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SEE 3263: SEE 3263: ELECTRONIC SYSTEMSELECTRONIC SYSTEMS

LECTURER:

CAMALLIL BIN OMARP05-415

[email protected]

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@ yTel: 07- 5535241

SEE 3263: ELECTRONIC SYSTEMS

Chapter 1:Chapter 1:Voltage RegulatorsVoltage Regulators

2

SEE 3263 VOLTAGE REGULATORS

1.0 REGULATED POWER SUPPLYREGULATED POWER SUPPLY1.0 REGULATED POWER SUPPLYREGULATED POWER SUPPLYPower supplies are the most commonly used circuits in electronics.Virtually every electronic system requires the use of a power supply to convert the ac line voltage to the dc voltages that are required for the system’s internalvoltages that are required for the system s internal operation.Power supplies range from simple batteries to regulated electronic circuits where an accurate output voltage is automatically maintained.A battery is a dc power supply that converts chemicalA battery is a dc power supply that converts chemical energy into electrical energy.Electronic power supplies normally convert 240V,

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50Hz ac from a wall outlet into a regulated dc voltage at a level suitable for electronic components.


A basic power supply consists of a rectifier, a filter p pp y ,and a regulator.A power supply filter greatly reduces the fluctuations i th t t lt f h lf f llin the output voltage of a half-wave or full-wave rectifier and produces a nearly constant-level dc voltage.Filtering (accomplished using capacitors) is necessary because electronic circuits require a constant source of dc voltage and current to provideconstant source of dc voltage and current to provide power and biasing for proper operation.Voltage regulationVoltage regulation is usually accomplished with integrated circuit voltage regulators.A voltage regulator prevents changes in the filtered dc voltage due to variations in line voltage or load

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dc voltage due to variations in line voltage or load.


DC POWER SUPPLY BLOCKDC POWER SUPPLY BLOCKDC POWER SUPPLY BLOCK DC POWER SUPPLY BLOCK DIAGRAM DIAGRAM

5


TYPES OF POWER SUPPLYTYPES OF POWER SUPPLY

Linear Power Supply.

Non-Linear Power Supply.

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LINEAR POWER SUPPLYLINEAR POWER SUPPLY

Used power devices that operated at linear/active region.ea /act e eg o

Dissipates more powerDissipates more power.

7


NONNON--LINEAR POWER SUPPLYLINEAR POWER SUPPLY

Used power devices that operated at saturation and cutoff alternately.satu at o a d cuto a te ate y

Dissipates less powerDissipates less power.

Also named as switching power supply or switching regulator.

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These power supplies were constructedThese power supplies were constructed using discrete components, integrated circuits or combination of bothcircuits or combination of both.

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

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POWER SUPPLY REGULATIONPOWER SUPPLY REGULATIONPOWER SUPPLY REGULATIONPOWER SUPPLY REGULATION

A id l l idAn ideal power supply provides a constant dc voltage despite changes to th i t lt l d ditithe input voltage or load conditions.

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

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VOLTAGE REGULATIONVOLTAGE REGULATIONVOLTAGE REGULATIONVOLTAGE REGULATION• 2 basic categories:

(i) Load Regulation.( ) g• Output voltage nearly constant

when load change.g

(ii) Line Regulation(ii) Line Regulation.• Output voltage nearly constant

when line voltage change11

when line voltage change.


LOAD REGULATIONLOAD REGULATION•• Load regulationLoad regulation is a measure of how well a

power supply is able to maintain the dc

LOAD REGULATIONLOAD REGULATION

power supply is able to maintain the dc output voltage between no load and full load with the input voltage constant.with the input voltage constant.

• For real power supply, output voltage will drop when load current increases.p

VO(NL) – output voltage with noload.∞ ∞

VO(FL) – output voltage with fullload.

IL(FL) – full load current (maximumcurrent that coming out

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current that coming outfrom power supply).


• Load regulation can be expressed as a gpercentage change in load voltage.

VV )FL(O)NL(O −Load Regulation = %100

VVV

)FL(O

)FL(O)NL(O ×

L d l ti l b d• Load regulation can also be expressed in terms of percent change in the

t t A h i l d toutput per mA change in load current (%/mA).

⎞⎛

%100V

VV

%100VV

V O(FL)

O(FL)O(NL)

O

O⎟⎟⎠

⎞⎜⎜⎝

⎛ −⎟⎟⎠

⎞⎜⎜⎝

⎛ ∆

13

%100II

%100I

VL(NL)L(FL)

O(FL)

L

Oreg ×

−⎠⎝=×

∆⎠⎝=


EXAMPLE:A regulated power supply with an output resistance of 1 Ω deliver a full load current of 1Aresistance of 1 Ω deliver a full load current of 1A to a 25 Ω load. What is the load regulation?

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V25)25)(A1(RIV L)FL(L)FL(O =Ω=×=

25R ⎞⎜⎛⎞

⎜⎛

)NL(O)NL(OOL

L)FL(O V

12525V

RRRV ×

⎠⎞

⎜⎝⎛

+=×⎟

⎠

⎞⎜⎜⎝

⎛+

=

V26V =∴ V26V )NL(O =∴

%4%1002526%100VV

V% )FL(O)NL(O =×⎞⎜⎛ −

=×⎞

⎜⎜⎛ −

=

15

%4%10025

%100V

V%)FL(O

reg =×⎠

⎜⎝

=×⎠

⎜⎜⎝

=


LINE REGULATIONLINE REGULATION•• Line regulationLine regulation is a measure of how well a

l i bl t i t i th d

LINE REGULATIONLINE REGULATION

power supply is able to maintain the dc output voltage for a change in the ac input line voltageline voltage.

