1 CHAPTER 2 Diode Applications By: Syahrul Ashikin Azmi School of Electrical System Engineering.

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CHAPTER 2CHAPTER 2

Diode ApplicationsDiode ApplicationsBy:

Syahrul Ashikin AzmiSchool of Electrical System Engineering

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ObjectivesObjectives 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 clamping circuits

Explain and analyze the operation of diode voltage multipliers Interpret and use a diode data sheet

Troubleshoot simple diode circuits

33

Lecture’s contentsLecture’s contents 2-1 Half-wave rectifier 2-2 Full-wave rectifier 2-3 Power supply filters and regulators 2-4 Diode limiting and clamping

circuits 2-5 Voltage multipliers 2-6 Diode data sheet 2-7 Troubleshooting Summary

44

2-1 Half-Wave Rectifiers2-1 Half-Wave Rectifiers

Diode – ability to conduct current in one direction Diode – ability to conduct current in one direction and block current in other directionand block current in other direction

used in circuit called used in circuit called RECTIFIER (ac RECTIFIER (ac dc)dc)

Objective:Objective: Discuss the operation of half-wave rectifiersDiscuss the operation of half-wave rectifiers Describe a basic dc power supply & half-wave rectificationsDescribe a basic dc power supply & half-wave rectifications Determine the average value, VDetermine the average value, VAVGAVG of half-waves rectified of half-waves rectified

voltagevoltage Discuss the effect of barrier potential, VDiscuss the effect of barrier potential, VPP on a half-wave on a half-wave

rectifier outputrectifier output Define Define Peak Inverse VoltagePeak Inverse Voltage (PIV) (PIV) Describe Transformer-couple half-wave rectifierDescribe Transformer-couple half-wave rectifier

55

The basic function of a DC power supply is to convert an AC voltage to a constant DC voltage (AC DC)

Either half or full-waverectifier convert ac input voltageto a pulsating dc voltage.

Eliminates the fluctuations- produce smooth dc voltage

Maintains a constant dcvoltage

2-1 Half-Wave Rectifiers 2-1 Half-Wave Rectifiers (cont.)(cont.)

(The basic DC power supply)(The basic DC power supply)

66

•A half wave rectifier(ideal) allows conduction for only 180° or half of a complete cycle..•During first one cycle:

-Vin goes positive – diode FB – conduct current

-Vin goes negative – diode RB – no current- 0V

•The output frequency is the same as the input (same shape).

The average value VDC or VAVG :

Ideal diode model

pAVG

VV

-Measure on dc voltmeter


(The Half-Wave Rectifier)(The Half-Wave Rectifier)ac source load resistor

77

Practical Diode – barrier potential of 0.7V (Si) taken into account.Practical Diode – barrier potential of 0.7V (Si) taken into account. During +ve half-cycle – VDuring +ve half-cycle – Vinin must overcome V must overcome Vpotentialpotential for forward bias. for forward bias.

Example 1: Calculate the peak o/p voltage, VExample 1: Calculate the peak o/p voltage, Vp(oup(out)t)??

The peak o/p voltage:The peak o/p voltage: VVV inpoutp 7.0)()(


(Effect of the Barrier Potential on the Half-Wave (Effect of the Barrier Potential on the Half-Wave Rectifier Output)Rectifier Output)

V

VV

VVV inpoutp

30.4

7.05

7.0)()(

88


(Effect of the Barrier Potential on the Half-Wave (Effect of the Barrier Potential on the Half-Wave Rectifier Output)Rectifier Output)

Example 2:

Sketch the output V0 and determine the output level voltage for thenetwork in above figure.

99

- Peak inverse voltage (PIV) is the maximum voltage across the diode when it is in reverse bias.

The diode must be capable of withstanding this amount of voltage.

)(inpVPIV


[Peak Inverse Voltage (PIV)][Peak Inverse Voltage (PIV)]

1010

Transformers are often used for voltage change and isolation.The turns ratio, n of the primary to secondary determines the output versus the input.

The advantages of transformer coupling: 1) allows the source voltage to be stepped up or down 2) the ac source is electrically isolated from the rectifier, thus prevents shock hazards in the secondary circuit.

to couple ac input to the rectifier

VVV poutp 7.0(sec))(

(sec)pVPIV priN

Nn sec

prinVV sec


(Half-Wave Rectifier with Transformer-Coupled Input (Half-Wave Rectifier with Transformer-Coupled Input Voltage)Voltage)

If n>1, Vsec is greater than Vpri.If n<1, Vsec is less than Vpri.

