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ABCs of Power Electronic Systems

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1 ABCs of Power Electronic Systems
By Dr. Doug Hopkins & Dr. Ron Wunderlich DCHopkins & Associates Denal Way, m/s 408 Vestal, New York

2 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.

3 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 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.

4 Course Topics 1. Overview of Power Electronics Technology
1a. Introduction to the power electronics system 2. Knowing your specifications 2a. Design for safety 3. Choosing the correct topologies 3b. Knowing where disaster can strike 4. Characterizing power components 4a. A safe operating area 4b. The dual faces of MOSFETS 4c. The circuit is a component 5. Design approaches and tools 5a. Simulating reality 5b. Input filtering 6. Design approaches and tools 6a. Design case study

5 DCHopkins & Associates - Products
Products designed by our Associates, photographed by our Associates. 600W family of isolated DC/DC building blocks Multi-output telecom power supply Pictures courtesy of Celestica, Incorporated

6 DCHopkins & Associates - Products
30A high efficiency, high-transient isolated power supply Isolated power supply for high-end micro-processor Pictures courtesy of Celestica, Incorporated

7 Where to go for news (other than suppliers)?
News Sources Where to go for news (other than suppliers)? (PowerPulse Daily) (see electricnet) http//www.electricnet.com (see poweronline) (see attached catalog) Conferences: (the IEEE Power Electronics Society)

8 Introduction to The System
Source Load Power Processor

9 “Conversion” changes one energy form to another.
Conversion or Supply “Conversion” changes one energy form to another. Power Processor Load Source Electrical Source Types of Loads Motor drives Linear Rotational Lighting Fluorescent HID Halogen Pulsed power Ignition Flash lamp Pulsed propulsion POWER CONVERSION

10 “Supply” changes only the attributes.
Conversion or Supply “Supply” changes only the attributes. Power Processor Load Source LOAD Computer Applications Desktops Workstations Servers Mainframes Circuits: CPU Memory Bus Terminators Logic Graphics Handheld Applications PDA’s Notebooks Cell-phones Circuits: RF Amps CPU/Logic Memory Display Audio Amps Telecom Applications Routers Tele. Switches Circuits: Optical Amps CPU Memory Switch Cards Logic POWER SUPPLY

11 Uninterruptible Power Supply Systems
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 Power Processor Electronic Circuit Clean AC Utility Noisy AC

12 The System - Source Characteristics
Power Processor Load Source SOURCE

13 The System - Source Characteristics
Load Power Processor 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

14 Knowing Your Specifications and the User’s Requirements

15 Developing User Requirements
Responsible Design is from Cradle to Grave 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

16 Grouping User Requirements
Characteristic Unspoken Expectations Articulated Needs Unexpected Features Taxonomy Financial Legal Social Environmental Technical MATRIXED

17 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.”

18 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.

19 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.

20 Defining Specifications
Power electronic circuits condition and convert many energy forms! Power Supply Iin Vin Iout Vout Electric Magnetic Electromagnetic Thermal Mechanical Chemical Photonic Technical User Requirements provide the SPECIFICATIONS for each Energy Form.

21 Framework leading to Specifications
Responsible Design is from Cradle to Grave. Characteristics Taxonomies Technical Characteristics Energy Forms Conditions Start-up Shut-down Normal operation Fault operation

22 Electrical Specs Electrical Spec Input Output Controls Misc AC DC
Vout, Iout PGood, On/Off Efficiency Vin, Iin Vin, Iin

23 Specifying Vin depends on the source voltage range.
DC Input Spec Specifying Vin depends on the source voltage range. 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.

24 DC Input Spec - Iin, Pout, Pin, 
Iin is the current drawn by the PS and derived by 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 Iin Iin = (Vout x Iout) / (Vin x ) Note: Worst case - Iin occurs at lowest value of Vin, e.g. for telecom PS most current is at Vin=36 volts.

25 DC Input Spec Iin will have ripple current, Irip, from the switching stage within the PS. 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 Irip Iin Time

26 Iin will have switching noise.
DC Input Spec Iin will have switching noise. 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

27 Iin will have a surge during start-up.
DC Input Spec Iin will have a surge during start-up. 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.

