© 2006 DCHopkins ABCs of Power Electronic Systems By Dr. Doug Hopkins & Dr. Ron Wunderlich DCHopkins & Associates Denal Way,

© 2006 DCHopkins www.DCHopkins-Associates.Com

ABCs of Power ABCs of Power Electronic SystemsElectronic Systems

ByBy

Dr. Doug Hopkins & Dr. Ron WunderlichDr. Doug Hopkins & Dr. Ron Wunderlich

DCHopkins & AssociatesDCHopkins & Associates

Denal Way, m/s 408Denal Way, m/s 408

Vestal, New York 13850-3035Vestal, New York 13850-3035

[email protected]@dchopkins-associates.com


Our Professional Challenge

“The illiterate of the 21st century will not be

those who cannot read and write, but those

who cannot learn, unlearn and relearn.”

-- Alvin Toffler

Dr. Toffler, Ph.D., is one of the world's preeminent futurists. As co-author of War and Anti-War, he

sketches the emerging economy of the 21st century, presenting a new theory of war and revealing how

changes in today's military parallel those in business.


About the Course Authors?

• Dr. Doug Hopkins– PhD. Virginia Tech, VA Power Electronics Center– GE-CR&D, Carrier Air Conditioning Company(UTC), University

at Buffalo, and DCHopkins & Associates (President)– R&D for advanced power electronic systems– [email protected]

• Dr. Ron Wunderlich – Ph.D. Binghamton University– IBM Power Systems, Celestica Power Systems, Transim Corp,

and Innovative Design and Development (President)– Chief Engineer in design and development of power supplies for

the computer and telecom industries.– [email protected]


Course Topics

1. Overview of Power Electronics Technology1a. Introduction to the power electronics system

2. Knowing your specifications2a. Design for safety

3. Choosing the correct topologies3b. Knowing where disaster can strike

4. Characterizing power components4a. A safe operating area

4b. The dual faces of MOSFETS4c. The circuit is a component

5. Design approaches and tools5a. Simulating reality

5b. Input filtering6. Design approaches and tools

6a. Design case study


DCHopkins & Associates - Products

• 600W family of isolated DC/DC building blocks

Pictures courtesy of Celestica, Incorporated

Products designed by our Associates,photographed by our Associates.

• Multi-output telecom power supply


DCHopkins & Associates - Products

• 30A high efficiency, high-transient isolated power supply

Pictures courtesy of Celestica, Incorporated

• Isolated power supply for high-end micro-processor


Where to go for news (other than suppliers)?

News Sources

• http://www.darnell.com (PowerPulse Daily)

• http://www.poweronline.com (see electricnet)

• http//www.electricnet.com (see poweronline)

• http://www.powersystems.com• http://www.eedesign.com• http://www.psma.com• http://www.ejbloom.com (see attached catalog)

• Conferences:– http://www.pels.org (the IEEE Power Electronics Society)

• http://www.apec-conf.org• http://www.pesc06.org• http://www.intelec.org


Introduction toIntroduction to The SystemThe System

PowerProcessor

LoadSource


Conversion or Supply

Motor drives• Linear• Rotational

Lighting• Fluorescent• HID• Halogen

Pulsed power• Ignition• Flash lamp• Pulsed propulsion

POWER CONVERSION

PowerProcessor

LoadSource

Types of Loads

“Conversion” changes one energy form to another.

Electrical Source


Conversion or Supply

Computer Applications

– Desktops– Workstations– Servers– Mainframes

Circuits:– CPU– Memory– Bus Terminators– Logic– Graphics

Telecom Applications– Routers– Tele. Switches

Circuits:– Optical Amps– CPU– Memory– Switch Cards– Logic

POWER SUPPLY

LOAD PowerProcessor

LoadSource

Handheld Applications– PDA’s– Notebooks– Cell-phones

Circuits:– RF Amps– CPU/Logic– Memory– Display– Audio Amps

“Supply” changes only the attributes.


Time

Vo

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Time

Vo

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Uninterruptible Power Supply Systems

PowerProcessor

Electronic Circuit

Clean AC UtilityNoisy AC

Utility

• Electronic Circuits are– Any electronic equipment that requires clean, reliable AC utility

• Computers, Telecom equipment, Home appliances• Sources are

– DC such as a battery or solar cells– AC utility that is of poor quality


The System - Source Characteristics

PowerProcessor

LoadSource

IF THE SOURCE THEN THE LOAD

matches the load flashlight

is directly regulated generator field control

has over capacity requires regulating circuit

SOURCE


The System - Source Characteristics

PowerProcessor

LoadSource

THE POWER PROCESSOR

Converts an unregulated power source to a regulated output.Like CPU’s processing information - Power Supplies process energy.

Linear Regulator

Absorbs the energy difference

Switch-mode Regulator

Chops and averages energy packets


Knowing Your Knowing Your SpecificationsSpecifications

and theand theUser’s RequirementsUser’s Requirements


Developing User Requirements

• Typically, User Requirements are derived through a polling process.

• This brings forward the highest-priority requirements, but are limited to personal experiences.

• A comprehensive approach uses a matrix of

Five Taxonomies

and

Three Characteristics

Responsible Design is from Cradle to Grave


Grouping User Requirements

Characteristic

Unspoken Expectations

Articulated Needs

Unexpected FeaturesTaxonomy

Financial

Legal

Social

Environmental

Technical

MATRIXEDMATRIXED


Taxonomies in User Requirements

• Financial requirements: represent cost and is base metric for other matrix entries.

• Legal requirements: include intellectual property as a source of revenue, strategic positioning or enticement.

• Social requirements: represent the corporate culture and image, global perceptions, and ethical conduct.

• Environmental requirements: represent government regulations and broader global concerns.

• Technical requirements: science based metrics related to ‘energy forms’ and provide the “SPECIFICATIONS.”


Characteristics of User Requirements

• Unspoken Expectations: – requirements for a product, process or service to be acceptable to

all end users. Though labeled as unspoken, these may be new requirements that develop while a business has not been keeping up with the competition or market place, or basic requirements for entry into new markets.

• Articulated Needs:– typical, open and printed “specifications. ” Discerns one user

from another. There should be no question that these needs are requirements that must be met for each user.