• When the dc input (line) voltage changes theWhen the dc input (line) voltage changes, the voltage regulator must maintain a nearly constant output voltages.p g

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LINE REGULATIONLINE REGULATION• Line regulation can be expressed as:

LINE REGULATIONLINE REGULATION

%100VV

i

O ×⎟⎟⎠

⎞⎜⎜⎝

⎛∆∆

Line Regulation =

• Line regulation can also be expressed in f h i V lterms of percent change in VO per volt

change on the Vi (%/V).

%100VV

VO

O

×∆

⎟⎠⎞⎜

⎝⎛∆

Line Regulation =

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Vi∆Line Regulation


EXAMPLE:When the input to a particular voltage regulator decreases by 5V, the output decreases by 0.25V.decreases by 5V, the output decreases by 0.25V. The nominal output is 15V. Determine the line regulation in %/V.

( )V25.0( )V/%333.0%100

V5V15 =×Line Regulation =

Note : For ideal voltage regulation, both categories will give zero percent regulation(0%)

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regulation(0%).


ZENERZENER REGULATORREGULATORZENER ZENER REGULATORREGULATOR

Output voltage constant as long as V > V- Output voltage constant as long as VIN > VZ

- 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

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- Higher power dissipation in zener

- Unable to control the changes in current


EXAMPLE:Determine:(a) IZ(min) and IZ(max) for Zener.(b) PDZ( i ) and PDZ( ) for Zener(b) PDZ(min) and PDZ(max) for Zener. (c) Suitable power rating, PRS for resistor, RS.

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1218VV mA60100

1218IS =−

=−

=S

Oi

RVV

A45512A60VIIII O mA45.512mA60R

VIIII(min)L

OS(max)LS(min)Z =−=−=−=

220

12V mA4012mA60R

VIIII(max)L

OS(min)LS(max)Z =−=−=−=

600

mW4.65)12)(mA45.5(VIP Z(min)Z(min)DZ ==×=

mW480)12)(mA40(VIP Z(max)Z(max)DZ ==×=

mW360100)mA60(R)I(P 22

21

mW36.0100)mA60(R)I(P 2S

2SRS =×=×=


EXAMPLE:Determine:(a) The branch currents and power dissipated by

circuit devicescircuit devices.(b) Percentage voltage regulation when the load RL

is open circuit and VO increased to 9.2 V.

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EXERCISE:For the regulator circuit shown below, determine the minimum and the maximum load currents.Given: VZ = 5 1 V at IZT = 35 mAGiven: VZ = 5.1 V at IZT = 35 mA

IZK = 1 mA, rZ = 12 Ω, IZM = 70 mA

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add a series-pass transistor to greatly improve the ffi i d h dli bilit llefficiency and power-handling capability as well as

to control the changes in output current.

)1(βI

)1(βII LE

B +=

+=

)1(βII-III L

SBSZ +−==

)1(β +

BEZO -VVV =

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EXAMPLE:If β = 50, determine:(a) output voltage, VO (b) voltage, VCE1 (c) current, IS (d) current, IZ( ) , S ( ) , Z

(b) Vi = VCE + VOVCE = Vi – VO = 20 –11 35 = 8 65 VVCE Vi VO 20 11.35 8.65 V

(c) Vi = IS RS + VZ

I 0 04 AZi VV − 1220 −IS = = = 0.04 A

(d)S

Zi

R 200

mA35.11k1

V35.11RVI

L

OL ===

A55.222mA40III

A55.22251

mA35.111

I1

II

k1R

BSZ

LEB

L

µ−=−=∴

µ==β+

=β+

=

(a) VO = VZ – VBE =12 – 0.65 = 11.35 V

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= 39.78 mABSZ µ( ) O Z BE


A Darlington pair transistor (a very high βDC) can be d t i th t i Thi ill dused to increase the current gain. This will reduce

the base current and the zener power rating will be low.

L1E2B

IIIβ

=β

=

2121DP

DPDP2B

IIIββ+β+β=β

ββ

LS

2BSZ

II

III

β−=

−=

BEZO

DPS

V2VV −=β

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Design a Darlington series-pass voltage regulator lik th t f fi h b l f th f ll ilike that of figure shown below from the following requirements: VDC(in) = 18V, VDC(out) = VE = 12V, IL(max) = 2A.

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REGULATOR CIRCUIT WITH REGULATOR CIRCUIT WITH FEEDBACKFEEDBACK

Q1Q1

R4

R1

IL

IB1

VRV

VVV

2

Z2BE2

=

+=

Q2 RL

I4

IB2

IC2

+ +

- VZ +

V = V

VIN +VO-

VRR

RV

VRR

V

221

2O

O21

2

+=

+=

R3R2

B2 +VBE2

-

+V2-

VB1 = VCE2

)VV(RR1V

RR

Z2BE2

1O

21

+⎟⎟⎠

⎞⎜⎜⎝

⎛+=∴

+

Any change in VO must cause a change in VBE1 to maintain the equality. If VO decreases, VBE1 must

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q y O BE1increase since VZ is constant. Similarly if VOincreases, VBE1 must decrease.


SIMPLE SERIES VOLTAGESIMPLE SERIES VOLTAGESIMPLE SERIES VOLTAGE SIMPLE SERIES VOLTAGE REGULATOR BLOCK DIAGRAMREGULATOR BLOCK DIAGRAM

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Series Regulators

Series Regulator block diagram:Series Regulator block diagram:

VIN VOUTControlelement

Basic series regulator circuit:Errordetector

Samplecircuit

Referencevoltage

VIN VOUT

Control element

R1Q1

VREF+

– E d t t R2The control element

D1Error detector 2

R3

Samplecircuit

maintains a constant output voltage by varying the collector-emitter voltageacross the transistor

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across the transistor.