28 Specifying Vin depends on the source voltage range
AC Input Spec Specifying Vin depends on the source voltage range 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

29 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

30 Vin is from the wall outlet or a UPS for “Off-Line”converters
AC Input Spec - Vin-rms Vin is from the wall outlet or a UPS for “Off-Line”converters AC sources are: Single Phase Three Phase (>5kW, not covered) Vin is understood to be Vin-rms; Vin-rms = Vpk / * RMS makes calculations easier For DC, Pin = Vin x Iin For AC, Pin = Vin-rms x Iin-rms For single frequency sine wave Vpk Power Supply Iin Vin Iout Vout

31 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

32 AC Input Spec - Hold-up Time
When AC momentarily is interrupted 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.

33 AC Input Spec - Power Factor
Ideally, Iin should follow Vin emulating a resistor 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 input to have the same usable energy flow. The distortion adds frequency harmonics.

34 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

35 AC Input Spec - Inrush Current
Like DC, Iin has inrush issues with AC applications. 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.

36 Total Harmonic Distortion, THD -
AC Input Spec - THD Total Harmonic Distortion, THD - the same for your stereo as for the power supply Any waveform can be broken down into a sum of sine waves with different amplitudes If there is any distortion, then I = x [I1sin(2ft)+I2sin(4ft)+I2sin(6ft)+…] 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%

37 Conducted versus Radiated Noise
AC Input Spec - Noise Conducted versus Radiated 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

38 Line, Load & Temperature
Vout Specs Line, Load & Temperature Static Regulation Load Step Dynamic Regulation VOUT Noise Ripple & HF Noise Drift Long Term Stability

39 Static Regulation Line Regulation Load 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%

40 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 %

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

42 Another effect shows up as L x (di/dt)
Dynamic Regulation Another effect shows up as L x (di/dt) This is due to inductance of Output capacitor Connector Bus distribution This is not always included in the spec. Could typically be < 5%

43 Ripple and Noise Ripple High Frequency Noise Typically 0.2-3%
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% Vout Vrip Time

44 Over time, a reference voltage can change.
Drift Over time, a reference voltage can change. Drift is due to Aging Soldering Package compression Typically < 0.2%

45 Question - How can you improve the transient response of the converter without… changing the components or changing the switching frequency?

46 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

47 Over current trip point
Iout Specs Below is a typical Iout load behaviour Iout Time di/dt rate Minimum current Maximum current I step Over current trip point

48 Question What happens to current in COUT if IOUT’s frequency
>> than the bandwidth of the converter ?

49 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

50 Design For Safety Standards, Certificates & Regulations

51 Standards, Certificates & Regulations
A power supply has many standards and regulations to meet Only the major ones will be covered Safety Corporate Standards Pisces, Fielday IBM) are FEM based simulators which simulate at the holes/electrons level. Very limited external circuits can be added. Ansoft is a FEM program for magnetics SMS – Switchers Made Simple is a canned program that designs the components around a power supply chip. EMC Features Robustness

52 Safety - http://www.i-spec.com
Many countries have their own safety agencies Europe has Conformity European Mark Canada has Canadian Safety Agency US has Underwriters Laboratories To sell a product and/or to be protected from liability, the product must be approved by a safety agency Most countries follow standard IEC-60950 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 C , AS/NZS 3260.

53 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

54 Electro-Magnetic Compatibility (EMC)
Electro-Magnetic Compatibility - (Love / Hate) EM Emission - EM Susceptibility EM emission limits are required by law for products For the US, FCC part 15 For Europe, CSIPR Both are similar Class A typically for industrial equipment Class B typically for commercial / home equipment Class B is 10dB more stringent

55 <30 MHz FREQUENCIES >30 MHz
Conducted or Emitted <30 MHz FREQUENCIES >30 MHz 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

56 Why 30 MHz? Question Answer
Why are measurements done through the line cord at <30Mhz and with an antennae at 10m for >30Mhz? Answer The 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

57 Lower Susceptibility is increased Robustness
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.

58 Susceptibility - Circuit Card Effects
The Institute for Interconnecting and Packaging Electronic Circuits developed standards for the packaging of products 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

59 Susceptibility - AC Utility Effects
The AC utility line has surges and transients Surges are caused by abrupt load changes and “bank” switching Transients are caused by lightning strikes and line faults. IEC 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

