Introduction to Electronics and Semiconductor Diodes

Question 1

Pentavalent Impurities

Answer 1

P(Phosphorous), As(Arsenic), Sb (Antimony)

Question 2

Trivalent Impurities

Answer 2

Al, Ga, In (Al not used for doping)

Question 3

n-type and p type

Answer 3

5 valence e- (pentavelent) (nigga)

formed by doping with trivalent

ex: silicon with Sb => valence e-

P type:
Si with B (trivalent) => hole

Question 4

Diode

Answer 4

p-type and n-type sandwiched together, to form depletion region

p => positive terminal
n=> negative terminal

Question 5

forward biased

reverse biased

Answer 5

a material connected to the same polarity terminal of the voltage source

a material connected to opposite polarity terminal of the voltage source

Question 6

No Bias

Answer 6

Depletion => recombination of holes and e-

• remaining ions of (+) e- (-) hole, ion carriers present due to depletion region => repulsion, ions cant move

Question 7

Reverse Bias

Answer 7

p terminal = (-) terminal
n terminal = (+) terminal

thus holes are e are pulled, forming a greater depletion region

minority charge carriers= recombination,

greater depletion region = more energy for recombination

thus no current in reverse bias

Question 8

Forward Bias

Answer 8

pushes holes in p and
e- in n to recombine with ions => smaller depletion region

Question 9

Knee voltage/cut- in voltage.

Answer 9

minimum V across the diode for it to start conducting

Question 10

Avalanche breakdown

Answer 10

in reverse bias as V ↑ free charges get v(m/s) => collide with other atoms => more charge carries produced (energy from acquired p.e.)

cycle is exponential

=> covalent bonds broken

Question 11

Zener Diode

Answer 11

when P and N are heavily doped in a semiconductor diode

• narrow depletion region
• small reverse bias V => strong electric field

=> due to field => covalent bonds broken => lot of free charge carriers

Question 12

Effect of variation in temperature across a semiconductor diode

Answer 12

rise in temp = more electron-hole pair => greater I, conductivity

Question 13

Ideal diode

Answer 13

forward biased = no resistance (closed switch)
reverse biased = infinite resistance (open switch )

Question 14

Practical diode

Answer 14

forward biased:
conducting at knee voltage

reverse biased: no current due to majority of charges (minority charges ignored)
(open switch )

very small resistance (not zero) when forward biased => forward resistance

high resistance (not ∞) when reverse biased => reverse resistance

Question 15

DC or Static resistance

Answer 15

application of a dc voltage to a circuit containing a semiconductor diode

Typically,
Forward bias : 10 Ω to 80 Ω
Reverse Bias: 10 MΩ

Question 16

Dynamic resistance or AC

Answer 16

application of a small AC voltage to semiconductor
diode => AC resistance

straight line drawn tangent to the curve through the Q –point
= AC resistance

ac resistance of a diode in the active region will range 1 Ω - 100 Ω.

Question 17

Average AC Resistance

Answer 17

applied input signal is sufficiently large to produce a broad swing
R = straight line drawn btw 2 by the max and min values

Question 18

Diode approximation

Answer 18

used to approximate the nonlinear behavior of real diodes to enable
calculations and circuit analysis.

Question 19

First Approximation

Answer 19

Ideal Diode Characteristics

diode => closed switch
with 0 V drop when forward-biased

open switch when reverse biased

Question 20

Second approximation

Answer 20

Simplified Diode Characteristics

Under forward-bias =>
ON when a V of VK
or VB is present

off if V < VK

diode is represented by
VK in series with closed switch.

Under reverse bias, it is an open switch

Question 21

Third Approximation

Answer 21

Piecewise-linear equivalent

increase in the voltage across diode when I increases.

closed switch in series with VK and resistance RB
when forward biased.

closely = practical diode.

reverse – bias, => open switch and no current
flows through it

Question 22

why should forward resistance be ignored

Answer 22

It’s assumed that the forward resistance of the diode is
usually so small compared to the other series elements
of the network that it can be ignored.

Question 23

AND circuit with diode

Answer 23

output can either be 9.3V or zero as V is measured after diode

Question 24

OR circuit with diode

Answer 24

output can either be 0 or 0.7V as voltage of diode is measured

Question 25

clippers

Answer 25

clip” away a portion of an input signal without distorting the remaining part of the applied waveform.

Question 26

when is a clipper biased

Answer 26

with DC supply =biased

Question 27

what is a clamper

Answer 27

shifts waveform to a new DC waveform without change in shape of signal

Question 28

what is Peak Inverse Voltage (PIV)

Answer 28

(For both Ideal & NonIdeal) is the maximum reverse biased voltage (Vm) the diode can withstand without entering the breakdown region.

