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Diodes
Networks and Embedded Software
Module 3.1.1
by Wolfgang Neff
Semiconductors (1)
• Classification
– Conductor
• Silver, copper
• High conductivity
– Insulator
• Porcelain, plastics
• High resistivity
– Semiconductor
• Silicon, germanium
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Elec
tric
al R
esis
tivi
ty ρ
[Ωcm
]
Semiconductors10
104
kΩcm
Conductors10-6
10-5
μΩcm
Insulator
1010
1020
GΩcm
Semiconductors (2)
• Conductivity (simple model)
Free electrons
Conductor
Tightly bound electrons
Insulator
Loosely bound electrons
Semiconductor
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Semiconductors (3)
• Conductivity (band model)
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Conduction band
Valence bandEner
gy
Conductor
Conduction band
Valence bandEner
gy
Semiconductor
Tiny energy gap
Conduction band
Valence band
Ener
gy
Insulator
Huge energy gap
Overlap
Semiconductors (4)
• Intrinsic conduction
– Semiconductors are insulators
– Electrons can cross the energy gap
– Heat can provide this energy.
– Conductivity depends on temperature
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Conduction band
Valence bandEner
gy
Semiconductor
Semiconductors are NTC. The hotter the
conductiver.
Doping (1)
• Donors
– Some atoms replaced by donors
– Extra electrons
– Better conductivity
– N-type doping
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N-typesemiconductor
Donor
Free extra electron
Doping (2)
• Acceptors
– Some atoms replaced by acceptors
– Lack of electrons
– Better conductivity
– P-type doping
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P-typesemiconductor
Acceptor
Hole acts as positive charge
Doping (3)
• P–n junction
– Electrons migrate into holes
– No free charges in depletion zone
– Depletion zone is insulating
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P-type semi-conductor
N-type semi-conductor
Depletion region(insulating)
P-type semi-conductor
N-type semi-conductor
Doping (4)
• P–n junction (continued)
• Power supply
– P-type side: –
– N-type side: +
• Depletion zone larger
• Insulation remains
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P-type semi-conductor
N-type semi-conductor
Depletion regionDepletion region
N-type semi-conductor
P-type semi-conductor
Doping (5)
• P–n junction (finished)
• Power supply
– P-type side: +
– N-type side: -
• Depletion zone smaller
• Insulation diminishes
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P-type semi-conductor
N-type semi-conductor
Depletion region
N-type semi-conductor
P-type semi-conductor
Diodes (1)
• P–n junctions are diodes
– Flow Control Valve
• One-Way Road
– Forward
• P-type: +, n-type: -
• Current flows
– Reverse
• P-type: -, n-type: +
• Current gets blocked
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Electric current flows
p-type n-type+ -
Electric current is blocked
p-type n-type- +
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Diodes (2)
• Example: 1N4148
– Maximum forward current
• IF = 300 mA
– Maximum reverse voltage
• VR = 100 V
– Reverse Leakage
• IR = 0.025 μA (VR = 20 V)
• IR = 5.0 μA (VR = 70 V)
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Forward
+ -
p-type n-type
Anode Cathode
Reverse
- +
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Diodes (3)
• Applications
– Reverse voltage protection
– Rectifier
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~ UAC
- UDC(not really)
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+ -+ -device
- ++ -device