liits the mximum switching frequency and electronic problems

26
Q

what is the reverse recovery time in a diode

A

the time for the charge carriers to change

27
Q

during the reverse recovery time how does the diode act

A

as a short circuit

28
Q

forward recovery time

A

time taken for a diode to assume a low impedance state following a change from reverse bias to forward bias.

29
Q

what is a switched mode power supply

A

chopped Dc signal - smoothed and transformed

30
Q

purpose of protection

A

limit current to prevent power surges

31
Q

how does a linear series regualtor work

A

it use BJT to drop the input to the output voltage

32
Q

why may a heat sink be required by a regualtor

A

there ay be a small voltage drop that can result in a large power loss

33
Q

what is required to improve the stability of a regulator

A

decoupling capacitors

34
Q

what is a linear shunt regulator

A

BJT connected in parrallel to the load

35
Q

what does a linear shunt regulator behave like

A

like a zener diode

36
Q

how does overvoltage protection work

A

the protection will use a latching device that will blow once the current is removed

37
Q

why are there so many components in an amplifier

A

to minimise distortion - very high loop gains

38
Q

princple of class B amplifier

A

half of the period of the signal is used

39
Q

what is cross over distortion

A

the transistor only conducts above 0.7V this results in distortion of results

40
Q

how is cross over distortion prevented

A

ensure the transistor operate slightly above cut off using forward biased diodes

41
Q

which is more efficient class A or B amplifiers

A

Class A

42
Q

role of resistors in a class b amplifier

A

help set up desired q-point and prevent transistor thermal runaway

43
Q

2 types of power amplifier

A

linear and digital

44
Q

why is temperature anagement important

A

components stop workingat certain temperatures

45
Q

forms of thermal management

A

heatsink
fans
liquid cooling

46
Q

each component has thermal resistance and

A

coeffiecient of therml expansion

47
Q

in a thermal equivalent what V, I and R

A

V- T
I - power
R- therml resistance

48
Q

what is an SCR

A

a thyristor with 4 levels of semiconductor

49
Q

what is required to activate the device

A

an external ulse current

50
Q

is an SCR thyristor latching or non latching

A

latching

51
Q

basic concept of a MOSFET

A

uses a chanel from a silicon diode

52
Q

2 basic MOSFET types

A

ehancement and depletion

53
Q

basic concept of an enhancement MOSFET

A

a positive voltage pulls the ions to create a chanel

54
Q

what is required to turn a MOSFET on and off

A

turn on V around 12V

and turn off 0V

55
Q

wht affects switching speed

A

parasitic capacitance

56
Q

advantages and disadvantages of MOSFETS

A

small area of good capabilities
The switching times are short, the gate driver is simple and
requires very little power

57
Q

how can a IGBT be thought of in comparison to a BJT

A

the same but with faster switching speeds

Electrical (9 decks)

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