Transcript Lecture 4 - Rabie A. Ramadan

Lecture 3
Introduction to Electronics
Rabie A. Ramadan
[email protected]
http://www.rabieramadan.org/classes/2014/electronics/
Zener Diode
2
Zener Diode
• The linear approximation to the I-V
characteristic of a zener diode in the
reverse bias and breakdown regions is as
follows.
Lecture 4, Slide 3
Zener Diode
• The slope of the line at Q is 1/rZ
• rZ is called the incremental resistance of the
zener diode
• This is exaggerated for clarity in the figure.
In practice rZ is small (a few ohms) and the
breakdown voltage is approximately
constant irrespective of the reverse current.
Lecture 4, Slide 4
Zener Diode
• Zener breakdown occurs when the electric
field in the depletion layer increases to the
point where it can break covalent bonds
and generate electron-hole pairs.
• Electrons generated in this way are swept
by the electric field into the n side.
• Holes generated in this way are swept by
the electric field into the p side.
Lecture 4, Slide 5
Zener Diode
• With this notation, in the zener region:
•
Vz = Vzo + rzIz
Lecture 4, Slide 6
Relation between the temperature and Zener
Voltage
•
•
•
•
•
Tc: Temperature coefficient (given)
T1 : applied temperature
T0 : operational temperature
Vz : applied voltage
New VZ = VZ +
Lecture 4, Slide 7
Group Activity
• Determine the nominal voltage for the Zener
diode of Table 1.4 at a temperature of 100°C.
Lecture 4, Slide 8
Solution
Lecture 4, Slide 9
LIGHT-EMITTING DIODES
Lecture 4, Slide 10
What is LED?
LED are semiconductor p-n junctions that under forward bias conditions can emit
radiation by electroluminescence in the UV, visible or infrared regions of the
electromagnetic spectrum. The qaunta of light energy released is approximately
proportional to the band gap of the semiconductor.
Applications of LEDs
Your fancy telephone, i-pod, palm pilot and
digital camera
Getting to know LED
Advantages of Light Emitting Diodes (LEDs)
Longevity:
The light emitting element in a diode is a small
conductor chip rather than a filament which greatly
extends the diode’s life in comparison to an
incandescent bulb (10 000 hours life time compared
to ~1000 hours for incandescence light bulb)
Efficiency:
Diodes emit almost no heat and run at very low
amperes.
Greater Light Intensity:
Since each diode emits its own light
Cost:
Not too bad
Robustness:
Solid state component, not as fragile as
incandescence light bulb
Lecture 4, Slide 14
LOAD-LINE ANALYSIS
• Given the following :
–Forward Biased Diode
Lecture 4, Slide 15
LOAD-LINE ANALYSIS
• The intersections of the load line on the characteristics can easily
be determined if one simply employs the fact that anywhere on the
horizontal axis ID = 0 A and anywhere on the vertical axis VD = 0
V.
Lecture 4, Slide 16
LOAD-LINE ANALYSIS
Lecture 4, Slide 17
LOAD-LINE ANALYSIS
Lecture 4, Slide 18
LOAD-LINE ANALYSIS
The point of operation is
usually called the quiescent
point (abbreviated “Q-pt.”)
Lecture 4, Slide 19
Group Work
Lecture 4, Slide 20
Solution
Lecture 4, Slide 21
Solution (Cont.)
Lecture 4, Slide 22
Group Activity
Lecture 4, Slide 23
Solution
Lecture 4, Slide 24
Lecture 4, Slide 25