If n=1, Vsec= Vpri.

1111

Example 3:Example 3:

Determine the peak value of output voltage as shown in below Figure.

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Objective:Objective: Explain & Analyze the operation of Full-Wave Explain & Analyze the operation of Full-Wave

Rectifier.Rectifier. Discuss how full wave rectifier differs from half-wave Discuss how full wave rectifier differs from half-wave

rectifier rectifier Determine the average valueDetermine the average value Describe the operation of center-tapped & bridge.Describe the operation of center-tapped & bridge. Explain effects of the transformers turns ratioExplain effects of the transformers turns ratio PIVPIV Comparison between center-tapped & bridge.Comparison between center-tapped & bridge.

2-2 Full-Wave Rectifiers2-2 Full-Wave Rectifiers (Introduction)(Introduction)

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Twice output

p

AVG

VV

2

2-2 Full-Wave Rectifiers (cont.)2-2 Full-Wave Rectifiers (cont.) (Introduction)(Introduction)

A full-wave rectifier allows current to flow during both the positive and negative half cycles or the full 360º whereas half-wave rectifier allows only during one-half of the cycle.

The no. of +ve alternations is twice the half wave for the same time interval

The output frequency is twice the input frequency.

The average value – the value measured on a dc voltmeter

63.7% of Vp

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Coupled inputvoltage

•This method of rectification employs two diodes connected to a secondary center-tapped transformer.

•The i/p voltage is coupled through the transformer to the center-tapped secondary.

2-2 Full-Wave Rectifiers2-2 Full-Wave Rectifiers (i - The Center-Tapped Full-Wave Rectifier)(i - The Center-Tapped Full-Wave Rectifier)

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•+ve half-cycle input voltage (forward-bias D1 & reverse-bias D2)-the current patch through the D1 and RL

•-ve half-cycle input voltage (reverse-bias D1 & forward-bias D2)-the current patch through D2 and RL

•The output current on both portions of the input cycle – same direction through the load.

•The o/p voltage across the load resistors – full-wave rectifiers

2-2 Full-Wave Rectifiers (cont.)2-2 Full-Wave Rectifiers (cont.) (i - The Center-Tapped Full-Wave Rectifier)(i - The Center-Tapped Full-Wave Rectifier)

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priVV 2sec


If n=1, Vp(out)=Vp(pri) - 0.7V 2 Vp(sec)=Vp(pri)

If n=2,

7.0)()( pripoutp VV

-Effect of the Turns Ratio on the Output Voltage--Effect of the Turns Ratio on the Output Voltage-

priVV 2sec

• In any case, the o/p voltage is always one-half of the total secondary voltageminus the diode drop (barrier potential), no matter what the turns ratio.

VV

Vout 7.02sec

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-Peak Inverse Voltage (PIV)-

Maximum anode voltage:Maximum anode voltage:2(sec)

1pV

D 2(sec)

2pV

D

D1: forward-bias – its cathode is at the same voltage of its anode minus diode drop;

This is also the voltage on the cathode of D2. PIV across D2 :

VV

VV

VPIV

p

pp

7.0

27.0

2

(sec)

(sec)(sec)

VVV

VV

V

outpp

poutp

4.12

7.02

)((sec)

(sec))(

We know thatWe know that

Thus;Thus;

VVPIV outp 7.02 )(

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It employs four diodes arranged such that current flows in the direction through the load during each half of the cycle.

When Vin +ve, D1 and D2 FB and conduct current. A voltage across RL

looks like +ve half of the input cycle. During this time, D3 and D4 are RB.

When Vin –ve, D3 and D4 are FB and conduct current. D1 and D2 are RB.Used 4 diode:2 diode in forward2 diode in reverse

2 diode always in series with load resistor during +ve and –ve half cycle .

Without diode drop (ideal diode):

With diode drop (practical diode):

(sec))( poutp VV

VVV poutp 4.1(sec))(

2-2 Full-Wave Rectifiers (cont.)2-2 Full-Wave Rectifiers (cont.) (ii - The Bridge Full-Wave Rectifier)(ii - The Bridge Full-Wave Rectifier)

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)(outpVPIV

VVPIV outp 7.0)(

Note that in most cases we take the diode drop into account.

