Ch9 Intro to Power Supplies

7/30/2019 Ch9 Intro to Power Supplies

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Bridging Theory in Practice

Transferring Technical Knowledge

to Practical Applications


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Introduction to Power Supplies


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Introduction to Power Supplies

Intended Audience: Electrical engineers with little or no power supply

background

An understanding of electricity (voltage and current) is

assumed

A simple and functional understanding of transistors is

assumed

Expected Time:

Approximately 60 minutes


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Outline

1) What is a Power Supply?2) Types of Power Supplies

3) Linear Voltage Regulator

4) Characteristics of Linear Voltage Regulators

5) Auxiliary Functions of Voltage Regulators

6) Types of Switching Voltage Regulators

7) Characteristics of Switching Voltage Regulators

8) Choosing Between Linear and Switching Voltage

Regulators


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What is Electrical Power?

Time(s)

Energy(J)P

Time(s)

(C)Charge

Charge(C)

Energy(J)P

IVPCurrentVoltagePower

Electrical power (P) is equal to the product of electrical

current (I) and a voltage (V).

C1.6x10-electron1

s

JWatts

Secondss

JoulesJ

ColoumbsC

:Units

19-

J/sW10P1A10VP

:PowerCalculate

1AI

V10V

CurrentandVoltageGiven

:Example

Power has not changed since collegiate physics: P = V * I

Output power is the product of the output current and the output voltage

Input power is the product of the input current and the input voltage

Input power must always be greater than output power


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What is a Power Supply?

Electrical Definition of Power Supply

Conversion of a voltage into an desired voltage

Example: Car Battery (12 V)Microprocessor (5 V)

Efficiency Example:

PIN = (12 V) x (1 A) = 12 W

POUT = (5 V) x (1 A) = 5 W

The remaining 7W (12 W 5 W) of power is lost as heat

The efficiency is:

Power Supply OutputInput Load1) LED

2) Micro

Source1) Battery (DC)

2) Wall Outlet (AC)

5 V

1 A

12 V

1 A

%24W12

W5

INP

OUTP

Power supplies are not

100% efficient.


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Outline



4) Characteristics of Linear Voltage Regulators5) Auxiliary Functions of Voltage Regulators


7) Characteristics of Switching Voltage Regulators8) Choosing Between Linear and Switching Voltage

Regulators


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Types of Power Supplies AC-DC and

DC-DC Converters

Vin = 110VacVout =12Vdc

AC-to-DCConverter

V

t

V

t

DC-to-DCConverter

V

t

V

t

Vin =

12Vdc Vout = 5Vdc

AC to DC

DC to DC

Power supplies can be categorized into AC-DC and DC-DC.


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DC-to-DCConverterBuck

VIN > VOUT

V

t

V

t

Vin = 12VVOUT = 5V

DC-to-DCConverterBoost

Vin < Vout

V

t

V

t

Vin = 5VVOUT = 12V

Boost - Step Up (Switching Regulator)

Buck - Step Down (Linear orSwitching Regulators)

Types of Power Supplies DC-to-DC

Converters Types

DC-DC Converters can be categorized as Boost or Buck.

Buck can be Linear or Switching regulator.


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Types of Power Supplies Input Voltage of

Step Down Converter

Buck -

Step Down

Converter

VIN > VOUT

VOUT

t

15V

10V

5V

0V

VIN

t

15V

10V

5V

0V

The actual input voltage does not need to be a true DC value.

However VIN > VOUT for step down converter.


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Types of Power Supplies

What is a Switching and Linear Power Supply?

Switching Power Supply

The pass transistor operates in a digital fashion.

When in regulation, the pass transistor (power transistor between the input and

output) is either completely on or completely off.

An external passive component is used in the architecture for energy storage and

transfer

Linear Power Supply

The pass transistor operates in an analog fashion.

When in regulation, the pass transistor (power transistor between the input and

output) is always on.

