Magnetics, FETs and PFC ideas about converter design process 2006

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Magnetics, FETs and PFC(ideas about converter
design process) 2006

• Power
• By
• Bo Rohde Pedersen

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MOSFET

• Basically FETs (in relation to use it as a
  switch)
• Switching loss
• What is to be aware of in a design with a FET

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Characteristics of MOSFET
iD g (uGS - UT), aktive område
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RDS,on dependence of temperature
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MOSFETmetal-oxide semiconductor field-effect
transistor
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MOSFET more details
- Pasitic capaciters are often in datasheets
described as input, output and transfer
capacitance
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Turn-on of a MOSFET
Switching losses Lost energy for
switching (energy put in to the gate) Energy
lost in the switch doing switching
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Turn-off of a MOSFET
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Basic lows Amperes Law
H Magnetic field intensity A/m,(magnetiske
feltstyrke)
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Basic lows Flux Density or B-Field
B Wb/m2 or T µ H/m µ0 4p 10-7 H/m
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Basic lows Magnetic Flux
F Flux Wb
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Electrical Magnetic Analogy
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Self-Inductance L
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Designing of Inductor Core
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Thermal limitation

• - Remember skin effect.
• Temperature often limit by the core.
• Also loss in the core.

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Energy in Inductor
Energy in Inductor
No Magnitic spred in the Air Gab!! In this
calculation
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Summery of Converter Design

• Loss in FET increases with increasing switch
  frequency
• Magnetics decrease in size and loss with
  increasing frequency
• Ripple current in capacitors decreases when the
  inductor is increased.

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Diode Bridge Rectifier
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Norm for Harmonics drown from the Net
Minimum 75W
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Perfect Converter
Flyback with HF-filter
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Regulation System for PFC(Power Factor
Correction)