60 Susceptibility - Electro-static Discharge
Products must also be protected or withstand electro-static discharges (ESD) These occur when products are physically handled IEC 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

61 Susceptibility - ElectroMagnetic
EM Susceptibility tests how sensitive a product is to EM emissions The product should behave as expected with EM fields up to a certain strength The standards for this are IEC for radiated susceptibly IEC for conducted susceptibly Testing for this is usually performed in EM shield chambers, same place as for FCC approval

62 Corporate standards are policed within the company
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

63 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

64 Corporate Standards - Features: PFC & THD
Low Power Factor and Low THD apply to AC off-line supplies 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

65 Choosing the Correct Topology

66 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 = (VIN - VOUT) * IOUT

67 Switchmode Regulators
Switch is used as a chopper Dynamic response depends on switching frequency Requires filtering High efficiency High density PL : steady state + switching dc source (VIN) chopper (fT) filter (fF) load (VOUT)

68 Demystifying the Circuits - Duality
Using Simple principles of Duality Duality Current 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

69 Demystifying the Circuits – Non-isolated
load Boost dc source Buck load dc source DUALITY CASCADE dc source load Buck/Boost Cuk not covered DUALITY

70 Demystifying the Circuits – Conversion Ratios
Buck Regulator (Step-down converter) Boost Regulator (Step-up converter) Buck/Boost (Up/down converter) VOUT VIN = D VOUT VIN 1 1-D = D: duty cycle of switch TON TPERIOD VOUT VIN -D 1-D = TON TPERIOD D =

71 Demystifying the Circuits – Transformer Isolated
dc source • • load Flyback Buck/Boost Isolated dc source • • load Forward Buck Isolated

72 Demystifying the Circuits – Bridge
dc source LOAD Half Bridge Buck derived topologies dc source LOAD Full Bridge

73 Demystifying the Circuits – Resonant Bridge
dc source LOAD Series Resonant LOAD dc source Parallel Loaded Series Resonant

74 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

75 Knowing Where Disaster Can Strike
Do you have the “knack?”

76 Disaster is Only Nanoseconds Away
Inductive Switching 101 or Understanding the Waveforms 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 Buck Load Buck-Boost Load

77 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 device All parameters work against you Thank you, Mother Nature

78 Inductive Switching - Ideal Circuit

79 Inductive Switching - Ideal Circuit, Real Switch

80 Inductive Switching - Diode Inductance

81 Inductive Switching - Diode Capacitance

82 Inductive Switching - Circuit Inductance

83 Inductive Switching - Slower Switch Transition
Vds is worse if Fet is slowed down. Suspect something with model. Everything else ok.

84 Inductive Switching - Snubbing transients

85 Characterizing Power Components

86 Semiconductors Zeners Diodes Varistors (MOVs) Transistors
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

87 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

88 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

89 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

90 Diode Reverse Recovery
Recovery produces sharp current transients and EMI ta tb tn IRR IF Soft Recovery ta tb tn IRR IF Abrupt Recovery Buck Load

91 Safe Operating Area - the holy grail
SOA combines transient and thermal limits ID Transient thermal limit Steady state (DC) limit Fusing current Thermal path limit Switching speed dc -to- pulsed Breakdown limit MAXIMUM POWER AREA VDS

92 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 C ESL ESR leakage Equivalent Circuit R, L, C limited internal temperature from “RMS heating,” i.e. current ripple Staged for reducing ESR

93 Magnetics - Circuit Equivalent
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 Rp Xp Xs Xl Cs Approx.: Xl = 10 *Xp

94 The Dual Faces of Power MOSFETS
Getting the heat out with Synchronous Rectification

95 Synchronous Rectification - Output Drop
As voltage requirements from micro-processor’s and logic drop, efficiency becomes a problem For output voltages < 3.3V, the best case efficiency can be approximated by Vd is the voltage drop due to the output diodes load Boost dc source

96 Synchronous Rectification - Efficiency
The best Schottky diode voltage is 0.25V and high current Schottky diodes are as high as 1V For example, 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

97 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 power supply! I

98 Synchronous Rectifiers - Notables
What to watch out for 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 converter, 2% efficiency loss to gate drives is not uncommon This ramp down effect is because the inductances of the Fet and diode are in separate packages. Even though the inductances is low so is the voltage across them. So it takes time for the current to ramp down from Schottky to Fet. Times of 700ns are typical. At 1Mhz, sync. Rect. Is useless with a parallel Schottky. Just use the body diode.

