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ABCs of Power Electronic Systems By Dr. Doug Hopkins & Dr. Ron Wunderlich DCHopkins & Associates Denal Way, m/s 408 Vestal, New York 13850-3035 [email protected] © 2006 DCHopkins www.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. © 2006 DCHopkins www.DCHopkins-Associates.Com 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] © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com DCHopkins & Associates - Products • 30A high efficiency, hightransient isolated power supply • Isolated power supply for highend micro-processor Pictures courtesy of Celestica, Incorporated © 2006 DCHopkins www.DCHopkins-Associates.Com News Sources Where to go for news (other than suppliers)? • • • • • • • • 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Introduction to The System Source Load Power Processor © 2006 DCHopkins www.DCHopkins-Associates.Com Conversion or Supply “Conversion” changes one energy form to another. Source Electrical Source Power Processor Load Types of Loads Motor drives • Linear • Rotational Lighting • Fluorescent • HID • Halogen Pulsed power • Ignition • Flash lamp • Pulsed propulsion POWER CONVERSION © 2006 DCHopkins www.DCHopkins-Associates.Com Conversion or Supply “Supply” changes only the attributes. LOAD Source Power Processor Load Computer Applications – Desktops Handheld Applications – Workstations Telecom Applications – PDA’s – Servers – Notebooks – Routers – Mainframes – Cell-phones – Tele. Switches Circuits: Circuits: Circuits: – CPU – RF Amps – Optical Amps – Memory – CPU/Logic – CPU – Bus Terminators – Memory – Memory – Logic – Display – Switch Cards – Graphics – Audio Amps – Logic POWER SUPPLY © 2006 DCHopkins www.DCHopkins-Associates.Com 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 Voltage Time © 2006 DCHopkins Power Processor Electronic Circuit Voltage Noisy AC Utility Clean AC Utility Time www.DCHopkins-Associates.Com The System - Source Characteristics Source Power Processor Load SOURCE © 2006 DCHopkins IF THE SOURCE THEN THE LOAD matches the load is directly regulated has over capacity flashlight generator field control requires regulating circuit www.DCHopkins-Associates.Com The System - Source Characteristics Source Power Processor Load THE POWER PROCESSOR Converts an unregulated power source to a regulated output. Like CPU’s processing information - Power Supplies process energy. © 2006 DCHopkins Linear Regulator Switch-mode Regulator Absorbs the energy difference Chops and averages energy packets www.DCHopkins-Associates.Com Knowing Your Specifications and the User’s Requirements © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Grouping User Requirements Characteristic Unspoken Expectations Articulated Needs Unexpected Features Taxonomy Financial Legal Social MATRIXED Environmental Technical © 2006 DCHopkins www.DCHopkins-Associates.Com 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.” © 2006 DCHopkins www.DCHopkins-Associates.Com 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. © 2006 DCHopkins www.DCHopkins-Associates.Com 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. © 2006 DCHopkins www.DCHopkins-Associates.Com Defining Specifications Power electronic circuits condition and convert many energy forms! Iin • Electric • Magnetic Vin Iout Power Supply Vout • Electromagnetic • Thermal • Mechanical Technical User Requirements provide the • Chemical SPECIFICATIONS • Photonic for each Energy Form. © 2006 DCHopkins www.DCHopkins-Associates.Com Framework leading to Specifications Responsible Design is from Cradle to Grave. Taxonomies Characteristics © 2006 DCHopkins Technical Characteristics – Energy Forms – Conditions • Start-up • Shut-down • Normal operation • Fault operation www.DCHopkins-Associates.Com Electrical Specs Electrical Spec Input AC DC Vin, Iin Vin, Iin © 2006 DCHopkins Output Controls Misc Vout, Iout PGood, On/Off Efficiency