0V (ideal diode)

For each diode, VVPIV outp 7.0)(

2-2 Full-Wave Rectifiers (cont.)2-2 Full-Wave Rectifiers (cont.) (ii - The Bridge Full-Wave Rectifier)(ii - The Bridge Full-Wave Rectifier)

For ideal diode, PIV = Vp(out)

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2-3 Power Supply Filters And 2-3 Power Supply Filters And RegulatorsRegulators

(introduction)(introduction) ObjectiveObjective::

Explain & Analyze the operation & characteristic of Explain & Analyze the operation & characteristic of power supply filters & Regulatorspower supply filters & Regulators

Explain the purpose of a filterExplain the purpose of a filter Describe the capacitor-input filterDescribe the capacitor-input filter Define ripple voltage & calculate the ripple voltageDefine ripple voltage & calculate the ripple voltage Discuss surge current in capacitor-input filterDiscuss surge current in capacitor-input filter Discuss voltage regulation & integrated circuit Discuss voltage regulation & integrated circuit

regulatorregulator

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Power Supply FiltersPower Supply Filters

To reduce the fluctuations in the output voltage of half / full-To reduce the fluctuations in the output voltage of half / full-wave rectifier – wave rectifier – produces constant-level dc voltage..

It is necessary – electronic circuits require a constant source to It is necessary – electronic circuits require a constant source to provide power & biasing for proper operation.provide power & biasing for proper operation.

Filters are implemented with Filters are implemented with capacitorscapacitors..

RegulatorsRegulators Voltage regulation in power supply done using integrated Voltage regulation in power supply done using integrated

circuit voltage regulators.circuit voltage regulators. To To prevent changes in the filtered dc voltage/ / to fix output dc

voltage due to variations in input voltage or load.

2-3 Power Supply Filters And 2-3 Power Supply Filters And Regulators (cont.)Regulators (cont.)

(introduction) (introduction)

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•In most power supply – 60 Hz ac power line voltage is converted to constant dc voltage.

•60Hz pulsating dc output must be filtered to reduce the large voltage variation.

•Small amount of fluctuation in the filter o/p voltage - ripple

ripple


(introduction) (introduction)

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For half-wave rectifier:

• +ve first quarter cycle –diode is FB-capacitor is charging within 0.7V of i/p peak

• I/p decreased below its peak-capacitor retains its charge-diode become RB (cathode is more +ve than the anode)

• Capacitor can discharge through load resistance – at rate by the RLC time constant (>> time constant, << capacitor will discharge)

• Next cycle-diode is FB when i/p voltage exceeds the Vc by 0.7V

• A capacitor-input filter will charge and discharge such that it fills in the “gaps” between each peak. This reduces variations of voltage. This voltage variation is called ripple voltage.


(Capacitor-Input Filter) (Capacitor-Input Filter) load

capacitor

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Ripple Voltage: the variation in capacitor voltage due to the charging and discharging.

The advantage of a full-wave rectifier over a half-wave is quite clear. The capacitor can more effectively reduce the ripple when the time between peaks is shorter.

Easier to filter-shorted time between peaks.-smaller ripple.


(Capacitor-Input Filter) (Capacitor-Input Filter)

2525

DC

ppr

V

Vr )(

Ripple factor: indication of the effectiveness of the filter

Vr(pp) = peak to peak ripple voltage; VDC = VAVG = average value of filter’s output voltage.•Lower ripple factor better filter

[can be lowered by increasing the value of filter capacitor or increasing the load resistance]

[half-wave rectifier]

•For the full-wave rectifier:

)(

)()(

2

11

1

rectpL

AVGDC

rectpL

ppr

VCfR

VV

VCfR

V

Vp(rect) = unfiltered

peak.



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Surge Current in the Capacitor-Input Filter:

Being that the capacitor appears as a short during the initial charging, the current through the diodes can momentarily be quite high. To reduce risk of damaging the diodes, a surge current limiting resistor is placed in series with the filter and load.

FSM

psurge I

VVR

4.1(sec) IFSM = forward surge current rating specified on diode data sheet.