BASIC OPBASIC OP--AMP SERIES AMP SERIES REGULATORREGULATOR

Z2

O VR1V ×⎞

⎜⎜⎛+=

31

Z3

O VR

1V ×⎠

⎜⎜⎝+


EXAMPLE:For the series regulator circuit shown below:(a) What is the output voltage?(b) If the load current is 200mA what is the power

R ⎞⎜⎛

(b) If the load current is 200mA, what is the power dissipated by Q1?

Q1

R14 7k

IL

R2

V93k1001

VRR1V Z

3

2O

⎞⎜⎛ Ω

×⎟⎠

⎞⎜⎜⎝

⎛+=

+

-

4.7k

RL

V

VIN18V

+ VO

-

100k

R3V2.12

V9.3k47k1001

=

×⎠⎞

⎜⎝⎛

ΩΩ

+=

VZ 3.9V

347k

( ) )A2.0(V2.12V18VIP

−==

32

( )W16.1

)A2.0(V2.12V18=


PROTECTION CIRCUITPROTECTION CIRCUITPROTECTION CIRCUITPROTECTION CIRCUIT

2 types of current limiting circuit:

Linear/Constant Current LimitingLinear/Constant Current Limiting

Fold-back Current Limiting

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LINEAR CURRENT LIMITINGLINEAR CURRENT LIMITINGLINEAR CURRENT LIMITING LINEAR CURRENT LIMITING CIRCUITCIRCUIT

I LQ

1

15VControlCircuit

RL

+

-

20VVOV i

VO is constant until IL(max) is reached. When IL > IL(max), VOdecreases and IL will slightly greater than IL(max). This value

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L g y g L(max)of IL will remain constant even when RL is short circuit.


SERIES REGULATOR WITHSERIES REGULATOR WITHSERIES REGULATOR WITH SERIES REGULATOR WITH CONSTANT CURRENT LIMITINGCONSTANT CURRENT LIMITING

Current limitingCurrent limiting prevents excessive Th tCurrent limitingCurrent limiting prevents excessive load current. Q2 will conduct when the current through RSC develops 0.7V V7.0I

The current limit is:

35

across Q2’s VBE. This reduces base current to Q1, limiting the load current. . SC

(max)L RI =


EXAMPLE:

A series regulator circuit shown above maintain a A series regulator circuit shown above maintain a constant output voltage of 25 V. What is the value of constant output voltage of 25 V. What is the value of resistor, Rresistor, RSCSC in order to limit the maximum current, in order to limit the maximum current, IIL( )L( ) to 0 5 A? With the calculated value of Rto 0 5 A? With the calculated value of RSCSC what iswhat is

36

IIL(max)L(max) to 0.5 A? With the calculated value of Rto 0.5 A? With the calculated value of RSCSC, what is , what is the value of Vthe value of VOO when Rwhen RLL = 100 = 100 ΩΩ and Rand RLL = 10 = 10 ΩΩ??


FOLDBACK CURRENTFOLDBACK CURRENTFOLDBACK CURRENT FOLDBACK CURRENT LIMITING CIRCUITLIMITING CIRCUIT

37

SEE 3263 VOLTAGE REGULATORSDuring short circuit where VO = 0 V and IL = ISC,

PD =(Vi–VO)ISC = (20 – 0)1A= 20 W (for constant current limiting)

PD =(Vi–VO)ISC = (20 – 0)0.5A=10 W (for foldback current limiting)limiting)

During maximum operation where VO = 15 V and IL = 1 A,

PD= (Vi–VO)IL= (20 – 15)1 A = 5 W (for both current limiting)

During short circuit condition, a regulator with constant current limiting has to dissipate 20 W of power in

38

g p ptransistor Q1 compared to regulator with foldback current limiting i.e only 10 W.


SERIES REGULATOR WITHSERIES REGULATOR WITHSERIES REGULATOR WITH SERIES REGULATOR WITH FOLDBACK CURRENT LIMITINGFOLDBACK CURRENT LIMITING

FoldFold--back current limitingback current limiting drops the load current well below the peak during overload conditions. Q2

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conducts when VR4 + VBE2 = VRSC and begins current limiting.


VBE2 = VRSC – VR4

VR4 will increase or decrease if VO increases or decreases. At this instant, Q2 is still not conducting. V i f d b l i th lt di id lVR4 is found by applying the voltage-divider rule:

( )ORSC4

4R VVRV +⎞

⎜⎜⎛

= ( )ORSC54

4R VVRR

V +⎠

⎜⎜⎝ +

When IL increase to IL(max) or during overload, VR4 will L L(max) R4 drop because VO drops. A smaller value of VRSC is required to maintain VBE2 ≈ 0.7V. This means that less current is needed to maintain conduction in Q2 and thecurrent is needed to maintain conduction in Q2 and the load current drops.

At this point, current limiting occurs. IL will be limited

40

p , g L and Q2 conducting (ON).


If th l t d t t lt i 10 V d t iIf the regulated output voltage is 10 V, determine:(a) The short circuit current, ISC(b) The maximum load current, IL(max)

41

( ) , L(max)(c) Power dissipation in transistor 2N3055 during

shorted load.


Test Question Example:For the circuit shown below, determine :(a) Maximum load current.(b) Output voltage range.