• Unexpected Features:– exciters that make the product, process or service unique and

readily distinguishable from the competition. (This is what the sales force lives for.) Features are speculative requirements.


Example User Requirements

• Unspoken Environmental Expectation: the product is not lethally hazardous to shippers

• Articulated Technical Need: the products will operate from -40°C to +100°C.

• Unexpected Legal Feature: the product can have exclusive patent

protection.


Defining Specifications

PowerSupply

Iin

Vin

Iout

Vout

Technical User Requirements provide the

SPECIFICATIONS

for each Energy Form.

Power electronic circuits condition and convert

many energy forms!

• Electric

• Magnetic

• Electromagnetic

• Thermal

• Mechanical

• Chemical

• Photonic


Framework leading to Specifications

Responsible Design is from Cradle to Grave.

Characteristics

Tax

onom

ies

Technical Characteristics– Energy Forms– Conditions

• Start-up• Shut-down• Normal operation• Fault operation


Electrical Specs

Vin, Iin

AC

Vin, Iin

DC

Input

Vout, Iout

Output

PGood, On/Off

Controls

Efficiency

Misc

Electrical Spec


DC Input Spec

• Typical DC sources:– Car Battery typical 12 volts with 11 to 14 volts variation– Solar Cell 0.5 to 1 volt per cell depending on sunlight– Telecom Bus typical 48 volts with 36 to 72 volts variation– PC Internal 5V Bus 5 volts, +/- 10%

• Example: A Telecom bus has a Vin operating range of 36 to 72 volts– If the input voltage drops below 36V, typically, a PS will shut down.– If the input voltage exceeds 72V, typically, a PS will be damaged by the

excessive high voltage.• A PS can be designed so it can handle short duration of high

input voltage such as line transients due to lightning.• This is known as a surge rating.• For example, this PS may have a surge rating of 100V for

100usec.

Specifying Vin depends on the source voltage range.


DC Input Spec - Iin, Pout, Pin,

• Pout (output power) = Vout x Iout

• Pin (input power) = Vin x Iin

(efficiency of the PS) = Pout / Pin– Typically between 0.5 to 0.98

• Substituting and solving for IinIin = (Vout x Iout) / (Vin x )

Iin is the current drawn by the PS and derived by

Note: Worst case - Iin occurs at lowest value of Vin, e.g.for telecom PS most current is at Vin=36 volts.


IripIin

Time

DC Input Spec

• Specified as peak-to-peak.

• Occurs at usually < 10Mhz

• Typically, < 10% of max Iin

• E.g., if Iin max is 10A, Irip p-p should < 1A

Iin will have ripple current, Irip, from the switching stage within the PS.


Time

Iin

Time

Iin Vin

DC Input Spec

• Iin will have switching noise that occurs at >10Mhz.

• The noise is due to the internal capacitive coupling parasitics

• Typically, the peak-to-peak noise is less than 1% of max Iin

Iin will have switching noise.


Time

Iin Vin

DC Input Spec

• Surge current, Isurge, is due to charging of internal capacitors

• Usually Isurge is less than 5 times max Iin

• This can cause problems with fusing.

Iin will have a surge during start-up.


Specifying Vin depends on the source voltage rangeAC Input Spec

• Typical AC sources for the home– Doorbell, heating systems 24Vrms +/- 30%– Household wiring Typically 110Vrms with 90 to 130 range– Electric stoves Typically 220Vrms with 180 to 260 range

• Actually, 220Vrms with a center-tap is delivered to the home. 110Vrms is derived from the center-tap

• Typical AC sources for business (single phase derived from three phase)– Office wiring Typically 120Vrms with 90 to 140 range– Industrial/Computer Typically 208Vrms with 180 to 260– Smaller businesses will use the household AC utility

• Europe and some other countries are wired with either 208Vrms or 220Vrms


AC Input Spec

• Vin for typical products– Desktop PC sold in the US, 90Vrms – 140Vrms– Desktop PC sold Worldwide, 180Vrms – 260Vrms– High-end servers sold worldwide, 180Vrms – 260Vrms– Desktop PC with “universal” PS, 90Vrms – 260Vrms– Why not use a “universal” PS in all desktop PC’s ?

• “Universal” PS are more expensive and difficult to design

• Operating frequency for Vin is specified as– USA - 60Hz; Europe and other countries - 50Hz, range is +/-3Hz

• A “universal” PS operates from 47Hz to 63Hz– This is not a cost or a design problem


AC Input Spec - Vin-rms

• AC sources are:– Single Phase– Three Phase (>5kW, not covered)

• Vin is understood to be Vin-rms; – Vin-rms = Vpk / 1.4142 *

• RMS makes calculations easier– For DC, Pin = Vin x Iin– For AC, Pin = Vin-rms x Iin-rms

* For single frequency sine wave PowerSupply

Iin

Vin

Iout

Vout

Time

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Vpk

Vin is from the wall outlet or a UPSfor “Off-Line”converters


AC Input Spec - sags, surges, and transients

• AC voltage will have transients and surges– 2000V spikes are not uncommon

• Florida is the worst US state– Due to lightning, industrial equipment and solar flares– The “front-end” PS circuitry must be able to shunt this energy

The PS cannot have direct connection between input and output.Hence, isolation is required. This is a safety

requirement.

• AC supply has brown outs, sags, or drop outs in power– This occurs when

• The utility transformer in a sub-station goes bad• The grid becomes overloaded from air-conditioners, etc.• Solar flares induce too much voltage and “pop” the breakers

– These occur quite often• More than 99% of the drop outs are less than 20ms in length


When AC momentarily is interruptedAC Input Spec - Hold-up Time

• For non-mission-critical devices – e.g., televisions, radios, VCRs– PS can shut down temporarily

• For mission-critical devices– e.g., high-end servers– PS shall maintain operation for a loss of AC up to 20ms– After 20ms it can shut down

This is known as hold-up time

• This is accomplished by a large energy storage device such as a capacitor in the input (PFC).– Typical specifications for hold-up is 20ms.


Time

Vin

Iin

Ideally, Iin should follow Vin emulating a resistor

Time

Vin

Iin

AC Input Spec - Power Factor

• A bridge rectifier with a large capacitance is usually at the PS input.– Iin, with respect to Vin, will be

distorted.– Iin-rms is now significantly

higher than for a resistor inputto have the same usable energy flow.

