Voltage Regulator

SEE 3263: ELECTRONIC SYSTEMS LECTURER: CAMALLIL BIN OMAR P05-415 @ y [email protected] Tel: 07- 5535241 1

SEE 3263: ELECTRONIC SYSTEMS

Chapter 1: Voltage Regulators

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SEE 3263 VOLTAGE REGULATORS

1.0 REGULATED POWER SUPPLY … …

…

… …

Power 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 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 chemical 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 p power supply pp y consists of a rectifier,, a filter and a regulator. A power supply filter greatly reduces the fluctuations i th in the output t t voltage lt off a half-wave h lf or full-wave f ll 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 provide power and biasing for proper operation. Voltage 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 load. 4

SEE 3263 VOLTAGE REGULATORS

DC POWER SUPPLY BLOCK DIAGRAM

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SEE 3263 VOLTAGE REGULATORS

TYPES OF POWER SUPPLY „

Linear Power Supply.

„

Non-Linear Power Supply.

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SEE 3263 VOLTAGE REGULATORS

LINEAR POWER SUPPLY „

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

„

Dissipates more power. power

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SEE 3263 VOLTAGE REGULATORS

NON--LINEAR POWER SUPPLY NON „

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

„

Dissipates less power. power

„

Also named as switching power supply or switching regulator. 8

SEE 3263 VOLTAGE REGULATORS

„

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

„

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

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POWER SUPPLY REGULATION „

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

„

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

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SEE 3263 VOLTAGE REGULATORS

VOLTAGE REGULATION • 2 basic categories: ((i)) Load Regulation. g • Output voltage nearly constant g when load change. (ii) Line Regulation. Regulation • Output voltage nearly constant when line voltage change. change 11

SEE 3263 VOLTAGE REGULATORS

LOAD REGULATION • Load regulation is a measure of how well a power supply is able to maintain the dc output voltage between no load and full load with the input voltage constant. • For real power supply, output voltage will drop p when load current increases. ∞

∞

VO(NL) – output voltage with no load. VO(FL) – output voltage with full load. IL(FL) – full load current (maximum current that coming out from power supply). 12

SEE 3263 VOLTAGE REGULATORS

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

VO ( NL ) − VO ( FL ) VO ( FL )

× 100%

• L Load d regulation l ti can also l be b expressed d in terms of percent change in the output t t per mA A change h in i load l d currentt (%/mA).

Vreg

⎛ VO(NL) − VO(FL) ⎞ ⎛ ∆VO ⎞ ⎜ ⎟ ⎟⎟ ⎜⎜ ⎜ ⎟ V V O(FL) O ⎠ ⎝ ⎝ ⎠ ×100% = ×100% = ∆I L I L(FL) − I L(NL)

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SEE 3263 VOLTAGE REGULATORS

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

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SEE 3263 VOLTAGE REGULATORS

VO(FL ) = IL(FL ) × RL = (1A )(25Ω) = 25V VO(FL )

⎛ RL ⎞ ⎛ 25 ⎞ = ⎜⎜ × V = × VO(NL ) ⎜ O( NL ) ⎟ ⎝ 25 + 1⎠ ⎝ RL + R O ⎠

∴ VO(NL ) = 26 V

%Vreg

⎛ VO(NL ) − VO(FL ) ⎞ ⎛ 26 − 25 ⎞ ⎜ = × 100% = ⎜ × 100% = 4% ⎜ VO(FL ) ⎝ 25 ⎠ ⎝ ⎠ 15

SEE 3263 VOLTAGE REGULATORS

LINE REGULATION • Line regulation is a measure of how well a power supply l is i able bl to t maintain i t i the th dc d output voltage for a change in the ac input line voltage. voltage • When the dc input (line) voltage changes changes, the voltage regulator must maintain a nearly constant output p voltages. g

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SEE 3263 VOLTAGE REGULATORS

LINE REGULATION • Line regulation can be expressed as: ⎛ ∆VO ⎞ Line Regulation = ⎜⎜ ∆V ⎟⎟ × 100% i ⎠ ⎝

• Line regulation can also be expressed in terms off percent change h in i VO per volt l change on the Vi (%/V). ⎛ ∆VO ⎞ ⎜ ⎟ V O⎠ ⎝ × 100 % Line Regulation = ∆Vi 17

SEE 3263 VOLTAGE REGULATORS

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

Line Regulation = „

(0 .25 V 15 V ) × 100 % = 0 .333 % / V 5V

Note : For ideal voltage regulation, both categories will give zero percent regulation(0%) regulation(0%). 18

SEE 3263 VOLTAGE REGULATORS

ZENER REGULATOR

-

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

-

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. (b) PDZ(min) Zener DZ( i ) and PDZ(max) DZ( ) for Zener. (c) Suitable power rating, PRS for resistor, RS.

