semiconductor

Question 1

advantages of transformer in rectifier

Answer 1

allows us to step up/step down ac input voltage as per need

isolates rectifier circuit from mains supply to reduce risk of electric shock

Question 2

why is rectifier w 2 diodes more useful

Answer 2

output of half wave rectifier is only available in positive half cycles
negative half cycles are lost
thus efficiency is poor

Question 3

advantages of full wave rectifier

Answer 3

rectification in both cycles
efficiency higher
ripple is less

Question 4

what is ripple factor

Answer 4

ac component present in dc output is called ripple

ripple is undesirable and responsible for fluctuations in output

smaller ripple means rectifier is more efficient

Question 5

ripple factor formula

Answer 5

rms value of ac component
______________________________
value of dc component

Question 6

why do we need filter in power supple

Answer 6

output does not have a steady value
keeps fluctuating due to ripple factor
filter circuit removes the ripple factor

Question 7

filter circuit

Answer 7

a circuit which removes ac component from rectifier output and only allows dc component

Question 8

uses of capacitor filter

Answer 8

low cost
light weight
small size
battery eliminators

Question 9

unregulated power supply

Answer 9

a power supply whose output changes when a load is connected across it

Question 10

reverse breakdown voltage

Answer 10

when reverse bias voltage of junction diode
is increased
the reverse current
increases sharply to a high value
this critical voltage is called reverse breakdown voltage

Question 11

how is zener diode different from regular diode

Answer 11

has a very thin depletion region due to heavy doping
ordinary diode gets damages when reverse voltage is increased
zener diode is designed to operate here
zener diode is used mainly for

voltage regulation and not rectification

Question 12

formula for max power of zener diode

Answer 12

p=Iz (max)Vz

Question 13

applications of zener diode

Answer 13

voltage regulator
peak clipper/ limiter in a wave shaping circuit
protector from accidental fluctuations

Question 14

what is a photodiode

Answer 14

special pn junction diode which converts light energy to electrical energy
-generates current when exposed to light

aka photodetector /photosensor

only operates in reverse biased mode
minority current flows thru it

Question 15

schematic for photodiode

Question 16

principle of photodiode

Answer 16

photo electric effect

Question 17

what is dark resistance of photodiode

Answer 17

• it is resistance of diode when it is not illuminated
  = maximum reverse voltage
  _____________________________
  dark current

Question 18

applications of photodiode use and disadvantage

Answer 18

1)
counters and switches
burglar alarm systems
fibre optic communication
smoke detectors

uses
quick response
high speed
low cost

disadvantage
properties are temp dependent
low reverse current for low illumination levels.

Question 19

principle and use of solar cells

Answer 19

converts solar energy into electric energy
aka
photovoltaic cell

uses
charging batteries
remote places supplying current
measure intensity of light in lux meter

Question 20

led

Answer 20

light emitting diode
emits light when large forward current passes thru it

Question 21

application use and disadvantage of led

Answer 21

counters
burglar alarm system
switches
led tv
street lighting

use
brightness can be controlled
long lifetime
energy efficient
excellent colour rendering
do not contain mercury / harmful substances

disadvantage
high cost
temp dependence
voltage sensitive

Question 22

what is junction transistor

Answer 22

semiconductor w 2 junctions and 3 terminals

Question 23

two types of junction transistors

Answer 23

npn
pnp

Question 24

most common method of biasing ____ is forward and reverse biased?.

Answer 24

emitter base junction= forward biased
collector base junction= reverse biased

Question 25

input dynamic resistance of transistor

Answer 25

ratio of change in base emitter voltage and
resulting change in base current
at constant cb voltage

Question 26

amplifier

Answer 26

increases amplitude of alternating signal

Question 27

which method of biasing is used for operating transistor as amplifier

Answer 27

eb junction is forward biased
cb junction is reverse biased