Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
Department of EECE
Special-Purpose Diodes
Electronic Circuits
Dr. Manar Mohaisen Office: F208
Email: [email protected]
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Explain the Operation of the Zener Diode
₪ Explain Applications of the Zener Diode
₪ Explain the Operation and Applications of the Varactor Diode
₪ Explain the Operation and Applications of the Optical Diodes
₪ Other Types of Diodes
₪ Discussions
Class Objectives
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Zener Diode ■ It is named after Clarence Melvin Zener.
₪ Characteristics ■ Works in the reverse breakdown region.
■ In the operation region, the voltage is almost constant even though the current changes drastically.
■ Two types of breakdowns: ►Avalanche breakdown: Occurs at high
reverse voltages (> 5V).
►Zener breakdown: Occurs at low reverse voltages ( ~ 5V ).
The Zener Diode
Breakdown
VZ
IF
IR
VF
Reverse-breakdownregion
VR
C. Zener (1905 ~ 1993)
Anode (A)
Cathode (K)
Zener diode symbol
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Breakdown Characteristics ■ For currents less than IZK, as VR
increases, negligible change occurs in the current.
■ Breakdowns starts at a reverse current of IZK. ►The internal resistance of the Zener
diode decreases.
►Current increases drastically but voltage remains almost constant.
■ To keep the Zener diode in the breakdown region ►] IZK, IZM [.
● Avoid working near the boundaries, i.e., close to IZK or IZM.
■ Zener diode acts as a regulator? YES!
The Zener Diode – contd.
Preferable range of current to maintain the Zener diode in
the breakdown region.
Zener nominal voltage
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Zener Models ■ Ideal Model
►The Zener diode is represented as a DC voltage.
● The value of the DC voltage is VZ.
● Zener doesn't produce voltage but it is modeled as a DC voltage.
►Zener diode’s resistance and reverse current are neglected.
The Zener Diode – contd.
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Zener Models – contd. ■ Practical Model
►The Zener diode is represented as a DC voltage in series with a resistance ZZ.
The Zener Diode – contd.
ZZ
Z
VZI
Δ=Δ
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Zener Models – contd. ■ Example 3-1
The Zener Diode – contd.
50 mV 105 mA
ZZ
Z
VZI
Δ=Δ
= = Ω
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Temperature Coefficient ■ First Formula
►VZ : nominal Zener voltage at a reference temperature of 25oC
►TC : temperature coefficient (%/oC)
● Positive value voltage increases with increase in temperature.
● Negative value voltage decreases with increase in temp.
►ΔT : change in temperature from the reference temperature
■ Second Formula
►With TC : temperature coefficient (mV / oC)
The Zener Diode – contd.
Z ZV V TC TΔ = × × Δ
ZV TC TΔ = × Δ
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Temperature Coefficient – contd. ■ Example 3-2
►An 8.2 V Zener diode (i.e., 8.2 V at 25 oC)
►TC equals 0.05%/ oC
►What is the Zener voltage at 60 oC?
►Therefore,
The Zener Diode – contd.
o o o(8.2V)(0.0005 C)(60 C 25 C)144 mV
Z ZV V TC TΔ = × × Δ= −=
at 60 C8.2V 144mV = 8.344 V
oZ ZV V V= + Δ = +
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Power Dissipation and Derating ■ Power Dissipation (loss)
■ Power Derating ►The operation of reducing the rated maximum power according to a
derating factor to prolong the device’s life.
■ Example ►Maximum power rating of 400 mW at 50oC
►Derating factor of 3.2 mW/oC.
►Determine the maximum power the Zener can dissipate at 90 oC.
The Zener Diode – contd.
D Z ZP V I=
o(derated) (max) (mW / C)D DP P T= − Δ
o(derated) (max)
o o o
(mW / C)400mW (3.2 mW / C)(90 C 50 C)400mW 128 mW 272 mW
D DP P T= − Δ
= − −= − =
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Explain the Operation of the Zener Diode
₪ Explain Applications of the Zener Diode
₪ Explain the Operation and Applications of the Varactor Diode
₪ Explain the Operation and Applications of the Optical Diodes
₪ Other Types of Diodes
₪ Discussions
Class Objectives
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Note ■ Zener diode is operating in the reverse breakdown region.