99 Synchronous Rectifiers - Parallel Modules
Some PS can source and sink current At light loads, this could happen with parallel modules Circulating current can be as high as several hundred amps Solution is to shut sync rect off at light loads

100 The Circuit is a Component
Insights into Power Packaging

101 Electrical v. Physical Circuits
Power electronic circuits [PHYSICAL CIRCUITS] condition and convert many energy forms! Electric Magnetic Electromagnetic Thermal Mechanical Chemical Photonic + We do not do ONLY electrical designs

102 Typical Electrical Structure
Lead Inductance Finite resistance Skin Effect Inter-Conductor Capacitance Coupled Capacitance

103 Conductor Resistance -Sheet Resistance
l R = r l / (t × w) let l / w = 1 = “one square” Rsheet = r / t [ W / sq. ] A corner is squares l t w

104 “1 oz. copper” is weight for one square foot
Conductor Thickness “1 oz. copper” is weight for one square foot Thickness and Resistance from Common Conductors

105 DC Power Supply Example - Output Conductor Resistance
Terminal Calculate the voltage drop and power loss of the output leads for a 5V, 100A supply. Consider 1oz., 2oz. and 3oz. copper conductors. ~1 ~.22 Cap No. of squares for both sides is: Squares = = For 2oz. copper Rtotal = Vleads = Pleads = ? Terminal

106 DC Power Supply Example - Output Conductor Resistance
Terminal Calculate the voltage drop and power loss of the output leads for a 5V, 100A supply. Consider 1oz., 2oz. and 3oz. copper conductors. ~1 0.56 0.56 Cap ~.22 No. of squares for both sides is: Squares = 2( ) = 4.68 sq. For 2oz. copper Rtotal =(0.252 mW/sq) (4.68 sq) =1.18 mW Vleads = (1.18 mW) (100 A) = 118mV or 2.8% Pleads = (118 mW) (100 A) 2 = 12 W 0.56 ~1 0.56 Terminal

107 Output Conductor Resistance

108 Coupled Capacitance Substrate Coupling Example:
Conductor #1: 100mils x 1 inch Conductor #2: 400mils x 1 inch Substrate: ceramic loaded polymer, 3 mils thick, er = 6.4 Find Capacitance: C =

109 Coupled Capacitance Substrate Coupling Example:
Conductor #1: 100mils x 1 inch Conductor #2: 400mils x 1 inch Substrate: ceramic loaded polymer, 3 mils thick, er = 6.4 Find Capacitance: C1 = 47.9 pF, C2 = 192 pF C = C1 series with C2 = 38.3 pF

110 Ground Coupling 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, er = 9.4 Voltage source: 425 Vdc continued Vd

111 Ground Coupling (continued)
Bond Pad 100mils2 Find Capacitance: Find switching current: i = C (dV/dt ) i = ? 20mils 400mils2 Drain Lead 100x200mils

112 Ground Coupling (continued)
Bond Pad 100mils2 20mils Find Capacitance: A = in2 = 183 mm2 d = 25 mils = mm Then: C = 24 pF (d-s Cap) Find switching current: i = C (dV/dt ) = 24 pF (425/20ns) i = 0.51 A 400mils2 Drain Lead 100x200mils For ceramic loaded polymer C = 136 pF and i = 2.9 A

113 Inductive Effects Non-Transmission Line Mode
Self Inductance of Conductors Minimum is non-coupled in free space Xe ( W / sq ) = Ld Gl Ld = Rd = ( 2 s d )-1 Gl = (sinh n - sin n ) / ( cosh n - cos n ) n = t / d t is the thickness (m) d = ( p f m s )-1/ 2, skin depth s is conductivity in (s/m) f is frequency m is permeability ( m0 = 4 p x H/m)

114 Inductive Effects 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: d = 66.0 mm, n = t / d = 0.516 Ld = mW / sq, Gl = 0.172 Xe = 22.4 mW / sq, or Le = 3.57 pF / sq Note: max self-inductance = ( 4p fs / m ) -1 / 2 Self-Inductance, 1MHz

