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# Chapter : Common Diode Applications, PPT, Semester, Engineering Electronics and Communication Engineering (ECE) Notes | EduRev

## Electronics and Communication Engineering (ECE) : Chapter : Common Diode Applications, PPT, Semester, Engineering Electronics and Communication Engineering (ECE) Notes | EduRev

The document Chapter : Common Diode Applications, PPT, Semester, Engineering Electronics and Communication Engineering (ECE) Notes | EduRev is a part of Electronics and Communication Engineering (ECE) category.
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Common Diode Applications
Basic Power Supply Circuits

Common Diode Applications------------------------------------------------------------------------ Next Slide

Power Supply

A group of circuits used to convert ac to dc.
Rectifier – Converts ac to pulsating dc.
Filter – Reduces variations in the rectifier output.
Voltage regulator – Maintains a constant dc output voltage.

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Transformers

Transformers are described in terms of the relationship between secondary voltage (VS) and primary voltage (VP).
Step-up – VS is greater than VP.
Step-down – VS is less than VP.
Isolation – VS is approximately
equal to VP.

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Transformer Voltage and Current Ratios

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Half-wave Rectifiers

Half-wave rectifier – A diode placed in series between a transformer (or ac line input) and its load.

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Positive Half-wave Rectifiers

This circuit converts an ac input to a series of positive pulses.

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 Average voltage (Vave) – The dc equivalent of a voltage waveform.
 Average current (Iave) – The dc equivalent of a current waveform.

For the output from a half-wave rectifier:

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Negative Half-wave Rectifiers

This circuit converts an ac input to a series of negative pulses.

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Peak Inverse Voltage (PIV)

Peak inverse voltage (PIV) – The maximum diode
reverse bias produced by a given circuit.
For the diode in a half-wave rectifier:

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Full-wave Rectifier

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Full-wave Rectifier Operation

Diodes conduct during alternate half cycles of the input signal.
VL(pk) is approximately half the value of VS(pk).
The circuit produces two positive half-cycles for each input cycle.

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 Average voltage (Vave) – The dc equivalent of a voltage waveform.
 Average current (Iave) – The dc equivalent of a current waveform.

For the output from a full-wave rectifier:

Common Diode Applications------------------------------------------------------------------------ Next Slide

Peak Inverse Voltage (PIV)

 Peak inverse voltage (PIV) – The maximum diode reverse bias produced by a given circuit.

For the diode in a full-wave rectifier:

Common Diode Applications------------------------------------------------------------------------ Next Slide

Negative Full-wave Rectifiers

The negative full-wave rectifier converts an ac input to a series of negative pulses

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Full-Wave Bridge Rectifiers

The most commonly used because:
It does not require the use of a center-tapped transformer.
It can be coupled directly to the ac power line.
It produces a higher dc output than a comparable full-wave center-tapped rectifier.

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Bridge Rectifier Operation

Conduction alternates between two diode pairs.

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Calculating load voltage and current relationships

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Working with Rectifiers

Rectifiers are high current circuits, so IFRB can have a significant impact on diode forward voltage (VF ).
Cooling is often used to minimize the effects of high power rectifier reverse current. Components may be cooled using a fan and/or a heat sink.
High transformer tolerances can introduce significant discrepancies between calculated and measured current and voltage values.

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Integrated Rectifiers

Integrated Rectifier – A rectifier circuit that is etched on a single piece of silicon (housed in a single case). IC rectifiers are:
Cheaper to produce
Easier to troubleshoot
The diodes in an IC rectifier operate at the same temperature, so they have equal values of forward voltage and leakage current.
IC rectifier cases are designed to be attached easily to a heat sink.

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Filters

A filter reduces the voltage and current variations in the output from a rectifier.

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Ripple Voltage (Vr)

Ripple voltage (Vr) – The variation in the filter output voltage.

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The Basic Capacitive Filter

 The capacitor:
 charges through the rectifier diode.

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Surge Current

The high initial current through a power supply.
Surge current lasts only long enough for the filter capacitor to charge.

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Limiting Surge Current

Surge current can be limited by:

Inserting a current limiting resistor between the filter capacitor and the rectifier.
Using a low-value filter capacitor (which shortens the duration of the surge).
Using an inductive filter.

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Filter output voltages

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Filtering and Half-wave Rectifier PIV

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LC Filters

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Voltage Regulators

Voltage regulator – The final circuit in the dc power supply.

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Zener Voltage Regulators

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Zener Reduction of Vr

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A Basic DC Power Supply

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