electronics fundamentals
circuits, devices, and applications
THOMAS L. FLOYD
DAVID M. BUCHLA
Lesson 1: Diodes and Applications
Diode characteristics
Figure 1-25 Forward-bias measurements show general
changes in VF and IF as VBIAS is increased.
Diode characteristics
Figure 1-26 Relationship of voltage and current
in a forward-biased diode.
Diode characteristics
Figure 1-27 V-I characteristic curve for a
reverse-biased diode.
Diode characteristics
The forward and reverse characteristics are shown on a V-I
characteristic curve.
In the forward bias region, current
increases dramatically after the
barrier potential (0.7 V for Si) is
reached. The voltage across the
diode remains approximately
VR
equal to the barrier potential.
The reverse-biased diode
effectively acts as an insulator
until breakdown is reached.
IF
Forward
bias
VBR (breakdown)
0.7 V
Reverse
bias
Barrier
potential
IR
VF
Diode characteristics
Figure 1-29Temperature effect on the diode V-I
characteristic. The 1 mA and 1 µA marks on the
vertical axis are given as a basis for a relative
comparison of the current scales.
Diode characteristics
Figure 1-30 Diode schematic symbol.
Diode characteristics
Figure 1-31 Forward-bias and reverse-bias
connections showing the diode symbol.
Diode models
Figure 1-32 The ideal model of a diode.
Diode models
Figure 1-33 The practical model of a diode.
Diode models
Figure 1-34 The complete model of a diode.
Diode models
The characteristic curve for a diode can be approximated by various models
of diode behavior. The model you will use depends on your requirements.
IF
The ideal model assumes the diode is
either an open or closed switch.
The practical model includes the VR
barrier voltage in the approximation.
The complete model includes the
forward resistance of the diode.
Forward
bias
0.7 V
Reverse
bias
IR
VF
Figure 1-36 Typical diode packages with terminal identification. The letter K is
used for cathode to avoid confusion with certain electrical quantities that are
represented by C. Case type numbers are indicated for each diode.
Diode Testing
Figure 1-37 DMM diode test on a properly functioning diode.
Diode Testing
Figure 1-38 Testing a defective diode.
Problem 1: For each energy diagrams in the given figure, determine the class of
material based on relative comparison.
Insulator
Semiconductor
Conductor
Problem 2: Determine whether each diode is forward-biased or reverse-biased
The diode is reverse-biased
The diode is forward-biased
The diode is forward-biased
The diode is forward-biased
Problem 3: Examine the meter indications in each circuit and determine whether the
diode if functioning properly, or whether it is open or shorted.
Problem 4: Determine the voltage across each diode.
The diode is forward-biased
The diode is reverse-biased
V
VR  8V  5V  3V
The diode is forward-biased
VF  0.7V
VF  0.7V
The diode is forward-biased
VF  0.7V
Problem 5: Determine the voltage with respect to ground at each point in the
given figure.
VA  VS1  25V
VB  VA  0.7V  24.3V
VC  VS 2  0.7V  8.7V
VD  VS 2  8V
Half-wave Rectifier
Rectifiers are circuits that convert ac to dc. Special diodes, called rectifier
diodes, are designed to handle the higher current requirements in these
circuits.
The half-wave rectifier
converts ac to pulsating
dc by acting as a closed
switch during the
positive alteration.
The diode acts as an
open switch during the
negative alteration.
+
D

RL
D
 +
RL
Half-wave Rectifier
FIGURE 16–22 Operation of a half-wave
rectifier.
Half-wave Rectifier
FIGURE 16–23 Average value of the half-wave
rectified signal.
Half-wave Rectifier
Example: What is the average (dc) value of the
half-wave rectified output voltage waveform in
the figure below.
Solution:
VAVG 
Vp ( out)


100V

 31.8V
Half-wave Rectifier
FIGURE 16–25 Effect of barrier potential on
halfwave rectified output voltage.
Half-wave Rectifier
Example: Determine the peak output voltage
and the average value of the output voltage of
the rectifier in the figure below for the indicated
input voltage.
Solution:
Vp ( out)  Vp ( in )  0.7V  5V  0.7V  4.3V
VAVG 
Vp ( out)


4.3V

 1.37V
Half-wave Rectifier
The PIV equals the peak value of
the input voltage, and the diode
must be capable of withstanding
this amount of repetitive reverse
voltage.
FIGURE 16–27 The PIV occurs at the peak of each
half-cycle of the input voltage when the diode is
reverse-biased. In this circuit, the PIV occurs at the
time (tp) of the peak of each negative half-cycle.
Full-wave Rectifier
The difference between full-wave and half-wave rectification is that a full-wave
rectifier allows unidirectional current to the load during the entire input cycle.
Full-wave Rectifier
The average value for a full-wave rectified output voltage is twice that of the
half-wave rectified output voltage, expressed as follows:
VAVG 
Since
can
2  0you
.637
, calculate

2V p ( out)

as 0.637 V
AVG
Vp (out)
Full-wave Rectifier
Find the average value of the full-wave rectified output voltage in the given
figure below:
Solution:
VAVG 
2V p ( out)


2(15V )

 9.55V