diode intro

7/24/2019 Diode Intro

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Department of Electronics and Communication Engineering, MIT, Manipal

Department of Electronics and Communication Engineering, MIT, Manipal 21

ECE 1001 : BASIC ELECTRONICS


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Part I : Analog Electronics

1

CHAPTER-1: DIODES AND APPLICATONS

Reference:

Robert L. Boylestad, Louis Nashelsky, Electronic Devices &

Circuit Theory, 11thEdition, PHI, 2012


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Module 1 : Diodes

Learning outcomes

At the end of this module, students will be able to: Explain the operation of PN junction diode under different biasing

condition.

Draw the I-V characteristic of diode and differentiate between ideal andpractical diodes

Explain the concept of static and dynamic resistance of the diode.

Explain various breakdown phenomenon observed in diodes.

Describe the working of Zener diode and its I-V characteristic.

Explain the operation of diode as capacitor.

3


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Department of Electronics and Communication Engineering, MIT, Manipal 2

Review

Basic of Semiconductors

Doping in Semiconductors


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Semiconductors

5

Common semicond uct ing mater ialsCrystal st ructure of s i l icon

http://fourier.eng.hmc.edu/e84/le

ctures/ch4/node1.htmlhttp://www.austincc.edu/HongXiao/overvie

w/basic-semi/sld007.htm
http://fourier.eng.hmc.edu/e84/lectures/ch4/node1.htmlhttp://fourier.eng.hmc.edu/e84/lectures/ch4/node1.htmlhttp://www.austincc.edu/HongXiao/overview/basic-semi/sld007.htmhttp://www.austincc.edu/HongXiao/overview/basic-semi/sld007.htmhttp://www.austincc.edu/HongXiao/overview/basic-semi/sld007.htmhttp://www.austincc.edu/HongXiao/overview/basic-semi/sld007.htmhttp://www.austincc.edu/HongXiao/overview/basic-semi/sld007.htmhttp://www.austincc.edu/HongXiao/overview/basic-semi/sld007.htmhttp://fourier.eng.hmc.edu/e84/lectures/ch4/node1.htmlhttp://fourier.eng.hmc.edu/e84/lectures/ch4/node1.html


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Doping in Sem iconductors

6

Schemat ic o f a si l icon crys tal latt ice doped with impu r i t ies to

produ ce n- type and p -type semico ndu ctor material .

[ht tp: / /www.pveducat ion.org/pvcdrom/pn- junct ion/dopingl] .


7/34Department of Electronics and Communication Engineering, MIT, Manipal

Self test

7

1.Why silicon is preferred over germanium for

semiconductor devices?

2.List different elemental and compound semiconductors.



P-N Junct ion Diode

8

P N

Anode Cathode

Common pract ical diodes avai lable in market



P-N Junc t ion Diode- conti

9

Used in numerous applications Switch,

Rectifier,

Regulator,

Voltage multiplier, Clipping,

Clamping, etc.



P-N Junc t ion Diode under b ias ing

10

P-N junc t ion (a) in contact (b) form ation of deplet ion region

[http://www.imagesco.com/articles/photovoltaic/photovoltaic-pg3.html].



P-N Junct ion Diode under bias ing cond i tion

11

Unbias condition

Diode under zero b ias c ondi t ions


12/34Department of Electronics and Communication Engineering, MIT, Manipal 12

Forw ard bias

Positive of battery connected to p-type (anode)

Negative of battery connected to n-type (cathode)

Diode under forward biasing c ondi t ions



Reverse b ias

Positive of battery connected to n-type material (cathode) Negative of battery connected to p-type material (anode)

Diode under reverse biasing condit io ns



Self test

14

1. The arrow direction in the diode symbol indicates

a. Direction of electron flow.

b. Direction of hole flow (Direction of conventional current)

c. Opposite to the direction of hole flow

d. None of the above

2.When the diode is forward biased, it is equivalent to

a. An off switch b. An On switch

c. A high resistance d. None of the above

.



I-V character ist ic of pract ical diode

15

P N

Diode symbol

Vis 0.6 ~ 0.7 Vfor Si

0.2 ~ 0.3 V for Ge

(mA)

(A)

I-V characterist ic of Practical dio de



Sil icon vs. Germanium

16

I-V characteristic of silicon and germanium practical diode

http://www.technologyuk.net/physics/electrical_principles/the_diode.shtm

l

Di d t t i



Diode cu rrent equat ion

IDis diode current

Iois reverse saturation current

VDis voltage across diode VTis thermal voltage = T / 11600

is a constant = 1 for Ge and 2 for Si

)1( TD VVoD eII

o

VV

o IeI TD

For positive values of VD(forward bias),

For large negative values of VD(reverse bias), ID Io

TD VV

oD eII



Effect of Temperature on the Reverse cu rrent

18

10/)(

12 122 TT

oo II

Q. A Silicon diode has a saturation current of 1pA at 200C. Determine (a)

Diode bias voltage when diode current is 3mA (b) Diode bias current when

the temperature changes to 1000C, for the same bias voltage.

