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Electrical Engineering: Principles and Applications, 6eAllan R. Hambley
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EE292CHAPTER 10 DIODESSupplemental Info
Contains information from internet websites,for EE292 class reference only
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Electrical Engineering: Principles and Applications, 6eAllan R. Hambley
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EE292Chapter 10 References
Various Diodes and Applications
1. Light Emitting Diodes (LED)
2. Photodiodes
3. Silicon Controlled Rectifier (SCR)
4. Triac
5. Term project ideas?
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Electrical Engineering: Principles and Applications, 6eAllan R. Hambley
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EE292
4/11/2006 BAE 5413 3
Diode devices
• Check valve behavior
Diffusion at the PN junctionof P into N and N into Pcauses a depleted non-conductive region
Depletion is enhanced byreverse bias
Depletion is broken down byforward bias
• When forward biased
High current flow junctionvoltage
• When reverse biased
Very low current flow unlessabove peak inverse voltage(PIV) (damaging torectifying diodes, OK forzeners)
D1
cathode
-
anode
+
+ -
Depletion region
1N412
Diode
Schematic Symbol
Semiconductor
Elements
Typical
Component
Appearance
P -
doped
N -
doped
Breakdown
voltage
(PIV)
V
I
Junction
Voltage
0.7 - silicon
0.3 - germanium
Forward
bias
current
Reverse
bias
current
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EE292Light Spectrum
Red, green and blue LEDs
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EE292
When a light-emitting diode is forward biased,
electrons are able to recombine with holes within the device, releasing energy in the form
of photons.
This effect is called electroluminescence and
the color of the light (corresponding to theenergy of the photon) is determined by the
energy gap of the semiconductor.
LED Light Emitting Diodes
Source http://en.wikipedia.org/wiki/Light-emitting_diode
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EE292
Deep UV LED for SpaceApplications
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EE292
4/11/2006 BAE 5413 8
Semicoductor Quantum Devices
• Absorption of a photon of sufficient energy
elevates an electron into the conduction bandand leaves a hole in the valence band.
• Conductivity of semi-conductor is increased.
• Current flow in the semi-conductor is
induced.
•
External circuit to read out the current
Conduction band
Energy gap
Valence band
Energy
level
+
-
Photon
(hv)
Hole
Electron
n- region
p+ Active AreaInsulation
Depletion region
Back Metalization
n+ Back Diffusion
Front
Contact
Rear
Contact
Incident light
Absorbtion in the
depletion layer
causses current to
flow across the
photodiode and if
the diode isreverse biased
considerable
current flow will be
induced
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EE292
4/11/2006 BAE 5413 9
Photodiode fundamentals
• Based on PN or PIN junction diode
photon absorption in the depletion
region induces current flow
Depletion layer must be exposed
optically to source light and thick
enough to interact with the light
• Spectral sensitivity
Material Band gap
(eV)
Spectral sensitivity
silicon (Si) 1.12 250 to 1100 nm indium arsenide
(InGaAs)
~0.35 1000 to 2200 nm
Germanium (Ge) .67 900 to 1600 nm
I
P
N
+
-
h
RL
IL
electron
hole
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EE292
4/11/2006 BAE 5413 10
Photodiode characteristics
• Circuit model
– I0 Dark current (thermal) – Ip Photon flux related current
• Noise characterization
Shot noise (signal current related)
– q = 1.602 x 10 –19 coulombs
– I = bias (or signal) current (A)
– is = noise current (A rms)
Johnson noise (Temperature related)
– k = Boltzman’s constant = 1.38 x 10 –23 J/K
– T = temperature (°K)
– B = noise bandwidth (Hz) – R = feedback resistor (W)
– eOUT = noise voltage (Vrms)
qii s 2
kTBReout 4
Ip Rj Cj
Rs
I0
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Electrical Engineering: Principles and Applications, 6eAllan R. Hambley
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EE292
4/11/2006 BAE 5413 11
Photodiode current/voltagecharacteristics
Isc (light level dependent)
Current
V o l t a g e
Increasing Light level
Dark current
P ho t o c o nd u c t i v e m o d e l o ad l i ne
P ho t o v o l t ai c m o d e l o ad l i ne
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EE292
4/11/2006 BAE 5413 12
Trans-impedance amplifierfunction
• Current to voltage converter (amplifier)
• Does not bias the photodiode with a voltage as current
flows from the photodiode (V 1 = 0)
•
Circuit analysis
s f I I
0o I
01 V
s f f f f I R I RV +
-
+
-
Is
Vout
Vf
Io
+
If V
1
s f f out I RV V
–Note: current to voltage conversion
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Electrical Engineering: Principles and Applications, 6eAllan R. Hambley
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EE292
4/11/2006 BAE 5413 13
Diode operating modes
•
Photovoltaic mode Photodiode has no bias voltage
Lower noise
Lower bandwidth
Logarithmic output with light intensity
• Photoconductive mode
Higher bandwidth
Higher noise
Linear output with light intensity
+
-
+
-
Vout
+
-
+
-
VoutVs
-
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EE292 Solar Zone & Photovoltaics
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EE292 Photovotaic System In Power Grids
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Electrical Engineering: Principles and Applications, 6eAllan R. Hambley
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EE292Silicon Controlled RectifierMore control than rectification
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Electrical Engineering: Principles and Applications, 6eAllan R. Hambley
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EE292 Triac: Bidirection SCR
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Electrical Engineering: Principles and Applications, 6eAll R H bl
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EE292 How to Connect a LED:
•
Requires 1.5~2.5V and 10 mA• To prevent overloading, use resistor 470 Ω