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SEE 3263 VOLTAGE REGULATORS

Vi − VO 18 − 12 IS = = = 60mA RS 100

IZ(min) = IS − IL(max)

VO 12 = IS − = 60mA A− = 5.45mA A 220 RL(min)

IZ(max) = IS − IL(min) = IS −

VO RL(max)

12 = 60mA − = 40mA 600

PDZ(min) = IZ(min) × VZ = (5.45mA )(12) = 65.4mW PDZ(max) = IZ(max) × VZ = ( 40mA )(12) = 480mW PRS = (IS )2 × R S = (60mA )2 × 100 = 0.36mW 21

SEE 3263 VOLTAGE REGULATORS

EXAMPLE: Determine: (a) The branch currents and power dissipated by circuit devices 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 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 efficiency ffi i and d power-handling h dli capability bilit as well ll as to control the changes in output current.

IE IL IB = = (β + 1) (β + 1)

IL IZ = IS -IB = IS − (β + 1) VO = VZ -VBE 24

SEE 3263 VOLTAGE REGULATORS

EXAMPLE:

If β = 50, determine: (a) output voltage, VO ((c)) current,, IS

(b) ((d))

voltage, VCE1 current,, IZ

(b) Vi = VCE + VO VCE = Vi – VO = 20 –11 11.35 35 = 8.65 8 65 V (c) Vi = IS RS + VZ Vi − VZ IS = = RS

20 − 12 = 0.04 0 04 A 200

(d) I = VO = 11 .35 V = 11 . 35 mA L RL

1k

IE I 11 .35 mA = L = = 222 . 55 µ A 1+ β 1+ β 51 ∴ IZ = IS − IB = 40 mA − 222 .55 µ A IB =

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

= 39.78 mA 25

SEE 3263 VOLTAGE REGULATORS „

A Darlington pair transistor (a very high βDC) can be used d to t increase i the th currentt gain. i This Thi will ill reduce d the base current and the zener power rating will be low.

IB 2

IE1 IL = = βDP βDP

βDP = β1 + β2 + β1β2 IZ = IS − IB 2 IL = IS − βDP VO = VZ − 2VBE 26

SEE 3263 VOLTAGE REGULATORS „

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

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REGULATOR CIRCUIT WITH FEEDBACK Q1 R4

VIN

I4

IL

V2 = VBE 2 + VZ

IB1

R1

IC2

- VZ +

Q2 VB1 = VCE2

RL IB2 R3

„

V2 =

+ VBE2 -

+ V2 -

R2

+ VO -

R2 VO R1 + R 2

R2 VO = V2 R1 + R 2 ⎛ R ⎞ ∴ VO = ⎜⎜1 + 1 ⎟⎟( VBE 2 + VZ ) ⎝ R2 ⎠

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

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SIMPLE SERIES VOLTAGE REGULATOR BLOCK DIAGRAM

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Series Regulators Series Regulator block diagram: Control element

VIN

Reference voltage

Error detector

VOUT

Sample circuit

Basic series regulator circuit: Control element VIN

VOUT Q1

R1

The control element maintains a constant output voltage by varying the collector-emitter voltage across the transistor. transistor

+

VREF

– D1

E Error detector d t t

R2 Sample circuit R3

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BASIC OPOP-AMP SERIES REGULATOR

⎛ R2 ⎞ VO = ⎜⎜1 + × VZ ⎝ R3 ⎠ 31

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EXAMPLE: For the series regulator circuit shown below: (a) What is the output voltage? (b) If the load current is 200mA 200mA, what is the power dissipated by Q1? ⎛ R2 ⎞ VO = ⎜⎜1 + × VZ ⎟ ⎝ R3 ⎠ ⎛ 100kΩ ⎞ = ⎜1 + × 3 .9 V 47kΩ ⎠ ⎝ = 12.2V

P = VI = (18 V − 12.2V )(0.2A ) = 1.16 W

Q1 R1 4 7k 4.7k

IL R2 100k

+

VIN 18V VZ 3.9V

-

R3 47k

+ RL VO -

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PROTECTION CIRCUIT 2 types of current limiting circuit: …Linear/Constant …Fold-back

Current Limiting

Current Limiting 33

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LINEAR CURRENT LIMITING 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 IL will slightly g y greater g than IL(max). This value of IL will remain constant even when RL is short circuit. 34

SEE 3263 VOLTAGE REGULATORS

SERIES REGULATOR WITH CONSTANT CURRENT LIMITING

Current limiting prevents excessive 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..