115 Inductive Loops 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)

116 Temperature as the Culprit
Junction Life Statistics 150, 0.2 Failure Rate ( /105 runs) 100, 0.05 50, 0.005 Junction Temp (C)

117 Thermal Issues Factors affecting DT Convection/conduction in medium
Chip size Chip attach Heat spreader Conductor type and thickness Substrate type and thickness Substrate attach Heatsink

118 Rule of Areas (Hoppy’s Rule)
Power Supply h = P0 / Pi , Pl = P0 ( 1 - h ) / h Load P0, zero % efficient electrically Load PwrSupply heat heat For first-level type packaging (e.g.. chip and wire) the thermal area densities are equal: P0 Pi h, Pl PL Pl / Aps = PL / AL

119 Rule of Areas (continued)
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. Aps/AL TDr=1 Then TDr ( Pl / Aps ) = PL / AL Aps / AL = TDr ( h ) h

120 Thermal Resistance Model - 1D
k A Chip Rq = Solder Spreader 1 l s A R = Conductor Substrate i q Attach R [W] = v[V] / i [A] R [oC/W] = T [oC] / q [W] Baseplate Dv DT Attach R Rq Heatsink

121 Comparative Thermal Resistances (°C/kW cm2)
Thermal Typical Thickness DT(°C) Material Conductivity Rq/cm (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 Ceramic Glass Epoxy (FR-4) Thermal Grease 84 63 146 20-26 170 240 393 3.2 1.1 42 16 17 244 37 26 - 2.6 476 3000 924 14 4 10 25 - 4 (3oz) 6 20 8.4 8 3.4 49 - 5.2 0.52 95 600 185

122 Example Structure width (mm) depth (mm) thick (mm) Material k (W/m °C)
Si width (mm) depth (mm) thick (mm) k (W/m °C) Material DBC Si Solder Cu Al2O3 Al AlSiC 10.2 12.7 15.2 10.2 12.7 15.2 360 102 204 635 51 1.27* 84 63 393 26 240 170 Al2O3 Al AlSiC * in mm

123 One-Dimensional Model -Using Bulk Dimensions-
Rq = (t / A) / k Si t = thickness, A= width x depth DBC Rq(°C/W) layer t (mm) w(mm) w’(mm) D(mm) D’(mm) Ae(mm2) Si Solder Cu Al2O3 Al AlSiC 360 102 203 635 51 1.27* 10.2 10.4 11.0 12.3 12.7 15.2 103 107 121 122 152 0.041 0.016 0.003 0.105 0.001 0.002 Al2O3 10.2 12.7 15.2 Al AlSiC *in mm Rq, total = °C/W

124 - ” 45° ” Spreading Angle - Hence: A = (Wu + t)(Du + t)
Assumption : For an isotropic material, heat flows laterally at the same rate it flows vertically. Hence: A = (Wu + t)(Du + t) Rq = (t / A) / k width (mm) depth (mm) thick (mm) Si k (W/m °C) Material DBC Si Solder Cu Al2O3 Al AlSiC 10.2 12.7 15.2 10.2 12.7 15.2 360 102 204 635 51 1.27* 84 63 393 26 240 170 Al2O3 Al * in mm Rq = 0.232° C/W AlSiC

125 - Adjustable Spreading Angle -
Thermal interaction of layers changes the thermal spreading angle, a an = tan-1(kn / kn+1) A’n = [W’n + 2tn tan (an)] Rq,n = (tn / A’n) Kn DW > tn tan (an) Asi Acu Example Spreading Angles Composite Material Spreading Angle in * a2 a2 Acer DBC* on Al2O3 DBC* on BeO Cu* on Fr-4 AlSiC* on Al 85° 57° 89.8° 30°

126 Adjusted Spreading for Structure
Layer Angle (°) W’(mm) D’(mm) A’(mm2) Rq (°C/W) Si Si Solder Cu Al2O3 Al AlSiC 86 6.2 55 30 10.2 16.0 (12.7) 12.8 13.0 14.5 10.2 16.0 (12.7) 12.8 13.0 14.5 104 --- 107 165 169 209 0.041 0.016 --- 0.003 0.148 0.001 0.036 DBC Al2O3 Al Rq = 0.290° C/W AlSiC

127 Presentation Goes Off-Line
We break to another topic. See supplemental material. Review of packaging paraphernalia

128 Design Approaches and Tools

129 The Good the Bad and the Ugly
In the Best of Designs... Compliments of Celestica, Inc. The Good the Bad and the Ugly

130 Presentation Goes Off-Line
We break to another topic. See supplemental material. Review of physical hardware Compliments of Celestica, Inc.