www.DCHopkins-Associates.Com 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. © 2006 DCHopkins www.DCHopkins-Associates.Com 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. © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com DC Input Spec • Iin will have switching noise that occurs at >10Mhz. Iin Iin will have switching noise. • The noise is due to the internal capacitive coupling parasitics • Typically, the peak-to-peak noise is less than 1% of max Iin Time Iin Vin Time © 2006 DCHopkins www.DCHopkins-Associates.Com DC Input Spec Iin will have a surge during start-up. • Surge current, Isurge, is due to charging of internal capacitors Iin Vin • Usually Isurge is less than 5 times max Iin • This can cause problems with fusing. © 2006 DCHopkins Time www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com AC Input Spec - Vin-rms Vin is from the wall outlet or a UPS for “Off-Line”converters • Vin is understood to be Vin-rms; Vpk Voltage • AC sources are: – Single Phase – Three Phase (>5kW, not covered) – Vin-rms = Vpk / 1.4142 * • RMS makes calculations easier – For DC, Pin = Vin x Iin – For AC, Pin = Vin-rms x Iin-rms Time Iin * For single frequency sine wave Vin © 2006 DCHopkins Iout Power Supply Vout www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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. © 2006 DCHopkins www.DCHopkins-Associates.Com 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. Vin Iin Time Vin Iin Time © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com AC Input Spec - Inrush Current Like DC, Iin has inrush issues with AC applications. • Usually, peak Iin is specified to be <5X the steadystate 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. © 2006 DCHopkins www.DCHopkins-Associates.Com 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 = 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% © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Vout Specs Line, Load & Temperature Load Step VOUT Ripple & HF Noise Long Term Stability © 2006 DCHopkins www.DCHopkins-Associates.Com 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% © 2006 DCHopkins www.DCHopkins-Associates.Com 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% © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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% © 2006 DCHopkins www.DCHopkins-Associates.Com Ripple and Noise – Triangular-shaped current at the switch frequency – Due to inductor current x ESR of output cap Vout • Ripple Time • Typically 0.2-3% Voltage • High Frequency Noise – Noise > 10 x fSW – Either random or the excitation of high-frequency parasitics. Vrip Time © 2006 DCHopkins www.DCHopkins-Associates.Com Drift Over time, a reference voltage can change. • Drift is due to – Aging – Soldering – Package compression • Typically < 0.2% © 2006 DCHopkins www.DCHopkins-Associates.Com Question - How can you improve the transient response of the converter without… changing the components or changing the switching frequency? © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Iout Specs • Below is a typical Iout load behaviour Maximum current Over current trip point Iout di/dt rate I step Minimum current Time © 2006 DCHopkins www.DCHopkins-Associates.Com Question What happens to current in COUT if IOUT’s frequency >> than the bandwidth of the converter ? © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Design For Safety Standards, Certificates & Regulations © 2006 DCHopkins www.DCHopkins-Associates.Com Standards, Certificates & Regulations A power supply has many standards and regulations to meet Only the major ones will be covered Safety Corporate Standards Vin Iin Time EMC Features Robustness © 2006 DCHopkins www.DCHopkins-Associates.Com Safety - http://www.i-spec.com • Many countries have their own safety agencies – US has Underwriters Laboratories – Canada has Canadian Safety Agency – Europe has Conformity European