1. Principles & Applications
Electronics
Principles & Applications
Sixth Edition
Charles A. Schuler
Chapter 3
Diodes
(student version)
© Glencoe/McGraw-Hill

2. INTRODUCTION The PN Junction Characteristic Curves of Diodes
Diode Lead Identification
Diode Types and Applications

3. Dear Student:
This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow you
to view that segment again, if you want to.

4. Concept Preview
Diodes have both P-regions and N-regions. The boundaries are called junctions.
The P-region is the anode side. The N-region is the cathode side.
There are three possible bias conditions: zero, forward, and reverse.
Zero bias is accompanied by a depletion region.
Forward bias can collapse the depletion region.
Reverse bias enhances the depletion region.
Bias determines if diodes will be off or on.

5. P N A silicon crystal Anode Cathode Schematic Symbol junction
The P-side of a junction diode is doped with acceptor atoms. N
The N-side of a junction diode is doped with donor atoms.
junction
A silicon crystal
Anode
Cathode
Schematic Symbol

6. Zero Bias Depletion region
The electrons near the junction cross
over and fill the holes near the junction.
Depletion region
Having no carriers, the depletion region is an insulator.

7. Forward Bias The diode is on. The carriers move toward the junction
and collapse the depletion region.
The diode is on.

8. Reverse Bias The depletion region is reestablished
The carriers move away from the junction.
The depletion region is reestablished
and the diode is off.

9. Concept Review
Diodes have both P-regions and N-regions. The boundaries are called junctions.
The P-region is the anode side. The N-region is the cathode side.
There are three possible bias conditions: zero, forward, and reverse.
Zero bias is accompanied by a depletion region.
Forward bias can collapse the depletion region.
Reverse bias enhances the depletion region.
Bias determines if diodes will be off or on.
Repeat Segment

10. Concept Preview
The volt-ampere graph for a resistor is a straight line (a resistor is a linear device).
The volt-ampere graph for a diode is non-linear.
The knee voltage for a silicon diode is approximately 0.7 volts. This is the voltage required to collapse the depletion region.
Excess reverse bias will result in diode breakdown.
The cathode end might be marked with a band.
Diodes can be tested with an ohmmeter.

11. Resistor volt-ampere characteristic curves
5 ohms
200
175
150
10 ohms
125
100 mA 75
20 ohms 50 25
0.5
1.0
1.5
Volts
Resistor volt-ampere characteristic curves

12. Silicon diode volt-ampere characteristic curve
200
175
150
125
100
Forward current in mA 75 50
knee 25
0.5
1.0
1.5
Forward bias in volts
Silicon diode volt-ampere characteristic curve

13. Linearity
The volt-ampere characteristic curve for a resistor is a straight line (linear).
A diode has a non-linear characteristic curve.
The barrier potential produces a knee in the diode curve.
The knee voltage is approximately 0.6 to 0.7 volts for silicon diodes.

14. The effect of temperature
200
175
100 oC
150
125
25 oC
100
Forward current in mA 75
-50 oC 50 25
0.5
1.0
1.5
Forward bias in volts
The effect of temperature

15. Silicon diode reverse bias characteristic curve
breakdown
Reverse bias in Volts
600
400
200 20 40
Reverse
current
in mA 60 80
100
120
140
Silicon diode reverse bias characteristic curve

16. Cathode lead
Anode lead

17. The diode is forward biased by the ohmmeter.
Cathode lead V mA
Anode lead

18. The diode is reverse biased by the ohmmeter.
Cathode lead V mA
Anode lead
The diode is reverse biased by the ohmmeter.

19. Silicon Diode Ohmmeter Testing
Low resistance in both directions: the diode is shorted.
High resistance in both directions: the diode is open.
Relatively low resistance in the reverse direction: the diode is leaky.
The ratio of reverse resistance to forward resistance is > 1000: the diode is good.

