PN Junction / DIODE

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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
DIODE characteristic DIODE DC and ac
resistance DIODE load line DIODE flipped
resistorline DIODE DC resistance DIODE 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 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-valen
ce bounding Electrical neutral N material has
got one extra electron out of the bounding,
this is called a free electron
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P material and N material
N material Free electrons
P material Free holes
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PN junction
Anode Pmaterial 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
Forward Depletion layer is gone Ud gt 0V7 Current
can flow
Reverse Depletion layer is wider Ud lt 0V0 Current
can NOT 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 For shure id ir i 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 ?vd/?id 26 mV /
Id Where kT/q 26 mV
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