Download - Electronics Circuit and Devices
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 1/35
Electronics Circuit andDevicesEDC:132
Ajay Singh Raghuvanshi
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 2/35
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 3/35
Conductor, Insulator,Semiconductor
• The term conductor is applied to any material that will support a generousflow of charge when a voltage source of limited magnitude is applied across itsterminals.
• An insulator is a material that offers avery low level of conductivity under
pressure from an applied voltagesource.
• A semiconductor, therefore, is a material that has a conductivity level somewherebetween the extremes of aninsulator and a conductor.
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 4/35
Band Theory of Conduction
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 5/35
Intrinsic Semiconductor
• Intrinsicmaterials arethose
semiconductorsthat have beencarefully refined to
reduce theimpurities to avery low level—essentially as
pure as can be
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 6/35
Extrinsic Semiconductor
• A semiconductor material that has been subjected to thedoping process is called an
extrinsic semiconductor.(one part in 10 million)
• Depending upon the doping
agent weather a pentavalent or trivalent we can have twotypes of extrinsic
semiconductors ie n-type or p-
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 7/35
N-Type Semiconductor
• The n-type is created by introducing those impurityelements that have fivevalence electrons(pentavalent), such as
antimony, arsenic, and phosphorus.
• Diffused impurities withfive valence electronsare called donor atoms
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 8/35
P-Type Semiconductor
• The p-type material isformed by doping a
pure germanium or silicon crystal with
impurity atomshaving threevalence electrons.ie.Trivalent. Theelements most
frequently used for this purpose areboron, gallium, and indium
• The diffused
impurities withthree valence
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 9/35
Majority Carriers and MinorityCarriers
• N-type• Majority Carrier are
electrons and minoritycarrier are holes
-P Type
Majority Carrier are holes and minority carrier are
electrons
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 10/35
Semiconductor Diode• The semiconductor diode is formed up by simply bringing n-
type and p-type materials together. At the instant twomaterial are joined, the electron and holes in the region of the junction will combine, resulting in lack of carriers in theregion near the junction.
+
+
+
+
+
+
+
+
+
+
+
+
+ + +
+ +
+ + +
+ +
+
+ +
+
++
+
+
+
++
+
+
+
+
+
+
+
+
+
++ +
+
+
-p type Depletion
-n type Region Acceptorions
+
Donarions
VD= ( )0V no bias
ID=0mA
p n
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 11/35
he p side of a pnjunction has trivalent atoms with a core+ . +harge of 3 This core attracts electrons less than a 5
.ore
brupt junction
-side
alence band
onduction band
-side
,n an abrupt junction the p side bands.re at a slightly higher energy level
eal diodes have a gradual change from one material. .o the other The abrupt junction is conceptual
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 12/35
-side
alence band
-side
onduction band
gy bands after the depletion layer has for
,o an electron trying to diffuse across the junction.he path it must travel looks like an energy hill It
.ust receive the extra energy from an outside source
nergy hill
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 13/35
Junction temperature
The junction temperature is thetemperature inside the diode, rightat the pn junction.
When a diode is conducting, its junction temperature is higher thanthe ambient.
There is less barrier potential atelevated junction temperatures.
The barrier potential decreases by 2
mV for each degree Celsius rise.
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 14/35
Forward Biased Diode
he carriers move toward the junction.nd collapse the depletion layer
f the applied voltage is greater than, .he barrier potential the diode conducts
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 15/35
.he carriers move away from the junction
-he depletion layer is re established.nd the diode is off
everse BiasedDiode
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 16/35
I V CHARACTERISTIC OF DIODE
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 17/35
Reversebias
region
Reversebreakdown
region
Forwardbias
region
iD
v D V
Complete i-v curve of a semiconductor diode
_V Z
iD
v D
_
+
- I V CHARACTERISTIC OF DIODE
( )100 −=−=⋅ kT vq
d D De I I I i
A)10to(10smallverytypically15-9-
0 I
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 18/35
–Characteristic
= ; = ° ; =s 1 0 fA T 2 7 C n 1
0
6
12
18
24
30
36
-0.500 -0.375 -0.250 -0.125 0.000 0.125 0.250 0.375 0.500 0.625 0.750
Forward Voltage (volts
F o r w a r
d C u r r e n t ( m A ) ( )100 −=−=
⋅ kT vqd D
De I I I i
DIODE EQUATION
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 19/35
DIODE EQUATION
( )100 −=−=⋅ kT vq
d D De I I I i
I : Current through diode in Amps
I0 : ’ “ ”The diode s Saturation Current value
q : , .electron charge 1 602 x 10
-19
CT : Temperature in degrees Kelvin
vd : Applied voltage in volts
k : ’ , .Boltzman s constant 1 380 x 10-23 /J K
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 20/35
Bulk resistance
With forward bias, diode currentincreases rapidly beyond theknee voltage.
