semiconductor Flashcards
advantages of transformer in rectifier
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
why is rectifier w 2 diodes more useful
output of half wave rectifier is only available in positive half cycles
negative half cycles are lost
thus efficiency is poor
advantages of full wave rectifier
rectification in both cycles
efficiency higher
ripple is less
what is ripple factor
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
ripple factor formula
rms value of ac component
______________________________
value of dc component
why do we need filter in power supple
output does not have a steady value
keeps fluctuating due to ripple factor
filter circuit removes the ripple factor
filter circuit
a circuit which removes ac component from rectifier output and only allows dc component
uses of capacitor filter
low cost
light weight
small size
battery eliminators
unregulated power supply
a power supply whose output changes when a load is connected across it
reverse breakdown voltage
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
how is zener diode different from regular diode
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
formula for max power of zener diode
p=Iz (max)Vz
applications of zener diode
voltage regulator
peak clipper/ limiter in a wave shaping circuit
protector from accidental fluctuations
what is a photodiode
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
schematic for photodiode
principle of photodiode
photo electric effect
what is dark resistance of photodiode
- it is resistance of diode when it is not illuminated
= maximum reverse voltage
_____________________________
dark current
applications of photodiode use and disadvantage
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.
principle and use of solar cells
converts solar energy into electric energy
aka
photovoltaic cell
uses
charging batteries
remote places supplying current
measure intensity of light in lux meter
led
light emitting diode
emits light when large forward current passes thru it
application use and disadvantage of led
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
what is junction transistor
semiconductor w 2 junctions and 3 terminals
two types of junction transistors
npn
pnp
most common method of biasing ____ is forward and reverse biased?.
emitter base junction= forward biased
collector base junction= reverse biased