– The distortion adds frequency harmonics.


AC Input Spec - Power Factor (con’d)

• Apparent power is Pa = Vin-rms x Iin-rms

• Real power is the average Pr = Vin x Iin

• Power Factor, PF

PF = Real Power / Apparent Power

• The lower the PF, the higher the Iin-rms for the given power

• The problems with lower PF are– Wire sizes must be increased to handle the higher Iin-rms current

• Power Loss increases by the square of current!– This is extra power for which the feeders and fuses must be size– Iin is rich in harmonics which adds noise and circulating currents

in 3-phase systems


AC Input Spec - Inrush Current

• Usually, peak Iin is specified to be <5X the steady- state Iin-rms.

• Another factor to consider is fusing and circuit breakers.

• If the inrush current is too high or can occur throughout the day, fuses and circuit breakers can be weakened, damaged, or open up.

Like DC, Iin has inrush issues with AC applications.


Total Harmonic Distortion, THD - the same for your stereo as for the power supply

AC Input Spec - THD

• Any waveform can be broken down into a sum of sine waves with different amplitudes

• If there is any distortion, then– I = 1.414 x [I1sin(2ft)+I2sin(4ft)+I2sin(6ft)+…]

– I1 is the rms of the “fundamental” current waveform

– I2 is the second-order harmonic, I3 is third, etc.

– The Total Harmonic Distortion is then

THD = {sqrt[ (I2)^2 + (I3)^2 + (I4)^2 + …] / (I1)} x 100%

• A good value for THD < 5%


AC Input Spec - Noise

• Conducted noise current is measured on the line cord.– The frequency is less than 30Mhz– A “LISN” box is connected to the cord to filter out the 50/60hz – A frequency-spectrum analyzer then displays the noise spectrum

• Federal specifications must be met

• If the frequency is > 30Mhz, this is known as radiated– This is measured with an antennae usually 10 meters away– At these frequencies, line cords and cables become very effective

antennae

• Federal specifications that must be met

Conducted versus Radiated Noise


Vout SpecsLine, Load & Temperature

Load Step

Ripple & HF Noise

Long Term Stability

Static Regulation

Dynamic Regulation

Noise

Drift

VOUT


Static Regulation

• Line Regulation– % change in output voltage versus input voltage at a given load– Typically 1-2%

• Load Regulation– % change in output voltage versus load at a given input voltage– Typically 0.1-3%

• Vout Temperature Effect– % change in output voltage versus temperature for given input

and load– Typically 0.2-1%


Static Regulation

• Cross-Regulation (multi-output converters)– Change in output voltage of channel 2 for a change in load on

channel 1 at a given input voltage– Typically 0.1-10%


Change in output voltage is due to the dynamic behavior of the power supply

Dynamic Regulation

• The output voltage initially changes because of the I step x ESR of the output cap (5A x 0.3ohms)

• The second part is due to the loop response of the converter

• The change in output voltage is measured from the nominal output voltage

• 5% for this example


Another effect shows up as L x (di/dt)

Dynamic Regulation

• This is due to inductance of– Output capacitor– Connector– Bus distribution

• This is not always included in the spec.

• Could typically be < 5%


Vou

t

Time

Vrip

Time

Vo

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Ripple and Noise

• Ripple– Triangular-shaped current at

the switch frequency– Due to inductor current x

ESR of output cap

• High Frequency Noise– Noise > 10 x fSW– Either random or the

excitation of high-frequency parasitics.

• Typically 0.2-3%


Over time, a reference voltage can change.

Drift

• Drift is due to– Aging– Soldering– Package compression

• Typically < 0.2%


Question -

How can you improve the transient response of the converter without…

changing the components or changing the switching frequency?


Answer

• Use adaptive control (positioning)– At no load, start at +X1%

above nominal Vout

– At full load, change Vout to be X2% below nominal Vout

• In the previous example, dynamic regulation was 5%

• This can be changed to 3% dynamic regulation by modifying VREF for the control loop scheme

• Common in IC’s


Iout Specs

• Below is a typical Iout load behaviourIo

ut

Time

di/dt rate

Minimum current

Maximum current

I step

Over current trip point


Question

What happens to current in COUT if IOUT’s frequency

>> than the bandwidth of the converter ?


Answer

• Normally, the ripple current in Cout is the same as the inductor current

• If the load is switching faster than the bandwidth of the converter– the ripple current in Cout is due to Iout (load shift).– the converter will not respond to the load changes so the current it

delivers will be the average of Iout

• The ripple current in Cout due to Iout may be significantly higher than that due to the inductor current

• This condition occurs with most modern micro-processors when executing certain software

• Local decoupling caps help solve this problem


Design For Design For SafetySafety

Standards, Standards, Certificates & Certificates & RegulationsRegulations


Time

Vin

Iin

Safety

EMC

Robustness

Features

Corporate Standards

Standards, Certificates & RegulationsA power supply has many standards and regulations to meet

Only the major ones will be covered


Safety - http://www.i-spec.com

• To sell a product and/or to be protected from liability, the product must be approved by a safety agency

– Europe has Conformity European Mark

– Canada has Canadian Safety Agency

– US has Underwriters Laboratories

• Many countries have their own safety agencies

The Product Designer's “on-line guide”to compliance with the

International Safety Standard for Information Technology Equipment,

IEC 60950

i-Spec also covers national standards based on IEC 60950, including EN 60950, UL 1950/CSA C22.2

950, AS/NZS 3260.http://www.i-spec.com

• Most countries follow standard IEC-60950


Safety

• For example:– A product that will operate from 240VAC requires that the

primary-secondary spacing be greater than 8mm– The FR4 Card must meet UL 94V-0 standard for flammability

• There is even safety consideration for battery-operated equipment when the battery fails short

• To obtain safety approval– The product must be taken to an agency for testing – Performed by a person within the company who has been

certified by the safety agency

• Approval by one safety agency will be accepted by others– To obtain CE and CSA approval for a power supply that has been

approved by UL, only the test report need be shown

• Many labs will do all the required testing and the paper work for a fee


Electro-Magnetic Compatibility (EMC)

• EM emission limits are required by law for products– For the US, FCC part 15 – For Europe, CSIPR – Both are similar

Electro-Magnetic Compatibility - (Love / Hate)EM Emission - EM Susceptibility

Class Atypically for industrial

equipment

Class Btypically for commercial / home

equipment

Class B is 10dB more stringent


Conducted or Emitted

• Noise is measured through a device called a LISN on the AC cord

• LISN – Line Impedance Stabilizer Network is a set of filters that filters signals above 60Hz to a spectrum analyzer

• The noise is measured with an antennae 10 meters away

• All testing is done in a shielded chamber

• Certifications must come from approved sites

<30 MHz FREQUENCIES >30 MHz


Why 30 MHz?

