Docsity
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Electronics Overview: Lecture 8 - Basic Circuits, Power Supplies, Diodes, and Impedances, Slides of Electrical Engineering

Jaypee University of Engineering & TechnologyElectrical Engineering

A lecture note from docsity.com, dated 02/12/2008, covering the topic of electronics overview. The lecture discusses the basics of circuits, power supplies, diodes, and impedances. It explains ohm's law, power, resistors and inductors in series and parallel, voltage dividers, real batteries and their output impedance, diodes, leds, getting dc from ac, smoothing out the bumps, zener regulators, voltage regulator ics, and transistors. It also touches upon impedance phasor diagrams, transmission line models, and typical transmission lines.

Typology: Slides

2012/2013

Uploaded on 07/24/2013

bulla.baba
bulla.baba 🇮🇳

5

(7)

87 documents

1 / 9

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Electronics Overview 02/12/2008
Lecture 8 1
ElectronicsOverview
BasicCircuits,PowerSupplies,
Transistors,CableImpedance
diode bridge
BasicCircuitAnalysis
•Whatwewon’tdo:
–commonelectronics‐classthings:RLC,filters,
detailedanalysis
•Whatwewilldo:
–setoutbasicrelations
–lookatafewexamplesoffundamental
importance(mostlyresistivecircuits)
–lookatdiodes,voltageregulation,transistors
–discussimpedances(cable,output,etc.)
TheBasicRelations
•Visvoltage(volts:V);Iiscurrent(amps:A);Ris
resistance(ohms:);Ciscapacitance(farads:F);
Lisinductance(henrys:H)
•Ohm’sLaw:V=IR;V=;V=L(dI/dt)
•Power:P=IV=V2/R=I2R
•Resistorsandinductorsinseriesadd
•Capacitorsinparalleladd
•Resistorsandinductorsinparallel,andcapacitors
inseriesaddaccordingto:
1
C
Idt

1
Xtot
1
X1
1
X2
1
X3
Example:Voltagedivider
•Voltagedividersareaclassicwaytoseta
voltage
•Works ontheprinciplethatallcharge
flowingthroughthefirstresistorgoes
throughthesecond
–soVR‐value
–providedanyloadatoutputisnegligible:
otherwisesomecurrentgoestheretoo
•SoVout=V(R2/(R1+R2))
•R2hereisavariableresis tor,or
potentiometer,or“pot”
–typicallythreeterminals:R12isfixed,tap
slidesalongtovaryR13andR23,though
R13+R23=R12always
1
2
3
R1
R2
V Vout
Docsity.com
pf3
pf4
pf5
pf8
pf9

Partial preview of the text

Download Electronics Overview: Lecture 8 - Basic Circuits, Power Supplies, Diodes, and Impedances and more Slides Electrical Engineering in PDF only on Docsity!

Electronics

Overview

Basic

Circuits,

Power

Supplies,

Transistors,

Cable

Impedance

diode bridge

Basic

Circuit

Analysis

What

we

won’t

do:

common

electronics

class

things:

RLC,

filters,

detailed

analysis

What

we

will

do:

set

out

basic

relations

look

at

a

few

examples

of

fundamental

importance

(mostly

resistive

circuits)

look

at

diodes,

voltage

regulation,

transistors

discuss

impedances

(cable,

output,

etc.)

The

Basic

Relations

V

is

voltage

(volts:

V);

I

is

current

(amps:

A);

R

is

resistance

(ohms:

C

is

capacitance

(farads:

F);

L

is

inductance

(henrys:

H)

Ohm’s

Law:

V

IR

V

V

L

dI

dt

Power:

P

IV

V

R

I

R

Resistors

and

inductors

in

series

add

Capacitors

in

parallel

add

Resistors

and

inductors

in

parallel,

and

capacitors

in

series

add

according

1 C to:

Idt

X

tot

X

1

X

2

X

3

Example:

Voltage

divider

Voltage

dividers

are

a

classic

way

to

set

a

voltage

Works

on

the

principle

that

all

charge

flowing

through

the

first

resistor

goes

through

the

second

so

V

R

value

provided

any

load

at

output

is

negligible:

otherwise

some

current

goes

there

too

So

V

out

V

R

2

R

1

R

2

R

2

here

is

a

variable

resistor,

or

potentiometer

or

“pot”

typically

three

terminals:

R

12

is

fixed,

tap

slides

along

to

vary

R

13

and

R

23

though

R

13

R

23

R

12

always

1 2

3

R

1

R

2

V

V

out

Docsity.com

Real

Batteries:

Output

Impedance

A

power

supply

(battery)

is

characterized

by

a

voltage

V

and

an

output

impedance

R

sometimes

called

source

impedance

Hooking

up

to

load:

