Tài liệu Power Supply Block Diagram ppt

Line Regulationis a measure of the effectiveness of a voltage regulator to maintain the output dc voltage constant despite changes in the supply voltage... Transistor Series Voltage Regu

Power Supply Block Diagram

Half Wave Rectifier Wave Rectifier

7 0 V

0 1

V V

C R

V 0048 0

F L

P r

C R

V 0048

0

V =

F L

t

Full Wave Rectifier Wave Rectifier

7 0 V

707

00417

0 1

C R

V 0024 0

V

F L

P r

C R

V 0024

0

t

Bridge Type Rectifier Type Rectifier

4 1 V

0 1

C R

V 0024 0

V

F L

P r

C R

V 0024

0

t

More Equations

R i th i ti V V + 1 736 V

Rearranging the previous equations: VP = Vdc + 1.736 Vr

The ripple voltage as a percentage of the dc voltage is:

Comparison of Different Types of Rectifiers

 Half-wave rectifier needs only a single diode but ripple is twice those of the other types

 Full-wave rectifier requires a centre-tapped

transformer and its output voltage is about half those of the other types

 Bridge-type rectifier is best overall even though

it requires four diodes because the diode bridge is often available in a single package However, if

a single diode in the bridge is defective, the

whole package has to be replaced

whole package has to be replaced

Line Regulation

is a measure of the effectiveness of a voltage regulator

to maintain the output dc voltage constant despite

changes in the supply voltage

o

V V

mV regulation

= ) /

regulation

Line

Δ

) /

V regulation

Δ

mV regulation

Load

Δ

Δ

= ) /

Δ

o L

o

V

x I

V regulation

%

Δ Δ

=

) (

log 20

)

(

in r

out r

V

V dB

Zener Diode Voltage Regulator

I-V Characteristic

Circuit

IZMZM

Notes on Zener Diode Regulator

 VZ depends on I and temperature

 Zener diodes with rated voltage < 6 V have

negative temperature coefficient; those rated > 6

V have positive temperature coefficient

 In order to maintain a constant V I varies in

 In order to maintain a constant Vo, IZT varies in response to a change of either IL or Vi For

example, when RL increases, IL decreases, then

IZT has to increase to keep the current through Rsconstant Since the voltage drop across Rs is

constant V stays constant

constant, Vo stays constant

Formulae for Zener Regulator Circuit

R establishes the zener bias current I :

Rs establishes the zener bias current, IZT:

Z i

Z i

s

I I

V V

I

V

V R

For fixed Vi, but variable RL:

Z i

Z s Rs

Z L

V V

V R I

V R

−

=

=

min

Z Z

L

Z i

Rs

I I

V I

V R

−

=

=

max

ZM Rs

I (min)

Z s

R i

Z L

i

V R

I V

R

+

= (max).

max

L ZM

I where (max) = +

The output ripple voltage of the zener regulator is:p pp g g

) ( )

(

//

//

in r

Z L

out

R R

R

R

R V

Transistor Series Voltage Regulator

The simple zener regulator

can be markedly improved

by adding a transistor

Since VBE = VZ - VL any

tendency for VL to decrease

or increase will be negated

by an increase or decrease in IE The dc currents for thecircuit are: V V −V V −V

circuit are:

R

V

V I

R

V V

L

L L

Transistor Shunt Voltage Regulator

i BE

Z

I

V V

V

S

BE Z

i Rs

L

BE Z

L

L L

R

)

( I

; R

R

I = I - I = h I

IE IRs - IL hFEIZT

Notes on Op

Notes on Op Amp Voltage Regulator Amp Voltage Regulator

 More flexibility possible in design of voltage

output than IC voltage regulator packages

h i l i i l

 The essential circuit elements are: a zener

reference, a pass or shunt transistor, a sensing

circuit, and an error/amplifier circuit

 Equation indicates that Vo depends on R2, R3,

and VZ

 The shunt configuration is less efficient but R2

offers short-circuit current limiting

Constant Current Limiting

can be used for short-circuit or overload protection ofthe series voltage regulator