• Question– Why are measurements done through the line cord at <30Mhz

and with an antennae at 10m for >30Mhz?

• AnswerThe speed of light, c, is 300 x 106m/s

At f = 30Mhz (30 x 106/s), the wavelength (=c/f) is 10m

– At frequencies <30Mhz, the emitted noise is carried out in the wiring which is not an effective antennae

– At frequencies >30Mhz, emitted noise is radiated from the line cord and circuit wiring since these now become effective antennas


Susceptibility

• These standards help the user design a product that will last a reasonable time in every day environments.

• There are no requirements to meet any of these standards. However, they contain a wealth of experience.

Lower Susceptibility is increased Robustness


Susceptibility - Circuit Card Effects

• For example– For connectors, FR4 cards and sheet metal – Spacing between primary to secondary wring on a FR4 card is

well defined in safety guidelines– IPC defines the spacing between primary-to-primary and

secondary-to-secondary wiring – If the primary-to-primary spacing is reduced below the IPC

guidelines, arcing can occur

• There is no facility to test against the IPC spec.

• This is left up to the designer

The Institute for Interconnecting and Packaging Electronic Circuits developed standards for the

packaging of products


Susceptibility - AC Utility Effects

• Surges are caused by abrupt load changes and “bank” switching

• Transients are caused by lightning strikes and line faults.

• IEC 801-4 and IEC801-5 provide test procedures that ensure your product survives most cases

• These tests can be performed by the designer with the right equipment or by outside labs

The AC utility line has surges and transients


Susceptibility - Electro-static Discharge

• These occur when products are physically handled

• IEC 801-2 provide test procedures to ensure your product survives most cases

• These tests can be performed by the designer with the right equipment or by outside labs

Products must also be protected or withstand electro-static discharges (ESD)


Susceptibility - ElectroMagnetic

• The product should behave as expected with EM fields up to a certain strength

• The standards for this are – IEC 810-3 for radiated susceptibly– IEC 810-6 for conducted susceptibly

• Testing for this is usually performed in EM shield chambers, same place as for FCC approval

EM Susceptibility tests how sensitive a product is to EM emissions


Corporate Standards

• Corporate Standards should be all encompassing– They can toughen existing requirements, such as IPC

guidelines– They can be guidelines on how a product should be designed

• Topology A is chosen over topology B• SMT vs. PTH

– They can be guidelines on how a product looks• Placement of labels• Color of products

– They can be guidelines on de-rating of components• Some product specs will cite MIL-217F or Bellcore

Corporate standards are policed within the company


Corporate Standards - Features: ENERGY STAR

• Features are specifications that make a product more valuable

• Some features later become requirements

• ENERGY STAR– A “feature” developed by the US-EPA – Products must reduce their power consumption

significantly for a period of time or when not in use, known as sleep mode

– These tests can be performed by the designer with the right equipment or by outside labs

The guideline for computers can be found at

http://www.epa.gov/nrgystar/purchasing/6a_c&m.html#specs_cm


Corporate Standards - Features: PFC & THD

• In US, still a feature

• In Europe, this has become a requirement

• This is an example of a feature that has become a requirement

• The standard for this is IEC-555

• This test can be performed by the designer with the right equipment or by outside labs

Low Power Factor and Low THD apply to AC off-line supplies


Choosing the Choosing the Correct TopologyCorrect Topology


Load(VOUT)

dc source(VIN)

PL = (VIN - VOUT) * IOUT

Linear Regulators

• Switch is used as programmable resistor

• Fast dynamic response

• Minimal filtering

• Poor efficiency

• Relatively large with heat sink


load(VOUT)

dc source(VIN)

PL : steady state + switching

Switchmode Regulators

• Switch is used as a chopper

• Dynamic response depends on switching frequency

• Requires filtering

• High efficiency

• High density

chopper(fT)

filter(fF)


Demystifying the Circuits - Duality

Using Simple principles of Duality

DualityCurrent is voltage; Voltage is current

L is C; C is L

R is R is R

Series is parallel; Parallel is series

Transistor is diode; Diode is Transistor

Open is closed; Closed is open


Demystifying the Circuits – Non-isolated

Buck

loaddc source

dc source load

Buck/Boost

load

Boost

dc source

DUALITY

CASCADE

DUALITY Cuk

not covered


Demystifying the Circuits – Conversion Ratios

Buck Regulator

(Step-down converter)

Boost Regulator

(Step-up converter)

Buck/Boost

(Up/down converter)

VOUT

VIN

= DVOUT

VIN

1

1-D=

VOUT

VIN

-D

1-D=

D: duty cycle of switch

TON

TPERIOD

TON

TPERIOD

D =


Demystifying the Circuits – Transformer Isolated

Buck/Boost

Isolated

Buck

Isolated

dc source

• •

load

Flyback

dc source

• •

load

Forward


Demystifying the Circuits – Bridge

Half Bridge

Full Bridge

Buck derived topologies

dc source LOAD

dc source LOAD


Demystifying the Circuits – Resonant Bridge

Series Resonant

dc source LOAD

Parallel LoadedSeries Resonant

LOAD

dc source


Partially Resonant Topologies

• Discontinuous-Resonant topologies known as – Zero-Voltage Switched circuits– Zero-Current Switched circuits

• Resonant Transition topologies– Zero-Voltage PWM topologies

• Characteristics:– Uses internal parasitics for nearly lossless switching– Fairly involved design approach– Next level of sophistication

Beyond this course


Knowing Where Knowing Where Disaster Can Disaster Can

StrikeStrikeDo you have the “knack?”