The min. surgeResistor values:

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Connected to the output of a filtered & maintains a constant output voltage (or current) despite changes in the input, load current or temperature.

Combination of a large capacitor & an IC regulator – inexpensive & produce excellent small power supply

Popular IC regulators have 3 terminals:(i) input terminal

(ii) output terminal(iii) reference (or adjust) terminal

Type number: 78xx (xx –refer to output voltage) i.e 7805 (output voltage +5.0V); 7824 (output voltage +24V)


(IC Regulators) (IC Regulators)

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Regulation is the last step in eliminating the remaining ripple and maintaining the output voltage to a specific value. Typically this regulation is performed by an integrated circuit regulator. There are many different types used based on the voltage and current requirements.

Fig. 2-23 : A basic +5.0V regulated power supply

Gnd

output

Connected to the outputof filtered rectifier

Bridge-full waverectifier filter regulators



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Adjustable regulators

1

2125.1R

RRVVout



FIGURE 2-34FIGURE 2-34 A basic power supply with a variable output voltage (from A basic power supply with a variable output voltage (from 1.25 V to 6.5 V).1.25 V to 6.5 V).

Adjustable resistor0 – 1.0kOhm

Keeps a constant 1.25V between the o/pand adjust terminals const. current in R1

min. 1.25V , max 6.5 V

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(Percent Regulations) (Percent Regulations)

How well the regulation is performed by a regulator is measured by it’s regulation percentage. There are two types of regulation, line and load. Line and load regulation percentage is simply a ratio of change in voltage (line) or current (load) stated as a percentage.

%100Regulation Load

%100Regulation Line

FL

FLNL

in

out

V

VV

V

V

VNL :out put voltage with no loadVFL :output voltage with full load

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2-4 Diode Limiting & Clamping Circuits2-4 Diode Limiting & Clamping Circuits

(Introduction) (Introduction) Objectives:Objectives:Analyze the operation of diode limiting, clamping circuit, voltage Analyze the operation of diode limiting, clamping circuit, voltage multipliers and interpret and use diode data sheet.multipliers and interpret and use diode data sheet.Determine V of biased limiter & used voltage-divider bias to set Determine V of biased limiter & used voltage-divider bias to set limiting level.limiting level.Discuss voltage doublers, triplers & quadruples.Discuss voltage doublers, triplers & quadruples.Identify V & current ratings.Identify V & current ratings.Determine the electrical characteristics of a diode.Determine the electrical characteristics of a diode.Analyze graphical data Analyze graphical data Select an appropriate diode for a given set of specifications.Select an appropriate diode for a given set of specifications.

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2-4 Diode Limiting & Clamping Circuits2-4 Diode Limiting & Clamping Circuits

(Diode Limiters) (Diode Limiters) • Diode limiters/clippers – that limits/clips the portion of signal voltage above or below certain level.

• Limiting circuits limit the positive or negative amount of an input voltage to a specific value.

• When i/p is +ve – the diode becomes FB – limited to +0.7 V because cathode is at ground.

• When i/p << 0.7 V-diode is RB – o/p voltage likes –ve part of i/p voltage

• Turn the diode around-negative part of i/p voltage is clipped off.

• When diode is FB-negative part of i/p voltage-diode drop -0.7Vin

L

Lout V

RR

RV

1

3333

Question 4:What would you expect to see displayed on an oscilloscope connectedacross RL in the limiter shown below.

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Solution question 4Solution question 4 The diode is forward biased and conducts when input The diode is forward biased and conducts when input

voltage goes below -0.7V. So, for –ve limiter, the voltage goes below -0.7V. So, for –ve limiter, the peak output voltage across RL is:peak output voltage across RL is:

The waveform is shown below:The waveform is shown below:

VVk

kV

RR

RV inp

L

Loutp 09.910

1.1

0.1)(

1)(

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2-4 Diode Limiting & Clamping Circuits 2-4 Diode Limiting & Clamping Circuits (cont.)(cont.) (Diode Limiters) (Diode Limiters)