Mark • 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 C22.2 950, AS/NZS 3260. © 2006 DCHopkins http://www.i-spec.com www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Conducted or Emitted <30 MHz FREQUENCIES >30 MHz • Noise is measured through a device called a LISN on the AC cord • The noise is measured with an antennae 10 meters away • LISN – Line Impedance Stabilizer Network is a set of filters that filters signals above 60Hz to a spectrum analyzer • All testing is done in a shielded chamber © 2006 DCHopkins • Certifications must come from approved sites www.DCHopkins-Associates.Com Why 30 MHz? • Question – 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Susceptibility 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. © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Susceptibility - Electro-static Discharge Products must also be protected or withstand electro-static discharges (ESD) • 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Corporate Standards 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Choosing the Correct Topology © 2006 DCHopkins www.DCHopkins-Associates.Com Linear Regulators • Switch is used as programmable resistor • Fast dynamic response • Minimal filtering • Poor efficiency • Relatively large with heat sink PL = (VIN - VOUT) * IOUT dc source (VIN) © 2006 DCHopkins Load (VOUT) www.DCHopkins-Associates.Com 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) © 2006 DCHopkins chopper (fT) filter (fF) load (VOUT) www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Demystifying the Circuits – Non-isolated dc source dc source load Buck DUALITY load Boost CASCADE dc source load Buck/Boost © 2006 DCHopkins DUALITY not covered Cuk www.DCHopkins-Associates.Com Demystifying the Circuits – Conversion Ratios Buck Regulator (Step-down converter) Boost Regulator (Step-up converter) VOUT =D VIN VOUT = 1 VIN 1-D Buck/Boost (Up/down converter) VOUT -D = VIN 1-D © 2006 DCHopkins D: duty cycle of switch TON TPERIOD D= TON TPERIOD www.DCHopkins-Associates.Com Demystifying the Circuits – Transformer Isolated • • Buck/Boost Isolated load dc source Flyback • • Buck Isolated load dc source Forward © 2006 DCHopkins www.DCHopkins-Associates.Com Demystifying the Circuits – Bridge Half Bridge dc source LOAD Buck derived topologies Full Bridge dc source © 2006 DCHopkins LOAD www.DCHopkins-Associates.Com Demystifying the Circuits – Resonant Bridge Series Resonant dc source LOAD Parallel Loaded Series Resonant dc source LOAD © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Knowing Where Disaster Can Strike Do you have the “knack?” © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins Buck-Boost Load Buck Load www.DCHopkins-Associates.Com 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 © 2006 DCHopkins All parameters work against you Thank you, Mother Nature www.DCHopkins-Associates.Com Inductive Switching - Ideal Circuit © 2006 DCHopkins www.DCHopkins-Associates.Com Inductive Switching - Ideal Circuit, Real Switch © 2006 DCHopkins www.DCHopkins-Associates.Com Inductive Switching - Diode Inductance © 2006 DCHopkins www.DCHopkins-Associates.Com Inductive Switching - Diode Capacitance © 2006 DCHopkins www.DCHopkins-Associates.Com Inductive Switching - Circuit Inductance © 2006 DCHopkins www.DCHopkins-Associates.Com Inductive Switching - Slower Switch Transition Vds is worse if Fet is slowed down. Suspect something with model. Everything else ok. © 2006 DCHopkins www.DCHopkins-Associates.Com Inductive Switching - Snubbing transients © 2006 DCHopkins www.DCHopkins-Associates.Com Characterizing Power Components © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins • Transistors – Power Mosfets • vertical structure – IGBTs – “TopSwitch” – modules – Bipolars • Triggered semiconductors – SCR’s • crowbar applications • Phase-controlled bridges • high power – Unijunctions www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Diode