Disaster is Only Nanoseconds Away

Inductive Switching 101 or Understanding the Waveforms

Buck Load

Buck-Boost Load

You can be a rich power electronics designer too! It is all in battling Mother Nature.

She likes continuity and easy flow, e.g. Sinewaves, exponentials and Gaussians.

We give her

v=L*di/dt and i=C*dv/dt


Inductively Induced Voltage

• Power Mosfets can switch 10A in 5ns

• Internal lead inductance could be 5 nH each terminal

v=L*di/dt, or lead inductance creates a 20 V spike.

Lower the Mosfet rating, the faster the

deviceAll parameters work against

you Thank you, Mother Nature


Inductive Switching - Ideal Circuit


Inductive Switching - Ideal Circuit, Real Switch


Inductive Switching - Diode Inductance


Inductive Switching - Diode Capacitance


Inductive Switching - Circuit Inductance


Inductive Switching - Slower Switch Transition

Vds is worse if Fet is slowed down. Suspect something with model. Everything else ok.


Inductive Switching - Snubbing transients


Characterizing Characterizing Power Power

ComponentsComponents


Semiconductors• Zeners

– typical operation– transient suppression

• Diodes• Rectifiers• Fast recovery• Ultra-fast recovery

– Reverse Recovery Charge– Forward turn-on delay– Package parasitics

• Varistors (MOVs)– clamps (not crowbars)– should thermally fuse

• Transistors– Power Mosfets

• vertical structure– IGBTs– “TopSwitch”– modules– Bipolars

• Triggered semiconductors– SCR’s

• crowbar applications• Phase-controlled bridges• high power

– Unijunctions


Do's and Don'ts of Using MOSFETs• Be Mindful of

– Reverse blocking characteristics of the device• A vertically conducting device

– Handling and testing power HEXFETs– Unexpected gate-to-source voltage spikes– Drain or collector voltage spikes induced by switching

• Pay attention to circuit layout

• Do not exceed the peak current rating• Stay within the thermal limits of the device• Be careful when using the integral body-drain diode• Be on your guard when comparing current ratings


MOSFET Gate Drive Characteristics • Gate drive -vs- base drive

– Driving HEXFETs from linear circuits– TTL gate drive for a standard HEXFET?– The universal buffer

• The most important factor in gate drive: The impedance of the gate drive circuit

• Gate drive approaches– Simple and inexpensive isolated gate-drive supplies

• Optocouplers, pulse transformers, choppers, photovoltaic generators

– Bootstrap gate-drive supply

• Maximum gate voltage and the use of Zeners

• Driving in the MHz? Use resonant gate drivers – Power dissipation of the gate drive circuit is seldom a problem


Paralleling MOSFETs

• General Guidelines– Steady State Sharing

• The inherent positive temperature coefficient provides dc (steady state) sharing while in the on-state!

– Dynamic Sharing at Turn-On• Requires close matching of gate-threshold voltages• Avoid gate resonance by using ferrite gate beads (few nH)• Must have matched inductive paths• Clamping MOSFETS are beneficial

– Dynamic Sharing at Turn-Off• Requires some matching of gate-threshold voltages• Requires close matching of “Miller Capacitance” path• Must have matched inductive paths


Diode Reverse Recovery

Buck Load

tatb

tn

IRR

IF

Abrupt Recovery

Recovery produces sharp current transients and EMI

tatb

tn

IRR

IF

Soft Recovery


Safe Operating Area - the holy grail

SOA combines transient and thermal limits

ID

VDS

Steady state (DC) limitFusing currentThermal path limit

Transient thermal limit

Breakdown limit

Switc

hing s

peed

dc -t

o- pu

lsed

MAXIMUM POWER AREA


Capacitors - Circuit Equivalent

• Ceramic– high frequency– sensitive to thermal transient

• Tantalum– polarized, also organic leads– high energy density

• Electrolytic, also oscon– polarized – highest energy density

Staged for reducing ESR

C

• Equivalent Circuit– R, L, C– limited internal temperature

from “RMS heating,” i.e. current ripple

ESL

ESR

leakage


Magnetics - Circuit Equivalent

Xl

Xp XsRp

Cs

Approx.: Xl = 10 *Xp

• Transformers– Leakage is loss of coupling from primary to secondary– Skin effect is determined by copper and core magnetic fields

• litz wire and foil help in high-frequency designs– Thermal hot-spots of most concern:

• from high flux densities in core• from eddy current losses in core and wires• potting can trap heat


The Dual Faces The Dual Faces ofof

Power MOSFETSPower MOSFETSGetting the heat out with Getting the heat out with Synchronous RectificationSynchronous Rectification


Synchronous Rectification - Output Drop

• For output voltages < 3.3V, the best case efficiency can be approximated by

Vd is the voltage drop due to the output diodes

%100xVdVout

Vout

As voltage requirements from micro-processor’s and logic drop, efficiency becomes a problem

load

Boost

dc source


Synchronous Rectification - Efficiency

• The best Schottky diode voltage is 0.25V and high current Schottky diodes are as high as 1V

• For example, 1V@100A converter with 0.5V for Vd, can have an efficiency of 67% best case

• For every 100W out, 50W is wasted as heat!

• Other advantages for increasing efficiency– Greater utilization of AC feeder capacity– Reduced electrical bill for the customer – Increased reliability with less thermal issues – More “green” friendly


Synchronous Rectifiers• Solution is to use Synchronous

Rectifiers

• Replace or parallel the output diode with a low Rds-on Fet

• For this to work, the Fet must turn on when the current is in the direction of the diode

• I x Rds-on < Vd

• Efficiency of 90% can be achieved with 1V@100A power supply!

I


Synchronous Rectifiers - Notables

– If the current reverses and the Fet is on, you have a short-circuit condition across, usually, a transformer

– Timing is critical– The MOSFET body diode may come on– Placing a Schottky diode in parallel with the body diode will not,

in all cases, reduce power loss – Ramp down effect– Very low Rds-on Fets require a large amount of gate drive energy

• For example, a 1V@100A converter, 2% efficiency loss to gate drives is not uncommon

What to watch out for


– Circulating current can be as high as several hundred amps

– Solution is to shut sync rect off at light loads

Synchronous Rectifiers - Parallel Modules– Some PS can source and sink current– At light loads, this could happen with parallel modules


The Circuit is aThe Circuit is aComponentComponent

Insights into Power Insights into Power PackagingPackaging


+

Electric

Magnetic

Electromagnetic

Thermal

Mechanical

Chemical

Photonic

Electrical v. Physical Circuits

Power electronic circuits [PHYSICAL CIRCUITS] condition and convert many energy forms!

