CED, INU Peshawar.

1. Chapter 2:
Diode Applications

2. Load
Load-
-Line Analysis
Line Analysis
The load line plots all possible
combinations of diode current (ID)
and voltage (VD) for a given circuit.
The maximum ID equals E/R, and
the maximum VD equals E.
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky 2
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The point where the load line and
the characteristic curve intersect is
the Q-point, which identifies ID and
VD for a particular diode in a given
circuit.

3. Series Diode Configurations
Series Diode Configurations
Constants
• Silicon Diode: VD = 0.7 V
• Germanium Diode: VD = 0.3 V
Analysis (for silicon)
Forward Bias
Forward Bias
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
• VD = 0.7 V (or VD = E if E < 0.7 V)
• VR = E – VD
• ID = IR = IT = VR / R
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3

4. Series Diode Configurations
Series Diode Configurations
Diodes ideally behave as open circuits
Analysis
• VD = E
• VR = 0 V
Reverse Bias
Reverse Bias
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
R
• ID = 0 A
4
4

5. Parallel Configurations
Parallel Configurations
V
.7
V
10
D
V
E
V
9.3
R
V
V
0.7
O
V
D2
V
D1
V
V
0.7
D
V
−
−
=
=
=
=
=
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky 5
5
mA
14
2
mA
28
D2
I
D1
I
mA
28
.33kΩ
V
.7
V
10
R
D
V
E
R
I
=
=
=
=
−
=
−
=

6. Half
Half-
-Wave Rectification
Wave Rectification
The diode only
conducts when it is
forward biased,
therefore only half
of the AC cycle
passes through the
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky 6
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passes through the
diode to the
output.
The DC output voltage is 0.318Vm, where Vm = the peak AC voltage.

7. PIV (PRV)
PIV (PRV)
Because the diode is only forward biased for one-half of the AC cycle, it is
also reverse biased for one-half cycle.
It is important that the reverse breakdown voltage rating of the diode be
high enough to withstand the peak, reverse-biasing AC voltage.
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PIV (or PRV) > Vm
• PIV = Peak inverse voltage
• PRV = Peak reverse voltage
• Vm = Peak AC voltage

8. Full
Full-
-Wave Rectification
Wave Rectification
The rectification process can be improved by
using a full-wave rectifier circuit.
Full-wave rectification produces a greater
DC output:
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• Half-wave: V
Vdc
dc = 0.318
= 0.318V
Vm
m
• Full-wave: V
Vdc
dc = 0.636
= 0.636V
Vm
m
DC output:

9. Full
Full-
-Wave Rectification
Wave Rectification
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Bridge Rectifier
Bridge Rectifier
• Four diodes are connected in a
bridge configuration
• VDC = 0.636Vm

10. Full
Full-
-Wave Rectification
Wave Rectification
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Center
Center-
-Tapped Transformer
Tapped Transformer
Rectifier
Rectifier
Requires
• Two diodes
• Center-tapped transformer
VDC = 0.636Vm

11. Summary of Rectifier Circuits
Summary of Rectifier Circuits
Rectifier
Rectifier Ideal
Ideal V
VDC
DC Realistic
Realistic V
VDC
DC
Half Wave Rectifier VDC
DC = 0.318Vm VDC
DC = 0.318Vm
m – 0.7
Bridge Rectifier VDC
DC = 0.636Vm VDC
DC = 0.636Vm – 2(0.7 V)
Center-Tapped Transformer
V = 0.636V V = 0.636V – 0.7 V
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Vm = peak of the AC voltage.
I
In the center tapped transformer rectifier circuit, the peak AC voltage
is the transformer secondary voltage to the tap.
Center-Tapped Transformer
Rectifier
VDC
DC = 0.636Vm VDC
DC = 0.636Vm – 0.7 V

12. Diode Clippers
Diode Clippers
•
The diode in a series clipper
series clipper “clips”
any voltage that does not forward
bias it:
•A reverse-biasing polarity
•A forward-biasing polarity less than
0.7 V (for a silicon diode)
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13. Biased Clippers
Biased Clippers
Adding a DC source in
series with the clipping
diode changes the
effective forward bias of
the diode.
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14. Parallel Clippers
Parallel Clippers
The diode in a parallel clipper
parallel clipper
circuit “clips” any voltage that
forward bias it.
DC biasing can be added in
series with the diode to change
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series with the diode to change
the clipping level.

15. Summary of Clipper Circuits
Summary of Clipper Circuits
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more…
more…

16. Summary of Clipper Circuits
Summary of Clipper Circuits
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17. Clampers
Clampers
A diode and capacitor can be
combined to “clamp” an AC
signal to a specific DC level.
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18. Biased Clamper Circuits
Biased Clamper Circuits
The input signal can be any type
of waveform such as sine, square,
and triangle waves.
The DC source lets you adjust
the DC camping level.
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Electronic Devices and Circuit Theory, 10/e
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18
the DC camping level.

19. Summary of Clamper Circuits
Summary of Clamper Circuits
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20. Zener Diodes
Zener Diodes
The Zener is a diode operated
in reverse bias at the Zener
Voltage (Vz).
• When Vi ≥
≥
≥
≥ VZ
– The Zener is on
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky 20
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– Voltage across the Zener is VZ
– Zener current: IZ = IR – IRL
– The Zener Power: PZ = VZIZ
• When Vi < VZ
– The Zener is off
– The Zener acts as an open circuit

21. Zener Resistor Values
Zener Resistor Values
ZK
R
L I
I
I −
=
min
min
max
L
Z
L
I
V
R =
If R is too large, the Zener diode cannot conduct because the available amount of
current is less than the minimum current rating, IZK. The minimum current is
given by:
The maximum value of resistance is:
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky 21
21
min
max
L
Z
L
L
L
R
V
R
V
I =
=
Z
i
Z
L
V
V
RV
R
−
=
min
If R is too small, the Zener current exceeds the maximum current
rating, IZM . The maximum current for the circuit is given by:
The minimum value of resistance is:

22. Voltage
Voltage-
-Multiplier Circuits
Multiplier Circuits
• Voltage Doubler
• Voltage Tripler
• Voltage Quadrupler
Voltage multiplier circuits use a combination of diodes and
capacitors to step up the output voltage of rectifier circuits.
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Electronic Devices and Circuit Theory, 10/e
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23. Voltage Doubler
Voltage Doubler
This half-wave voltage doubler’s output can be calculated by:
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky 23
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This half-wave voltage doubler’s output can be calculated by:
Vout = VC2 = 2Vm
where Vm = peak secondary voltage of the transformer

24. Voltage Doubler
Voltage Doubler
• Positive Half-Cycle
o D1 conducts
o D2 is switched off
o Capacitor C1 charges to Vm
• Negative Half-Cycle
o D1 is switched off
o D2 conducts
o Capacitor C charges to V
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o Capacitor C2 charges to Vm
Vout = VC2 = 2Vm

25. Voltage Tripler and Quadrupler
Voltage Tripler and Quadrupler
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26. Practical Applications
Practical Applications
• Rectifier Circuits
– Conversions of AC to DC for DC operated circuits
– Battery Charging Circuits
• Simple Diode Circuits
– Protective Circuits against
– Overcurrent
– Polarity Reversal
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
– Polarity Reversal
– Currents caused by an inductive kick in a relay circuit
• Zener Circuits
– Overvoltage Protection
– Setting Reference Voltages
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