No additional passive component is needed to create the desired output voltage


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Types of Linear Power Supplies1. NPN or Standard

2. PNP or Low Drop Out (LDO)

3. MOS Low Quiescent Current

Linear Power Supply

Input OutputPass Transistor

Control

Linear power supply can be broadly labeled:1. Standard

2. Low Drop Out

3. Low Quiescent

T f P S li


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VIN VOUT

CONTROL

VCE ~ 0.5V

VBE ~ 0.7V

VBE ~ 0.7V

~ 2.0V


NPN or Standard Linear Regulators

NPN or Standard linear regulators use a NPNDarlington pass transistor and ~ 2.0 V drop out


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~ 1.2V

VIN VOUT

CONTROL

VCE ~ 0.5V

VBE ~ 0.7V


Quasi Low Drop Out Linear Regulator

Quasi linear regulators use a single NPN pass

transistor ~ 1.2 V drop out


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VIN VOUT

CONTROL

VEC < 0.5V

IQUIESCENT


PNP or Low Drop Out (LDO) Regulator

PNP or Low Drop Out (LDO) linear regulators use asingle PNP pass transistor and < 0.5 V drop out


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VIN VOUT

CONTROLCharge

Pump

VDS < 0.5V

IQUIESCENT 0


MOS LDO Low Quiescent Current Regulator

MOS linear regulators use a MOSFET as the pass transistor

offering low quiescent current and low drop out < 0.5 V.


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Summary of Linear Voltage Regulators

Standard Linear

Regulator

Low Drop Linear

Regulator

Low Quiescent

MOS LinearRegulator

Drop Out Voltage 3 1 (Tie) 1 (Tie)

Quiescent

Current

3 2 1

Features 3 2 1

Cost 1 2 3

Total

(Lower is better)

10 7 6

VIN VOUT

CONTROL

VIN VOUT

CONTROL

VIN VOUT

CONTROLCharge

Pump

VIN VOUT

CONTROLCharge

Pump


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Outline






Regulators

Li V lt R l t


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VREF

VINVOUT

VINTControl

Block

OVERTEMP

VREF

PassTransistor

Voltage

Divider

1) Op Amp

2) Protection

Bandgap

Reference

Linear Voltage Regulator

Functional Diagram

Li V lt R l t


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Pass (Output) Transistor Below, the output transistor is PNP bipolar junction transistor

The emitter-base voltage of the transistor will be adjusted in

an analog fashion to maintain the proper output voltage

VIN

VOUT

VINT

VREF

Li V lt R l t


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Resistor Divider The resistor divider is from the output to

ground

Resistors are sized such that the intermediatenode is equal to the bandgap reference voltageunder typical conditions

Voltage Regulator

VOUT

R6

R7

VINT

VINT = (VOUT)(R7) = VREF

R6 + R7

Li V lt R l t


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Operational Amplifier If V

INT

is higher (lower) than VREF

, the operational

amplifiers output voltage increases (decreases).

This decreases (increases) the VEB voltage, and VOUT

will decrease (increase).V

IN

VOUT

VINT

VREF

+

-

VEB

IB

IC

Linear Voltage Reg lator


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Bandgap Voltage Reference Internally generated with tight tolerance, traditionally ~

1.2V

VOUTwill be built from reference voltage (VREF)

TARGET

VREF

+ 2%

+ 1%

VREF, nom

- 1%

- 2%

l . i .

,

,

,

,

,

,

,

,

,

-50 -25 0 25 50 75 100 125

Temp

VREF

VREF = VBE+2(R2/R1)VTln10


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Current Limit and Short Circuit Detection

The current through an alternate collector tap is measured. If

it is too high, the regulator can limit the current from

increasing further (current limit) or turn itself off (short circuit

detect)

VIN

VOUT

VINT

VREF

Control

Block

Li V l R l


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Over Temperature Detect At temperature increases, the V

BEnecessary to turn

on a NPN decreases, so above 150C, the transistor

turns on and OVERTEMP goes LO

VIN

VOUT

VINT

VREF

Control

Block

OVERTEMP

VREF

+

-VBE


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Outline






Regulators

Characteristics of Linear Voltage


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Characteristics of Linear Voltage

Regulators

1.Output Voltage Accuracy

2.Output Current

3.Dropout Voltage4.Quiescent Current

5.Thermal Resistance


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Characteristics of Linear Voltage Regulators

Output Voltage Accuracy

Characteristic

Output Voltage

Output Voltage

Symbol

VOUT

VOUT

Min

4.90

4.80

Typ

5.00

5.00

Max

5.10

5.20

Unit

V

V

Condition

IOUT = 1mA

VIN = 14V

1mA < IOUT < 50mA

6V < VIN < 30V

1

2

Output Voltage Accuracy characterizes how reliable the output voltage

will be under various operating conditions.

Consider the entire operating condition when viewing the accuracy.

