Bridging Theory in Practice Transferring Technical Knowledge to Practical Applications.

Bridging Theory in PracticeTransferring Technical Knowledgeto Practical Applications

Introduction to Power Supplies

Introduction to Power SuppliesIntended 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

Outline1) What is a Power Supply?2) Types of Power Supplies3) Linear Voltage Regulator4) Characteristics of Linear Voltage Regulators5) Auxiliary Functions of Voltage Regulators6) Types of Switching Voltage Regulators7) Characteristics of Switching Voltage Regulators8) Choosing Between Linear and Switching Voltage

Regulators

What is Electrical Power?

Time(s)

Energy(J)P

Time(s)

(C)Charge

Charge(C)

Energy(J)P

IVP

CurrentVoltagePower

Electrical power (P) is equal to the product of electrical current (I) and a voltage (V).

C 1.6x10- electron 1

s

J Watts

Seconds s

Joules J

Coloumbs C

:Units

19-

J/s W 10P

1A 10V P

:Power Calculate

1A I

V 10 V

Current and VoltageGiven

: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

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 η is:

Power Supply OutputInput Load1) LED2) Micro

Source1) Battery (DC)

2) Wall Outlet (AC)

5 V1 A

12 V 1 A

%24 W12

W5

INPOUT

Pη Power supplies are not

100% efficient.


Regulators

Types of Power Supplies AC-DC and DC-DC Converters

Vin = 110VacVout = 12VdcAC-to-DC

Converter

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.

DC-to-DCConverter“Buck”

VIN > VOUT

V

t

V

t

Vin = 12VVOUT = 5V

DC-to-DCConverter“Boost”

Vin < Vout

V

t

V

t

Vin = 5V VOUT = 12V

Boost - Step Up (Switching Regulator)

Buck - Step Down (Linear or Switching 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.

Types of Power Supplies Input Voltage of Step Down Converter

Buck -Step DownConverterVIN > 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.

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

Types of Power Supplies What is a “Linear” Power Supply?

BC IβI

Linear Power Supply

VIN VOUTPass Transistor

ControlIB = 100 uA

IB = 200 uA

IB = 300 uA

Collector to Emitter Voltage(VCE)

Col

lect

or C

urre

nt(I

C)

Saturation Linear

Cutoff

A “linear” power supply regulates the output by operating the pass transistor in the “linear/active” region.

Types of Power Supplies Types of Linear Power Supplies

1. “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

VIN VOUT

CONTROL

VCE ~ 0.5V

VBE ~ 0.7V

VBE ~ 0.7V

~ 2.0V

Types of Power Supplies“NPN” or Standard Linear Regulators

NPN or “Standard” linear regulators use a NPN Darlington pass transistor and ~ 2.0 V drop out

~ 1.2VVIN VOUT

CONTROL

VCE ~ 0.5V

VBE ~ 0.7V

Types of Power Supplies“Quasi” Low Drop Out Linear Regulator

“Quasi” linear regulators use a single NPN pass transistor ~ 1.2 V drop out

VINVOUT

CONTROL

VEC < 0.5V

IQUIESCENT

Types of Power Supplies“PNP” or Low Drop Out (LDO) Regulator

PNP or “Low Drop Out” (LDO) linear regulators use a single PNP pass transistor and < 0.5 V drop out

VIN VOUT

CONTROLChargePump

VDS < 0.5V

IQUIESCENT 0

Types of Power Supplies 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.

Types of Power Supplies Summary of Linear Voltage Regulators

Standard Linear Regulator

Low Drop Linear Regulator

Low Quiescent MOS Linear Regulator

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

CONTROLChargePump

VIN VOUT

CONTROLChargePump


Regulators

VREF

VIN

VOUT

VINTControlBlock

OVERTEMP

VREF

Pass Transistor

VoltageDivider

1) Op Amp2) Protection

BandgapReference

Linear Voltage RegulatorFunctional Diagram

Linear Voltage RegulatorPass (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

Linear Voltage RegulatorResistor Divider• The resistor divider is from the output to

ground• Resistors are sized such that the intermediate

node is equal to the bandgap reference voltage under typical conditions

Voltage Regulator

VOUT

R6

R7

VINT

VINT = (VOUT)(R7) = VREF

R6 + R7

Linear Voltage RegulatorOperational Amplifier

• If VINT is higher (lower) than VREF, the operational amplifier’s output voltage increases (decreases). This decreases (increases) the VEB voltage, and VOUT will decrease (increase).