Q1

Vi =23VRSC

( ) p g g(c) Values of VB1 and IR2 if RL = 10 Ω and VO = 15 V.

Q

R13k

R

1.2

VB1

Q2

Q3

R23k

R33.3k

R4

RL

VZ =10V

5k

R510k

IR2

42

10k


Final Exam Question Example:

A series voltage regulator circuit above produce an output voltage,A series voltage regulator circuit above produce an output voltage, VO = 10 V and a maximum load current, IL(max) = 1 A. Given for all transistors, Q1, Q2, and Q3 : β = hFE = 100, VBE(ON) = 0.7 V; for Zener diode, DZ : VZ = 4.3 V, rZ = 0 Ω, IZK = 1 mA and IZM = 40 mA. The

43

, Z Z , Z , ZK ZMunregulated input voltage, Vi is 20 V. During optimum operation, I1=2 mA, IZ = 14 mA, I3 = 1 mA and IB3 can be neglected.



D b i bl k di f hi l i iDraw a basic block diagram for this regulator circuit.

Sketch an label clearly the graph of VO versus IO.

44

Briefly explain how the output voltage, VO is maintain constant evenwhen the input voltage, Vi varies within the permitted range.



Explain the function of resistors R and RExplain the function of resistors, R1 and R2.

Determine the resistor value of R1 and R2.


45


Determine the suitable range value of RL.



Determine the power dissipation in Q1, Q2 and DZ at Optimum operation.

The pass transistor Q1 will easily burnt when load RL is shorted.Suggest one circuit that can be used to overcome the problem

46

Suggest one circuit that can be used to overcome the problem. Briefly explain how this additional circuit works.


SHUNTSHUNT--TYPE VOLTAGETYPE VOLTAGESHUNTSHUNT TYPE VOLTAGE TYPE VOLTAGE REGULATOR BLOCK DIAGRAMREGULATOR BLOCK DIAGRAM

47


Shunt Regulators

Shunt Regulator block diagram:

VIN

R1VOUT

Basic shunt regulator circuit:

IN OUT

Controlelement(shunt)

Sample

Errordetector

Referencevoltage

VOUTSamplecircuit VIN

OUT

R2

Q

–VREF

Error detectorControlelement

R1

The control element Q1

+D1

R4

R3RL

Samplecircuit

The control element maintains a constant output voltage by varying the collector current in the

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collector current in the transistor.


SHUNT VOLTAGESHUNT VOLTAGESHUNT VOLTAGE SHUNT VOLTAGE REGULATOR WITH OPREGULATOR WITH OP--AMPAMP

Shunt regulators use a parallel transistor for the control element. If the output voltage changes, the g g ,op-amp senses the change and corrects the bias on Q A

Although it is less efficient than the series regulator, the shunt regulator h i h t h t i it t ti

the bias on Q1. A decrease in output voltage causes a

49

has inherent short-circuit protection. The maximum current when the output is shorted is VIN/R4.

decrease in VB and an increase in VC.


SWITCHING REGULATORSSWITCHING REGULATORSSWITCHING REGULATORSSWITCHING REGULATORSTo reduce power dissipation in pass transistor.Gives higher efficiency.Able to supply very large load current with low voltage as required in the PCvoltage as required in the PC.3 basic configurations

step-downpstep-upinverting

Step-down switching regulator is widely used as the power supply in PC.

50


Switching Regulators

All it hi l t t l th t t lt bAll switching regulators control the output voltage by rapidly switching the input voltage on and off with a duty cycle that depends on the load. Because they use high y p y gfrequency switching, they tend to be electrically noisy.

V

ton toff ton toff ton toff tonon/off control

VC

VOUT

51




An increase in the duty cycle increases the output voltage.

ton toff ton toff ton toff ton

VC

on/off control

VOUT

52




A decrease in the duty cycle decreases the output voltage.

ton toff ton toff ton toff tonon/off control

VC

VOUT

53


BASIC SWITCHING REGULATORBASIC SWITCHING REGULATORBASIC SWITCHING REGULATORBASIC SWITCHING REGULATOR

Q ILQ1

R

I L

CD1PWM

R1 R L

+Vo-

ViGatedLatch

Pengayun

R 3

V+

-V2

+

-

+

-VZ

R2

Vralat

54


A STEPA STEP--DOWN SWITCHING DOWN SWITCHING SS O S C GO S C GREGULATORREGULATOR

A stepstep--down switching regulatordown switching regulator control the output voltage by controlling the duty cycle to a series transistor. The duty cycle changes depending on the load y y g p grequirement.

VIN

VOUTQ1 L

onC charges

VIN

VOUTQ1 LL reverses

polarityoffBecause the transistor is either ON or OFF on all switching regulators, the power dissipated in the

IN

R1

R2

RLD1

Variablepulse-width

oscillator

Con + −IN

R1

R2

RLD1

Variablepulse-width

oscillator

C− +polarityoff

power dissipated in the transistor is very small and the regulator is very efficient The pulses are

R3

–

+

DVREF

R3

–

+

DVREF

55

efficient. The pulses are smoothed by an LC filter.

D2D2


A STEPA STEP--UP SWITCHING UP SWITCHING SS U S C GU S C GREGULATORREGULATOR

In a stepstep--up switching regulatorup switching regulator, the control element operates as a rapidly pulsing switch to ground. The switch ON and OFF times are controlled by the output y pvoltage.