Biased Limiters :• The level to which an ac voltage is limited can be adjusted by adding bias voltage VBIAS in series with diode.• Voltage at point A : VA = VBIAS + 0.7V (forward-biased & conduct). So, all Vin > VA is clipped off.• For –ve level, then VA = -VBIAS - 0.7V to forward-biased.• Turning diode around, +ve limiter – modified to limit Vout to the portion of Vin waveform above VBIAS – 0.7V.• -ve limiter; below -VBIAS - 0.7V.• By tuning the diode around- the +ve limiter can modified to limit the o/p voltage to the portion of the i/p voltage waveform above VBIAS-0.7V• Negative limiter – limit the o/p voltage to the i/p voltage below –VBIAS+0.7V

A positive limiter A negative limiter

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2-4 Diode Limiting & Clamping Circuits 2-4 Diode Limiting & Clamping Circuits (cont.)(cont.) (Diode Limiters) (Diode Limiters)

Voltage-Divider Bias:• The bias voltage source – used to illustrate the basic operation of diode limiters can be replace by a resistive voltage divider that derives the desired bias voltage from dc Vsupply .• VBIAS – set by the resistor values according to the voltage-divider formula:

• The desired amount of limitation can be attained by a power supply or voltage divider. The amount clipped can be adjusted with different levels of VBIAS.

• The bias resistor << R1- the forward current through the diode will not effect VBIAS

SUPPLYBIAS VRR

RV

32

3

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Example 5:Example 5:

1. Sketch the output voltage waveform as shown in the circuit combining a positive limiter with negative limiter in Figure 5-1.

Figure 5-1

+15V

-15V6V 6V

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Example 5 (cont.):Example 5 (cont.):

2. A student construct the circuit as shown in Figure 5-2. Describe the output voltage waveform on oscilloscope CH2.

Figure 5-2

+20V

-20V

CH2

+15V

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2-4 Diode Limiting & Clamping Circuits 2-4 Diode Limiting & Clamping Circuits (cont.)(cont.) (Diode Clampers) (Diode Clampers)

A diode clamper adds a DC level to an AC voltage. The capacitor charges to the peak of the supply minus the diode drop. Once charged, the capacitor acts like a battery in series with the input voltage. The AC voltage will “ride” along with the DC voltage. The polarity arrangement of the diode determines whether the DC voltage is negative or positive. For negative clamper, the diode is turn around. A negative dc voltage is added to the input voltage to produce the output.

Also known asdc restorers.

For a good clamping actionRC time constant ~ 10 finPositive clamper operation

Negative clamper operation

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2-4 Diode Limiting & Clamping Circuits 2-4 Diode Limiting & Clamping Circuits (cont.)(cont.) (Diode Clampers) (Diode Clampers)

A Clamper Application:

A clamping circuit is often used in TV receivers as a dc restorer.

The incoming composite video signal is normally processed through capacitively coupled amplifiers that eliminate the dc component, thus losing black and white reference levels and the blanking level. Before applied to the picture tube, these reference level must be restored.

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2-5 Voltage Multiplier 2-5 Voltage Multiplier (Introduction)(Introduction)

• Use clamping action to increase peak rectified voltages without necessary to increase input transformer’s voltage rating.• Multiplication factors: two, three or four.• Three types of voltage multipliers:

* Voltage doubler- Half – wave voltage doubler

- Full – wave voltage doubler* Voltage tripler* Voltage Quadrupler

• Voltage multipliers are used in high-voltage, low current applications, i.e TV receivers.

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2-5 Voltage Multiplier (cont.) 2-5 Voltage Multiplier (cont.) (Voltage Doubler)(Voltage Doubler)

Half-wave voltage Doubler:

Clamping action can be used to increase peak rectified voltage. Once C1 and C2 charges to the peak voltage they act like two batteries in series, effectively doubling the voltage output. The current capacity for voltage multipliers is low.

Half-wave voltage doubler operation. Vp is the peak secondary voltage.

By applying Kirchhoff’s Law at (b):

12 CpC VVV ~ approximately 2Vp (neglecting diode drop D2)

PIV = 2Vp

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2-5 Voltage Multiplier (cont.) 2-5 Voltage Multiplier (cont.) (Voltage Doubler)(Voltage Doubler)

Full-wave voltage doubler:

Arrangement of diodes and capacitors takes advantage of both positive and negative peaks to charge the capacitors giving it more current capacity. forward-bias

charges

Secondary voltage positive Secondary voltage negative

forward-bias

outputcharges

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2-5 Voltage Multiplier (cont.) 2-5 Voltage Multiplier (cont.) (Voltage Tripler & Voltage Quadrupler)(Voltage Tripler & Voltage Quadrupler)

Voltage triplersVoltage triplers and and quadruplersquadruplers utilize utilize threethree and and fourfour diode capacitor diode capacitor arrangements, respectively.arrangements, respectively.