The currentt Th limit is: 0 .7 V IL(max) = R SC 35

SEE 3263 VOLTAGE REGULATORS

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, IL(max) 0 5 A? With the calculated value of RSC, what is L( ) to 0.5 the value of VO when RL = 100 Ω and RL = 10 Ω? 36

SEE 3263 VOLTAGE REGULATORS

FOLDBACK CURRENT LIMITING CIRCUIT

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During 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) During maximum operation where VO = 15 V and IL = 1 A, PD= (Vi–VO)IL= (20 – 15)1 A = 5 W limiting)

(for both current

During short circuit condition, a regulator with constant g has to dissipate p 20 W of power p in current limiting transistor Q1 compared to regulator with foldback current limiting i.e only 10 W. 38

SEE 3263 VOLTAGE REGULATORS

SERIES REGULATOR WITH FOLDBACK CURRENT LIMITING

Fold-back current limiting drops the load current Foldwell below the peak during overload conditions. Q2 conducts when VR4 + VBE2 = VRSC and begins current limiting.

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VBE2 = VRSC – VR4 VR4 will increase or decrease if VO increases or decreases. At this instant, Q2 is still not conducting. VR4 is i found f d by b applying l i the th voltage-divider lt di id rule: l VR 4

⎛ R4 ⎞ (VRSC + VO ) = ⎜⎜ ⎝ R 4 + R5 ⎠

When IL increase to IL(max) or during overload, VR4 will 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 the load current drops. At this p point,, current limiting g occurs. IL will be limited and Q2 conducting (ON). 40

SEE 3263 VOLTAGE REGULATORS

If th the regulated l t d output t t voltage lt is i 10 V, V determine: d t i (a) The short circuit current, ISC ((b)) The maximum load current,, IL(max) (c) Power dissipation in transistor 2N3055 during shorted load. 41

SEE 3263 VOLTAGE REGULATORS

Test Question Example: For the circuit shown below, determine : (a) Maximum load current. ((b)) Output p voltage g range. g (c) Values of VB1 and IR2 if RL = 10 Ω and VO = 15 V. RSC

Q1 Vi =23V

1.2

R1 3k

VB1 Q3 Q2

R3 3.3k RL

R2 3k

R4 5k

IR2 VZ =10V

R5 10k

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Final Exam Question Example:

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

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Final Exam Question Example:

D Draw ab basic i block bl k diagram di for f this hi regulator l circuit. i i Sketch an label clearly the graph of VO versus IO. Briefly explain how the output voltage, VO is maintain constant even when the input voltage, Vi varies within the permitted range.

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Final Exam Question Example:

Explain the function of resistors, resistors R1 and R2. Determine the resistor value of R1 and R2. Determine the resistor value of R3 and R4. Determine the suitable range value of RL.

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Final Exam Question Example:

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. problem Briefly explain how this additional circuit works. 46

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SHUNT--TYPE VOLTAGE SHUNT REGULATOR BLOCK DIAGRAM

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Shunt Regulators Shunt Regulator block diagram: R1 VIN

VOUT

Reference voltage

Error detector

Control element (shunt)

Basic shunt regulator circuit: Sample circuit

VOUT

VIN R1 R2 VREF

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

Error detector –

Control element Q1

+

RL

R3

D1

Sample circuit R4

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SHUNT VOLTAGE REGULATOR WITH OPOP-AMP Shunt regulators use a parallel transistor for the control element. If the output voltage g changes, g , the op-amp senses the change and corrects the bias on Q1. A decrease in output voltage causes a decrease in VB and an increase in VC.

Although it is less efficient than the series regulator, the shunt regulator h inherent has i h t short-circuit h t i it protection. t ti The maximum current when the output 49 is shorted is VIN/R4.