Question 29

for calculations of V in centroid why is pi taken and not 2pi as limits

Answer 29

because its symmetrical and one of the curve is enough as its a repeating pattern

Question 30

arrangement of capactior and inductor in filter circuit and why

Answer 30

a capacitor in parallel inductor in series with the load, Vo is connected to inductor as only DC can pass in inductor and only AC can pass through capacitor

Question 31

explain the process capacitor in filter

Answer 31

when diodes are forward biased capacitor C will charge from 0 V towards the peak value of input Vm When input Vi reaches Vm the charge on capacitor will also be equal to Vm, diodes will turn off Now the capacitor starts discharging through the load RL, when load V starts to dip and cycle repeats again it charges back to Vm

Question 32

zener diode properties

Answer 32

under forward Bias condition works normal under reverse bias = Voltage regulator heavily doped diodes hence the depletion layer = narrow

Question 33

zener diode conditions

Answer 33

in Reverse Biased Condition Vin should be Greater than Vz ➢ Iz should be greater than Izmin ➢ Iz should be less than or equal to Izmax

Question 34

Worst case conditions for Zener Diode case 4 to enter into to the breakdown region,

Answer 34

𝐼𝑍 can become less than 𝐼𝑍𝑚𝑖𝑛 when (i) IL increases or RL decreases. (ii) R increases or IRdecreases. (iii) Vin decreases.

Question 35

Worst case conditions for Zener Diode: 2. The upper limit for the Zener current 𝐼𝑍 can become greater than 𝐼𝑍𝑚𝑎𝑥 when

Answer 35

𝐼𝑍 can become greater than 𝐼𝑍𝑚𝑎𝑥 when IL decreases or RL increases. (ii) R decreases or IR increases. (iii) Vin increases.

Question 36

series clipper with negative bias negative clipper

Answer 36

until Vin>V bias there is a flat line then a rise in curve, which is Vin- V bias then curve falls and another flat line as Vin

Question 37

parallel clipper with positive bias negative clipper

Answer 37

bias shorts the diode, thus only vdc is measured, some flat line until vsource is reverse bias thus makes diode open cirucuit and v source is measured until it decreases and flat line of vdc is measured before end of positive cycle negative cycle both are forward bias thus only vdc is measured knee V = 0.7V, and its opposite to DC V thus DC- Vde

Question 38

series clipper with positive bias negative clipper

Answer 38

since both are postive bias, ex bias = 5v curve starts from 5 V and then increases and before positive cycle ends it becames 5V bias only negative cycle the negative source overpowers thus it becames 0, and bias comes back to normal at the ending

Question 39

parallel clipper negative bias voltage(reverse voltage) positive clipper

Answer 39

exact opposite graph of the positive voltage bias positive cycle V in is positive bias, as its equal to Vdc then its shorts the diode then output is vdc from increase to Vdc value and a line is formed negative cycle Vdc shorts the diode so the output is just Vin Diode = ideal, but knee V = 0.7V, and its opposite to DC V thus DC- Vd

Question 40

clamper V no bias 2 ways

Answer 40

if positive side of diode is facing the capactor than positve cycle is removed negative cycle is increased if negative side of diode faces the capacitor postive side is doubled, negative side is removed

Question 41

clamper with negative bias Dc

Answer 41

v source is reverse bias thus diode is open circuit, thus capacitor discharging negative cycle diode is replaced by wire, thus diode is charging, and only Vbias is present in the output negative cycle when the vi is reverse bias, diode is open circuit Vdc only remains

Question 42

parallel and series clippers diode arrangments

Answer 42

series, bias doesnt change but diode changes direction parallel, diode and bias are always in reverse bias, for positive clipper diode is forward bias for negative clipper diode is reverse bias with vi

Question 43

clamper circuit for both negative and positive V source

Answer 43

if diode is open circuit diode discharges, else closed circuit capacitor charges thus no voltage present on the graph

Question 44

Centre tap vs bridge rectifier ADV, DIS

Answer 44

Bridge Lesser PIV Comparatively higher PIV Centre tap transformer not required Uniform input for both half cycles 4 diodes are required 2 diodes are required More voltage drop due to two diodes in the path CT- FWR Comparatively higher PIV Centre tap transformer required Difficult to balance both the half cycles due to CT 2 diodes are required Comparatively less voltage drop due to only one diode in the path

Question 45

when is the zener diode actually on

Answer 45

If the Zener diode is in the “on” state, the voltage across the diode is not V volts. The Zener diode will turn on as soon as the voltage across the Zener diode is VZ volts. It will then “lock in” at this level and never reach the higher level of V volts.