Voltage triplerVoltage tripler and and quadrupler quadrupler gives output gives output 3V3Vp p and and 4V4Vpp, respectively., respectively.

Tripler output is taken across Tripler output is taken across CC11 and C and C33, thus , thus VVoutout = 3V = 3Vpp

Quadrupler output is taken across Quadrupler output is taken across CC22 and and CC44 , thus , thus VVoutout = 4V = 4Vpp

PIV for both cases: PIV for both cases: PIV = 2VPIV = 2Vpp

Voltage Triple Voltage Quadruple

4545

• The data sheet for diodes and other devices gives detailed information about specific characteristics such as the various maximum current and voltage ratings, temperature range, and voltage versus current curves (V-I characteristic).

• It is sometimes a very valuable piece of information, even for a technician. There are cases when you might have to select a replacement diode when the type of diode needed may no longer be available.

• These are the absolute max. values under which the diode can be operated without damage to the device.

2-6 The Diode Data Sheet 2-6 The Diode Data Sheet (Introduction)(Introduction)

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2-6 The Diode Data Sheet (cont.) 2-6 The Diode Data Sheet (cont.) (Maximum Rating) (Maximum Rating)

RatingRating SymbolSymbol 1N40011N4001 1N40021N4002 1N40031N4003 UNITUNIT

Peak repetitive reverse voltagePeak repetitive reverse voltage

Working peak reverse voltageWorking peak reverse voltage

DC blocking voltageDC blocking voltage

VVRRMRRM

VVRWMRWM

VVRR

5050 100100 200200 VV

Nonrepetitive peak reverse Nonrepetitive peak reverse voltagevoltage

VVRSMRSM 6060 120120 240240 VV

rms reverse voltagerms reverse voltage VVR(rms)R(rms) 3535 7070 140140 VV

Average rectified forward Average rectified forward current (single-phase, resistive current (single-phase, resistive load, 60Hz, Tload, 60Hz, TAA = 75 = 75ooCC

IIoo

11

AA

Nonrepetitive peak surge Nonrepetitive peak surge current (surge applied at rated current (surge applied at rated load conditions)load conditions)

IIFSMFSM

30 (for 1 30 (for 1 cycle)cycle)

AA

Operating and storage junction Operating and storage junction temperature rangetemperature range

TTjj, T, Tstgstg -65 to -65 to +175+175

ooCC

4747

FIGURE 2-56FIGURE 2-56 A selection of rectifier diodes based on maximum ratings of I A selection of rectifier diodes based on maximum ratings of IOO, I, IFSMFSM, ,

and Iand IRRMRRM..

2-6 The Diode Data Sheet (cont.) 2-6 The Diode Data Sheet (cont.) (Maximum Rating)(Maximum Rating)

4848

2-7 Troubleshooting2-7 Troubleshooting(introduction)(introduction)

Objective: Objective:

Troubleshoot diode circuits using accepted techniques.Troubleshoot diode circuits using accepted techniques. Discuss the relationship between symptom & cause, power check, Discuss the relationship between symptom & cause, power check,

sensory check, component replacement method and discuss the sensory check, component replacement method and discuss the signal tracing technique in the three variations.signal tracing technique in the three variations.

Fault analysis.Fault analysis.

Our study of these devices and how they work leads more effective troubleshooting. Efficient troubleshooting requires us to take logical steps in sequence. Knowing how a device, circuit, or system works when operating properly must be known before any attempts are made to troubleshoot. The symptoms shown by a defective device often point directly to the point of failure. There are many different methods for troubleshooting. We will discuss a few.

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2-7 Troubleshooting (cont.)2-7 Troubleshooting (cont.)(Troubleshooting Techniques)(Troubleshooting Techniques)

Here are some helpful troubleshooting techniques:

Power Check: Sometimes the obvious eludes the most proficient troubleshooters. Check for fuses blown, power cords plugged in, and correct battery placement.

