SEMICONDUCTORS LECTURE 15 DIODES

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SEMICONDUCTORSLECTURE 15 DIODES
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LECTURE15
SEMICONDUCTORS ARE CRYSTALS THATHAVE THE
PROPERTIES OF BOTH A CONDUCTOR AND A INSULATOR.
SILICON (MOSTLY SAND, 27.75 OF EARTHS CRUST) IS
THE MOST COMMON.
SILICON HAS 4 ELECTRONS IN ITS OUTER SHELL
(VALENCE). IT WOULD LIKE AN ADDITONAL 4 FOR A
OVERALL NEUTRAL CHARGE. IT DOES THIS BY SHARING
ELECTRONS WITH OTHER SILICON ATOMS.
THIS STRUCTURE IS NOW A CRYSTAL
VALENCE ELECTRONS
YOU TUBE Description of the Silicon Atom
http//www.youtube.com/watch?vWvd3hj93Iog
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PURIFIED SILICON
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PURE SILICON MUST HAVE TRACT AMOUNTS OF OTHER
ELEMENTS ADDED TO IT TO MAKE IT A SEMICONDUCTOR.
BORON AND PHOSPHORUS ARE THE MOST COMMON USED,
THIS PROCESS IS CALLED DOPING.
BORON HAS 3 ELECTRONS IN ITS OUTER SHELL WHEN
ADDED TO SILICON THIS LEADS TO A DEFICIENCY OF 1
VALENCE ELECTRON (CALLED A HOLE) THIS GIVES THE
SILICON A OVERALL POSITIVE CHARGE. THIS IS CALLED
P TYPE SILICON. THESE HOLES CAN MOVE THRU THE
CRYSTAL AND CARRY CURRENT.
PHOSPHORUS HAS 5 ELECTRONS IN ITS OUTER SHELL
WHEN ADDED TO SILICON THIS LEADS TO A EXCESS OF 1
VALENCE ELECTRON THIS GIVES THE SILICON A OVERALL
NEGATIVE CHARGE. THIS IS CALLED N TYPE SILICON.
THESE ELCTRONS CAN MOVE THRU THE CRYSTAL AND
CARRY CURRENT.
N TYPE ATOM
P TYPE ATOM
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http//www.youtube.com/watch?vcRvJouvITug
YOU TUBE Semiconductors Theory 1 Segment 2A -
Doped Silicon Crystal
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http//www.youtube.com/watch?featureendscreenvL
WfCqpJzJYMNR1
Silicon Wafer Processing Animation
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THE DIODE IS AN ELECTRONIC ONE WAY VALVE
BOTH P AND N TYPE SILICON CAN CONDUCT CURRENT. BY
BUTTING P AND N TYPE SILICON AGAINST EACH
OTHER CURRENT WILL FLOW IN ONE DIRCTION ONLY.THIS
INTERFACE BEWTEEN THE TWO IS CALLED A P-N JUNCTION
DIRECTION OF CURRENT FLOW
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(ENCLOSED IN SMALL GLASS CYLINDER)
MAKE presents The Diode
http//www.youtube.com/watch?vAqzYsuTRVRc
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At the junction, free electrons from the N-type
material fill holes from the P-type material.
This creates an insulating layer in the middle of
the diode called the depletion zone.
When the positive end of the circuit is hooked up
to the N-type layer and the negative end is
hooked up to the P-type layer, free electrons
collect on one end of the diode and holes collect
on the other. The depletion zone gets bigger.
THIS DIODE IS REVERSE BIASED, NO CURRENT FLOWS
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BY PLACING A POTENTIAL DIFFERENCE (VOLTAGE)
ACROSS THE DIODE WITH THE CORRECT POLARITY
CURRENT WILL FLOW THRU THE DIODE. HOLES IN ONE
DIRECTION,ELECTRONS IN THE OTHER DIRECTION
When the negative end of the circuit is hooked up
to the N-type layer and the positive end is
hooked up to P-type layer, electrons and holes
start moving and the depletion zone disappears.
THIS DIODE IS FORWARD BIASED, CURRENT FLOWS
http//www.youtube.com/watch?v4SlfaocMfdA
.Formation and Properties of Junction Diode -
Physics .
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DIODE OPERATION
A DIODE WILL NOT CONDUCT UNTIL THE FOEWARD
VOLYAGE REACHES A CERTAIN LEVEL. FOR SICILON
DIODES THIS IS ABOUT 0.6V.
IF THE FORWARD CURRENT BECOMES TOO GREAT THE
DIODE MAY CRACK OR MELT. AT THIS POINT THE DIODE
MAY CONDUCT IN BOTH DIRECTIONS AND VAPORIZE THE
CHIP.
TOO MUCH REVERSE VOLTAGE WILL CAUSE IT TO CONDUCT
IN THE WRONG DIRECTION WHICH WILL DESTROY THE
CHIP.
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TYPES OF DIODES
MANY TYPES EXIST
SMALL SIGNAL CONVERT AC TO DC, DETECT RADIO
SIGNALS, MULTIPLY VOLTAGE, PERFORM LOGIC
OPERATIONS.
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POWER RECTIFIER
WORK AT MUCH HIGHER CURRENT LEVELS, CONSTRUCTED
IN LARGE METAL PACKAGES TO ABSORBE HEAT AND
TRANSFER IT TO HEAT SINKS. USED MAINLY IN POWER
SUPPILES
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ZENER DIODES
WORK AT SPECIFIC BREAKDOWN VOLTAGE. FUCTION AS A
VOLTAGE SENSITIVE SWITCH. THIS VOLTAGE (VZ) VARY
FROM 2 TO 200 VOLTS
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LIGHT EMITTING DIODE (LED)
ALL DIODES EMIT SOME EM RADIATION WHEN FORWARD
BIASED. DIODES MADE FROM CERTAIN SEMICODUCTORS
EMIT LOTS OF LIGHT. THESE ARE CALLED LEDS
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LEDS CAN EMIT AND DETECT LIGHT
http//www.youtube.com/watch?vP3PDLsJQcGI
YOU TUBE MAKE presents The LED
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(PHOTODIODES)
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PHOTODIODES
ARE DESIGNED TO DETECT LIGHT. ( ALL PN JUNCTIONS
ARE LIGHT SENSITIVE) THEY HAVE A WINDOW WHERE
LIGHT ENTERS TO A LARGE EXPOSED JUNCTION REGION.
SOME COMMON USES INCULDE CAMERAS, ALARMS,
LIGHTWAVE DIODES (LASERS).
PHOTODIODE SYMBOL
PHOTODIODES CAN BE USED TO DETECT FAST PULSES OF
INFRARED LIGHT, USED IN LIGHTWAVE COMMUNICATIONS
http//www.youtube.com/watch?vU6Wvmrc3akc
how photodiode works
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HOW PHOTODIODES WORK
A INCOMING PHOTON WILL CREATE A HOLE ELECTRON
PAIR AT THE PN JUNCTION. A CURRENT WILL FLOW IF
BOTH SIDES ARE CONNECTED.
INCOMING PHOTONS
HOLES