Output current

is limited to:

4 (max)

7.0

R

Fold back Current Limiting back Current Limiting

is a better method of short-circuit protection

L B

BE V V R V I R V

V BE2 = B2 − o = 6 (V o + I L R4) −V o

R R

V V

2 2

Design Equations for Fold

Design Equations for Fold back Current Limitingback Current Limiting

Maximum load current without fold-back limiting:g

6 5

5 (max)

)(

7.0

R R

R R

(7

L

L o

R R R

R

R R

R V

5 6

4

6

(7

0'

−

+

=

The short circuit current (i e when V = 0) is:

The short circuit current (i.e when Vo = 0) is:

6

(7.0

R R

short

(i.e constant) only after

RL > a certain critical value.

 For designing purpose

I  For designing purpose,

7 0 (

07 o

I V

I

V R

− +

=

(max)

7 0 )

7 0

I + −

Transistor Current Regulators

are designed to maintain a fixed current through ag g

load for variations in either Vi or RL

For the BJT circuit V = V V

For the BJT circuit, VEB = VZ - VRE.Any tendency for IL to change willcause an opposing change in Vpp g g EBEB,,thus nullifying the perturbation

For the JFET circuit, IL = ID = IDSS aslong as VL < VSS - VP

IC Voltage Regulators

 There are basically two kinds of IC voltage

regulators:

Š Multipin type, e.g LM723C

Š 3-pin type, e.g 78/79XX

 Multipin regulators are less popular but they

provide the greatest flexibility and produce the highest quality voltage regulation

 3-pin types make regulator circuit design simple

Multipin IC Voltage Regulator

 The LM723 has an equivalent circuit that contains most of the

contains most of the parts of the op-amp voltage regulator discussed earlier.

 It has an internal voltage reference, error

amplifier pass transistor

LM 723C S h i

amplifier, pass transistor, and current limiter all in one IC package.

LM 723C Schematic

Notes on LM723 Voltage Regulator

 Can be either 14-pin DIP or 10-pin TO-100 can

 May be used for either +ve or -ve, variable or

fi d l d l

fixed regulated voltage output

 Using the internal reference (7.15 V), it can

operate as a high voltage regulator with output

operate as a high-voltage regulator with output from 7.15 V to about 37 V, or as a low-voltage regulator from 2 V to 7.15 V

 Max output current with heat sink is 150 mA

 Dropout voltage is 3 V (i.e VCC > Vo(max) + 3)

R R

Choose R1 + R2 10 kΩ,and Cc = 100 pF

To make Vo variable,

pcurrent sensing added o

,replace R with a pot

LM723 in Low

LM723 in Low Voltage Configuration Voltage Configuration

5 4

4 V 0 7 ( R R )

R

sens 5

5 4

o 4 (max)

L

R R

)

(

) R R

( 7

sens 5

5 4

short

R R

) R R

( 7

0

=

V 7 0

With external pass transistor

(max) L o

short

o sens

I 7 0 )

7 0 V

( I

V 7

0 R

− +

=

Under foldback condition:

With external pass transistor

and foldback current limiting

5 4

L o

R R R

R

) R R

( R 7

0 '

Three Terminal Fixed Voltage Regulators Terminal Fixed Voltage Regulators

 Less flexible, but simple to use

 Come in standard TO-3 (20 W) or TO-220 (15

W) transistor packages

 78/79XX series regulators are commonly

available with 5 6 8 12 15 18 or 24 V output

 Max output current with heat sink is 1 A

 Built-in thermal shutdown protection

 Built-in thermal shutdown protection

 3-V dropout voltage; max input of 37 V

 Regulators with lower dropout higher in/output

 Regulators with lower dropout, higher in/output, and better regulation are available

Basic Circuits With 78/79XX Regulators

 Both the 78XX and 79XX regulators can be used to

provide +ve or -ve output voltages

 C1 and C2 are generally optional C1 is used to cancel any inductance present, and C2 improves the transient

response If used, they should preferably be either 1 μF y y μ tantalum type or 0.1 μF mica type capacitors.