We do not do ONLY electrical designs


Skin Effect

Finite resistance

Lead Inductance

Coupled Capacitance

Inter-Conductor Capacitance

Typical Electrical Structure


R = l / (t × w)

let l / w = 1 = “one square”

Rsheet = / t [ / sq. ]

A corner is 0.559 squares

wt l

l

Conductor Resistance -Sheet Resistance


Metal Density Resistivity Thickness (mils) DC Resistance (msq)(gm/cc) ( cm) 1oz 2oz 3oz 1oz 2oz 3oz

Al (6061) 2.72 2.83 4.41 8.83 13.24 0.252 0.126 0.084Cu (110) 8.94 1.72 1.34 2.68 4.03 0.504 0.252 0.168

Gold 19.3 2.2 0.62 1.24 1.87 1.393 0.696 0.464Silver 10.19 1.59 1.18 2.36 3.53 0.531 0.266 0.177Tin 7.29 11.5 1.65 3.29 4.94 2.75 1.375 0.917

“1 oz. copper” is weight for one square foot

Thickness and Resistance from Common Conductors

Conductor Thickness


Calculate the voltage drop and power loss of the output leads for a 5V, 100A supply. Consider 1oz., 2oz. and 3oz. copper conductors.

No. of squares for both sides is: Squares =

=For 2oz. copper Rtotal =

= Vleads = Pleads =

Terminal

Terminal

~.22

~1

Cap

??

DC Power Supply Example - Output Conductor Resistance


Calculate the voltage drop and power loss of the output leads for a 5V, 100A supply. Consider 1oz., 2oz. and 3oz. copper conductors.

No. of squares for both sides is: Squares = 2(1 + 0.56 + 0.56 + 0.22)

= 4.68 sq.For 2oz. copper Rtotal =(0.252 msq) (4.68 sq)

=1.18 m Vleads = (1.18 mmV

or 2.8% Pleads = (118 m) (100 A) 2 = 12 W

Terminal

Terminal

0.56

~.22

~1

Cap

~1

0.56

0.56

0.56

DC Power Supply Example - Output Conductor Resistance


Cu "thickness" 1oz 2oz 3ozResistance (mOhm) 2.8 1.4 0.7Voltage Drop (mV) 280 140 70Power Loss (W) 28 14 7

Output Conductor Resistance


• Substrate Coupling

Example:

Conductor #1: 100mils x 1 inch


Substrate: ceramic loaded polymer, 3 mils thick, r = 6.4

Find Capacitance:

C =

Coupled Capacitance


Coupled Capacitance

• Substrate Coupling

Example:



Substrate: ceramic loaded polymer, 3 mils thick, r = 6.4

Find Capacitance:

C1 = 47.9 pF, C2 = 192 pF

C = C1 series with C2 = 38.3 pF


Example: Switching current

coupled into header from FET drain.

FET: 400mils2, tf = 20 ns

(+20 mil conductor periphery)

(+100 mils2 drain bond pad)

(+200 mils x 400 mils drain lead)

Substrate: Al2O3

25 mils thick, r = 9.4

Voltage source: 425 Vdc

continued

Vd

Ground Coupling


Find Capacitance:

Find switching current:

i = C (dV/dt )

i =

400mils2

Bond Pad100mils2

Drain Lead100x200mils

??20mils

Ground Coupling (continued)


400mils2

For ceramic loaded polymerC = 136 pF and i = 2.9 A

For ceramic loaded polymerC = 136 pF and i = 2.9 A

Bond Pad100mils2

Drain Lead100x200mils

20mils

Ground Coupling (continued)

• Find Capacitance:A = 0.284 in2 = 183 mm2d = 25 mils = 0.635 mmThen: C = 24 pF (d-s Cap)

• Find switching current:i = C (dV/dt )

= 24 pF (425/20ns)i = 0.51 A


•Self Inductance of Conductors

Minimum is non-coupled in free space

Xe ( sq ) = Ll

L = R = ( 2 )-1

l = (sinh sin ) / ( cosh cos )

t /

t is the thickness (m)

f, skin depth

is conductivity in (s/m)

f is frequency

is permeability ( x 10-7 H/m)

Inductive Effects Non-Transmission Line Mode


Example - High Frequency Lead Inductance

Calculate the per-square self-inductance of a 1oz, 2oz and 3oz

copper lead needing to conduct a 1MHz signal.

For 1oz copper:

m, t /

Lmsq, l = 0.172

Xe = 22.4 sq, or Le = 3.57 pF / sq

1oz 2oz 3ozXe ( sq ) 22 45 67Le ( pH / sq ) 3.6 7.1 11

Self-Inductance, Cu @ 1MHzNote: max self-inductance =

( 4f-1 /

2

Inductive Effects


Non-ferrous headers

Aluminum

Copper

Si C

Al Si C

Ferrous headers / substrates

Invar ( 64% iron, 36% nickel )

Kovar ( 54% iron, 29% nickel, 16% cobalt)

Ferrite (substrates)

Porcelainized steel (substrate)

Inductive Loops


Junction Temp (C)

Fai

lure

Rat

e (

/105 r

uns)

Junction Life Statistics

50, 0.005

100, 0.05

150, 0.2

Primary Causes of failure in avionics equipment

Vibration20%

Dust6%

Humidity19%

Temperature

55%

Temperature as the Culprit


Factors affecting T

Convection/conduction in medium Chip size Chip attach Heat spreader Conductor type and thickness Substrate type and thickness Substrate attach Heatsink

Thermal Issues


Power Supply

P0 / Pi , Pl = P0 ( 1 -

Load

P0, zero % efficient electrically

For first-level type packaging (e.g.. chip and wire) the thermal area densities are equal:

Pl / Aps = PL / AL

Load

Pl

P0Pi PL

heat heat

PwrSupply

Rule of Areas (Hoppy’s Rule)


0

0.2

0.4

0.6

0.8

1

0.5 0.6 0.7 0.8 0.9 1

For thermal enhancements (e.g. thermal vias) a Thermal Density ratio, TDr , is defined

TDr = ke, l / ke, ps

where ke is an equivalent thermal conductivity for that area.

