Packaging Optimization in Isolation Power

Magnetics of AC-DC Front-end

KK ChinStaff Engineer

kk.chin@artesyn.com

The Quest for Higher Power DensityThe Quest for Higher Power DensityThe industry typically achieves 20W/in3 today with the PSMA projecting 30W/in3 by 2010We are developing a 30W/in3 platform with minimal cost impactIncreased density is always a challenge

Passive device technology is trailing activesRegulatory restrictions

Isolation magnetics are broadly usedPower transformer, current sensor transformer, gate drive transformer, auxiliary transformer.

Labor Content AnalysisLabor Content AnalysisMagnetics account for 40 – 50% of labor content in a typical AC-DC front end Almost 80% of the magnetics’ labor content is consumed in isolation magnetics (power transformer(s), aux transformer, gate drive transformer(s), current sense transformer(s)…)

AC-DC Front End Labor Content

PCB assembly, mech assembly, test & inspection, etc55%

Magnetics - non-isolated9%

Magnetics - isolated36%

For this reason….For this reason….We have a number of design and manufacturing initiatives that will address

SizeAutomation

Automation starts with design innovation

Recent Design Concepts (1)Recent Design Concepts (1)Compact Current Sense Transformer (US Patent no. 6,753,749)

50% footprint reduction vs typical industry designGood for medical safetyHigh SRF for high switching frequency

59% higher than off-the-shelf equivalentOff-the-shelf transformer makers seldom control this parameter

Today Tomorrow

Compact Current Sense TransformerCompact Current Sense TransformerDesign Example:

Housing with labyrinth for safety creepage (US Patent # 6,753,749)

CUP

TOROIDHOUSING

LOCKINGLATCH

TERMINALPINSFOR TOROIDWINDING

INNERSLEEVE

OUTERSLEEVE

CUP

HIGHCURRENTWIRES

LOCKINGRAMP

Compact Current Sense TransformerCompact Current Sense Transformer

Safety CreepageCompliance

All 4 critical creepage paths shown are longer than 8mm

Compact Current Sense TransformerCompact Current Sense TransformerSimplicity…

High degree of manufacturing automation & improved reliability by reducing manual labor content by 29%

No potting or manual insertion of bus wire

Power Transformer – Size Reduction DilemmaPower Transformer – Size Reduction Dilemma

High Frequency requires a smaller transformerBy Faraday’s Law (-V=N*dΦ/dt, or –V=NA*dB/dt),

Higher frequency takes less winding turns, and/orHigher frequency takes smaller coreResults in smaller transformerAlso results in less Rdc loss due to shorter winding length

However, High Frequency reduces efficiencySkin effect in conductor drives up Rac lossProximity effect pushes Rac loss even higherSwitching loss of other circuit devices hurts efficiency badlyPhysical isolation of primary and secondary dictates size

Therefore, selecting a reasonably higher frequency with optimal physical construction reduces Rac

Recent Design Concept (2) - Quasi-planar Transformer Recent Design Concept (2) - Quasi-planar Transformer

Physical Realization with Multiple Interleaving of primary and secondary

Lowers high frequency lossMaximizes window utilization

Transformer in PQ2620-EI delivering 1KW in a 1U AC-DC front end

US Patent pending on some aspects of the internal construction

Quasi-planar TransformerQuasi-planar Transformer

55% footprint reduction after integration of current sense transformer67% cost reduction relative to planar equivalent (no expensive multi-layer heavy copper PCB)

Physical Benefits

Quasi-planar Transformer Quasi-planar Transformer

Power Loss proven by:Bench Test & Thermal MeasurementFEA

Functional Performance

Toroidal TransformersToroidal Transformers

Toroidal transformer and an equivalent conventional transformer

Optimum use of ferrite

All windings on exterior for better cooling

Integrated heatsink(patent pending)

ConclusionConclusion

Innovative packaging of isolation magnetics is essential for

improving power density of AC-DC front end without increasing cost