R

load

we

form

a

voltage

divider,

so

that

the

voltage

applied

by

the

battery

terminal

is

actually

V

out

V

R

load

R

R

load

thus

the

smaller

R

is,

the

“stiffer”

the

power

supply

when

V

out

sags

with

higher

load

current,

we

call

this

“droop”

Example:

If

V

power

supply

droops

by

V)

when

loaded

to

Amp

load):

internal

resistance

is

called

output

impedance

or

source

impedance

may

vary

with

load,

though

(not

a

real

resistor)

V

R

D-cell example: 6Aout of 1.5 V batteryindicates 0.

output

impedance

Power

Supplies

and

Regulation

A

power

supply

typically

starts

with

a

transformer

to

knock

down

the

V

peak

to

peak

V

AC)

to

something

reasonable/manageable

We

will

be

using

a

center

tap

transformer

(A’

B’)

(winding

ratio)

(A

B)

when

A

B,

so

is

A’

B’

geometry

of

center

tap

(CT)

guarantees

it

is

midway

between

A’

and

B’

(frequently

tie

this

to

ground

so

that

A’

B’)

note

that

secondary

side

floats:

no

ground

reference

built

in

A B

A’ CT B’

AC input

AC output

Diodes

Diodes

are

essentially

one

way

current

gates

Symbolized

by:

Current

vs.

voltage

graphs:

V

I

V

I

V

I

V

I

0.6 V

plain resistor

diode

idealized diode

WAY idealized diode

no current flows

current flows

the direction thearrow points in thediode symbol is thedirection that current will

flow

acts just like a wire(will support arbitrarycurrent) provided thatvoltage is positive

Diode

Makeup

Diodes

are

made

of

semiconductors

(usually

silicon)

Essentially

a

stack

of

p

doped

and

n

doped

silicon

to

form

a

p

n

junction

doping

means

deliberate

impurities

that

contribute

extra

electrons

n

doped)

or

“holes”

for

electrons

p

doped)

Transistors

are

n

p

n

or

p

n

p

arrangements

of

semiconductors

p

-type

n

-type

Docsity.com

Smoothing

out

the

Bumps

Still

a

bumpy

ride,

but

we

can

smooth

this

out

with

a

capacitor

capacitors

have

capacity

for

storing

charge

acts

like

a

reservoir

to

supply

current

during

low

spots

voltage

regulator

smoothes

out

remaining

ripple

A C

B

D

AC source

load capacitor

How

smooth

is

smooth?

An

RC

circuit

has

a

time

constant

RC

because

dV

dt

I

C

and

I

V

R

dV

dt

V

RC

so

V

is

V

exp(

t

Any

exponential

function

starts

out

with

slope

Amplitude/

So

if

you

want

ripple

over

Hz

ms)

timescale…

must

have

RC

ms

if

R

C

F

R

C

V

Regulating

the

Voltage

The

unregulated,

ripply

voltage

may

not

be

at

the

value

you

want

depends

on

transformer,

etc.

suppose

you

want

V

You

could

use

a

voltage

divider

to

set

the

voltage

But

it

would

droop

under

load

output

impedance

R

R

need

to

have

very

small

R

R

to

make

“stiff”

the

divider

will

draw

a

lot

of

current

perhaps

straining

the

source

p

ower

expended

in

divider

p

ower

in

load

1 2

3

R

1

R

2

V

in

V

out

R

load

The

Zener

Regulator

Zener

diodes

break

down

at

some

reverse

voltage

can

buy

at

specific

breakdown

voltages

as

long

as

some

current

goes

through

zener,

it’ll

work

good

for

rough

regulation

Conditions

for

working:

let’s

maintain

some

minimal

current,

I

z

through

zener

(say

a

few

mA)

then

V

in

V

out

R

1

I

z

V

out

R

load

sets

the

requirement

on

R

1

because

presumably

all

else

is

known

if

load

current

increases

too

much,

zener

shuts

off

(node

drops

below

breakdown)

and

you

just

have

a

voltage

divider

with

the

load

R

1

Z

V

in

V

out

V

z

R

load

zener voltage

high slope is what makes thezener a decent voltage regulator

Docsity.com

Voltage

Regulator

IC

Can

trim

down

ripply

voltage

to

precise,

rock

steady

value

Now

things

get

complicated!