Then TDr ( Pl / Aps ) = PL / AL

Aps / AL = TDr (

Aps/AL

TDr=1

Rule of Areas (continued)


R = 1 tk A

i q

v T

R R

Chip

Solder

Conductor

Spreader

Substrate

Attach

Attach

Baseplate

Heatsink

1 l A

R =

R [] = v[V] / i [A]

R [oC/W] = T [oC] / q [W]

Thermal Resistance Model - 1D


Thermal Typical Thickness T(°C) Material Conductivity R/cm2 (mils) IGBT

(W/m °C) (°C/kW cm2) @0.2kW/cm2

Silicon (Si) Solder (95Pb-5Sn)Molybdenum (Mo)Alumina (Al2O3)Aluminum Nitride (AlN)Beryllia (BeO)Aluminum Silicon Carbide (AlSiC)Aluminum (Al)Copper (Cu)Polymer CeramicGlass Epoxy (FR-4)Thermal Grease

42161724437

26-

-2.64763000924

1441025

2525-

-4 (3oz)6204

8.483.449-

5.2-

-0.5295600185

Comparative Thermal Resistances (°C/kW cm2)


36010220463551

1.27*

Materialwidth (mm)

depth(mm)

thick(m)

k(W/m °C)

SiSolderCuAl2O3

Al

AlSiC

10.210.212.715.215.2

15.2

10.210.212.715.215.2

15.2

* in mm

846339326240

170

Si

DBC

Al2O3

Al

AlSiC

Example Structure


Si

DBC

Al2O3 Al

AlSiC

R = (t / A) / k

t = thickness, A= width x depth

R, total = 0.198 °C/WR, total = 0.198 °C/W*in mm

10.210.212.715.215.215.2

R(°C/W)layer t (m) w(mm) w’(mm) D(mm) D’(mm) Ae(mm2)

SiSolderCuAl2O3

AlAlSiC

360102203635511.27*

10.210.210.411.011.012.3

10.210.212.715.215.215.2

10.210.212.715.215.215.2

103103107121122152

0.0410.0160.0030.1050.0010.002

One-Dimensional Model -Using Bulk Dimensions-


Assumption : For an isotropic material, heat flows laterally at the same rate it flows vertically.

Hence: A = (Wu + t)(Du + t)

R = (t / A) / k

Material

width (mm)

depth(mm)

thick(m)

k(W/m °C)

SiSolderCuAl2O3

AlAlSiC

10.210.212.715.215.215.2

10.210.212.715.215.215.2

360102204635511.27*

* in mm

846339326240170

R = 0.232° C/WR = 0.232° C/W

Si

DBC

Al2O3Al

AlSiC

- ” 45° ” Spreading Angle -


Acer

a2 a2

n = tan-1(kn / kn+1)

A’n = [W’n + 2tn tan (n)]

R,n = (tn / A’n) Kn

W > tn tan (n)

Example Spreading Angles

Composite Material

SpreadingAngle in *

DBC* on Al2O3

DBC* on BeOCu* on Fr-4AlSiC* on Al

85°57°89.8°30°

Acu

Asi

- Adjustable Spreading Angle -Thermal interaction of layers changes the thermal spreading

angle,


Si

DBC

Al2O3Al

AlSiC

Layer Angle (°) W’(mm) D’(mm) A’(mm2) Rq (°C/W)

SiSolderCu

Al2O3

AlAlSiC

0086

6.25530

10.2 10.2 16.0(12.7)12.813.014.5

10.2 10.2 16.0(12.7)12.813.014.5

104104 ---107165169209

0.0410.016 ---0.0030.1480.0010.036

Rq = 0.290° C/W

Adjusted Spreading for Structure


Presentation Goes Off-Line

We break to another topic.

See supplemental material.

Review of packaging paraphernalia


Design Design Approaches Approaches

and Toolsand Tools


In the Best of Designs...

The Goodthe Bad and the Ugly

Compliments of Celestica, Inc.


Presentation Goes Off-Line

We break to another topic.

See supplemental material.

Review of physical hardware

Compliments of Celestica, Inc.


Simulating Simulating RealityReality

Our best guess at Our best guess at Mother NatureMother Nature


Overview on Design Tools

DevicePhysics

ComponentModeling

CircuitSimulation

SpecificCircuits

Pisces, Fielday, Ansoft

FEM Based

Simulators

Pspice, AWB, SIMetrix, SimplisSPICE based

or State-Space

Simulator

Webench, SMS, SwitcherCAD

Design Programs for Power Supplies

Eas

e o

f U

se

Physical Level

Co

st $$$


FEM Design Tools

• Pisces and Fielday, IBM tools, simulate semiconductor devices at the electron level

• Ansoft simulator models electro-magnetic devices with FEM– On the right is a

gapped ferrite core showing the flux lines

Expensive and require significant learning

See additional Ansoft foils


SPICE Design Tools

• Pspice1, AWB1 and SIMetrix2 use time differentials for solving circuits.

• Good for modeling electrical circuits

• Transistor and op-amps are modeled as equivalent circuits

• On the right is a simple circuit and waveform from Pspice

Easy to use but requires circuit design experience and $$$

1=Cadence, 2=Simetrix inc


SPICE Design Tools - Limitations

• Need to simulate long times to look at control loop behavior in milliseconds, yet ...

• SPICE will calculate in nanoseconds because of the time domain calculations

• One solution is to use “Average Models,” where the switching waveform is averaged out.

• Models require mathematical definitions and a good understanding of the subject

When simulating switchmode supplies, SPICE has limitation


State-Space Design Tools

• Another solution is to use a state-space simulator such as Simplis1

• Simplis calculates based on the topology and only at the switching points

• Simulation speed for switchmode power supplies is improved up to 100X

• You can enter the circuit as is

1=Transim Corp


Webench Design Tool - www.webench.com• Webench is a design

tool from National Semi. in conjunction with Transim Corp.

