1. Principles & Applications
Electronics
Principles & Applications
Fifth Edition
Charles A. Schuler
Chapter 3
Junction Diodes
© Glencoe/McGraw-Hill

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

3. P N A silicon crystal Anode Cathode Schematic Symbol
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

4. Having no carriers, the depletion region is an insulator.
Zero Bias
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.

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

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

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

8. 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

9. 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 around 0.6 to 0.7 volts for silicon diodes.

10. The effect of temperature on the diode curve
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 on the diode curve

11. 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

12. Cathode lead
Anode lead

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

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

15. 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.

16. 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

17. 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.

18. 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.

19. Using a zener diode as a voltage regulator Load
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.

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

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

22. 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

23. CEMF
The inductive kick
can cause damage.

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

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

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

27. 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.

28. Input
Output
Output
Input
Optocoupler

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

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

31. 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

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

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

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

35. 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 photo-
diode 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

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