Ch t i ti f Li V lt R l t


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Output Current

Characteristic

Current Limit

Current Limit

Short Circuit

Current

Symbol

ILIM

ILIM

Min

100

150

200

Typ

200

300

---

Max

---

400

---

Unit

mA

mA

mA

Condition

VOUT = VOUT,TYP-100mV

TJUNCTION = 25C

VOUT = VOUT,TYP-100mV

-40C < TJUNCTION < 125C

-40C < TJUNCTION < 125CISC

Output Current Limit is the maximum amount of

current that can be sourced by the regulator.


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Drop Out VoltageCharacteristic

Dropout Voltage

Dropout Voltage

Symbol

VDROP

VDROP

Min

---

---

Typ

0.20

0.40

Max

0.30

0.60

Unit

V

V

Condition

IOUT = 1mA

VOUT = VOUT,TYP 100mV

IOUT = 100mA

VOUT = VOUT,TYP 100mV

Drop Out Voltage is the minimum voltage differential

between the linear regulators input and output

that is required for voltage regulation.

Example:Given:

VDROP = 0.3 VVOUTPUT = 5.0 V

Calculate Minimum Input Voltage (VINPUT = VOUTPUT + VDROP)VINPUT = 5.0 V + 0.3 V = 5.3 VVINPUT = 5.3 V MIN


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Quiescent (Ground) Current

Characteristic

Quiescent

Current

Quiescent

Current

Symbol

IQ

IQ

Min

---

---

Typ

100

4

Max

200

8

Unit

A

mA

Condition

IOUT < 1mA

VIN = 14V

IOUT = 50mA

TJUNCTION = 85C

Quiescent Current is the current

consumed by the voltage regulator.


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Thermal Resistance

Characteristic

Thermal

Resistance

Junction-Ambient

Thermal

Resistance

Junction-Case

Symbol

Rthja

Min

---

---

Typ

---

---

Max

120

35

Unit

C/W

C/W

Condition

Package mounted on

FR4 PCB

80x80x1.5mm3

To lead frameRthjc

Thermal resistance indicates how much heat can be conducted by the regulator.

Lower thermal resistance better thermal performance

thjaDAMBIENTJUNCTION RPTT

Ch t i ti f Li V lt R l t


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Thermal Resistance Calculation Example

Voltage Regulator

VIN

VOUT

IIN IOUT

Iq

C/W286W0.227

C85C150R

P

T-TR

:nCalculatioResistanceThermal

thja

D

AMBIENTJUNCTIONthja

W0.277P

mA)(0.5V)(14mA)(30V)5-V(14P

IVI)V-(VP

nCalculatioPower

D

D

qINOUTOUTIND

2 3

GIVEN:

1) VIN = 14 V

2) VOUT = 5 V

3) IOUT = 30 mA

4) Iq = 0.5 mA

5) TAMBIENT = 85 C6) TJUNCTION = 150 C

1


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Outline

1) What is a Power Supply?

2) Types of Power Supplies


4) Characteristics of Linear Voltage Regulators5) Auxillary Functions of Voltage Regulators


7) Characteristics of Switching VoltageRegulators

8) Choosing Between Linear and Switching

Voltage Regulators

A ill F ti f V lt R l t


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Auxillary Functions of Voltage Regulators

Inhibit Function

Some voltage regulator outputs that can be

enabled or disabled with an INHIBIT input

When a voltage regulator is turned off, the

quiescent current drops dramatically

Characteristic

Quiescent

Current

Quiescent

Current

Quiescent

Current

Symbol

IQ

IQ

IQ

Min

---

---

---

Typ

100

4

1

Max

200

8

2

Unit

A

mA

A

Condition

IOUT < 1mA

VIN = 14V

IOUT = 50mA

TJUNCTION = 85C

INHIBIT = TRUE



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Reset Function Most automotive modules are controlled by a microcontroller with a crystal

oscillator stabilization time of 1 10 ms. Only when a stable clock signal is available, can a microcontroller be correctly initialized

A Reset signal is sent from the linear voltage regulator to the microcontroller to

indicate an established and valid operating voltage.