► IZK < IZ < IZM
₪ Zener Regulation with a Varying Input Voltage ■ VZ = 10 V, IZK = 0.25 mA, PD(max) = 1W
■ Ideal Model ►Maximum current
►Minimum input voltage
● VIN(min) = 0.25 mA * 220 + 10 V = 10.055 V
►Maximum input voltage
● VIN(max) = 0.1 A * 220 + 10 V = 32 V
■ Note on Example 3-5
Zener Diode Applications
D(max)ZM
Z
1W 0.1A10VP
I V= = =
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Zener Regulation with a Variable Load
■ IT is divided between IZ and IL
►Low load has higher current IZ is reduced.
● IZ must remain larger than IZK to keep the diode regulating.
►High load has lower current IZ is increased.
● IZ must remain smaller than IZM to keep the diode regulating.
Zener Diode Applications – contd.
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Example 3-6 ■ Determine the maximum and
minimum load currents to
keep the Zener diode regulating. ►VZ = 12V, IZK = 1mA, IZM = 50 mA.
■ Solution ►The maximum Zener current occurs when IL = 0 (RL = ∞)
● Zener diode can handle this current because it is less than IZM.
►The maximum load current happens at the minimum IZ = IZK.
• Therefore,
Zener Diode Applications – contd.
IN ZZ(max)
24 12 25.5mA470V V V VI R
− −= = =Ω
T ZKL(max) 25.5 mA 1mA 24.5 mAI I I= − = − =
ZL
L(max)
12V 49024.5mAVR I= = = Ω
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Three-terminal Voltage Regulator
Zener Diode Applications – contd.
VIN VOUT
VIN VOUTVoltageregulator
Erroramplifier
Feedbackelement
Controlelement
Ref
Reference ground
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Zener Limiting
Zener Diode Applications – contd.
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Example 3-8 ■ Determine the output voltage
■ Solution
Zener Diode Applications – contd.
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Varactor Diode ■ It is a diode that always operates
in reverse-bias.
■ It is doped to maximize the inherit
capacitance of the depletion region.
■ The depletion region acts as a capacitor because of its nonconductive characteristic.
■ The capacitance is given by:
● A : Plate area
● ε : Dielectric constant
● d : Plate separation
The Varactor Diode
p n
VBIAS– +
Plate PlateDielectric
ACdε
=
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Varactor Diode ■ Capacitance vs. reverse voltage.
₪ Capacitance ■ Capacitance parameters are controlled by the method of doping
and the diode construction.
The Varactor Diode – contd.
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Applications ■ It acts as a variable capacitor
controlled by the reverse-bias
voltage. ►Tuning applications
(Resonant circuits)
► In the Figure
● R3 controls the bias voltage.
● As a result, the capacitance is modified,
● And the resonant frequency is modified.
The Varactor Diode – contd.
12rf LCπ
≅
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ LED ■ Free electrons (conduction band) move
from the n-region to combine with the holes (valence band) in the p-region.
■ When the recombination takes place, electrons release energy that is emitted as light. [Electroluminescence Process] ►The wavelength of the emitted light is
controlled by adding impurities.
The Light-Emitting Diode (LED)
1.00.90.80.70.60.50.40.30.20.1
0 500
Ligh
t out
put (
norm
aliz
ed)
540 580 620 660 700 740λ , wavelength (nm)
460420
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ LED ■ Radiation pattern is controlled
using lens. ►The narrower the radiation
pattern, the more the light is concentrated.
₪ Applications ■ Indicator lamps
■ Readout displays
■ LEDs are used in the seven-segment display device.
The Light-Emitting Diode (LED) – contd.
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
₪ Group Activity [10.xx] ■ High-Intensity LEDs [Group 1]
■ The Organic LED (OLED) [Group 2]
■ The Photodiode [Group 3] ►+ Current Regulator Diode
■ The Laser Diode [Group 4]
■ The Schottky Diode [Group 5] ►+ The Tunnel Diode
■ The PIN Diode [Group 6] ►+ Step-Recovery Diode
Let’s Express Ourselves in English!
Korea University of Technology & Education
Department of Electrical, Electronic, and Communications Engineering
Discussion & Notes
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