Small increases in voltage causelarge increases in current.
The ohmic resistance of the p and
n material is called the bulk resistance.
The bulk resistance is often less
than one Ohm.
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 21/35
Diode ratings
The maximum reverse bias ratingmust not be exceeded.
The maximum forward current
rating must not be exceeded.The power rating of a diode is
determined by its maximum
current rating and the forward voltage drop at that current flow.
Pmax = Vmax Imax
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 22/35
Diode firstapproximation
This models the diode as beingideal.
The first approximation ignores
leakage current, barrier potentialand bulk resistance.
When an ideal diode is forward
biased, the model is a closedswitch.
When an ideal diode is reverse
biased, the model is an open
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 23/35
Diode secondapproximation
• This model assumes that nodiode current flows until theforward bias across the diode
reaches 0.7 volts.• This model ignores the exact
shape of the knee.
• This model ignores the diode’sbulk resistance.
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 24/35
• This model assumes that nodiode current flows until theforward bias across the diode
reaches 0.7 volts.• This model ignores the exact
shape of the knee.
• This model does account for thediode’s bulk resistance.
Diode thirdapproximation
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 25/35
hird approximation
RB.7 V
everse bias
RB
.7 V
orward bias
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 26/35
Which approximation?
• The first approximation is oftenadequate in high voltagecircuits.
• The second approximation isoften adequate in low voltagecircuits.
• The third approximationimproves accuracy when thediode’s bulk resistance is more
than 1/100 of the Thevenin
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 27/35
Silicon diode ohmmetertesting
• Low resistance in bothdirections: the diode isshorted.
• High resistance in bothdirections: the diode is open.
• Relatively low resistance in thereverse direction: the diodeis leaky.
• The ratio of reverse resistance
to forward resistance is >
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 28/35
0 .0 5 .1 0 .1 5
0
25
50
75
100
125
150
175
200
orward bias in volts
ow to find bulk resistance
-75 mA 75 mA
. - .875 V 0 75 V
= .25 Ω
RB =
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 29/35
0 .0 5 .1 0 .1 5
0
25
50
75
100
125
150
175
200
orward bias in volts
.The forward resistance decreases as current increases
5 mA
.75 V
= 0 Ω
RF =
75 mA
.875 V
= Ω
RF =
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 30/35
Silicon diode resistance
The reverse resistance is veryhigh: typically tens or hundredsof megohms.
The forward resistance is not thesame as the bulk resistance.
The forward resistance is always
greater than the bulk resistance.The forward resistance is equal to
the bulk resistance plus the
effect of the barrier potential.
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 31/35
RS = 0 Ω
V = .5 V
rcuit like this can be solved in several w.se the first approximation.se the second approximation
.se the third approximation
.se a circuit simulator’ .se the diode s characteristic curve
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 32/35
RS = 0 Ω
V = .5 V
he characteristic curve is a graphical sol
’ .d the saturation current using Ohm s Law cutoff voltage is equal to the supply vol
’ .ate these two points on the diode s curve nect them with a oad line ..intersection is the graphical solution
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 33/35
0 .0 5 .1 0 .1 5
0
25
50
75
100
125
150
175
200
he o a d l i n e : graphical soluti
ISAT =
0 Ω
.5 V
.5 V
0 Ω = 50 mA
VCUTOFF
= .5 V
Q
stands or
.uiescent
Load
line
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 34/35
Electrical Properties of Materials
8/6/2019 Electronics Circuit and Devices
http://slidepdf.com/reader/full/electronics-circuit-and-devices 35/35
vsD 1
D 2
10 k Ω
30k ΩV
L
LR
30k Ω
30 k Ω
t [s]
0.10.0 0.2 0.3 0.4 0.5
-15
v [V]s
15