B-Stad CH 02

Electronic Devices and Circuit Theory
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Diode Applications
Chapter 2
Ch.2 Summary
Load-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.
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.
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Ch.2 Summary
Series Diode Configurations

Forward Bias
Constants Silicon Diode: VD = 0.7 V
Germanium Diode: VD = 0.3 V

Analysis (for silicon) VD = 0.7 V (or VD = E if E < 0.7 V) VR = E VD ID = IR = IT = VR / R
Ch.2 Summary
Series Diode Configurations

Reverse Bias
Diodes ideally behave as open circuits
Analysis VD = E VR = 0 V ID = 0 A

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2013 by Pearson Higher Education, Inc Upper Saddle River, New Jersey 07458 All Rights Reserved
Ch.2 Summary
Parallel Diode Configurations

V 0.7 V D V V V 0.7 V D1 D2 o V 9.3 V R E V 10 V .7 V D I 28 mA R R .33 k I D1 I D2 28 mA 2 14 mA

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Ch.2 Summary
Half-Wave Rectification
The diode conducts only when it is forward biased, therefore only half of the AC cycle passes through the diode to the output.
The DC output voltage is 0.318Vm, where Vm = the peak AC voltage.
Ch.2 Summary
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.
PIV (or PRV) > Vm

Where PIV = Peak inverse voltage
PRV = Peak reverse voltage Vm = Peak AC voltage
Ch.2 Summary
Full-Wave Rectification
The rectification process can be improved by using a full-wave rectifier circuit.
Full-wave rectification produces a greater DC output:
Half-wave: Vdc = 0.318Vm

Full-wave: Vdc = 0.636Vm
Ch.2 Summary
Bridge Rectifier
A full-wave rectifier with four diodes that are connected in a bridge configuration
VDC = 0.636Vm
Ch.2 Summary
Center-Tapped Transformer Rectifier

Requires two diodes and a center-tapped transformer
VDC = 0.636Vm
Ch.2 Summary
Summary of Rectifier Circuits

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

Ch.2 Summary
Diode Clippers
The diode in a 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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Ch.2 Summary
Biased Clippers
Adding a DC source in series with the clipping diode changes the effective forward bias of the diode.

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Ch.2 Summary
Parallel Clippers
The diode in a parallel clipper circuit clips any voltage that forward biases it.
DC biasing can be added in series with the diode to change the clipping level.

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Ch.2 Summary
Summary of Clipper Circuits

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Ch.2 Summary

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Ch.2 Summary

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Ch.2 Summary
Clampers
A diode and capacitor can be combined to clamp an AC signal to a specific DC level.

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Ch.2 Summary
Biased Clamper Circuits

The input signal can be any type of waveform such as a sine, square, or triangle wave.
The DC source lets you adjust the DC camping level.

Ch.2 Summary
Summary of Clamper Circuits

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Ch.2 Summary
Zener Diodes
The Zener is a diode that is operated in reverse bias at the Zener Voltage (Vz).
When Vi VZ The Zener is on 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
Ch.2 Summary
Zener Resistor Values

If R is too large, the Zener diode cannot conduct because IZ < IZK. The minimum current is given by:
ILmin IR IZK
The maximum value of resistance is:
RLmax
VZ ILmin IL max VL V Z RL RL min
If R is too small, IZ > IZM . The maximum allowable current for the circuit is given by:
The minimum value of resistance is:

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RL min
RVZ Vi VZ
Ch.2 Summary
Voltage-Multiplier Circuits
Voltage multiplier circuits use a combination of diodes and capacitors to step up the output voltage of rectifier circuits. Three common voltage multipliers are the:
Voltage Doubler
Voltage Tripler Voltage Quadrupler
Ch.2 Summary
Voltage Doubler
This half-wave voltage doublers output can be calculated using:
Vout = VC2 = 2Vm

where Vm = peak secondary voltage of the transformer
Ch.2 Summary
Voltage Doubler
Positive Half-Cycle
D1 conducts D2 is switched off Capacitor C1 charges to Vm D1 is switched off D2 conducts Capacitor C2 charges to Vm
Negative Half-Cycle
Vout = VC2 = 2Vm

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Ch.2 Summary
Voltage Tripler and Quadrupler

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Ch.2 Summary
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 Currents caused by an inductive kick in a relay circuit
Zener Circuits
Overvoltage Protection Setting Reference Voltages

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Electronic Devices and Circuit Theory

Series Diode Configurations

Germanium Diode: VD = 0.3 V

Series Diode Configurations

Electronic Devices and Circuit Theory

Parallel Diode Configurations

Electronic Devices and Circuit Theory

PIV (or PRV) > Vm

Half-wave: Vdc = 0.318Vm

Center-Tapped Transformer Rectifier

Summary of Rectifier Circuits

Vm = the peak AC voltage

Electronic Devices and Circuit Theory

Electronic Devices and Circuit Theory

Electronic Devices and Circuit Theory

Summary of Clipper Circuits

Electronic Devices and Circuit Theory

Summary of Clipper Circuits

Electronic Devices and Circuit Theory

Summary of Clipper Circuits

Electronic Devices and Circuit Theory

Electronic Devices and Circuit Theory

Biased Clamper Circuits

The DC source lets you adjust the DC camping level.

Summary of Clamper Circuits

Electronic Devices and Circuit Theory

Zener Resistor Values

The maximum value of resistance is:

VZ ILmin IL max VL V Z RL RL min

The minimum value of resistance is:

This half-wave voltage doublers output can be calculated using:

Vout = VC2 = 2Vm

Vout = VC2 = 2Vm

Electronic Devices and Circuit Theory

Voltage Tripler and Quadrupler

Electronic Devices and Circuit Theory

Simple Diode Circuits

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