SEE 3263 VOLTAGE REGULATORS

SWITCHING REGULATORS „ „ „ „

„

To reduce power dissipation in pass transistor. Gives higher efficiency. Able to supply very large load current with low voltage as required in the PC PC. 3 basic configurations … step-down p … step-up … inverting Step-down switching regulator is widely used as the power supply in PC.

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

on/off control

ton

toff

ton

toff

ton

toff

ton

VC

VOUT

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Switching Regulators All switching it hi regulators l t control t l the th output t t voltage lt by b rapidly switching the input voltage on and off with a duty cycle y that depends p on the load. Because they y use high g frequency switching, they tend to be electrically noisy. An increase in the duty cycle increases the output voltage. on/off control

ton

toff

ton

toff

ton

toff

ton

VC

VOUT

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Switching Regulators All switching it hi regulators l t control t l the th output t t voltage lt by b rapidly switching the input voltage on and off with a duty cycle y that depends p on the load. Because they y use high g frequency switching, they tend to be electrically noisy. A decrease in the duty cycle decreases the output voltage. on/off control

ton

toff

ton

toff

ton

toff

ton

VC

VOUT

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BASIC SWITCHING REGULATOR L

Q1

D1

PWM Vi

Gated Latch Pengayun

+ VZ

-

+

R1 Vralat

+

3

C

R

L

Vo -

-

R

IL

R2

+ V2

-

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AS STEP-DOWN STEPO SWITCHING S C G REGULATOR A step step--down switching regulator control the output voltage by controlling the duty cycle to a series transistor. The duty y cycle y changes g depending p g on the load requirement. CLcharges L reverses off on polarity + − +− Q1

Because the transistor is either ON or OFF on all switching regulators, the power dissipated in the transistor is very small and the regulator is very efficient The pulses are efficient. smoothed by an LC filter.

VIN

RL

C

D1

R1

VOUT

Variable pulse-width oscillator

R2 – + R3

D2

VREF

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AS STEP-U STEPUP S SWITCHING C G REGULATOR In a step step--up switching regulator, regulator the control element operates as a rapidly pulsing switch to ground. The switch ON and OFF times are controlled by y the output p voltage. Step-up action is due to the fact that the inductor changes polarity during switching and adds to VIN. Thus, the output voltage is larger than the input voltage voltage.

VIN

+

L field builds L field collapses +−

R1

D2

−+

L

Variable pulse-width oscillator

–

discharges on C Ccharges off + VOUT D1

C

on off Q1

RL R2

+

R3

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AN INVERTING G SWITCHING S C G REGULATORS In a voltage voltage--inverter switching regulator 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. off on

Q1

Inversion occur because the inductor reverses polarity when the diode conducts, conducts charging the capacitor with the opposite polarity of the input input.

off on

+VIN

D1 C discharges –V OUT

− + L

R1

Variable pulse-width oscillator ill t

C + − charges L field builds collapses

C R2

RL

+ – R3 D2

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THE OPERATION OF PULSE WIDTH MODULATOR (PWM) VIN

Output

t

PULSE-WIDTH MODULATOR (PWM)

VIN

t

Output

t

PULSE-WIDTH MODULATOR (PWM)

VIN

t

Output

t

PULSE WIDTH PULSE-WIDTH MODULATOR (PWM)

t 58

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THI Duty Cycle = T ⎛ THI ⎞ Vdc = VHI ⎜ ⎟ ⎝ T ⎠

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EXAMPLE By assuming an ideal LC, (a) Explain the function of PWM, D1, L and C. (b) E l i th Explain the operation ti off th the circuit i it if VOUT decreases. d (c) Calculate VOUT. ((d)) If Vi increase to15 V, sketch the waveform at point B in order to maintain the value found in (c).

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PWM is i used d to t produce d pulse l trains t i with ith pulse l width idth depend d d on the changes in output, VOUT. These pulse trains (at point B) will control the ON and OFF interval of Q1 thus will finally increase or decrease the value of VOUT. The diode D1 is used to eliminate the negative voltage. Inductor, L and capacitor, C is used as filter to average the switched voltage thus produce VDC. 61

SEE 3263 VOLTAGE REGULATORS

When VOUT reduced, VR2 will also reduced thus Verror will increase because VZ is constant. PWM will produce pulse trains with large pulse width. Q1 will ON and OFF with large duty cycle thus increase the dc current flowing through it. The increase of dc current in Q1 will then increase the VOUT that try to reduce previously. previously This regulating action maintains VOUT at an essentially constant level. 62

