Packaging Optimization in Isolation Power
Magnetics of AC-DC Front-end
KK ChinStaff Engineer
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