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ELECTRONS
http//www.youtube.com/watch?vU6Wvmrc3akc
The Photodiode
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TYPES OF PHOTODIODES
SMALL AREA PHOTODIODES THESE HAVE VERY FAST
RESPONS TIMES
LARGE AREA PHOTODIODES HAVE SLOWER RESPONSE TIMES
THEN SMALL AREA PHOTODIODES THESE LARGE SURFACE
AREA GIVES HIGH SENSITIVITY.
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COMPOENTS OF A PHOTODIODE
WINDOW
METAL CAN
LENS
CHIP
ANODE
CATHODE
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DIFFERENT PACKAGE STYLES FOR PHOTODIODES
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CHARGE COUPLED DEVICES (CCD)
Any CCD
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HOW DIODES ARE USED
Silicon rectifier diode
output voltage
Input voltage
circuit
Input and output of a simple rectifier circuit
Fig. 8-23 p.219 A single-phase half-wave
rectifier circuit produces one
output pulse of dc for each cycle of ac input.
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Power Diode Rectifier
Half Wave Rectifier Circuit
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Half-wave Rectifier with Smoothing Capacitor
                                                                                 
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Full Wave Rectifier Circuit
                                                   
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The Diode Bridge Rectifier
                                                                                                   
The Positive Half-cycle
The Negative Half-cycle
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Full-wave Rectifier with Smoothing Capacitor
                                                                                                                   
Full Wave Bridge Rectifier
http//www.youtube.com/watch?vaCfAdIRRw7M
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VARIOUS TYPES OF POWER RECTIFIERS
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Various printed circuit board mounted rectifiers
and voltage regulators
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