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Dang Nguyen ChauHo Chi Minh City University of TechnologyEmail: chaudn@hcmut.edu.vn

Diodes

Chapter 2

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What is a Diodes?

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What is a Diodes?

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Diodes Mode of operation

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Terminal Charac. Of Junc. Diodes (1)

The characteristics of curve consists of 3 distinct regions:

The forward-bias region, determined by v > 0

The reserve-bias region, determined byVZK< v < 0

The breakdown region, determined by v < VZK

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Terminal Charac. Of Junc. Diodes (2)

The forward-bias region, determined by v > 0

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Terminal Charac. Of Junc. Diodes (3)

The forward-bias region, determined by v > 0

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Terminal Charac. Of Junc. Diodes (4)

The reserve-bias region, determined byVZK

< v < 0

The breakdown region, determined by v < VZK

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Modeling The Diode Forward Charac.

3 model of diode characteristic:

Ideal diode model

Constant voltage drop model

The exponential model

Small signal model

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Ideal Diodes

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Ideal Diodes (1)

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Ideal Diodes

Example: Assuming the diode to be ideal, find the fraction of each

cycle during which the diode conducts and the peak value of the diode

current.

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Application: The rectifier (1)

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Constant-Voltage-Drop Model (1)

Example: Assuming the diode to constant-drop-voltage. Find the

value of output. Sketch output voltage and input-output voltage

relation.

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Constant-Voltage-Drop Model (2)

Example: Calculate the output voltage and current.

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Exponential Model

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Exponential Model Graphical Analysis

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Exponential Model Graphical Analysis

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Exponential Model Linear Model

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Notation

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Small signal Model

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Small signal Model

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Small signal Model

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Small signal Model

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Small signal Analysis

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Small signal Analysis

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Small signal Analysis

Step 1: Eliminate AC sources, find the DC solution (ID,VD) of the

circuit (use Constant-Voltage-Drop model, unless specified

otherwise).

Step 2: Calculate Small-Signal parameters (rd).

Step 3: Eliminate DC sources, replace the diode with its Small-

Signal equivalent model and find the Small-Signal solution. Verify the

assumptions (vd

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Small signal Analysis

Example:

Find output voltage?

( ) 5 0.2 sinSv t t

2n

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Small signal Analysis

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Small signal Analysis

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Small signal Analysis

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Summary

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Zener Diode

Zener diode is a silicon semiconductor device used especially as a

voltage regulator

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Example: The Zener diode has a constant reverse breakdown voltage

VZ = 8.2 V for 75mA iZ 1A. Find R so that VL= VZ is

maintained at 8.2 V while Vi varies by 10% from its nominal value

of 12 V.

Zener Diode

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Application: Rectifier Circuit

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Application: Rectifier Circuit

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Transformer

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Rectifier Circuit

Basic rectifier converts an AC voltage to a pulsating DC voltage.

A filter then eliminates AC components of the waveform to

produce a nearly constant dc voltage output.

Rectifier circuits are used in virtually all electronic devices to

convert the 120 V - 60 Hz AC power line source to the DC voltages

required for operation of the electronic device.

In rectifier circuits, the diode state changes with time and a given

piecewise linear model is valid only for a certain time interval.

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Rectifier Circuit

Half-wave rectifier

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Rectifier Circuit

Half-wave rectifier

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Rectifier Circuit

Half-wave rectifier

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Rectifier Circuit

Half-wave rectifier

Important parameter for design:

Current-handling capability required of the diode, determined

by the largest current the diode expected to conduct.

Peak inverse voltage (PIV): the maximum inverse voltage that

the diode must be able to withstand without breakdown,

determined by the largest reverse voltage that is expected to

appear across the diode.

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Rectifier Circuit

Full-wave center-tap rectifier

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Rectifier Circuit

Full-wave center-tap rectifier

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Rectifier Circuit

Full-wave center-tap rectifier

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Rectifier Circuit

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Rectifier Circuit

Full-wave bridge rectifier

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R ifi Ci i

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Rectifier Circuit

Full-wave bridge rectifier

Fil

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Filter

R tifi Ci it

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Rectifier Circuit

R tifi Ci it

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Rectifier Circuit

A li ti Cli (li it ) i it

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Application: Clipper (limiter) circuit

A li ti Cli (li it ) i it

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Application: Clipper (limiter) circuit

A li ti Cli (li it ) i it

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Application: Clipper (limiter) circuit

A li ti Cli (li it ) i it

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Application: Clipper (limiter) circuit

Application: Clampers (DC restorers) (Mch kp)

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Application: Clampers (DC restorers) (Mch kp)

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Application: Clampers (DC restorers) (Mch kp)

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Application: Clampers (DC restorers) (Mch kp)

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Application: Voltage multiplier

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Application: Voltage multiplier

Application: Voltage multiplier

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Application: Voltage multiplier