Reverse Recovery Recovery produces sharp current transients and EMI tn IF ta IF tb IRR tn ta tb IRR Abrupt Recovery Soft Recovery Buck Load © 2006 DCHopkins www.DCHopkins-Associates.Com Safe Operating Area - the holy grail SOA combines transient and thermal limits ID Steady state (DC) limit Fusing current Thermal path limit MAXIMUM POWER AREA © 2006 DCHopkins Transient thermal limit Breakdown limit VDS www.DCHopkins-Associates.Com Capacitors - Circuit Equivalent • Ceramic – high frequency – sensitive to thermal transient ESL • Tantalum ESR – polarized, also organic leads – high energy density • Electrolytic, also oscon C leakage – polarized – highest energy density • Equivalent Circuit – R, L, C – limited internal temperature from “RMS heating,” i.e. current ripple © 2006 DCHopkins Staged for reducing ESR www.DCHopkins-Associates.Com 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 Xl Xs Cs Approx.: Xl = 10 *Xp © 2006 DCHopkins www.DCHopkins-Associates.Com The Dual Faces of Power MOSFETS Getting the heat out with Synchronous Rectification © 2006 DCHopkins www.DCHopkins-Associates.Com 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 Vout x100% Vout Vd Vd is the voltage drop due to the output diodes dc source load Boost © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 I • Efficiency of 90% can be achieved with 1V@100A power supply! © 2006 DCHopkins www.DCHopkins-Associates.Com 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 1V@100A converter, 2% efficiency loss to gate drives is not uncommon © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com The Circuit is a Component Insights into Power Packaging © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Typical Electrical Structure Lead Inductance Finite resistance Skin Effect Inter-Conductor Capacitance Coupled Capacitance © 2006 DCHopkins www.DCHopkins-Associates.Com Conductor Resistance -Sheet Resistance R= r l l / (t × w) t let l / w = 1 = “one square” l w Rsheet = r / t [ W / sq. ] A corner is 0.559 squares © 2006 DCHopkins www.DCHopkins-Associates.Com Conductor Thickness “1 oz. copper” is weight for one square foot Thickness and Resistance from Common Conductors Metal Al (6061) Cu (110) Gold Silver Tin © 2006 DCHopkins Density Resistivity Thickness (mils) (gm/cc) (Wcm) 1oz 2oz 3oz 2.72 2.83 4.41 8.83 13.24 8.94 1.72 1.34 2.68 4.03 19.3 2.2 0.62 1.24 1.87 10.19 1.59 1.18 2.36 3.53 7.29 11.5 1.65 3.29 4.94 DC Resistance (mWsq) 1oz 2oz 3oz 0.252 0.126 0.084 0.504 0.252 0.168 1.393 0.696 0.464 0.531 0.266 0.177 2.75 1.375 0.917 www.DCHopkins-Associates.Com 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. No. of squares for both sides is: Squares = = For 2oz. copper Rtotal = = Vleads = Pleads = ? © 2006 DCHopkins ~1 Cap ~.22 Terminal www.DCHopkins-Associates.Com 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. 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 mWsq) (4.68 sq) =1.18 mW Vleads = (1.18 mW) (100 A) 118mV or 2.8% Pleads = (118 mW) (100 A) 2 = 12 W © 2006 DCHopkins ~1 0.56 0.56 Cap ~.22 0.56 ~1 0.56 Terminal www.DCHopkins-Associates.Com Output Conductor Resistance Cu "thickness" Resistance (mOhm) Voltage Drop (mV) Power Loss (W) © 2006 DCHopkins 1oz 2.8 280 28 2oz 1.4 140 14 3oz 0.7 70 7 www.DCHopkins-Associates.Com 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= © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Ground Coupling Example: Switching current coupled into header from FET drain. Vd 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Ground Coupling (continued) Bond Pad 100mils2 Find Capacitance: ? 