We

are

now

in

the

realm

of

integrated

circuits

(ICs)

ICs

are

whole

circuits

in

small

packages

ICs

contain

resistors,

capacitors,

diodes,

transistors,

etc.

note zeners

Voltage

Regulators

The

most

common

voltage

regulators

are

the

LM78XX

voltages)

and

LM79XX

voltages)

XX

represents

the

voltage

is

is

is

etc

typically

needs

input

volts

above

output

(reg.)

voltage

A

versatile

regulator

is

the

LM

or

LM

beware that housing is not always ground

Transistors

Transistors

are

versatile,

highly

non

linear

devices

Two

frequent

modes

of

operation:

amplifiers/buffers

switches

Two

main

flavors:

npn

(more

common)

or

pnp,

describing

doping

structure

Also

many

varieties:

bipolar

junction

transistors

(BJTs)

such

as

npn,

pnp

field

effect

transistors

(FETs):

n

channel

B

C E

B

E C

npn

pnp

BJT

Amplifier

Mode

Central

idea

is

that

when

in

the

right

regime,

the

BJT

collector

emitter

current

is

proportional

to

the

base

current:

namely,

I

ce

I

b

where

(sometimes

h

fe

is

typically

In

this

regime,

the

base

emitter

voltage

is

V

below,

I

b

V

in

R

b

I

ce

I

b

V

in

R

b

so

that

V

out

V

cc

I

ce

R

c

V

cc

V

in

R

c

R

b

ignoring

DC

biases,

wiggles

on

V

in

become

R

c

R

b

bigger

(and

inverted):

thus

amplified

out

R

c

R

b

in

V

cc

B

C E

Docsity.com

Switcher

topologies

from: http://www.maxim-ic.com/appnotes.cfm/appnote_number/

The FET switch is turned off or on in a pulse-width-modulation (PWM) scheme,

the duty cycle of which determines the ratio of

V

out

to

V

in

Step

Down

Calculations

If

the

FET

is

on

for

duty

cycle,

D

(fraction

of

time

on),

and

the

period

is

T

the

average

output

voltage

is

V

out

DV

in

the

average

current

through

the

capacitor

is

zero,

the

average

current

through

the

load

(and

inductor)

is

D

times

the

input

current

under

these

idealizations,

power

in

power

out

Step

down

waveforms

Shown

here

is

an

example

of

the

step

down

with

the

FET

duty

cycle

around

The

average

inductor

current

(dashed)

is

the

current

delivered

to

the

load

the

balance

goes

to

the

capacitor

The

ripple

(parabolic

sections)

has

peak

to

peak

fractional

amplitude

of

T

2

D

LC

so

win

by

small

T,

large

L

C

kHz

at

mH,

F

yields

ripple

means

mV

on

V

FET

Inductor Current Supply Current

Capacitor

Current

Output Voltage

(ripple exag.)

Cable

Impedances

RG

cable

is

characterized

as

cable

RG

is

some

antenna

cable

is

Isn’t

the

cable

nearly

zero

resistance?

And

shouldn’t

the

length

come

into

play,

somehow?

There

is

a

distinction

between

resistance

and

impedance

though

same

units

Impedances

can

be

real,

imaginary,

or

Docsity.com

Impedances,

cont.

Note

that:

capacitors

become

less

“resistive”

at

high

frequency

inductors

become

more

“resistive”

at

high

frequency

bigger

capacitors

are

more

transparent

bigger

inductors

are

less

transparent

i

indicates

phase

shift

between

voltage

and

current

after

all,

V

IZ

so

Z

V/I

thus

if

V

is

sine

wave,

I

is

cosine

for

inductor/capacitor

Impedance

Phasor

Diagram

Impedances

can

be

drawn

on

a

complex

plane,

with

pure

resistive,

inductive,

and

capacitive

impedances

represented

by

the

three

cardinal

arrows

An

arbitrary

combination

of

components

may

have

a

complex

impedance,

which

can

be

broken

into

real

and

imaginary

parts

Note

that

a

system’s

impedance

is

frequency

dependent

R

L

Z

Z

r

Z

i

C

real axis

imag. axis

Transmission

Line

Model

The

cable

has

a

finite

capacitance

per

unit

length

property

of

geometry

and

dielectric

separating

conductors

C

l

πε

/ln(

b

a

where

b

and

a

are

radii

of

cylinders

Also

has

an

inductance

per

unit

length

L

l

μ

π

)ln(

b

a

When

a

voltage

is

applied,

capacitors

charge

up

thus

draw

current;

propagates

down

the

line

near

speed

of

light

Question:

what

is

the

ratio

of

voltage

to

current?

because

this

is

the

characteristic

impedance

Answer:

Z

0

sqrt(

L/

C

sqrt(

L

C

π

)sqrt(

μ

ε

)ln(

b

a

note

that

Z

0

is

frequency

independent

C

L

input

output

Typical

Transmission

Lines

RG

coax

is

abundant

pF

per

foot;

nH

per

foot;

v

c

ns/m

RG

is

the

thin

version

same

parameters

as

above,

but

scaled

down

geometry

RG

used

for

video,

cable

TV

pF/ft;

nH

per

foot;

v

c

ns/m i

d

i

Docsity.com