VIN

VOUT

VINT

VREF

+

-VEB

IB

IC

Linear Voltage RegulatorBandgap Voltage Reference

• Internally generated with tight tolerance, traditionally ~ 1.2V

• VOUT will be “built” from reference voltage (VREF)

TARGET

VREF

+ 2%

+ 1%

VREF, nom

- 1%

- 2%

PACT s0784-b-1 ch. sta (29v*287c) 28-Dec-1 page 1

12345678910111213141516171819202122232425

lo 4.9 hi 5.1

TEMP

4,89

4,92

4,95

4,98

5,01

5,04

5,07

5,10

5,13

-50 -25 0 25 50 75 100 125

Temp

VREF

VREF = VBE+2(R2/R1)VTln10

Linear Voltage RegulatorCurrent 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

ControlBlock

Linear Voltage RegulatorOver Temperature Detect• At temperature increases, the VBE necessary to turn

on a NPN decreases, so above 150C, the transistor turns on and OVERTEMP goes LO

VIN

VOUT

VINT

VREF

ControlBlock

OVERTEMP

VREF

+

-VBE


Regulators

Characteristics of Linear Voltage Regulators

1.Output Voltage Accuracy 2.Output Current3.Dropout Voltage 4.Quiescent Current 5.Thermal Resistance

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 = 1mAVIN = 14V

1mA < IOUT < 50mA6V < 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.

Characteristics of Linear Voltage Regulators Output Current

Characteristic

Current Limit

Current Limit

Short CircuitCurrent

Symbol

ILIM

ILIM

Min

100

150

200

Typ

200

300

---

Max

---

400

---

Unit

mA

mA

mA

Condition

VOUT = VOUT,TYP-100mVTJUNCTION = 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.

Characteristics of Linear Voltage Regulators Drop Out Voltage

Characteristic

Dropout Voltage

Dropout Voltage

Symbol

VDROP

VDROP

Min

---

---

Typ

0.20

0.40

Max

0.30

0.60

Unit

V

V

Condition

IOUT = 1mAVOUT = VOUT,TYP – 100mV

IOUT = 100mAVOUT = VOUT,TYP – 100mV

Drop Out Voltage is the minimum voltage differential between the linear regulator’s 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

Characteristics of Linear Voltage Regulators Quiescent (Ground) Current

Characteristic

QuiescentCurrent

QuiescentCurrent

Symbol

IQ

IQ

Min

---

---

Typ

100

4

Max

200

8

Unit

A

mA

Condition

IOUT < 1mAVIN = 14V

IOUT = 50mATJUNCTION = 85C

Quiescent Current is the current consumed by the voltage regulator.

Characteristics of Linear Voltage Regulators Thermal Resistance

Characteristic

ThermalResistanceJunction-Ambient

ThermalResistanceJunction-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

Characteristics of Linear Voltage Regulators Thermal Resistance Calculation Example

Voltage Regulator

VIN

VOUT

IIN IOUT

Iq

C/W286 W0.227

C 85C 150R

P

T - TR

:nCalculatio Resistance Thermal

thja

D

AMBIENTJUNCTIONthja

W0.277 P

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

I V I )V - (V P

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° C

6) TJUNCTION = 150° C

1

Outline1) What is a Power Supply?2) Types of Power Supplies3) Linear Voltage Regulator4) Characteristics of Linear Voltage Regulators5) Auxillary Functions of Voltage Regulators6) Types of Switching Voltage Regulators7) Characteristics of Switching Voltage Regulators8) Choosing Between Linear and Switching Voltage