Dual Polarity Output with 78/79XX RegulatorsPolarity Output with 78/79XX Regulators

78XX Regulator with Pass Transistor

 Q1 starts to conduct when VR2 = 0.7 V.

 R2 is typically chosen so

 R2 is typically chosen so that max IR2 is 0.1 A.

7 0

I

R =

2 2

7 0

R

I

R =

; max V is only 1.4 V.

78XX Floating Regulator

 It is used to obtain an output > the Vreg value

2 1

R

I R

V V

=

1

1 2

) (

R I

V

V V

R R

Q reg

reg o

3 Terminal Variable Regulator Terminal Variable Regulator

 The floating regulator could be made into a

variable regulator by replacing R2 with a pot

However there are several disadvantages:

Š Minimum output voltage is Vreg instead of 0 V.

Š I is relatively large and varies from chip to chip

Š IQ is relatively large and varies from chip to chip.

Š Power dissipation in R2 can in some cases be quite

large resulting in bulky and expensive equipment.

 A variety of 3-terminal variable regulators are

available, e.g LM317 (for +ve output) or LM

337 (for ve output)

337 (for -ve output)

Basic LM317 Variable Regulator Circuits

Circuit with capacitors

Notes on Basic LM317 Circuits

 The function of C1 and C2 is similar to those used

in the 78/79XX fixed regulators

i d i i l j i

 C3 is used to improve ripple rejection

 Protective diodes in circuit (b) are required for

high current/high voltage applications

high-current/high-voltage applications

2

R

I R

V V

V o ref ref adj ⎟⎟

=

where Vref = 1.25 V, and Iadj is the current flowing into the adj.

2 1

) (V V

V + is typically 10 mA.

Other LM317 Regulator Circuits

Circuit with pass transistor Circuit to give 0V min and current limiting output voltage

Block Diagram of Switch

Block Diagram of Switch Mode Regulator Mode Regulator

It converts an unregulated dc input to a regulated dcoutput Switching regulators are often referred to asp g g

Comparing Switch

Comparing Switch Mode to Linear RegulatorsMode to Linear Regulators

Advantages:

Š 70-90% efficiency (about double that of linear ones)

Š can make output voltage > input voltage, if desired

Š can invert the input voltage

id bl i ht d i d ti i ll t

Š considerable weight and size reductions, especially at high output power

Disadvantages:

Š More complex circuitry

Š Potential EMI problems unless good shielding, loss ferrite cores and chokes are used

low-General Notes on Switch

General Notes on Switch Mode Regulator Mode Regulator

The duty cycle of the series transistor (power switch) determines y y (p ) the average dc output of the regulator A circuit to control the duty cycle is the pulse-width modulator shown below:

General Notes cont’d

 The error amplifier compares a sample of the regulator

Vo to an internal Vref The difference or error voltage is amplified and applied to a modulator where it is

amplified and applied to a modulator where it is

compared to a triangle waveform The result is an output pulse whose width is proportional to the error voltage.

 Darlington transistors and TMOS FETs with f of at least

 Darlington transistors and TMOS FETs with fT of at least

4 MHz are often used TMOS FETs are more efficient.

 A fast-recovery rectifier, or a Schottky barrier diode

(sometimes referred to as a catch diode) is used to direct current into the inductor.

 For proper switch-mode operation, current must always

be present in the inductor.

Step Down or Buck Converter Down or Buck Converter

 When the transistor is turned ON, VL is initially high but falls exponentially while IL increases to charge C.

 When the transistor turns OFF, VL reverses in polarity to maintain the direction of current flow IL decreases but its path is now through the forward-biased diode, D.