20mils 400mils2 Find switching current: i = C (dV/dt ) Drain Lead 100x200mils i= © 2006 DCHopkins www.DCHopkins-Associates.Com Ground Coupling (continued) Bond Pad 100mils2 20mils • Find Capacitance: A = 0.284 in2 = 183 mm2 d = 25 mils = 0.635 mm Then: C = 24 pF (d-s Cap) • Find switching current: i = C (dV/dt ) = 24 pF (425/20ns) i = 0.51 A © 2006 DCHopkins 400mils2 Drain Lead 100x200mils For ceramic loaded polymer C = 136 pF and i = 2.9 A www.DCHopkins-Associates.Com 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 ) nt/d t is the thickness (m) d ( f s )1 2, skin depth s is conductivity in (s/m) f is frequency is permeability ( 0 4 x 10-7 H/m) © 2006 DCHopkins www.DCHopkins-Associates.Com 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 m, n t / d 0.516 Ld 0.130 mW sq, Gl = 0.172 Xe = 22.4 W sq, or Le = 3.57 pF / sq Note: max selfinductance = ( 4 fs ) -1 / 2 © 2006 DCHopkins Self-Inductance, Cu @ 1MHz Xe ( W sq ) Le ( pH / sq ) 1oz 22 3.6 2oz 45 7.1 3oz 67 11 www.DCHopkins-Associates.Com 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) © 2006 DCHopkins www.DCHopkins-Associates.Com Temperature as the Culprit Vibration 20% Temperat ure 55% Dust 6% Humidity 19% © 2006 DCHopkins Failure Rate ( /105 runs) Primary Causes of failure in avionics equipment Junction Life Statistics 150, 0.2 100, 0.05 50, 0.005 Junction Temp (C) www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Rule of Areas (Hoppy’s Rule) Power Supply P0 / P i , Pl = P0 ( 1 - ) Load P0, zero % efficient electrically heat heat For first-level type packaging (e.g.. chip and wire) the thermal area densities are equal: Pl / Aps = PL / AL © 2006 DCHopkins Pi , Pl P0 PL www.DCHopkins-Associates.Com 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 1 TDr=1 0.8 0.6 0.4 0.2 Then TDr ( Pl / Aps ) = PL / AL Aps / AL = TDr ( 1 1 ) © 2006 DCHopkins 0 0.5 0.6 0.7 0.8 0.9 1 www.DCHopkins-Associates.Com Thermal Resistance Model - 1D Rq = 1 t k A 1 l R = s A i q Dv DT R Rq Chip Solder Spreader Conductor Substrate Attach Baseplate Attach R [W] = v[V] / i [A] R [oC/W] = T [oC] / q [W] Heatsink © 2006 DCHopkins www.DCHopkins-Associates.Com Comparative Thermal Resistances (°C/kW cm2) Material 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 © 2006 DCHopkins Thermal Conductivity (W/m °C) 84 63 146 2026 170230 Typical Rq/cm2 (°C/kW cm2) 42 16 17 244 37 Thickness (mils) 14 4 10 25 240320 170 26 - 25 25 - 240 393 3.2 0.21.7 1.1 2.6 476 3000 924 4 (3oz) 6 20 4 DT(°C) IGBT @0.2kW/cm2 8.4 8 3.4 49 5.2 0.52 95 600 185 www.DCHopkins-Associates.Com Example Structure Si width Material (mm) Si Solder Cu Al2O3 Al AlSiC 10.2 10.2 12.7 15.2 15.2 15.2 k depth thick (mm) (m) (W/m °C) 10.2 10.2 12.7 15.2 15.2 15.2 360 102 204 635 51 1.27* 84 63 393 26 240 170 DBC Al2O3 Al AlSiC * in mm © 2006 DCHopkins www.DCHopkins-Associates.Com One-Dimensional Model -Using Bulk Dimensions- Rq = (t / A) / k Si t = thickness, A= width x depth DBC layer t (m) w(mm) w’(mm) D(mm) D’(mm) Ae(mm2) Rq(°C/W) Si 360 10.2 Solder 102 10.2 Cu 203 12.7 Al2O3 635 15.2 Al 51 15.2 AlSiC 1.27* 15.2 10.2 10.2 10.4 11.0 11.0 12.3 10.2 10.2 12.7 15.2 15.2 15.2 10.2 10.2 12.7 15.2 15.2 15.2 103 103 107 121 122 152 0.041 0.016 0.003 0.105 0.001 0.002 Al2O3 Al AlSiC *in mm Rq, total = 0.198 °C/W © 2006 DCHopkins www.DCHopkins-Associates.Com - ” 45° ” Spreading Angle 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 Material Si Solder Cu Al2O3 Al AlSiC width (mm) 10.2 10.2 12.7 15.2 15.2 15.2 depth (mm) 10.2 10.2 12.7 15.2 15.2 15.2 360 102 204 635 51 1.27* Rq = 0.232° C/W © 2006 DCHopkins Si thick k (m) (W/m °C) 84 63 393 26 240 170 DBC Al2O3 Al * in mm AlSiC www.DCHopkins-Associates.Com - 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 © 2006 DCHopkins 85° 57° 89.8° 30° www.DCHopkins-Associates.Com Adjusted Spreading for Structure Layer Angle (°) W’(mm) D’(mm) A’(mm2) Rq (°C/W) Si Solder Cu 0 0 86 Al2O3 Al AlSiC 6.2 55 30 10.2 10.2 16.0 (12.7) 12.8 13.0 14.5 10.2 10.2 16.0 (12.7) 12.8 13.0 14.5 104 104 --107 165 169 209 Rq = 0.290° C/W © 2006 DCHopkins 0.041 0.016 --0.003 0.148 0.001 0.036 Si DBC Al2O3 Al AlSiC www.DCHopkins-Associates.Com Presentation Goes Off-Line We break to another topic. See supplemental material. Review of packaging paraphernalia © 2006 DCHopkins www.DCHopkins-Associates.Com