Electronics Circuit and Devices

8/6/2019 Electronics Circuit and Devices

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Electronics Circuit andDevicesEDC:132

Ajay Singh Raghuvanshi



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.



Band Theory of Conduction



Intrinsic Semiconductor

• Intrinsicmaterials arethose

semiconductorsthat have beencarefully refined to

reduce theimpurities to avery low level—essentially as

pure as can be



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-



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



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



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



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.

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-p type Depletion

-n type Region Acceptorions

+

Donarions

VD= ( )0V no bias

ID=0mA

p n



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



-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



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.



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



.he carriers move away from the junction

-he depletion layer is re established.nd the diode is off

everse BiasedDiode



I V CHARACTERISTIC OF DIODE



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



–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



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



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.



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



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



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.



• 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



hird approximation

RB.7 V

everse bias

RB

.7 V

orward bias



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



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 >



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 =



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 =



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.



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



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



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



Electrical Properties of Materials



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

Electronics Circuit and Devices

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