tronics1-clampers clippers multipliers rectifiers zener

7/29/2019 Tronics1-Clampers Clippers Multipliers Rectifiers Zener

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Chapter 2:

Diode Applications


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Copyright 2009 by Pearson Education, Inc.

Upper Saddle River, New Jersey 07458 All rights reserved.

Electronic Devices and Circuit Theory, 10/e

Robert L. Boylestad and Louis Nashelsky

Load-Line AnalysisLoad-Line Analysis

22

The load line plots all possible

combinations of diode current (ID)

and voltage (VD) for a given

circuit. The maximumID 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 identifiesID

and VD for a particular diode in a

given circuit.


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Series Diode ConfigurationsSeries Diode Configurations

Constants

Silicon Diode: VD = 0.7 V

Germanium Diode: VD = 0.3 V

Analysis (for silicon)

VD = 0.7 V (or VD =EifE< 0.7 V)

VR = E VD

ID = IR = IT= VR / R

33

Forward BiasForward Bias


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Series Diode ConfigurationsSeries Diode Configurations

Diodes ideally behave as open circuits

Analysis

VD = E

VR = 0 V

ID= 0 A

44

Reverse BiasReverse Bias


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Parallel ConfigurationsParallel Configurations

55

mA14

2

mA28

D2I

D1I

mA28

.33k

V.7V10

R

DVE

RI

V9.3R

V

V0.7O

VD2

VD1

V

V0.7D

V


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Half-Wave RectificationHalf-Wave Rectification

66

The diode only

conducts 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.


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PIV (PRV)PIV (PRV)

77

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

PIV = Peak inverse voltage

PRV = Peak reverse voltage

Vm

= Peak AC voltage


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Full-Wave RectificationFull-Wave Rectification

88

Half-wave: VVdcdc = 0.318= 0.318VVmm

Full-wave: VVdcdc = 0.636= 0.636VVmm

The rectification process can be improved by

using a full-wave rectifier circuit.

Full-wave rectification produces a greaterDC output:


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99

Bridge RectifierBridge Rectifier

Four diodes are connected in a

bridge configuration VDC = 0.636Vm


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1010

Center-Tapped TransformerCenter-Tapped Transformer

RectifierRectifier

Requires

Two diodes

Center-tapped transformer

VDC = 0.636Vm


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Summary of Rectifier CircuitsSummary of Rectifier Circuits

1111

Vm= peak of the AC voltage.

IIn the center tapped transformer rectifier circuit, the peak AC voltageis the transformer secondary voltage to the tap.

RectifierRectifier IdealIdeal VVDCDC RealisticRealistic VVDCDC

Half Wave Rectifier VDCDC = 0.318Vm VDCDC = 0.318Vmm 0.7

Bridge Rectifier VDCDC = 0.636Vm VDCDC = 0.636Vm 2(0.7 V)

Center-Tapped Transformer

RectifierVDCDC = 0.636Vm VDCDC = 0.636Vm 0.7 V


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Important Equations

TRANSFORMER EQUATIONS

=

=

= 0.707

HALF-WAVE RECTIFIER EQUATIONS (TRANSFORMER COUPLED)

= 0.7 = /

= = / = = /

= = /2 = = /2

PIV=V2 fout= fin

Efficiency of Rectification = n = (/)100%CENTER-TAPPED FULL-WAVE RECTIFIER EQUATIONS (TRANSFORMER COUPLED)

= /20.7 = /

= = 2/ = = 2/

=

=

/2

=

=

/2

PIV=V2 0.7 fout= 2fin


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Diode ClippersDiode Clippers

1212

The diode in a series clipperseries clipperclipsany voltage that does not forward

bias it:

A reverse-biasing polarity

A forward-biasing polarity less than0.7 V (for a silicon diode)


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Biased ClippersBiased Clippers

1313

Adding a DC source in

series with the clipping

diode changes the

effective forward bias of

the diode.


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Parallel ClippersParallel Clippers

1414

The diode in a parallel clipperparallel clipper

circuit clips any voltage that

forward bias it.

DC biasing can be added inseries with the diode to change

the clipping level.


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Summary of Clipper CircuitsSummary of Clipper Circuits

1515

moremore


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Summary of Clipper CircuitsSummary of Clipper Circuits

1616


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ClampersClampers

1717

A diode and capacitor can be

combined to clamp an AC

signal to a specific DC level.


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Biased Clamper CircuitsBiased Clamper Circuits

1818

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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Summary of Clamper CircuitsSummary of Clamper Circuits

1919


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Zener DiodesZener Diodes

2020

The Zener is a diode operatedin reverse bias at the Zener

Voltage (Vz).

When Vi VZ The Zener is on Voltage across the Zener is VZ Zener current:IZ=IRIRL The Zener Power:PZ= VZIZ

When Vi< VZ The Zener is off

The Zener acts as an open circuit


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Zener Resistor ValuesZener Resistor Values

2121

ZKRLIII

min

min

max

L

Z

L

I

VR

min

max

L

Z

L

L

L

R

V

R

VI

Zi

Z

L

VV

RVR

min

IfR 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:

IfR 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:


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Voltage-Multiplier CircuitsVoltage-Multiplier Circuits

Voltage Doubler

Voltage Tripler

Voltage Quadrupler

2222

Voltage multiplier circuits use a combination of diodes and

capacitors to step up the output voltage of rectifier circuits.


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Voltage DoublerVoltage Doubler

2323

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

Vout = VC2 = 2Vm

where Vm = peak secondary voltage of the transformer


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Voltage DoublerVoltage Doubler

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Positive Half-Cycle

o D1 conductso D2 is switched off

o Capacitor C1 charges to Vm

Negative Half-Cycle

o D1 is switched off

o D2 conductso Capacitor C2 charges to Vm

Vout = VC2 = 2Vm


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Voltage Tripler and QuadruplerVoltage Tripler and Quadrupler

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S R 0 4 8 A


R b t L B l t d d L i N h l k

Practical ApplicationsPractical 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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tronics1-clampers clippers multipliers rectifiers zener

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