Standard Transformer Applications

General Transformer Glossary

  • Input Voltage/Current
  • Output Voltage/Current
  • Frequency
  • Topology/Duty Cycle
  • OCL/Leakage Inductance.
  • Temperature rise
  • Ambient Temperature. Ta70B

Safety Related Info

  • Output Voltage Limit

    • EN60950… SELV for 42.4Vpk or 60VDC
    • UL5085… Class II 30Vmax & Class III 30-100V or 150V
    • EN61558-2-6… 50VRMS/120V ripple free DC
  • Transformer Class

    • Class I/II/III in EN60950/EN61558 -> Protection
    • Class I/II/III in UL5085 -> Voltage

Safety related info

  • Insulation Grade

    • Class A 105C -> 100C max
    • Class E 120C -> 115C max
    • Class B 130C -> 120C max
    • Class F 155C -> 140C max
    • Class H 180C -> 165C max
  • TEX-E or Twisted Wire

  • MW82 wire and etc.

Creepage and Clearance

Creepage and Clearance

Laminated Transformer Types

  • Print PCB Transformer
  • UI Core low profile pin type transformer
  • Current Sensing Transformer
  • Lead type transformer
  • Power everywhere
  • New edge why still use the laminated transformer?

Laminated transformer materials

  • Lamination material
    Lamination: Z11, H12, H14, H18, H23, H50
  • Standard Sizes
  • Insulation materials
    Bobbin (PET, NYLON), TAPE (Polyester), Varnish (C1105, AC43)
Laminated Transformer

Standard Ferrite Magnetics SMPS Application

Standard Ferrite Magnetics SMPS Application

Choke Types

  • Choke Types by Application

    • Common Mode Choke
    • Differential Mode Choke
    • Energy Stock Choke (PFC, BUCK)
  • Choke Types by Material

    • Ferrite Core
    • Powdered Core (iron, MPP, Sendust)
    • Laminated Core (EI, taped, Amorphous)

Ferrite XFMR Types

  • Ferrite XFMR Types by Application

    • Flyback XFMR (with Gap)
    • Forward XFMR
    • PushPull
    • Full bridge
  • Ferrite XFMR Types by Shapes

    • EE 13, EE 16… …
    • EFD20,
    • ER28, ETD34…
    • Planar E40

Ferrites (continued)

  • Ferrite XFMR Material

    • TDK PC-40
    • Nicera NC-2H
    • China Material TDG, DMEGC ……
  • Ferrite XFMR Bobbins

    • EE 13, EE 16… …
    • EFD20,
    • ER28, ETD34…
    • Phenolic PM9820 T375J

Core Suppliers

Core Suppliers

Core Suppliers 2

Key Parameters Affect to your power supply

  • Leakage Inductance

Leakage Inductance

Leakage Inductance

Leakage Inductance

Leakage Inductance

Key Parameters Affect to your power supply

Wire Diameter Skin Effect Copper loss

Leakage Inductance
  • Minimize eddy currents using Leitz wire bundle. Each conductor in bundle has a diameter less than a skin depth.
  • Twisting of paralleled wires causes effects of intercepted flux to be canceled out between adjacent twists of the conductors. Hence little if any eddy currents.

Proximity Effect

Proximity Effect

Gap Fringing Effect

  • Fringing cause significant eddy loss
  • Avoid the fringing loss by design
  • Fringing increases the OCL
Gap Fringing Effect

Core Losses

  • Core Loss mW/cm^3 or mW/gram
  • Different loss from different material
  • Select right materials
    Not over design
  • B vs Core loss
    No stress design
flux density

Gap, ue, Bdc

  • Bsat -> inherent characteristics
  • Bdc -> decided by peak current
  • OCL -> decided by turns and gapping size
  • Basic formula:

Powder Core Characteristics

  • Distribute gap
  • Soft Saturation
  • Different power size -> different core loss
  • Thermal Aging issue
  • Choose right core materials
Powder Core Characteristics

Common Mode Choke

  • Impedance
  • EMI Filtering Network
  • Mostly are low pass LC filtering circuit.

EMI Filtering Net Work

EMI Filtering Net Work
EMI Filtering Net Work

Magnetics Thermal Engineering

  • Temperature Rise. Ploss includes copper loss and core loss
  • Forced Ventilation Effect
Magnetics Thermal Engineering


  • Leakage Inductance by N.H. Crowhurst 1949
  • Soft Ferrites, Properties and Applications, 2nd Edition 1988 by Snelling E.C.
  • Switching Mode Power supply Handbook by Keith. H. Billings
  • Micrometals Catalogue Edition 2000
  • ZETTLER Magnetics Catalog