VINVOUT++

C dischargesoffL field buildsVIN

VOUT++ on C chargesL field collapsesVIN

VOUT++

Step-up action is due to the fact that the inductor changes polarity during switching and adds to V

VIN

R1Q1 R2

RL

D1 C

Variablepulse-widthoscillator

L+ −

on

VIN

R1Q1 R2

RL

D1 C


L

off

− +VIN

R1Q1 R2

RL

D1 C


L

switching and adds to VIN. Thus, the output voltage is larger than the input voltage RD2

oscillator

+–

RD2

oscillator

+–

RD2

oscillator

+–

5656

voltage. R3D2 R3D2 R3D2


AN INVERTING SWITCHING AN INVERTING SWITCHING G S C GG S C GREGULATORSREGULATORS

In a voltagevoltage--inverter switching regulatorinverter switching regulator the output is theIn a voltagevoltage--inverter switching regulatorinverter switching regulator, the output is the opposite polarity of the input. It can be used in conjunction with a positive regulator from the same input source.

+V–VOUT

Q1 D1

on

offC discharges

+VIN

–VOUTQ1 D1

onoff+VIN

–VOUTQ1 D1

Inversion occur because the inductor reverses polarity when the diode conducts

+VIN

R1

R2 RLVariablepulse-width

ill

L C+

−

on

L field builds

+VIN

R1


ill t

L C

L field collapses

−

+ Ccharges

off+VIN

R1


ill t

L C

the diode conducts, charging the capacitor with the opposite polarity of the input

R3

D

oscillator+

–R3

D

oscillator+

–R3

D

oscillator+

–

5757

polarity of the input. D2D2D2


THE OPERATION OF PULSE THE OPERATION OF PULSE WIDTH MODULATOR (PWM)WIDTH MODULATOR (PWM)V Output

PULSE-WIDTH MODULATOR

(PWM)

VIN

t t

Output

VIN

t t

Output

PULSE-WIDTH MODULATOR

(PWM)t t

PULSE-WIDTH

VIN Output

58

PULSE WIDTH MODULATOR

(PWM)t t


T

⎞⎛

=

TTTCycleDuty HI

⎟⎠⎞

⎜⎝⎛=

TTVV HI

HIdc

59


EXAMPLEEXAMPLEBy assuming an ideal LC,By assuming an ideal LC,(a)(a) Explain the function of PWM, DExplain the function of PWM, D11, L and C., L and C.(b)(b) E l i th ti f th i it if VE l i th ti f th i it if V dd(b)(b) Explain the operation of the circuit if VExplain the operation of the circuit if VOUTOUT decreases.decreases.(c)(c) Calculate VCalculate VOUTOUT..(d)(d) If VIf Vii increase to15 V, sketch the waveform at point Bincrease to15 V, sketch the waveform at point B( )( ) ii

in order to maintain the value found in in order to maintain the value found in (c).(c).

60


PWM i d t d l t i ith l idth d dPWM i d t d l t i ith l idth d dPWM is used to produce pulse trains with pulse width depend on PWM is used to produce pulse trains with pulse width depend on the changes in output, Vthe changes in output, VOUTOUT. These pulse trains (at point B) will . These pulse trains (at point B) will control the ON and OFF interval of Qcontrol the ON and OFF interval of Q11 thus will finally increase or thus will finally increase or decrease the value of Vdecrease the value of Vdecrease the value of Vdecrease the value of VOUTOUT..

The diode DThe diode D11 is used to eliminate the negative voltage.is used to eliminate the negative voltage.

61

Inductor, L and capacitor, C is used as filter to average the switched Inductor, L and capacitor, C is used as filter to average the switched voltage thus producevoltage thus produce VVDCDC..


When VWhen VOUTOUT reduced, Vreduced, VR2R2 will also reduced thus Vwill also reduced thus Verrorerror will increase will increase because Vbecause VZZ is constant.is constant.PWM will produce pulse trains with large pulse width.PWM will produce pulse trains with large pulse width.QQ11 will ON and OFF with large duty cycle thus increase the dc current will ON and OFF with large duty cycle thus increase the dc current flowing through it.flowing through it.The increase of dc current in QThe increase of dc current in Q11 will then increase the Vwill then increase the VOUTOUT that try to that try to reduce previouslyreduce previously

62

reduce previously.reduce previously.This regulating action maintains VThis regulating action maintains VOUTOUT at an essentially constant level.at an essentially constant level.


⎞⎛V5.712

m6m10m10V

TTTV i

OFFON

ONOUT =×⎟

⎠⎞

⎜⎝⎛

+=×⎟⎟

⎠

⎞⎜⎜⎝

⎛+

=

T

VT

TV iON

OUT

⎞⎛

×⎟⎠⎞

⎜⎝⎛= 8 ms

8 ms

63

ms815m16

T5.7 ON =×⎟⎠⎞

⎜⎝⎛=


SWITCHING REGULATORSWITCHING REGULATORSWITCHING REGULATOR SWITCHING REGULATOR WITH PWM CONSTRUCTIONWITH PWM CONSTRUCTION

64


VVOSCOSC , V, VERRORERROR AND PWMAND PWMVVOSC OSC , V, VERRORERROR AND PWM AND PWM OUTPUT VOLTAGESOUTPUT VOLTAGES

V

-

(V )

VERROR

VOSC

V1

+

(V )

(V )

TON

VAT

VH

TON

+

TOFF

ON

( )

0 t

VOSC

-

(V )VERROR

+

(V )

(a)

VH

V1

VDC

TON

65TON

+

TOFF (b)

0 t


PWM GENERATION USINGPWM GENERATION USINGPWM GENERATION USING PWM GENERATION USING SAWTOOTH GENERATOR AND SAWTOOTH GENERATOR AND

VOLTAGE COMPARATORVOLTAGE COMPARATORVOLTAGE COMPARATORVOLTAGE COMPARATOR

66


SWITCHING REGULATORS: SWITCHING REGULATORS: ADVANTAGESADVANTAGES•• Higher efficiency.Higher efficiency.