A small (~100nF) external capacitor controls the reset delay timing

A ill F ti f V lt R l t


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Watchdog Function A microcontroller can be monitored through a watchdog

circuit

Periodically, a microcontroller is expected to strobe (pet)

the watchdog to let the watchdog know it is still functioning

Voltage Regulator MicrocontrollerVOUT

STROBE

RESET

time

RESET

Voltage

STROBE

Watchdog

A illar F nctions of Voltage Reg lators


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Watchdog Function

However, if the microcontroller forgets to pet the watchdog,a software problem may have occurred

Therefore, the voltage regulator resets the microcontroller to

bring it to a known state

Voltage Regulator MicrocontrollerVOUT

STROBE

RESET

time

RESET

Voltage

Missing STROBE

Watchdog



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Early Warning Function Senses an analog input and then a transmits a digital signal to a

microcontroller once the analog input threshold has been

triggered.

Commonly used to provide an Early Warning to the

microcontroller that the battery voltage has dropped and reset

may occur.

Voltage

Regulator

VBA

TVIN

WARN_IN

RSI1

RSI2

VOUT

WARN_OUT

Microcontroller

RESET

V

oltage

VOUT

RESETVIN

WARN_OUT time


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Outline

1) What is a Power Supply?

2) Types of Power Supplies




7) Characteristics of Switching VoltageRegulators


Voltage Regulators

T f S it hi V lt R l t


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Types of Switching Voltage Regulators

Inductive and Capacitive

Inductive

Switching Regulators

Uses inductor or transformer

for passive charge control

Output current may range from

1mA to many Amps

PCB design is moderately

complex

Traditionally used in

automotive applications

Automotive grade parts

Capacitive


Uses external capacitor(s)

for passive charge control

Relatively low output

current for the price

PCB design is relatively

simple

Not traditionally used in

automotive applications Few automotive grade parts



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Inductive Buck Regulator (VOUT < VIN)

Buck

Regulator

VIN VSWITCHVOUT

VFEEDBACK



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Inductive Boost Regulator (VOUT > VIN)

Boost

Regulator

VIN

VSWITCH

VOUT

VFEEDBACK



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Additional Inductive Switching Regulators

Inverting Regulators

VOUT = - VIN

Buck-Boost Regulators

VIN,MIN < VOUT < VIN,MAX

Multiple Output Regulators

VOUT1 = 2VIN, VOUT2 = -VIN

VIN = 16V, VOUT1 = 3.3V, VOUT2 = 5V, VOUT3 = 12V


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Outline





7) Characteristics of Switching Voltage

Regulators


Voltage Regulators

Characteristics of Switching


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Characteristics of SwitchingVoltage Regulators

Linear & Switching

1. Output Voltage

Accuracy

2. Output Current

3. Dropout Voltage

4. Quiescent Current5. Thermal Resistance

+Switching

1. Switching

Frequency

2. External

Components Size

and Cost

3. Ripple Voltage

4. Efficiency

Characteristics of Switching Regulators


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Switching Frequency

Frequency is probably the most often cited

characteristic of a switching regulator

Usually (but not always!), high frequency translatesinto:

Higher efficiency

Smaller external components

Higher price

High frequency can also mean additional design

problems



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External Components, Size and Cost

The design of a power supply is a true engineering challengein the optimization of performance, price, and space

Larger valued, higher quality, higher price external

components usually translate into higher performance

An optimal power supply design, however, will meet the

required performance requirements while using acceptable

external components (smaller values of inductance andcapacitance, higher values of parasitic resistance)

Possible value ranges may approach two orders of magnitude



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Ripple Voltage

Because the switching power supply is constantly being

switched on and off, the output voltage will oscillate

around a typical value

VTYP

VMIN

VMAX

Power Supply

Charging COUT

Load

Discharging COUT


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Outline





7) Characteristics of Switching Voltage

Regulators


Voltage Regulators

Choosing Between Linear and


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When possible, most designers would prefer

to use a linear voltage regulator rather than a

switching voltage regulator

Why Linear?

1. Linear regulators are usually lower in price

2. Linear regulators are usually simpler to

implement3. Linear regulators do not have associated

noise/ripple problems apparent in switching

regulators



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Switching RegulatorsWhen to use a switching regulator:

1. When the minimum input voltage is at or below the desired outputvoltage because linear regulators cannot provide an output voltage

greater than the input voltage

2. The heat sinking of a linear regulator is prohibitive in price or space

3. The efficiency of a linear regulator cannot maintain the junction

temperature below the specified maximum (150 C)

mA152395-16

85-150I

RV-V

T-TI

R

T-TP

:nCalculatioCurrentOutput

OUT

thjaoutin

AMBIENTJUNCTIONOUT

thja

AMBIENTJUNCTIOND


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Ch9 Intro to Power Supplies

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