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VOUT

⎛ ⎞ TON ⎛ 10m ⎞ ⎟⎟ × Vi = ⎜ = ⎜⎜ ⎟ × 12 = 7.5 V ⎝ 10m + 6m ⎠ ⎝ TON + TOFF ⎠

⎛ TON ⎞ VOUT = ⎜ ⎟ × Vi ⎝ T ⎠ ⎛ TON ⎞ 7.5 = ⎜ ⎟ × 15 = 8ms ⎝ 16m ⎠

8 ms 8 ms 63

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SWITCHING REGULATOR WITH PWM CONSTRUCTION

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VOSC , VERROR AND PWM OUTPUT VOLTAGES -

VOSC (V ) +

VERROR (V ) V1

TON

VH VAT 0

t +

TON

TOFF

( ) (a) -

VOSC (V ) VERROR (V ) +

V1

TON

VH

VDC

0

t

+

TON TOFF

(b)

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PWM GENERATION USING SAWTOOTH GENERATOR AND VOLTAGE COMPARATOR

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SWITCHING REGULATORS: ADVANTAGES • Higher efficiency. • Light and compact. • Filtering is easy to achieve at high frequencies. • VO ≥ Vi

SWITCHING REGULATORS: DISADVANTAGES • Generate EMI (electromagnetic (electromagnetic interference) interference) where switching at high frequency for Q1 current will produce large magnetic fields which i d induced d noise i voltage lt around d conductor. d t • Limited performance of power transistor (pass transistor) to switch g speed. p ON and OFF at high • Contain large noise and ripple in VO. 67

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IC REGULATOR BLOCK DIAGRAM

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 inexpensive and avoid problems associated with large power distribution systems (such as noise pickup). 68

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IC REGULATOR 78XX SERIES The only external components required with the 78XX series are input and output capacitors and some form of heat sink. These IC include thermal shutdown protection and i t internal l currentt limiting. li iti The 78XX series is a fixed positive output regulator available in various packages and with standard voltage outputs. They are primarily used for fixed output p voltages, g , but with additional components, they can be set up for variable voltages or currents.

D-PAK

TO--220 TO

TO--3 TO 69

SEE 3263 VOLTAGE REGULATORS

IC REGULATOR 78XX SERIES 1

3

2

- C Can produce d output t t currentt iin excess of 1A - VIN must be at least 2V- 3V above the output voltage - C1 to prevent from unwanted oscillation - C2 act as a line filter to improve transient response

Type number

Output voltage

7805 7806 7808 7809 7812 7815 7818 7824

+5.0 V +6 0 V +6.0 +8.0 V +9.0 V +12.0 V +15.0 V +18.0 V +24.0 V 70

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IC REGULATOR 79XX SERIES 2

3

1

The 79XX series is the negative output counterpart to the 78XX series, however the pin assignments are different on this series. Other specifications Oth ifi ti are basically b i ll the same.

Type number

Output voltage

7905 7905 2 7905.2 7906 7908 7912 7915 7918 7924

–5.0 V –5 5.2 2V –6.0 V –8.0 V –12.0 V –15.0 V –18.0 V –24.0 V 71

SEE 3263 VOLTAGE REGULATORS

LINEAR IC REGULATOR LM317 The LM317 is an adjustable positive output IC regulator. There is a fixed reference voltage of +1.25 V between the output t t and d adjustment dj t t terminals. t i l There Th is i no ground d pin. i

• +ve output regulator • VREF = 1.25V • Maximum Current 1.5A • Output p may y varies 1.2V → 37V • Input voltage 4V → 40 V

⎛ R2 ⎞ ⎜ ⎟ + I ADJ R 2 V v 1 = + The output p voltage g is calculated by: y OUT REF ⎜ R1 ⎠ ⎝ The LM337 is an adjustable negative output IC regulator.