20. Diode Quiz
At zero bias, diodes show a depletion region which acts as an________.
insulator
The depletion region is collapsed by applying _________ bias.
forward
The depletion region is made wider by applying ________ bias.
reverse
A forward-biased diode has its anode ________ with respect to its cathode.
positive
Diode forward voltage drop decreases as temperature ________.
increases

21. Concept Review
The volt-ampere graph for a resistor is a straight line (a resistor is a linear device).
The volt-ampere graph for a diode is non-linear.
The knee voltage for a silicon diode is approximately 0.7 volts. This is the voltage required to collapse the depletion region.
Excess reverse bias will result in diode breakdown.
The cathode end might be marked with a band.
Diodes can be tested with an ohmmeter.
Repeat Segment

22. Concept Preview
Zener diodes have a relatively low breakdown voltage and are often used as voltage regulators.
Diode clippers limit signal amplitude.
Diode clamps produce a dc signal component.
Diodes can be used to suppress inductive kick.
Optocouplers combine light emitting diodes and photodiodes.
Fiber optic cables carry light signals.
Varicap diodes are used to tune electronic circuits.

23. A zener diode is designed to break down and
Reverse bias in Volts 6 4 2 20 40
Reverse
current
in mA 60 80
100
120
140
A zener diode is designed to break down and
conduct backwards at lower voltages.

24. The voltage across a conducting zener is relatively constant.
Reverse bias in Volts 6 4 2 20 I V 40
Reverse
current
in mA 60 80
100
120
140
The voltage across a conducting
zener is relatively constant.

25. Using a zener diode as a voltage regulator
Unregulated Supply
Load
The load is in parallel with the zener and will see a relatively constant voltage as long as the zener is conducting.

26. This circuit is called a clipper or limiter.
When VIN < 1.2 VPP
VIN
VOUT
VOUT is not clipped
The diodes do not conduct.

27. When VIN > 1.2 VPP VIN VOUT VOUT is clipped The diodes conduct.

28. This circuit is called a clamp or dc restorer.
0.6 V
When VIN > 1.2 VPP
C is charged. C
VIN
VOUT
VOUT is clamped. dc 2
VOUT(dc) =
VPP
- 0.6 V

29. The inductive kick can cause damage.
CEMF
The inductive kick
can cause damage.

30. Transient suppression diodes can be used with inductive loads.
CEMF
The coil discharges
through the diode and
there is no arc.

31. LED As the electrons cross the junction, they
lose energy in the form of photons.

32. The typical voltage drop for most LEDs is from 1.5 to 2.5 V.
LED circuit RS
LED
Power
supply VS VD
IS =
VS - VD RS
The typical voltage drop for most LEDs is from 1.5 to 2.5 V.

33. Photodiodes are reverse biased and conduct in the presence of light.
Power
supply VS
Photodiode
Photodiodes are reverse biased and
conduct in the presence of light.

34. Input
Output
Output
Input
Optocoupler

35. Step-index multimode fiber
Input pulse
Output pulse
The combined shorter and longer path lengths act to stretch the output pulse.

36. Step-index multimode fiber
Due to pulse stretching, high speed data transmission is not possible.
Input
Output

37. A single path means no pulse stretching and
Single mode fiber
A single path means no pulse stretching and
high speed data transmission is possible.
Input
Output

38. C is maximum and fR is minimum.
Tuning diode L C
ZERO BIAS
C is maximum and fR is minimum.

39. C is less and fR increases.
Tuning diode L C
REVERSE BIAS
C is less and fR increases.

40. C is minimum and fR is maximum.
Tuning diode L C
MAX. REVERSE BIAS
C is minimum and fR is maximum.

41. Diode Applications Quiz
A circuit used to control the amplitude of a signal is the ________.
clipper
A circuit used to add a dc component to a signal is the ________.
clamp
A device containing an LED and a photodiode is the ________.
optocoupler
A tuning diode shows less capacitance as reverse bias ________.
increases
The device that is often used to regulate
voltage is the ________ diode.
zener

42. Concept Review
Zener diodes have a relatively low breakdown voltage and are often used as voltage regulators.
Diode clippers limit signal amplitude.
Diode clamps produce a dc signal component.
Diodes can be used to suppress inductive kick.
Optocouplers combine light emitting diodes and photodiodes.
Fiber optic cables carry light signals.
Varicap diodes are used to tune electronic circuits.
Repeat Segment

43. REVIEW The PN Junction Characteristic Curves of Diodes
Diode Lead Identification
Diode Types and Applications