Chapter 2

Diode application

1

Objectives

● Explain and analyze the operation of both half and full wave

rectifiers

● Explain and analyze filters and regulators and their

characteristics

● Explain and analyze the operation of diode limiting and ● Explain and analyze the operation of diode limiting and

clamping circuits

● Explain and analyze the operation of diode voltage multipliers

● Interpret and use a diode data sheet

● Troubleshoot simple diode circuits

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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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Load-Line AnalysisExample

• For the series diode configuration of Fig. 2.3a , employing the diode characteristics of Fig. 2.3b , determine:

• a. VDQ and IDQ.

• b. VR

4

Series Diode Configurations

Forward BiasConstants

• Silicon Diode: VD = 0.7 V

• Germanium Diode: VD = 0.3 V

Analysis (for silicon)

• V = 0.7 V (or V = E if E < 0.7V)• VD = 0.7 V (or VD = E if E < 0.7V)

• VR = E – VD

• ID = IR = IT = VR / R

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Series Diode Configurations

Reverse BiasDiodes ideally behave as open circuits

Analysis

• VD = E

• V = 0 V• VR = 0 V

• ID = 0 A

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Series Diode ConfigurationsExample

For the series diode configuration of Figure below, determine VD, VR, and ID .

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Series Diode ConfigurationsExample

For the series diode configuration of Figure below, determine VD, VR, and ID .

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Series Diode ConfigurationsExample

For the series diode configuration of Figure below, determine I, V1, V2 and V0 .

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Series Diode ConfigurationsExample

For the series diode configuration of Figure below, determine I, V1, V2 and V0 .

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Parallel ConfigurationsExample

Determine Vo , I1 , ID1, and ID2 for

the parallel diode configuration of

Figure below

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Parallel ConfigurationsExample

Determine I1 , I2, and ID2 for the parallel diode configuration of Figure below

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Parallel ConfigurationsExample

Determine I1 , I2, and ID2 for the parallel diode configuration of Figure below

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Half-Wave Rectification

The diode only

conducts when it is

forward biased,

therefore only half

of the AC cycle

passes through thepasses through the

diode to the

output.

The DC output voltage (VDC) is 0.318Vm, where Vm = the peak AC voltage.

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Half-Wave Rectification

VK =0.7 V and vo = vi – VK

When Vm » VK

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Half-Wave RectificationExample

a. determine the dc level of the output for the network of Figure belowSketch

the output vo and

b. Repeat part (a) if the ideal diode is replaced by a silicon diode.

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Half-Wave RectificationExample

a. determine the dc level of the output for the network of Figure belowSketch

the output vo and

b. Repeat part (a) if the ideal diode is replaced by a silicon diode.

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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

• PIV = Peak inverse voltage

• PRV = Peak reverse voltage

• Vm = Peak AC voltage

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Full-Wave Rectification

The rectification process can be improved by using a

full-wave rectifier circuit.

Full-wave rectification produces a greater DCFull-wave rectification produces a greater DC

output:

• Half-wave: Vdc = 0.318Vm

• Full-wave: Vdc = 0.636Vm

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Full-Wave Rectification

Bridge Rectifier

• Four diodes are connected in a bridge configuration

• VDC = 0.636Vm

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Full-Wave Rectification

Center-Tapped Transformer

Rectifier

Requires

• Two diodes

• Center-tapped transformer

VDC = 0.636Vm

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Summary of Rectifier Circuits

Rectifier Ideal VDC Realistic VDC

Half Wave RectifierVDC = 0.318Vm VDC = 0.318Vm – 0.7

Bridge Rectifier VDC = 0.636Vm VDC = 0.636Vm – 2(0.7 V)

Vm = peak of the AC voltage.

In the center tapped transformer rectifier circuit, the peak AC voltage is the

transformer secondary voltage to the tap.

Center-Tapped Transformer

Rectifier VDC = 0.636Vm VDC = 0.636Vm – 0.7 V

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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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Diode Clippers

Series clipper with dc supply

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Diode Clippers

Adding a DC source in series with the clipping

diode changes the effective forward bias of the

diode.

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Biased ClippersExample

Determine the output waveform for the sinusoidal input of Figure below.

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Parallel Clippers

The diode in a parallel clipper

circuit “clips” any voltage that

forward bias it.

DC biasing can be added in DC biasing can be added in

series with the diode to change

the clipping level.

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Parallel ClippersExample

Determine vo for the network of Figure below.

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Parallel ClippersExample

Determine vo for the network of Figure below.

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Summary of Clipper CircuitsSeries

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Summary of Clipper CircuitsParallel

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Clampers

A diode and capacitor can be combined

to “clamp” an AC signal to a specific DC

level.

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Biased Clamper CircuitsExample 1

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.camping level.

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Summary of Clamper Circuits

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Voltage-Multiplier Circuits

Voltage multiplier circuits use a combination of diodes and capacitors to step

up the output voltage of rectifiercircuits.

• Voltage Doubler

• Voltage Tripler

• Voltage Quadrupler

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Voltage Doubler

This half-wave voltage doubler’s output can be calculated by:

Vout = VC2 = 2Vm

where Vm = peak secondary voltage of the transformer

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Voltage Doubler

• Positive Half-Cycle

o D1 conducts

o D2 is switched off

o Capacitor C1 charges toVm

• Negative Half-Cycle

o D1 is switched offo D1 is switched off

o D2 conducts

o Capacitor C2 charges toVm

Vout = VC2 = 2Vm

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Voltage Tripler and Quadrupler

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Practical Applications

• Rectifier Circuits

– Conversions of AC to DC for DC operated circuits

– Battery Charging Circuits

• Simple Diode Circuits

– Protective Circuits against– 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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