Regulators

Auxillary Functions of Voltage RegulatorsInhibit 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

QuiescentCurrent

QuiescentCurrent

QuiescentCurrent

Symbol

IQ

IQ

IQ

Min

---

---

---

Typ

100

4

1

Max

200

8

2

Unit

A

mA

A

Condition

IOUT < 1mAVIN = 14V

IOUT = 50mATJUNCTION = 85C

INHIBIT = TRUE

Auxillary Functions of Voltage Regulators 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

Auxillary Functions of Voltage Regulators 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

Vo

ltage

STROBE

Watchdog

Auxillary Functions of Voltage Regulators 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

Vo

ltage

Missing STROBE

Watchdog

Auxillary Functions of Voltage Regulators 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.

VoltageRegulator

VBAT VIN

WARN_INRSI1

RSI2

VOUT

WARN_OUT

Microcontroller

RESET

Vo

ltage

VOUT

RESETVIN

WARN_OUTtime


Regulators

Types of Switching Voltage RegulatorsInductive 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 Switching Regulators

• 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

Types of Switching Voltage Regulators Inductive Buck Regulator (VOUT < VIN)

BuckRegulator

VIN VSWITCH VOUT

VFEEDBACK

Types of Switching Voltage Regulators Inductive Boost Regulator (VOUT > VIN)

BoostRegulator

VIN

VSWITCH

VOUT

VFEEDBACK

Types of Switching Voltage Regulators Additional Inductive Switching Regulators

• Inverting RegulatorsVOUT = - VIN

• Buck-Boost RegulatorsVIN,MIN < VOUT < VIN,MAX

• Multiple Output RegulatorsVOUT1 = 2VIN, VOUT2 = -VIN

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


Regulators

Characteristics of Switching Voltage Regulators

Linear & Switching1. Output Voltage

Accuracy 2. Output Current3. Dropout Voltage 4. Quiescent Current 5. Thermal Resistance

+Switching1. Switching

Frequency2. External

Components Size and Cost

3. Ripple Voltage 4. Efficiency

Characteristics of Switching Regulators Switching Frequency

• Frequency is probably the most often cited characteristic of a switching regulator

• Usually (but not always!), high frequency translates into:

• Higher efficiency• Smaller external components• Higher price

• High frequency can also mean additional design problems

Characteristics of Switching Regulators External Components, Size and Cost

• The design of a power supply is a true engineering challenge in 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 and capacitance, higher values of parasitic resistance…)

• Possible value ranges may approach two orders of magnitude

Characteristics of Switching Regulators 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 SupplyCharging COUT

Load Discharging COUT

Characteristics of Switching Voltage Regulators Efficiency

• The most important characteristic of a switching regulator is efficiency because this is the primary reason for their use.

• Efficiency will also vary with output current load, input voltage, and temperature

95%

85%

75%

65%0.5A0A 1.0A

Load Current

Efficiency vs. Load Current

VIN = 24V

VIN = 12V

95%

85%

75%

65%2010 30

Input Voltage (V)

ILOAD = 100mA

ILOAD = 1A

Efficiency vs. Input Voltage


Regulators

Choosing Between Linear and Switching Regulators

• 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 price2. Linear regulators are usually simpler to implement3. Linear regulators do not have associated

noise/ripple problems apparent in switching regulators

Choosing Between Linear and Switching Regulators

When to use a switching regulator:1. When the minimum input voltage is at or below the desired output

voltage 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)

mA 152

395-16

85 - 150I

RV-V

T - TI

R

T - TP

:nCalculatioCurrent Output

OUT

thjaoutin

AMBIENTJUNCTIONOUT

thja

AMBIENTJUNCTIOND

Thank You!www.btipnow.com

Bridging Theory in Practice Transferring Technical Knowledge to Practical Applications.

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Transcript of Bridging Theory in Practice Transferring Technical Knowledge to Practical Applications.