Design Approaches and Tools © 2006 DCHopkins www.DCHopkins-Associates.Com In the Best of Designs... Compliments of Celestica, Inc. The Good the Bad and the Ugly © 2006 DCHopkins www.DCHopkins-Associates.Com Presentation Goes Off-Line We break to another topic. See supplemental material. Review of physical hardware Compliments of Celestica, Inc. © 2006 DCHopkins www.DCHopkins-Associates.Com Simulating Reality Our best guess at Mother Nature © 2006 DCHopkins www.DCHopkins-Associates.Com Overview on Design Tools Ease of Use SPICE based or StateSpace Simulator Webench, SMS, SwitcherCAD Pspice, AWB, SIMetrix, Simplis Pisces, Fielday, Ansoft Cost $$$ Design Programs for Power Supplies FEM Based Simulators Device Component Physics Modeling Circuit Simulation Specific Circuits Physical Level © 2006 DCHopkins www.DCHopkins-Associates.Com FEM Design Tools Expensive and require significant learning • Pisces and Fielday, IBM tools, simulate semiconductor devices at the electron level • Ansoft simulator models electromagnetic devices with FEM – On the right is a gapped ferrite core showing the flux lines See additional Ansoft foils © 2006 DCHopkins www.DCHopkins-Associates.Com SPICE Design Tools Easy to use but requires circuit design experience and $$$ • 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Input Filtering (Not selective hearing) © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 • 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 Irip Iin Time © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Input Filter Shown is a two-stage filter with input current and load current Beware of inter-stage oscillations © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com © 2006 DCHopkins Depreciation Production Cost Wages Materials Cost Packaging materials Comp. packaging (controllable) Other OH Packaging Materials & Production Costs Standard unit cost Overhead Full-Cost Model Minimum packaged components www.DCHopkins-Associates.Com 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) © 2006 DCHopkins www.DCHopkins-Associates.Com 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Centers of Cost (con’d) • Company business cost, i.e. return on investment for crossproduct 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 © 2006 DCHopkins www.DCHopkins-Associates.Com Production Cost Dependency by Volume yr - 2000 700% Production Cost 600% 500% 400% Other overhead costs 300% 200% Depreciation 100% 0% 10k © 2006 DCHopkins Wages 32k 100k Products/Year 320k 1000k www.DCHopkins-Associates.Com Cost Variation Within a Technology Packaging & Production Costs Relative Cost TF module & leadframe Packaging Performance: (electrical, thermal, mechanical 1 0.8 110 SMDs 14 leadet 0.6 FR4 0.4 Functional integration within technology 70 SMDs 7 leadet 0 5 10 15 20 25 0.2 0 30 Surface Density © 2006 DCHopkins www.DCHopkins-Associates.Com Relative Cost of Technologies Packaging Performance: electrical, thermal, mechanical 1 Packaging & Production Costs DBC TF & Plated Cu IMS Relative Cost 0.8 Performance Circuit cost by change in technology FR4 0.6 0.4 0.2 Hot Embossing 0 5 10 15 20 25 0 30 Surface Density © 2006 DCHopkins www.DCHopkins-Associates.Com Relative Packaging & Production Cost Relative to 1 in2 of FR4 a 12 b 10 8 c 6 a b c 4 d Z-strate Cu( 2 layer) DBC( 0,63 Al2O3 ) FR4 Cu( 4 layer ) FR4 Cu( 2x35um) Hot Embossing 0 TTF d d leaded auto/10 comp Substr/in2 Power chip& wire/10 comp SMD/10 comp Integrated res/10 comp TF multilayer 2 IMS (1 layer on Al) Relative Cost 14 Substrate Technology © 2006 DCHopkins www.DCHopkins-Associates.Com Relative Production Cost per Technology Cost/component 120% 100% 80% 60% 40% 20% 0% Leaded-manual Leaded-auto Power chip & wire SMD-auto Assembly Technology © 2006 DCHopkins www.DCHopkins-Associates.Com THE END Thank you for your interest in DCHopkins & Associates www.DCHopkins-Associates.Com © 2006 DCHopkins www.DCHopkins-Associates.Com