•• Light and compact.Light and compact.

•• Filtering is easy to achieve at high frequencies.Filtering is easy to achieve at high frequencies.

•• VVOO ≥≥ VVii

SWITCHING REGULATORS: SWITCHING REGULATORS: DISADVANTAGESDISADVANTAGES

•• Generate EMI (Generate EMI (electromagnetic interferenceelectromagnetic interference) where switching at high) where switching at high

frequency for Qfrequency for Q11 current will produce large magnetic fields whichcurrent will produce large magnetic fields which

i d d i lt d d ti d d i lt d d tinduced noise voltage around conductor. induced noise voltage around conductor.

•• Limited performance of power transistor (pass transistor) to switchLimited performance of power transistor (pass transistor) to switch

ONON and and OFFOFF at high speed.at high speed.

67

g pg p

•• Contain large noise and ripple in VContain large noise and ripple in VOO..


IC REGULATOR BLOCK IC REGULATOR BLOCK DIAGRAMDIAGRAM

IC voltage regulators are available as series regulators or as switching regulators. The popular three-terminal regulators are often used on separate pc boards within a system because they are

68

used on separate pc boards within a system because they are inexpensive and avoid problems associated with large power distribution systems (such as noise pickup).


IC REGULATOR 78XX SERIESIC REGULATOR 78XX SERIESThe only external components required with the 78XX series are input and output capacitors and some form of

IC REGULATOR 78XX SERIESIC REGULATOR 78XX SERIES

heat sink.

These IC include thermal shutdown protection and i t l t li itiinternal current limiting.

The 78XX series is a fixed positive output regulator available in various packages and with standard voltage outputs. DD PAKPAK TOTO 220220outputs.

They are primarily used for fixed output voltages, but with additional

DD--PAKPAK TOTO--220220

TOTO 33

69

p g ,components, they can be set up for variable voltages or currents.

TOTO--33


IC REGULATOR 78XX SERIESIC REGULATOR 78XX SERIESIC REGULATOR 78XX SERIESIC REGULATOR 78XX SERIES

11 33

22

C d t t t i- Can produce output current inexcess of 1A

- VIN must be at least 2V- 3V aboveType number Output voltage

78057806

+5.0 V+6 0 VIN

the output voltage- C1 to prevent from unwanted

oscillation

78067808780978127815

+6.0 V+8.0 V+9.0 V

+12.0 V+15.0 V

70

oscillation- C2 act as a line filter to improve

transient response

78187824

+18.0 V+24.0 V


IC REGULATOR 79XX SERIESIC REGULATOR 79XX SERIESIC REGULATOR 79XX SERIESIC REGULATOR 79XX SERIES

22 33

11

The 79XX series is the negative output counterpart to the 78XX 7905

7905 2–5.0 V–5 2 V

Type number Output voltage

series, however the pin assignments are different on this series.

Oth ifi ti b i ll

7905.27906790879127915

5.2 V–6.0 V–8.0 V

–12.0 V–15.0 V

71

Other specifications are basically the same.

79187924

–18.0 V–24.0 V


LINEAR IC REGULATOR LM317LINEAR IC REGULATOR LM317The LM317 is an adjustable positive output IC regulator. There is a fixed reference voltage of +1.25 V between the

t t d dj t t t i l Th i d ioutput and adjustment terminals. There is no ground pin.

• +ve output regulator

• VREF = 1.25VVREF 1.25V

• Maximum Current 1.5A

• Output may varies 1.2V → 37V

2ADJ2

REFOUT RIRR1vV +⎟

⎠

⎞⎜⎜⎝

⎛+=

p y

• Input voltage 4V → 40 V

The output voltage is calculated by:The output voltage is calculated by:

72

2ADJ1

REFOUT R ⎠⎜⎝

p g yp g y

The LM337 is an adjustable negative output IC regulator.


Example:What is the value of VOUT? (Assume IADJ is 50 µA):

)k2)(A50(150

k21V25.1VOUT Ωµ+⎟⎠⎞

⎜⎝⎛

ΩΩ

+=

73

V8.16=⎠⎝


IC REGULATOR WITH BOOSTER IC REGULATOR WITH BOOSTER CURRENTCURRENT

IC regulators are limited to a maximum allowable currentIC regulators are limited to a maximum allowable current before shutting down. The circuit shown is uses an external pass transistor to increase the maximum

il bl l d t

VINQext

available load current.

R sets the

VOUT

RextC1

Rext sets the point where Qext begins to

RL

OUT78XX

C2

conduct:

ext IV7.0R =

74

maxext I


IC REGULATOR WITH EXTERNAL IC REGULATOR WITH EXTERNAL CURRENT LIMITING CIRCUITCURRENT LIMITING CIRCUIT

Previous slide shows that the external transistor is not protected from excessive current, such as would result from a shorted output. An additional current-limiting

75

o a s o ted output add t o a cu e t t gcircuit (Qlim and Rlim) can be added to protect Qext from excessive current and possible burn out.


EXAMPLEEXAMPLEEXAMPLEEXAMPLEAn IC voltage regulator shown below is able to operate with a much higher output current, IL. If given VEB1(ON) = g p , L g EB1(ON)VEB2(ON) = 0.7 V, IO(max) = 1A and β1 = 15:(a) Explain the function of transistors Q1 and Q2.(b) Determine IC and IO when R = 100 Ω and 1 Ω(b) Determine IC1 and IO when RL = 100 Ω and 1 Ω.