Duty cycle is adjusted according to the level of V

V & I Waveforms for Buck Regulator

Equations for Buck Regulator

t t

V

T

t t

t

t V

off on

Selecting IL = 0.4Io where Io

is the max dc output current:

V V

V ( ) 5

osc i

o

o i

o

f V I

V V

osc rms

o

osc pp

o

f V

I or

f V

I C

Δ Δ

where V is the ripple voltage

Notes on Operation of Buck Regulator

 When IL = 0.4Io was selected, the average

minimum current, Imin, that must be maintained

in L for proper regulator operation is 0 2Io

 If IL is chosen to be 4% instead of 40% of Io, the 2.5 factor in the equation for L becomes 25

the 2.5 factor in the equation for L becomes 25 and Imin becomes 0.02Io

 L and C are both proportional to 1/fosc; hence, the higher fosc is the smaller L and C become But

for predictable operation and less audible noise,

f is usually between 50kHz to 100 kHz

fosc is usually between 50kHz to 100 kHz

Step Up, Flyback, or Boost Regulator Up, Flyback, or Boost Regulator

 Assuming steady-state conditions, when the transistor is turned ON, L reacts against Vin D is reverse-biased and

C li th l d t

C supplies the load current.

 When the transistor is OFF, VL reverses polarity causing current to flow through D and charges C Note that Vout

is > V because V adds on to V

Equations for Boost Regulator

t V

V

T

t V

i

f V I

V V

V

2

) (

5

=

Assuming IL = 0.4Io:

osc o

oV f I

I V V

I V

V − ) 0 3536 ( − ) (

rms o

osc

o i

o pp

o osc

o i

o

V V

f

I V

V or

V V

f

I V

V C

Δ Δ

= ( ) 0 . 3536 ( )

Voltage Inverting or BuckInverting or Buck Boost RegulatorBoost Regulator

 Vo can be either step-up or step-down and its polarity is opposite to input.

 During ON period, Vin is across L, and D is

reverse-biased.

 During OFF period, VL reverses polarity causing current

 During OFF period, VL reverses polarity causing current

to flow through C and D.

Equations for Buck

Equations for Buck Boost Regulator Boost Regulator

V

T

t V

V

V on

o i

o =+

For IL = 0.4Io:

o i

f V V

I

V

V L

) (

5

2 +

=

osc i

o

o V V f

V I V

I

osc o

i rms

o o osc

o i

pp

o o

f V

V V

V

I or

f V

V V

V

I C

) (

3536

0 )

Δ

=

Basic Push

Basic Push Pull Power Converter Pull Power Converter

Operates as a class D power amplifier Output rectifier converts the sq are a e to dc Each transistor m st ithstand 2 V pl s the square-wave to dc Each transistor must withstand 2xVin plus

Basic Half

Basic Half Bridge Power Converter Bridge Power Converter

Each transistor “sees” approx Vin Full flux reversal in the transformer and capacitors across DS prevent voltage spikes.

Basic Full

Basic Full Bridge Power Converter Bridge Power Converter

Either Q1 & Q3 or Q2 & Q4 are turned ON simultaneously Either Q1 & Q3 or Q2 & Q4 are turned ON simultaneously.

Single Package Switch Package Switch Mode Regulator Mode Regulator

 The LH1605 is a 5A step-down switching regulator.

 Voo is adjustable from 3 to 30 V by using a pot for R1.

 In the circuit above, Q1 turns ON when voltage across

Rsens is 0.7 V Q2 then turns ON shorting Vref to ground and driving Vo to zero .

and driving Vo to zero .

Equations for LH1605 Switching Regulator

00125 0

00125

0 5

2

or R

o

f V I

V V

oV f I

o osc

rms

o

f V

or f

V

C

Δ Δ

Basic Push

Basic Push Pull Power Converter Pull Power Converter

Operates as a class D power amplifier Output rectifier converts the sq are a e... class="page_container" data-page="50">

Basic Half

Basic Half Bridge Power Converter Bridge Power Converter

Each transistor “sees” approx Vin... class="page_container" data-page="51">

Basic Full

Basic Full Bridge Power Converter Bridge Power Converter

Either Q1 & Q3 or Q2 & Q4 are turned ON simultaneously