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PN Junction / DIODE
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AGENDA
SEMICONDUCTOR
Pure silicium
P material boron doped
N material stibium doped
P material and N material
PN junction
PN junction layer 0V7
PN junction characteristic
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DIODE
DIODE
DIODE
DIODE
DIODE
DIODE
characteristic
DC and ac resistance
load line
flipped resistorline
DC resistance
ac resistance
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Semiconductor, pure silicium
Pure silicium
4 electrons
Ideal is to have 8
So share with your neighbour
Co-valence bounding
Electrical neutral
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Semiconductor, pure silicium
Pure silicium
4 electrons
Ideal is to have 8
So share with your neighbour
Co-valence bounding
Electrical neutral
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Semiconductor, P material boron doped
P material = silicium (+4)
boron (+3) doped
Boron misses
1 positvie charge (positon) &
1 negative charge (electron)
Co-valence bounding
Electrical neutral
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P material misses one
electron, or has a place for
one electron,
this is called a free hole
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Semiconductor, N material stibium doped
N material = silicium (+4)
stibium (+5) doped
Stibium has got extra
1 positive charge (positon) &
1 negative charge (electron)
Co-valence bounding
Electrical neutral
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N material has got one extra
electron out of the
bounding,
this is called a free 6
electron
P material and N material
P material
=
Free holes
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N material
=
Free electrons
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PN junction
Anode = P=material
Kathode = N material
KNAP = handsome
K = Negative
A = Positive
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PN junction, depletion layer 0V7
Depletion layer
can be made
Wider by
external reverse voltage
Smaller by
External froward voltage
Depletion layer; Uth = 0V7
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PN junction, characteristic
Reverse
Depletion layer is wider
Ud < 0V0
Current can NOT flow
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Forward
Depletion layer is gone
Ud > 0V7
Current can flow
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Diode, characteristic
a Diode
Is a
one way
street
for
current
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Diode, characteristic
Assumption
Treshold
Voltage
for silicium
Ud = 0V7
for germanium
Ud = 0V2
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Diode, characteristic
Where
id = diode current
Vd= diode voltage
KT/q = 26 mV
Iss = leakage current (1uA)
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Diode, DC and ac resistance
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Diode, Load line
How to calculate the exact value of vd and id;
Graphical; use load line, indicates the load of the diode
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Diode, Load line
For shure
id = ir = i
For shure
vs = vd + vr
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Diode, Load line
For shure
id = ir = i
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For shure
vs = vd + vr
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Diode, Flipped resistor line
Flip the resistor line and push the two
curves horizontally to fit; vs = vd + vr
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Diode, Load line
The flipped
resistor line
is called
LOAD-LINE
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Diode, DC resistance
For DC resistance use the
load line method
For large voltages
normally Vd= 0V7 is used
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Diode, ac resistance
Differentiating gives
Rd = Δvd/Δid = 26 mV / Id
Where kT/q = 26 mV
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