Chapter 10Diodes

Goal

1. Diode Operation

2. Graphical Load-Line Technique.

3. Simple Voltage-Regulator Circuits.

4. Ideal-Diode & Piecewise-Linear Models.

5. Various Rectifier and Wave-shaping Circuits.

6. Small Signal Equivalent Circuits.

Forward

Anode Cathode

iD

+ -vD

Diode Characteristics

Bridge Diode

Array Diode

High Voltage Diode

High Current Diode

Normal Diode (Small Signal)

Various Diodes

Diode Checking

순방향 저항: 0Ω

-+

+-

역방향 저항: ∞Ω

RedBlack Red

Black

Small Signal Diode

Forward Voltage Drop at 10mA : 0.5 - 0.8VBreak Down Voltage : above 50V Near 100V

Note 1. No Ohm’s Law : Resistance : 0 or infinite 2. No Thevenin Circuit due to Nonlinearity

Note : Scale Change!

Shockley Equation

−

= 1exp

T

DsD nV

vIi

qkTVT =

k : Boltzmann’s constant 1.38 × 10–23 J/K q : electrical charge of an electron 1.60 × 10–19 C

mV 26≅TVAt a temperature of 300 K,

: Thermal Volatge

≅

T

DsD nV

vIi exp

+= 1ln

s

DTD I

inVv

at High Voltage

Load-Line Analysis of Diode Circuits

DDSS vRiV +=

)( DD vfi =KVL equation

Shockley equation

??, DD vi

Direct Solution by Mathematical or Numerical MethodSimpler Method with Graphical Method

DDSS vRiV +=

)( DD vfi =

: Solution of Two Equation

Load-Line Analysis

Zener Diodes

Diodes Intended to operate in the breakdown region

0=++ DDSS vRiV

Zener Diode Regulator

- Simple & Economic Device - Vz variation due to Temperature,Vdc,IL- Not adequate for fine controller

Load-Line Analysis of Complex Circuits

0=+= DDTT viRV

Example of Load-Line Analysis of Complex Circuits

Ideal diode : a short circuit for forward currents an open circuit with reverse voltage

Analysis of Ideal-Diode Circuits

1. Assume a state for each diode, either short or open circuit. (For n diodes , 2n possible combinations)

2. Determine the current through the diodes assumed to be on &the voltage across the diodes assumed to be off.

3. Check if consistent with the assumed state for each diode.Current flow in the forward direction for diodes Voltage across the diodes assumed to be off must be positive at the cathode (i.e., reverse bias).

4. If consistent with the assumed states, the analysis is finished.Otherwise, return to step 1 with a different combination

Example of Analysis of Ideal-Diode Circuits

Piecewise-Linear Diode Model

aa viRv +=

=

Simple Piecewise-Linear Diode Model

=

Example of Piecewise-Linear Model

Half Wave Rectifier Circuits

Most important application of Diode

DC Battery Charging Circuits

Current Limiting to Protect Surge Current to Battery

Resistance R

Diode OR Gate

Battery Backup

r

L

VTIC = 2

rmL

VVV −≅

Half Wave Rectifier Circuitswith Smoothing Capacitor

Cycle Diode ON : vs > vLDiode OFF : vs < vL

Full Wave Rectifier

Filtered Power Supply

VA

Single Polarity Power supplier : e.g. +5V , +15V, Adapter

A B

VB

Capacitor Energy Store & DischargeU=½CV2

Simple Application to AC to DC

r

L

VTIC

2=

Dual Polarity Power supplier : e.g. ±5V , ± 15V, Computer Power

Regulated Power supplier

Voltage Regulator

Voltage Multiplied Power Supply

Doubler

=

Tripler Quadrupler

Wave Shaping : Clipping Circuits

Wave form Characteristic Curve

Wave Shaping : Clamping Circuits

Clamping Voltage=5.6V

Clamp the Voltage above specified Valuee.g. CMOS input gate : prevent static charge

1.0k 2.0k

Diode Limiter

Voltage Limit between diode drop

Inductive Load

Signal Rectifier

High Pass Filter Signal RectifierForward Voltage Drop Occurs

Compensation offorward voltage drop

Linear Small-Signal Equivalent Circuits

The small-signal equivalentcircuit for a diode is a resistance.

DQD

DD v

dvdii ∆

≅∆

1−

≅

QD

Dd dv

dir

d

dd r

vi =