A.

10

T

D

V

V

D eII mV

TVT 25.25

11600

293

11600

V

I

IVV DTD 103.11ln

0

pA2562102II 10

)10100(

12)/10T(T0102

12

mAex xx 21.710256I )11015.322(

103.1

12D

3

Reverse current doublesfor every 10 degree rise in temperature.



Effect of Temperature on the Reverse cu rrent

19

I (mA)

V (volts)

I (A)

75oC

25oC125oC



Diode resistances

20

Static or DC resistance:

ratio of diode voltage and

diode current

D

DD

I

VR

AC resistance:

D

Dd

IVr

D

T

D

Dd

IV

IVr



Diode Equ ivalent Circui t

21

Used during circuit analysis Characteristic curve replaced by straight-line segments

Forward bias

Reverse bias

V

RF

A K

A K

A K

V

1/RF

RR

=



Ideal d iod e : I-V charac terist ics

22

I-V characterist ic of Ideal diod e and ideal models

[http://conceptselectronics.com/diodes/diode-equivalent-models/].


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23

As further approximation, we can neglect the slope of the

characteristic i.e., RF= 0

V

A K

A K

A K

Forward bias

Reverse biasV

RR

=

RF

= 0


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24

As third approximation, even the cut-in voltage can be

neglected (Ideal diode)

Forward bias

Reverse bias

A K

A K

A KV= 0

RR

=

RF

= 0


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Self test

1.The break-point voltage of Si diode is

a. 0.2V b. 0.7V c. 0.8V d. 1.0V

2.Why would you use silicon diodes instead ofgermanium diodes?

25


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Breakdown phenomenon in diodes

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Two breakdown mechanisms: Avalanche breakdown :

Occurs in Lightly doped diodes,

Occurs at high reverse Voltage.

Zener Breakdown:

Occurs in heavily doped diodes.

at lower reverse bias voltages.


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Avalanche Breakdown

27

Schematic of Avalanche phenomenon

http://shrdocs.com/presentations/12656/index.html


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Zener B reakdown

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Schematic of Zener phenomenon

http://shrdocs.com/presentations/12656/index.html

Z Di d d i h i i


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Zener Diode and its character ist ic s

29

Anode Cathode

P N

I-V characterist ic s of Zener diode

P N

IZKor IZminIZMor IZMax

PZMor PZMax

PZM= VZ.IZM

E i l t i i t


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Equivalent c ircui t

30

V

RF

RR R

Z

VZ

+

+N

P

N NN

P P P

Equivalent circuits of Zener diode

Forward Reverse Breakdown

Note: RZis usually very small, can be neglected

Diode as capacitor Varacto r diode


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Diode as capacitor- Varacto r diode

31

d

AxC

S lf t t


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Self test

32

1. Explain the principle of PIN diode.

2.What is the difference between PN diode and Schottky diode.

3.Which type of diode exhibits negative resistance and why?

4. Which of the following is not an essential element of a dcpower supply

a. Rectifier

b. Filter

c. Voltage regulator

d. Voltage amplifier

S lf t t


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Self test

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5. What is true about the breakdown voltage in a Zener diode?

a. It decreases when current increases.b. It destroys the diode.

c. It equals the current times the resistance.

d. It is approximately constant

6. Which of these is the best description of a Zener diode?a. It is a rectifier diode.

b. It is a constant voltage device.

c. It is a constant current device.

d. It works in the forward region.

E i


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Exercises

1. Calculate the dynamic forward and reverse resistance of a P - N

junction diode, when the applied voltage is 0.25V for Germanium

Diode. I0 = lAand T = 300 K.(Ans:rf=1.734 ; rr=390 M)

2. A germanium diode has reverse saturation current of 0.19A.

Assuming =1, find the current in the diode when it is forward biased

with 0.3 V at 27o

C. (Ans: 19.5mA)

3. The forward current in a Si diode is 15 mA at 27oC. If reverse

saturation current is 0.24nA, what is the forward bias voltage?

(Ans: 0.93V)

4. A germanium diode carries a current of 10mA when it is forward

biased with 0.2V at 27oC. (a) Find reverse sat current. (b) Find the

bias voltage required to get a current of 100mA.

(Ans: 4.42A,0.259V)

diode intro

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