• Webench helps you pick the IC, simulate and build.

• Within Webench is Websim which uses Simplis as the simulation engine

• Webench is a Web based tool

• Very easy to use and free but not flexible


SMS Design Tool

• The program – helps the user

select the appropriate controller IC

– designs and selects components

– easy to use but not flexible

– free

• Great for the novice that needs a quick power supply design

Switcher Made Simple (SMS) is a PC program from National Semi., in conjunction with Transim Corp


Input FilteringInput Filtering(Not selective hearing)(Not selective hearing)


Input Filter

• Why is an input filter needed ?– Reduce ripple current from the PS– Prevent filter oscillation– Reduce the di/dt of the load reflected back to the input


Input Filter

• Ideally, Iin should be a clean DC current

• There will be the ripple current, Irip, from the PS switching stage

• To reduce the input ripple, use an L-C network on the front-end of the power supply

• The resonant frequency << Fsw

IripIin

Time

– Reduce ripple current from the PS– Prevent filter oscillation– Reduce the di/dt of the load reflected

back to the input

Why is an input filter needed ?


Input Filter

• If the resonance of L1,C1 is around Fsw of the PS, a large amount of current can oscillate between L1 and C1

• The amount of current depends on the Q of L1 and C1

• Very common if L1 is just the board trace between the PS and the Vin source

• This oscillation can depend on the length of board trace!

• Adding an inductor will lower the resonance and make this parameter controllable

• If the resonance of L1 and C1 still a problem, dampen it with an R-C across L1 or use lossy core material for L1


Input Filter

• Another problem arises if L1 and C1 have a large Q

• Even if the resonance is less than Fsw, this peaking effect can cause problems with the control loop

• This resonant frequency can show up on the output of the power supply

• Again, solutions are either an R-C across L1 or use a lossy core material for L1


Input Filter

• Another characteristic is reduction of input di/dt during load transients– Problems caused in the Vin bus

• Ringing on the board traces• Vin not able to respond to load change

• Solution: absorb the load energy – How?

• Large cap on Vin bus – PTH parts on SMT board? No• Adding more output caps to absorb the energy? Expensive -

No• Add second stage filter? Inexpensive SMT parts - Yes

– First filter L1,C1 filters the high-frequency switching components. Second filter L2,C2 is a low-pass filter to smooth out the reflected load transient


Input Filter

Shown is a two-stage filter with input current and load current

Beware of inter-stage oscillations


A Different A Different Approach to a Approach to a

DESIGNDESIGNOptimally Selecting Packaging Technologies

and Circuit Partitions Based on Cost and PerformanceAPEC’ 2000 Conference

John B. Jacobsen and Douglas C. Hopkins


Full-Cost Model

Other OH

Depreciation

Wages

Packaging materials

MaterialsCost

Pac

kagi

ng M

ater

ials

& P

rodu

ctio

n C

osts

(con

trol

labl

e)

Minimum packaged

Comp. packaging

components

Ove

rhea

dS

tand

ard

unit

cos

t

MaterialsCost

ProductionCost


Centers of Cost

• Materials cost*

• Production cost*– *Full Cost

• Partitioning cost

• Product business cost (return on investment for development of one product)

• Company business cost (return on investment for cross products)


Centers of Cost (con’d)

• Materials cost represent direct costs of packaging materials.

• Production cost includes factors for wages and product volume, but are independent of material costs.

• Partitioning cost is incurred for each technology used.

• Full cost combines material costs and production costs.

• Product business cost, i.e. return on investment for development of one product, is an investment in future payback. The total cash flow from development until end of production determines the business costs for a product.

• continued


Centers of Cost (con’d)

• Company business cost, i.e. return on investment for cross-product usage, reflects the cost of sub-optimization within one single product. – Reusing the same packaging technologies, designs (diagrams)

and even physical circuits (building blocks) across different products should be measured at the company level. The value of building blocks becomes obvious through savings in repetitive development costs and maintenance of function


Production Cost Dependency by Volume

10k 32k 100k 320k 1000k

Products/Year

0%

100%

200%

300%

400%

500%

600%

700%

Pro

duct

ion

Cos

t

Other overhead costs

Depreciation

Wages

yr - 2000


Cost Variation Within a Technology

0 5 10 15 20 25 30

Surface Density

Rel

ativ

e C

ost

0

0.2

0.4

0.6

0.8

1

Packaging & Production Costs

Packaging Performance:(electrical, thermal, mechanical

TF module& leadframe

FR4 Chang

ing te

chno

logy

to ch

ange

dens

ity

Functionalintegration within

technology

110 SMDs14 leadet

70 SMDs7 leadet


Relative Cost of Technologies

0 5 10 15 20 25 30

Surface Density

Rel

ativ

e C

ost

0

0.2

0.4

0.6

0.8

1DBC

Packaging & Production Costs

Packaging Performance: electrical, thermal, mechanical

TF &Plated Cu

IMS

FR4

Hot Embossing

Performance

Circuit cost bychange in technology


Relative Packaging & Production Cost

Hot

Em

boss

ing

FR

4 C

u( 2

x35u

m)

FR

4 C

u( 4

laye

r )

IMS

(1

laye

r on

Al)

TT

F

DB

C(

0,63

Al2

O3

)

Z-s

trat

e C

u( 2

laye

r)

TF

mu

ltila

yer

Substrate Technology

0

2

4

6

8

10

12

14

Rel

ativ

e C

ost

Substr/in2

leaded auto/10 comp

SMD/10 comp

Power chip& wire/10 comp

Integrated res/10 comp

Relative to 1 in2 of FR4

ab

c

dd

a

b

d

c


Relative Production Cost per Technology

Leaded-manual Leaded-auto Power chip & wire SMD-auto

Assembly Technology

0%

20%

40%

60%

80%

100%

120%

Cos

t/co

mpo

nent


THETHEENDEND

Thank you for your interest inThank you for your interest inDCHopkins & AssociatesDCHopkins & Associates

www.DCHopkins-Associates.Comwww.DCHopkins-Associates.Com

© 2006 DCHopkins ABCs of Power Electronic Systems By Dr. Doug Hopkins & Dr. Ron Wunderlich DCHopkins & Associates Denal Way,

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