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Example:

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

VOUT

2kΩ ⎞ ⎛ = 1.25 V ⎜1 + ⎟ + (50µA )(2kΩ) ⎝ 150Ω ⎠ = 16.8 V 73

SEE 3263 VOLTAGE REGULATORS

IC REGULATOR WITH BOOSTER CURRENT IC regulators are limited to a maximum allowable current before shutting down. The circuit shown is uses an external pass transistor to increase the maximum available il bl load l d current. t Qext

VIN

Rext sets the point where Qext begins to conduct: 0.7V Rext = Imax

C1

Rext

78XX

VOUT

RL

C2

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IC REGULATOR WITH EXTERNAL CURRENT LIMITING CIRCUIT

Previous slide shows that the external transistor is not protected from excessive current, such as would result o as shorted o ted output output. An add additional t o a current-limiting cu e t t g from circuit (Qlim and Rlim) can be added to protect Qext from excessive current and possible burn out. 75

SEE 3263 VOLTAGE REGULATORS

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

76

SEE 3263 VOLTAGE REGULATORS R limit

R1

Q2

I C1

Q1

Ii

IO

IL

LM340 -5 3 ohm Vi

(a)

IQ

RL

+ V o -

Explain the function of transistors Q1 and Q2.

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 excessive maximum current. 77

SEE 3263 VOLTAGE REGULATORS R limit

R1

Q2

I C1

Q1

Ii

IO

IL

LM340 -5 3 ohm Vi

(b)

IQ

RL

+ V o -

Determine IC1 and IO when RL = 100 Ω and 1 Ω.

When VEB1 < VEB1(ON), Q1 is OFF. Thus IL = IO = IR1. If IL increase to IR1(max) = VEB1(ON)/R1 = 0.7/3 0 7/3 = 233 233.33 33 mA 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 Therefore IB1 = (IL - 233.33 mA) / (1+β1) where IL = VO/RL, IC1 = β1IB1 and IO = IL − IC1

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SEE 3263 VOLTAGE REGULATORS

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

RL

IL

IB1

IC1

IO

100Ω

50 mA

0A

0A

50 mA

1Ω

5000 mA 297.92 mA 4468.8 mA 531.2 mA

79

SEE 3263 VOLTAGE REGULATORS

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

IL =

V OUT R1

+ IG 80

SEE 3263 VOLTAGE REGULATORS

POWER SUPPLY WITH TWO TERMINAL VOLTAGES In

24V 240V 50 Hz

24V

4000 uF 30V

C1

7815

Out

Gnd

C2

10 uF VO1 20V

N1 : N2 In

4000 uF 30V

C3

7915

Out

Gnd

C4

10 uF V O2 20V

81

SEE 3263 VOLTAGE REGULATORS

IC Voltage Regulators The e 78S40 8S 0 is sa an IC C co containing ta ga all o of tthe ee elements e e ts needed eeded to configure a switching regulator, using a few external parts. It is i a universal i l switching it hi regulator subsystem because it can be configured as a step-down, step down step-up, step up or inverting regulator by the user. The data sheet shows typical circuits for these configurations. Here is the step-down configuration.

RCS VIN

Noninvert Invert input input 99

Gnd

10 10

CTTiming

cap

11 11

1212

Driver Switch Ipk sense collector collector

VCC VCC 13 13

14 14

15 15 16

Q1

S S Q Q

Oscillator Oscillator

Q1

Flip-flop

Flip-flop

R

– – Comp. Comp. +

16

Q2

R

Q2

+

–

1.25 V 1reference 1.25 25 V

– +

reference 8

R1

D1

D1

+ 7

6

5

4

8 7 6 5 4 R2 Reference Invert Noninvert VCC Output voltage input input op-amp

3

3 Switch emitter

2

1

2

L1 VOUT

Anode Cathode CO

82

SEE 3263 VOLTAGE REGULATORS

83

SEE 3263 VOLTAGE REGULATORS

84

SEE 3263 VOLTAGE REGULATORS

SERIES VOLTAGE REGULATOR WITH CONSTANT CURRENT LIMITING USING LM 723

85

SEE 3263 VOLTAGE REGULATORS

SERIES VOLTAGE REGULATOR WITH FOLDBACK CURRENT LIMITING USING LM 723

86

SEE 3263 VOLTAGE REGULATORS

Summary Regulator A electronic circuit that maintains an essentially constant output voltage with changing input voltage or load current current. Line regulation The percentage change in output voltage for a given change in input (line) voltage. L d regulation Load l ti The percentage Th t change h i output in t t voltage lt for a given change in load current. Linear regulator A voltage regulator in which the control element operates in the linear region. Switching A voltage regulator in which the control regulator element operates as a switch. 87

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS The e load oad regulation egu at o of o an a ideal dea power po e supply supp y is s ________. (a)

0%

((b))

25%

(c)

50

(d)

