Voltage Regulator

SEE 3263: ELECTRONIC SYSTEMS LECTURER: CAMALLIL BIN OMAR P05-415 camallil fke.utm.m Tel: 07- 553 553524 5241 1 1

SEE 3263: ELECTRONIC SYSTEMS

Chapter 1: Voltage Regulators

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SEE 3263 VOLTAGE REGULATORS



Power supplies are the most commonly used circuits in electronics.



Virtually every electronic system requires requires the use of a power supply to convert the ac line voltage to the dc ’ operation.



Power supplies range from simple batteries to regulated electronic circuits where an accurate output voltage is automatically maintained. maintained. energy into electrical energy.



Electronic power supplies normally convert 240V, 50Hz ac from a wall outlet into a regulated dc voltage at a level suitable for electronic components. 3

SEE 3263 VOLTAGE REGULATORS 

A basic ower su and a regulator.

l consists of a rectifier a filter



A power supply filter greatly reduces the fluctuations n e ou pu vo vo age o a a -wave or u -wave rectifier and produces a nearly constant-level dc voltage.



Filtering (accomplished using capacitors) is necessary because electronic circuits require a power and biasing for proper operation.





Voltage regulation is usually accomplished with integrated circuit voltage regulators. A voltage regulator prevents changes in the filtered . 4


DIAGRAM

5


TYPES OF POWER SUPPLY 

Linear Power Supply Supply..



Non-Linear Power Supply.

6


LINEAR POWER SUPPLY 

Used power devices that operated at linear/active re re ion. .

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NON--LINEAR NON -LINEAR POWER SUPPLY 

Used power devices that operated at satu sa tura rati tion on an and d cut cutof offf alt alter erna nate tell . .



Also named as switching power supply or switching regulator. 8


using discrete components, integrated . 

Discrete power transistor transistor,, op-amp and comparator were used to complete the circuit.

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

n ea power supp y prov es a constant dc voltage despite changes to e np npu vo age or oa oa con ons.



The output voltage of a real power supply changes under load and is also sensitive to input voltage changes.

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V LTA E RE

LATI N

• 2 basic categories: i Load Re ulation. • Output voltage nearly constant when load chan e. . • Output voltage nearly constant . 11


L AD RE

LATI N

• Load regulation is a measure of how well a

output voltage between no load and full load • For real power supply, output voltage will dro dr o wh when en lo load ad cu curr rren entt inc incre reas ases es..

∞

∞

VO(NL) – out output put volt voltage age with with no no load. VO(FL) – outp output ut voltag voltage e with full full load. IL(FL) – full load load current current (maxi (maximum mum from power supply). 12


• Load regulation can be expressed as a percentage change in load voltage. Load Regulation =

•

V

−V VO ( FL )

×100%

oa regu a on can a so e expresse in terms of percent change in the ou pu per m c ange n oa curren (%/mA).

Vreg

=

⎛ ∆VO ⎞ ⎜⎜ ⎟⎟ V ∆I L

×100% =

⎜ ⎜

VO(NL) − VO(FL) V I L(FL) − I L(NL)

⎟ ⎟

×100% 13


EXAMPLE: A regulated power supply with an output to a 25

load. What is the load regulation?

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VO(FL ) VO(FL )

= IL(FL) × RL = (1A )(25Ω) = 25V

L =⎜ × VO(NL ) = × VO(NL ) ⎟ ⎝ 25 + 1 ⎠ ⎝ RL + RO ⎠

O( NL )

⎛ VO(NL ) − VO(FL ) ⎞ reg

⎝

VO(FL )

⎠

⎛ 26 − 25 ⎞ ⎝ 25 ⎠ 15


LINE RE

LATI N

• Line regulation is a measure of how well a power supp y s a e o ma n a n e c output voltage for a change in the ac input . •

, voltage regulator must maintain a nearly constant output voltages.

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LINE RE

LATI N

• Line regulation can be expressed as:

⎛ ∆VO ⎞ Line Regulation = ⎜⎜ ∆V ⎟⎟ × 100 % ⎝ i • Line regulation can also be expressed in terms of percent change in V O per volt change on the Vi (%/V).

⎛ ∆VO ⎞ ⎜ ⎟ V O ⎠ ⎝ × 100% = ∆ i 17


EXAMPLE: When the input to a particular voltage regulator The nominal output is 15V 15V.. Determine the line regulation in %/V. 0 . 25 V

Line Regulation = 

15 V 5V

× 100 % = 0 .333 % / V

Note : For For ideal ideal volta voltage ge regula regulation tion,, both both categories will give zero percent . 18


-

IN

Z

-

Changes in IL will caused IZ to change in equal & opposite direction

-

When IZ changes, VL will also changes

-

The larger IZ change, the larger VL will change

-

Higher power dissipation in zener

-

Unable to control the changes in current

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EXAMPLE: Determine: (a) IZ(min) and IZ(max) for Zener Zener.. mn

max

(c) Sui Suitab table le power power rat rating ing,, PRS

. for resistor, RS.

