理解和控制高功率电子学中的共模幅射.pdf

文档介绍：Page 1
UNDERSTANDING AND CONTROLLING
COMMON-MODE EMISSIONS
IN HIGH-POWER ELECTRONICS
By
Henry W. Ott
Henry Ott Consultants
Livingston, NJ 07039
[phone]
t@
© 2001 Henry W. Ott HOC
IC
COMPATIBILITY
Page 2
THE BASIC PROBLEM
! Switching Power Supplies and Variable Speed Motor Drives
Produce Large Noise Currents Which are Conducted Out to
the Load, as Well as Conducted Back to The Power Source
! mon-Mode Noise Currents are the Cause of:
— Low Frequency Conducted Emission, and
— High Frequency Radiated Emission
! Once One Has an Understanding of the Noise Source and
Coupling Mechanism, a Solution Can be Determined
! Power Line Filters bination With Proper Load Side
Filtering, Grounding, and/or Shielding Will Usually Solve
mon-Mode Emission Problems.
© 2001 Henry W. Ott HOC
IC
COMPATIBILITY
Page 3
BASIC PRINCIPLE OF EMC
Return Current to its Source as Locally
pactly as Possible
Minimize the Loop Area
© 2001 Henry W. Ott HOC
IC
COMPATIBILITY
Page 4
COMMON-MODE & DIFFERENTIAL MODE NOISE
! Differential-Mode Noise ! Common-Mode Noise
— Involves the Normal — Does Not Relate to the
Operation of the Circuit Normal Operation of the
— Currents Flowing Around Circuit
Loops — Involves Parasitics
— Is Documented — Currents Flow Around Loops
• Schematics Usually Involving Parasitic
Capacitance
• PCB Layout
— Is Not Documented
• Wiring Diagrams
— Is More Difficult to
— Is Easy to Understand Understand
— The Noise Source and
Current Path Must First be
Visualized and Understood
Before a Solution Can be
Determined
© 2001 Henry W. Ott HOC
IC
COMPATIBILITY
Page 5
RADIATION MECHANISMS
DIFFERENTIAL-MON-MODE
RADIATION RADIATION
Radiated
Radiated Emission
Emission
PCB
I/O Cable
Icm
Signal
PWB
Gnd Plane
VN Or Grid
I0
Ground
Gnd Wire
2
E = K1 f A I0
E=K2 f L Icm
© 2001 Henry W. Ott HOC
IC
COMPATIBILITY
Page 6
BASIC ANTENNA TYPES
Ant