100%

( ) (e)

none off the th above b 88

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS An AC-DC C C co converter e te po power e supp supply y co contains ta s a all o of tthe e following except a ________. (a)

rectifier circuit

((b))

filter circuit

(c)

sample-and-hold circuit

(d)

regulator circuit

( ) (e)

none off the th above b 89

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS The e ideal dea voltage o tage regulator egu ato maintains a ta s a co constant sta t DC C output voltage regardless of changes in __________. (a)

its input voltage

(b)

its output voltage demand

(c)

its load current demand

(d)

both (a) and (c)

(e)

none of the above 90

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS Under full load condition, condition ___________. ((a))

the input p voltage g is at its maximum 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

((e))

none of the above 91

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS __________ is a measurement of how well the power supply maintains a constant voltage across the load with changes in load current. ( ) (a)

V lt Voltage control t l

((b))

Load voltage g control

(c)

Load regulation

(d)

Line regulation

( ) (e)

none off the th above b 92

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS What is the load regulation g of a power supply y with a no load voltage of 16.5 V and a full load voltage of 15 V? ( ) (a)

1 5% 1.5%

((b))

9.1%

(c)

10%

(d)

90.9%

( ) (e)

none off the th above b 93

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS __________ is a measurement of how well the power supply maintains a constant output voltage with changes in input voltage. ( ) (a)

V lt Voltage control t l

((b))

Load voltage g control

(c)

Load regulation

(d)

Line regulation

( ) (e)

none off the th above b 94

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS The pass transistor in linear regulators will _________. ((a))

t iin th operate the li linear area att all ll times ti

((b))

be in cutoff at all times

(c)

be in saturation at all times

(d)

switch between cutoff and saturation

( ) (e)

none off the th above b 95

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS Switching regulators have _________ than linear regulators. l t ( ) (a)

l longer life lif

((b))

simpler p circuitry y

(c)

a higher cost in all cases

(d)

greater efficiency

( ) (e)

none off the th above b 96

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS A correct formula for load regulation is _________. a.

⎛ ∆VOUT Load Regulation = ⎜ ⎝ ∆VIN

b.

⎛ VNL − VFL ⎞ Load Regulation = ⎜ ⎟100% ⎝ VFL ⎠

c.

⎛ VFL ⎞ Load Regulation g =⎜ ⎟100% ⎝ VNL − VFL ⎠

d.

Load Regulation =

⎞ ⎟100% ⎠

( ∆VOUT / VOUT )100% ∆VIN 97

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS An alternate way to express load regulation is in terms of the _________. (a)

output resistance and the full-load resistance

(b)

output resistance and the shorted-load resistance

( ) (c)

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

(d)

input resistance and the shorted-load resistance 98

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS In the circuit shown,, R4 = 0.7 Ω. The output p current will be limited to _________. (a) (b)

0.5 A 0.7 A

(c)

1.0 A

(d)

14A 1.4

Q1 VIN

R4 VOUT

0.7 Ω R1

Q2 +

R2 Current limiter

–

R3

99

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS The block diagram for a series voltage regulator is shown. The yellow box represents a _________. (a)

control element VIN

(b)

sample circuit

(c)

error detector

( ) (d)

g reference voltage

VOUT

?

100

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS The block diagram for a shunt voltage regulator is shown. The yellow box represents a _________. (a)

control element

(b)

sample circuit

(c)

error detector

(d)

reference voltage

R1 VIN

VOUT

?

101

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS The circuit in the blue shaded area is a _________. (a)

high speed switching circuit

(b)

fold-back current limiter

((c))

reference source

(d)

shunt regulator

Q1

R4 VOUT

+VIN R5

R1 +

–

R2 R6

Q2

D1 R3

102

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS A major advantage of all switching regulators is _________. (a)

low noise

(b)

high output impedance

(c)

high efficiency

(d)

all of the above

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UNDERSTANDING QUESTIONS The type of regulator circuit shown is a _________. (a)

series linear

offon

+VIN

(b)

series switching

(c)

shunt switching

(d)

none of the above

off on D1

Q1

R1

+

−

C discharges

L

–VOUT

C

C Variable + − pulse-width l id hL L fi field field fildcharge ld b builds ild oscillator collapses s

R2

RL

+ –

R3 D2

104

SEE 3263 VOLTAGE REGULATORS

UNDERSTANDING QUESTIONS The output p voltage g from a 7912 is a regulated g _________. (a)

+5 V

(b)

+12 V

(c)

−5 V

(d)

−12 V

105

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THE END

106