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IS

=

i

−

O

RS

Z (min)

= S−

IZ(max)

PDZ(max)

=

− 100

L (max)

= S−

= 60mA V RL(min)

= IS − IL(min) = IS −

PDZ(min)

RS

=

S

=

m

O

= 60mA −

RL(max)

−

12 220

= . m

600

= 40mA

= IZ(min) × VZ = (5.45mA )(12) = 65.4mW = IZ(max) × VZ = ( 40mA )(12) = 480mW ×

S

=

m

×

= . m 21


EXAMPLE: Determine: (a) The bra branch nch cur curren rents ts and and powe powerr diss dissipa ipated ted by . (b) Per Perce centa ntage ge volta voltage ge regu regulat lation ion when when the loa load d RL is open circuit and VO increased to 9.2 V.

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EXERCISE: For the regulator circuit shown below, below, determine the minimum and the maximum load currents. = . = IZK = 1 mA, r Z = 12 Ω, IZM = 70 mA

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SEE 3263 VOLTAGE REGULATORS 

add a series-pass transistor to greatly improve the e c ency an power- an ng capa y as we as to control the changes in output current.

IB

IZ

=

IE (β + 1)

=

IL (β + 1)

= IS -IB = IS − VO

IL

+1

= VZ -VBE 24


EXAMPLE: If = 50, determine: (a) output voltage, VO c current I

(b) d

voltage, VCE1 current I

(b) Vi = VCE + VO CE = i – O =

–

.

=

.

(c) Vi = IS RS + VZ S=

(d)

(a) V = V

–V

=12 – 0.65 = 11.35 V

V

−V RS

IL

=

VO R

IB

=

IE

=

1+ β

20 − 12

=

200

11 . 35 V 1k

=

IL 1+ β

=

= .

= 11 .35 mA 11 .35 mA 51

= 222 .55 µ A

∴ I = I − I = 40 mA − 222 .55 A = 39.78 mA 25


A Darlington Darlington pair transistor (a very high βDC) can be use o ncrease e curren ga n. s w re uce the base current and the zener power rating will be low.

I

=

IE1

=

IL

βDP βDP βDP = β1 + β2 + β1β2 IZ = IS − IB 2 =I −

IL DP

VO

= VZ − 2VBE 26


Design a Darlington series-pass voltage regulator e a o gure s own e ow rom e o ow ng requirements: VDC(in) = 18V, VDC(out) = VE = 12V, IL(max) = 2A.

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REGULATOR CIRCUIT WITH FEEDBACK IL R4

VIN

V2

IB1

R1 - VZ +

Q2 B1

CE2

RL I R3



R2 2

IC2

I4

= VBE 2 + VZ

VBE2 -

V2 -

R2

+ VO -

VO

R1 + R 2

=

R2 1

O

V2 2

⎛ R ⎞ ∴ VO = ⎜⎜1 + 1 ⎟⎟( VBE 2 + VZ ) ⎝ R 2 ⎠

Any change in VO must cause a change in VBE1 to maintain the equality. If V decreases, V must increase since VZ is constant. Similarly if VO increases, VBE1 must decrease.

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IMPLE ERIE V LTA E REGULATOR BLOCK DIAGRAM

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Series Regulators

Control element

V IN

Reference voltage

Error detector

V OUT

Sample circuit

Basic series regulator circuit: Control elem element ent V IN

V OUT Q1

R1

+

V REF

The control element maintains a constant output voltage by varying the collector-emitter voltage acro ac ross ss e ra rans ns s or or..

– D1

rror etector

R

Sample circuit R3

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BASIC OPOP-AMP -AMP SERIES REGULATOR

O

=

⎛ ⎝

R2 ⎞ R 3 ⎠

Z

31


EXAMPLE: For the series regulator circuit shown below: (a)) Wh (a What at is th the e out outpu putt vol volta tage ge? ? , dissipated by Q1? VO

= ⎜1 + 2 ⎟ × VZ ⎝ R3 ⎠ 100kΩ = + × . ⎝ 47kΩ ⎠ = 12.2V

Q1 R1 .

R2 100k +

VIN 18V

Z

P = VI

IL

3.9V

R3 47k

+ RL VO -

= − = 1.16 W 32


2 types of current limiting circuit:

Fold-back Current Limiting



33


LINEAR C RRENT LIMITIN CIRCUIT Q1

IL

+

Vi 20V

Control Circuit

RL

VO 15V -

VO is constant until IL(max) is reached. When IL > IL(max), VO decreases and I will sli htl reater than I . This value of IL will remain constant even when RL is short circuit. 34


CONSTANT CURRENT LIMITING

load current. Q2 will conduct when the current through RSC develops 0.7V across Q2’s VBE. This reduces base current to Q1, limiting the load current..

e curren limit is: 0.7 V L (max) = R SC 35


EXAMPLE:

A series regulator circuit shown above maintain a constant output voltage of 25 V. What is the value of resistor, RSC in order to limit the maximum current, . , max the value of VO when RL = 100 and RL = 10 ? 36


LIMITING CIRCUIT

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During short circuit where VO = 0 V and IL = ISC, PD =(V –V 0)1A= = 20 W (for const constant ant curre current nt i O)ISC = (20 – 0)1A limiting) PD =(V –V 0)0.5A=1 5A=10 0 W (for foldba foldback ck curre current nt i O)ISC = (20 – 0)0. limitin During maximum operation where VO = 15 V and IL = 1 A, PD= (V –V i O)IL= (20 – 15)1 A = 5 W limiting)

(for both curre current nt

During short circuit condition, a regulator with constant cur urre rent nt li lim mit itin in ha has s to di dis ssi ate 20 W of ow owe er in transistor Q1 compared to regulator with foldback current limiting i.e only 10 W.

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Voltage Regulator

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