Transcript 150LECTURE15 DIODES Lecture Notes Page

SEMICONDUCTORS
LECTURE 15 DIODES
LECTURE#15
SEMICONDUCTORS ARE CRYSTALS THATHAVE THE PROPERTIES OF BOTH A CONDUCTOR
AND A INSULATOR. SILICON (MOSTLY SAND, 27.75 OF EARTH’S 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.
VALENCE ELECTRONS
YOU TUBE :Description of the Silicon Atom
THIS STRUCTURE IS NOW A CRYSTAL
http://www.youtube.com/watch?v=Wvd3hj93Iog
PURIFIED SILICON
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
YOU TUBE : Semiconductors Theory 1 Segment 2A - Doped Silicon Crystal
http://www.youtube.com/watch?v=cRvJouvITug
Silicon Wafer Processing Animation
http://www.youtube.com/watch?feature=endscreen&v=LWfCqpJzJYM&NR=1
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
(ENCLOSED IN SMALL GLASS CYLINDER)
MAKE presents: The Diode
http://www.youtube.com/watch?v=AqzYsuTRVRc
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
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
.Formation and Properties of Junction Diode - Physics .
http://www.youtube.com/watch?v=4SlfaocMfdA
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.
TYPES OF DIODES
MANY TYPES EXIST
SMALL SIGNAL: CONVERT AC TO DC, DETECT RADIO SIGNALS, MULTIPLY VOLTAGE,
PERFORM LOGIC OPERATIONS.
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
ZENER DIODES
WORK AT SPECIFIC BREAKDOWN VOLTAGE.
FUCTION AS A VOLTAGE SENSITIVE SWITCH.
THIS VOLTAGE (VZ) VARY FROM 2 TO 200 VOLTS
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
LEDS CAN EMIT AND DETECT LIGHT
YOU TUBE: MAKE presents: The LED
http://www.youtube.com/watch?v=P3PDLsJQcGI
(PHOTODIODES)
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
how photodiode works
http://www.youtube.com/watch?v=U6Wvmrc3akc
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
+
ELECTRONS
The Photodiode
http://www.youtube.com/watch?v=U6Wvmrc3akc
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.
COMPOENTS OF A PHOTODIODE
WINDOW
METAL CAN
LENS
CHIP
ANODE
CATHODE
DIFFERENT PACKAGE STYLES FOR PHOTODIODES
CHARGE COUPLED DEVICES (CCD)
Any CCD
HOW DIODES ARE USED
anode
cathode
anode
cathode
device
symbol
Silicon rectifier diode
+
+
+
_
0
0
_
_
Input voltage
circuit
output voltage
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.
Power Diode Rectifier
Half Wave Rectifier Circuit
Half-wave Rectifier with Smoothing Capacitor
Full Wave Rectifier Circuit
The Diode Bridge Rectifier
The Positive Half-cycle
The Negative Half-cycle
Full-wave Rectifier with Smoothing Capacitor
Full Wave Bridge Rectifier
http://www.youtube.com/watch?v=aCfAdIRRw7M
VARIOUS TYPES OF POWER RECTIFIERS
Various printed circuit board mounted rectifiers and voltage regulators