76

SEE 3263 VOLTAGE REGULATORSQ1

R limitI C1

ILIOI iR 1

Q2

LM340 -5

Vi+Vo-

R L

L

IQ

1

3 ohm

(a) Explain the function of transistors Q1 and Q2.1 2

Q1 act as an external pass transistor to handle excess current that is unable to be handled by three-terminal IC regulator.

Q2 act as the current limiting circuit to protect Q1 from

77

Q2 act as the current limiting circuit to protect Q1 from excessive maximum current.

SEE 3263 VOLTAGE REGULATORSQ1

R limitI C1

ILIOI iR 1

Q2

LM340 -5

Vi+Vo-

R L

L

IQ

1

3 ohm

(b) Determine IC1 and IO when RL = 100 Ω and 1 Ω.C1 O L

When VEB1 < VEB1(ON), Q1 is OFF. Thus IL = IO = IR1.

If I increase to I = V /R = 0 7/3 = 233 33 mA thenIf IL increase to IR1(max) = VEB1(ON)/R1 = 0.7/3 = 233.33 mA, then Q1 is ON where IL = IO + IC1 ≈ Ii + IC1 = IR1(max) + IB1 + IC1= IR1(max) + IB1 + β1IB1 = 233.33 mA + (1+β1)IB1

78

Therefore IB1 = (IL - 233.33 mA) / (1+β1)where IL = VO/RL, IC1 = β1IB1 and IO = IL − IC1


When R = 100 Ω and 1 Ω the values of I and I canWhen RL = 100 Ω and 1 Ω, the values of IC1 and IO can be found as tabulated in the table below.

RL IL IB1 IC1 IO100Ω 50 mA 0A 0A 50 mA

1Ω 5000 mA 297.92 mA 4468.8 mA 531.2 mA

79


A CURRENT REGULATORA CURRENT REGULATORA CURRENT REGULATORA CURRENT REGULATORIC regulators can be used as a current source when an application requires that a constant current can beapplication requires that a constant current can be supplied to a variable load. R1 is the current-setting resistor.

GOUT

L IVI +=

80

G1

L IR

I +


POWER SUPPLY WITH TWOPOWER SUPPLY WITH TWOPOWER SUPPLY WITH TWO POWER SUPPLY WITH TWO TERMINAL VOLTAGES TERMINAL VOLTAGES

7815In Out

GndC 10 uF4000 uF240V C V

24VC1 20V30V

N N:

240V50 Hz

C2 VO124V

7915In Out

N1 N2:

GndC3 C4

10 uF20V

4000 uF30V VO2

81


IC Voltage Regulators

The 78S40 is an IC containing all of the elements needed e 8S 0 s a C co ta g a o t e e e e ts eededto configure a switching regulator, using a few external parts.It i i l it hii l it hi RCSIt is a universal switching universal switching regulator subsystem regulator subsystem because it can be configured as a step down step up or

10 11 12 13 14 15 16

VINCT

RCS

VCC

99 10 11 12 13 14 15 16

Noninvertinput

Invertinput Gnd Timing

capVCC

Ipksense

Drivercollector

Switchcollector

as a step-down, step-up, or inverting regulator by the user. The data sheet shows typical circuits for these

–

+

–

Q1

Q2

SOscillator

R

Q

Comp.

Flip-flop

1.25 V

–

+

Q1

Q2

SOscillator

R

Q

Comp.

Flip-flop

1 25 Vtypical circuits for these configurations.

7 6 5 4 3 2 1

+

VOUT

R1

L

CO

R2

referenceD1

88 7 6 5 4 3 2 1

Referencevoltage

Invertinput

Noninvertinput

VCCop-amp Output Switch

emitter Anode Cathode

–

+

1.25 Vreference

D1

Here is the step-down

82

R1 COconfiguration.


83


84


SERIES VOLTAGE REGULATOR SERIES VOLTAGE REGULATOR WITH CONSTANT CURRENT WITH CONSTANT CURRENT

LIMITING USING LM 723LIMITING USING LM 723LIMITING USING LM 723LIMITING USING LM 723

85


SERIES VOLTAGE REGULATOR SERIES VOLTAGE REGULATOR WITH FOLDBACK CURRENT WITH FOLDBACK CURRENT

LIMITING USING LM 723LIMITING USING LM 723LIMITING USING LM 723LIMITING USING LM 723

86


SummarySummarySummaryRegulator A electronic circuit that maintains an

essentially constant output voltage with changing input voltage or load current

Line regulation

changing input voltage or load current.

The percentage change in output

L d l ti

voltage for a given change in input (line) voltage.

Th t h i t t ltLoad regulation

Linear regulator

The percentage change in output voltage for a given change in load current.

A voltage regulator in which the controlLinear regulator

Switching

A voltage regulator in which the control element operates in the linear region.

A voltage regulator in which the control

87

Switching regulator

A voltage regulator in which the control element operates as a switch.


UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONS UNDERSTANDING QUESTIONS

The load regulation of an ideal power supply is e oad egu at o o a dea po e supp y s________.

(a) 0%

(b) 25%

(a) 0%

( )

(c) 50

(d) 100%

( ) f th b

88

(e) none of the above


UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONS UNDERSTANDING QUESTIONS

An AC-DC converter power supply contains all of the C C co e te po e supp y co ta s a o t efollowing except a ________.