Sensory Check: What you see or smell may lead you directly to the failure or to a symptom of a failure.

Component Replacement: Educated guesswork in replacing components is sometimes effective.

Signal Tracing: Look at the point in the circuit or system where you first lose the signal or incorrect signal.

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2-7 Troubleshooting (cont.)2-7 Troubleshooting (cont.)(Troubleshooting Techniques)(Troubleshooting Techniques)

Signal tracing techniques:

Input to output

Output to input

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2-7 Troubleshooting (cont.)2-7 Troubleshooting (cont.)(Fault Analysis)(Fault Analysis)

Can be applied when you measure an incorrect voltage at a test point using signal tracing and isolate the fault to a specific circuit.Example 1:

Effect of an Open Diode in a Half-Wave Rectifier:

- Zero o/p voltage- Open diode breaks the current path from transformer secondary winding to thefilter and load resistor – no load current.Other faults: open transformer winding, open fuse, or no input voltage.

5252


Example 2:

Effect of an Open Diode in a Full-Wave Rectifier:

-The effect of either of two diodes is open diode, the o/p voltage will have large than normal ripple voltage at 60 Hz rather than at 120 Hz.

- Another fault – open in one of the halves of the transformer secondary winding.- Open diode give same symptom to bridge full-wave rectifier. (See Figure 2-63)

5353


Example 3:

Effect of a Shorted Diode in a Full-Wave Rectifier:

Fuse should blow – cause by short circuit

D1,D4 will probably burn open.

5454


Example 4:

Effect of a fault filter capacitor:

Open – o/p is full-wave rectified voltage

Shorted – the o/p is 0V

Leaky – increase the ripple voltage on the o/p

Example 5:

Effect of a Faulty Transformer:

Open primary/secondary winding of a

transformer – 0V o/p

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2-7 Troubleshooting (cont.)2-7 Troubleshooting (cont.) (The complete Troubleshooting Process) (The complete Troubleshooting Process)

The complete troubleshooting process:The complete troubleshooting process:

(i) Identify the symptom(s).(i) Identify the symptom(s).

(ii) Perform a power check(ii) Perform a power check

(iii) Perform a sensory check(iii) Perform a sensory check

(iv) Apply a signal tracing technique.(iv) Apply a signal tracing technique.

(v) Apply fault analysis(v) Apply fault analysis

(vi) Use component replacement to fix the problem.(vi) Use component replacement to fix the problem.

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The basic function of a power supply to give us a smooth ripple free DC voltage from an AC voltage.

Half-wave rectifiers only utilize half of the cycle to produce a DC voltage.

Transformer Coupling allows voltage manipulation through its windings ratio

Full-Wave rectifiers efficiently make use of the whole cycle. This makes it easier to filter.

The full-wave bridge rectifier allows use of the full secondary winding output whereas the center-tapped full wave uses only half.

Filtering and Regulating the output of a rectifier helps keep the DC voltage smooth and accurate

SummarySummary

5757

Limiters are used to set the output peak(s) to a given value.

Clampers are used to add a DC voltage to an AC voltage.

Voltage Multipliers allow a doubling, tripling, or quadrupling of rectified DC voltage for low current applications.

The Data Sheet gives us useful information and characteristics of device for use in replacement or designing circuits.

Troubleshooting requires use of common sense along with proper troubleshooting techniques to effectively determine the point of failure in a defective circuit or system.

SummarySummary

5858

Solution 2:

The peak output voltage for the circuit is:Vp(out) = Vp(in) – 0.7V = 5 – 0.7 = 4.30 V

5959

Solution 3:

Vp(pri) = Vp(in) = 156 V

The peak secondary voltage is:

Vp(sec) = nVp(pri) = 0.5 (156 V) = 78 V

The rectified peak output voltage is:

Vp(out) = Vp(sec) – 0.7V = 78 – 0.7 = 77.3 Vwhere Vp(sec) is the input to the rectifier.

6060

Solution 5:1.

+6.7V

-6.7V

6161

Solution 5 (cont.):2.

V

VVRR

RV SUPPLYBIAS

31.10

15220100

220

32

3

+10.31V

-10.31V

1 CHAPTER 2 Diode Applications By: Syahrul Ashikin Azmi School of Electrical System Engineering.

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