131 Simulating Reality Our best guess at Mother Nature

132 Overview on Design Tools
Webench, SMS, SwitcherCAD Design Programs for Power Supplies Cost $$$ Pspice, AWB, SIMetrix, Simplis SPICE based or State-Space Simulator Ease of Use Pisces, Fielday, Ansoft FEM Based Simulators Pisces, Fielday IBM) are FEM based simulators which simulate at the holes/electrons level. Very limited external circuits can be added. Ansoft is a FEM program for magnetics SMS – Switchers Made Simple is a canned program that designs the components around a power supply chip. Device Physics Component Modeling Circuit Simulation Specific Circuits Physical Level

133 FEM Design Tools Expensive and require significant learning
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 See additional Ansoft foils

134 1=Cadence, 2=Simetrix inc
SPICE Design Tools Easy to use but requires circuit design experience and $$$ 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 1=Cadence, 2=Simetrix inc

135 SPICE Design Tools - Limitations
When simulating switchmode supplies, SPICE has limitation 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

136 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 Purple is the output voltage with a transient response Yellow is the primary switch current Red is the error voltage 1=Transim Corp

137 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 Purple is the output voltage with a transient response Yellow is the primary switch current Red is the error voltage

138 SMS Design Tool Switcher Made Simple (SMS) is a PC program from National Semi., in conjunction with Transim Corp 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 Purple is the output voltage with a transient response Yellow is the primary switch current Red is the error voltage

139 Input Filtering (Not selective hearing)

140 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

141 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 Irip Iin Time 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

142 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

143 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

144 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

145 Input Filter Shown is a two-stage filter with input current and load current Beware of inter-stage oscillations

146 A Different Approach to a DESIGN
Optimally Selecting Packaging Technologies and Circuit Partitions Based on Cost and Performance APEC’ 2000 Conference John B. Jacobsen and Douglas C. Hopkins

147 Full-Cost Model Other OH Overhead Production Cost Depreciation Wages
Packaging Materials & Production Costs (controllable) Wages Packaging materials Comp. packaging Standard unit cost Materials Cost Materials Cost Minimum packaged components

148 Centers of Cost Materials cost* Production cost* Partitioning 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)

149 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

150 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

151 Production Cost Dependency by Volume
yr 700% 600% 500% Other overhead costs 400% Production Cost 300% 200% Depreciation 100% Wages 0% 10k 32k 100k 320k 1000k Products/Year

152 Cost Variation Within a Technology
Packaging & Packaging Performance: Production Costs (electrical, thermal, mechanical 1 0.8 TF module Changing technology & leadframe 110 SMDs to change density 14 leadet 0.6 Relative Cost FR4 0.4 Functional 0.2 integration within 70 SMDs technology 7 leadet 5 10 15 20 25 30 Surface Density

153 Relative Cost of Technologies
Packaging & Packaging Performance: Production Costs electrical, thermal, mechanical 1 DBC TF & Plated Cu 0.8 Performance IMS 0.6 Circuit cost by Relative Cost FR4 change in technology 0.4 Hot 0.2 Embossing 5 10 15 20 25 30 Surface Density

154 Relative Packaging & Production Cost
Relative to 1 in2 of FR4 14 12 a a leaded auto/10 comp b 10 b Substr/in2 8 Relative Cost c c 6 Power chip& wire/10 comp 4 d 2 SMD/10 comp d d Integrated res/10 comp TTF TF multilayer Hot Embossing FR4 Cu( 2x35um) FR4 Cu( 4 layer ) IMS (1 layer on Al) DBC( 0,63 Al2O3 ) Z-strate Cu( 2 layer) Substrate Technology

155 Relative Production Cost per Technology
120% 100% 80% Cost/component 60% 40% 20% 0% Leaded-manual Leaded-auto Power chip & wire SMD-auto Assembly Technology

156 THE END Thank you for your interest in DCHopkins & Associates


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