(a) rectifier circuit

(b) filter circuit( )

(c) sample-and-hold circuit(c) sample-and-hold circuit

(d) regulator circuit

( ) f th b

89



UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONS

The ideal voltage regulator maintains a constant DC e dea o tage egu ato a ta s a co sta t Coutput voltage regardless of changes in __________.

(a) its input voltage(a) its input voltage

(b) its output voltage demand

(c) its load current demand

(d) both (a) and (c)


(d) both (a) and (c)

90




Under full load conditionUnder full load condition, ___________.

(a) the input voltage is at its maximum value ( ) p g

(b) the load resistance is at a minimum value (b) the load resistance is at a minimum value

(c) no load resistance is present

(d) the load current is at a minimum value


91

( )


UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONS__________ is a measurement of how well the power supply maintains a constant voltage acrosspower supply maintains a constant voltage across the load with changes in load current.

( ) V lt t l(a) Voltage control

(b) Load voltage control ( ) g

(c) Load regulation (c) Load regulation

(d) Line regulation

( ) f th b

92




What is the load regulation of a power supply with a g yno load voltage of 16.5 V and a full load voltage of 15 V?

( ) 1 5%(a) 1.5%

(b) 9.1% ( )

(c) 10% (c) 10%

(d) 90.9%

( ) f th b

93



UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONS__________ is a measurement of how well the power supply maintains a constant output voltagepower supply maintains a constant output voltage with changes in input voltage.

( ) V lt t l(a) Voltage control

(b) Load voltage control ( ) g

(c) Load regulation

(d) Line regulation

( ) f th b

(d) Line regulation

94



UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSThe pass transistor in linear regulators will _________.

( ) t i th li t ll ti( ) t i th li t ll ti(a) operate in the linear area at all times

(b) be in cutoff at all times

(a) operate in the linear area at all times

( )

(c) be in saturation at all times

(d) switch between cutoff and saturation

( ) f th b

95



UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSSwitching regulators have _________ than linear

l tregulators.

( ) l lif(a) longer life

(b) simpler circuitry ( ) p y

(c) a higher cost in all cases

(d) greater efficiency

( ) f th b

(d) greater efficiency

96



UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSA correct formula for load regulation is _________.

OUTLoad Regulation = 100%VV

⎛ ⎞∆⎜ ⎟∆⎝ ⎠

a. INV∆⎝ ⎠

NL FLLoad Regulation = 100%V VV

⎛ ⎞−⎜ ⎟⎝ ⎠

b.

FLLoad Regulation = 100%V⎛ ⎞⎜ ⎟c.

FLV⎝ ⎠

( )OUT OUT/ 100%Load Regulation =

V V∆d.

NL FL

gV V⎜ ⎟−⎝ ⎠

97

IN

Load Regulation V∆

d.


UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSAn alternate way to express load regulation is in terms of the _________.

(a) output resistance and the full-load resistance

(a) output resistance and the full-load resistance

(b) output resistance and the shorted-load resistance

( ) i t i t d th f ll l d i t(c) input resistance and the full-load resistance

(d) input resistance and the shorted-load resistanceresistance

98



In the circuit shown, R4 = 0.7 Ω. The output current , 4 pwill be limited to _________.

(a) 0.5 A

(b) 0.7 A

VIN VOUT

R1

Q1

Q2

R4

+

0.7 Ω

(b) 0.7 A

(c) 1.0 A

(d) 1 4 A

R2

Current limiter

+

–(c) 1.0 A

(d) 1.4 A R3

99


UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSThe block diagram for a series voltage regulator is shown. The yellow box represents a _________.

(a) control element

(b) sample circuit VIN VOUT

(c) error detector

(d) reference voltage

?(d) reference voltage( ) g(d) reference voltage

100


UNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSUNDERSTANDING QUESTIONSThe block diagram for a shunt voltage regulator is shown. The yellow box represents a _________.

(a) control element

(b) sample circuit VIN

R1VOUT

(b) sample circuit

(c) error detector

(d) reference voltage?

101



The circuit in the blue shaded area is a

(a) high speed switching circuit

The circuit in the blue shaded area is a _________.

(b) fold-back current limiter

(c) reference sourceQ

(b) fold-back current limiter

( )

(d) shunt regulator+VIN VOUT

R1

Q1

+

R4

R2

R5

–Q2

D1

R3

R6

102



A major advantage of all switching regulators isA major advantage of all switching regulators is _________.

(a) low noise

(b) high output impedance(b) high output impedance

(c) high efficiency

(d) all of the above

(c) high efficiency

(d) all of the above

103



The type of regulator circuit shown is a

(a) series linear offon

The type of regulator circuit shown is a _________.

(a) series linear

(b) series switching+VIN

–VOUTQ1

R2 RL

D1

Variable

L C+

−

on

off

L fi ld b ild

Cdischarges+VIN

–VOUTQ1

R2 RL

D1

Variablel id h

L C

on

L fi ld

−

+ Ccharge

off+VIN

–VOUTQ1

R2 RL

D1

Variablel id h

L C

(c) shunt switching

(d) none of the above

R1

R3

pulse-widthoscillator

+

–

L field buildsR1

R3


+

–

L field collapses

charges

R1

R3


+

–(d) none of the aboveD2D2D2

104



The output voltage from a 7912 is a regulated p g g_________.

(a) +5 V

(b) +12 V

(c) −5 V

(d) −12 V(d) −12 V

105


T H E T H E EE N DN D

106

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yellow box

final exam

foldback current

real power

control element

produce pulse

power supply

current limiting