Lecture 3 Introduction to Electronics Rabie A. Ramadan

2 Zener Diode

Lecture 4, Slide 3 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 4 Zener Diode The slope of the line at Q is 1/r Z r Z is called the incremental resistance of the zener diode This is exaggerated for clarity in the figure. In practice r Z is small (a few ohms) and the breakdown voltage is approximately constant irrespective of the reverse current.

Lecture 4, Slide 5 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 6 Zener Diode With this notation, in the zener region: V z = V zo + r z I z

Lecture 4, Slide 7 Relation between the temperature and Zener Voltage Tc: Temperature coefficient (given) T1 : applied temperature T0 : operational temperature Vz : applied voltage New V Z = V Z +

Lecture 4, Slide 8 Group Activity Determine the nominal voltage for the Zener diode of Table 1.4 at a temperature of 100°C.

Lecture 4, Slide 9 Solution

Lecture 4, Slide 10 LIGHT-EMITTING DIODES

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. Semiconductors bring quality to light! What is LED?

Applications of LEDs

Your fancy telephone, i-pod, palm pilot and digital camera

Lecture 4, Slide 14 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 ( 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 15 LOAD-LINE ANALYSIS Given the following : – Forward Biased Diode

Lecture 4, Slide 16 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 I D = 0 A and anywhere on the vertical axis V D = 0 V.

Lecture 4, Slide 17 LOAD-LINE ANALYSIS

Lecture 4, Slide 18 LOAD-LINE ANALYSIS

Lecture 4, Slide 19 LOAD-LINE ANALYSIS The point of operation is usually called the quiescent point (abbreviated “Q-pt.”)

Lecture 4, Slide 20 Group Work

Lecture 4, Slide 21 Solution

Lecture 4, Slide 22 Solution (Cont.)

Lecture 4, Slide 23 Group Activity

Lecture 4, Slide 24 Solution

Lecture 4, Slide 25