Integrated Elements

1
Filters and Components with Inductance
Cancellation
LEES
Timothy C. Neugebauer Joshua W. Phinney
Prof. David J. Perreault Massachusetts
Institute of Technology, Laboratory for
Electromagnetic and Electronic Systems

• Integrated Elements
• Cancellation windings can be integrated with a
  capacitor to form a three-terminal integrated
  filter element.
• Work in this area is ongoing.

• Printed Circuit Board Transformers
• An air core transformer made from printed circuit
  board traces can be used to cancel the ESL of a
  capacitor.
• The PCB transformer can fit under the capacitor
  so that little or no additional board space is
  needed.
• PCB transformers provide repeatable inductances
  that can be estimated using empirical or
  analytical equations.

Abstract Abstract --- Electrical filters are
important for attenuating electrical ripple,
eliminating electromagnetic interference (EMI)
and susceptibility, improving power quality, and
minimizing electromagnetic signature. Capacitors
are critical elements in such filters, and filter
performance is strongly influenced by the
capacitor parasitics. This project introduces a
new design technique that overcomes the capacitor
parasitic inductance that limits filter
performance at high frequencies. Coupled magnetic
windings are employed to effectively cancel the
parasitic inductance of capacitors, and to add
inductance in filter branches where it is
desired.
Discrete filters using Cornell Dubilier 935C4W10K
capacitors with end-tapped cancellation windings
printed in the PCB. The board on the left has
both capacitors mounted. The board in the middle
shows the top (component) side of the board,
while the board on the right shows the bottom
side of the board.

• Inductance Cancellation
• A high frequency model of a capacitor includes an
  ideal capacitor, a resistor and an inductor. The
  inductance dominates the impedance at high
  frequency.
• Coupled magnetic windings (center-tapped or
  end-tapped) are configured to provide the desired
  effect. The coupled windings can be modeled as a
  T network, in which one branch of the T model
  can be a negative inductance.
• The windings and capacitor combine to nullify
  shunt path inductance.

• Filtering Applications
• Capacitors with inductance cancellation are well
  suited for filtering applications.
• Experimental results in the input filter of a
  power converter demonstrate the advantages of
  inductance cancellation.

Performance curves. The higher curve is a
capacitor alone (no cancellation). The lower
curves are results with six nominally identical
circuits incorporating printed cancellation
windings. More than a factor of 10 in performance
improvement is obtained (20 dB).

LISN power spectra for the case of (a) the
capacitor alone and (b) the integrated filter
element. The converter was operated at 50 duty
cycle at 10 A DC output current.
Published Literature T. C. Neugebauer, J. W.
Phinney, and D. J. Perreault, Filters and
components with inductance cancellation, 2002
IEEE Industrial Applications Society Annual
Meeting, October 2002, pp. 939-947. T. C.
Neugebauer and D. J. Perreault, Filters with
inductance cancellation using Printed Circuit
Board Transformers, 2003 Power Electronics
Specialist Conference, June 2003.
Application of coupled magnetic windings to
cancel the series inductance of a capacitor.
Capacitor ESR and ESL are shown explicitly, along
with the equivalent T model of the
magnetic windings.
Effects of varying degrees of cancellation below
and above optimal. The highest curve in both
figures represents the performance of a capacitor
without any inductance cancellation. The curves
in figure a are the results with center-tapped
transformers having mutual inductances between 6
nH and 26 nH at intervals of 4 nH each. Figure b
shows the results of having a mutual inductance
that is too large these curves are the results
with transformers having mutual inductances
between 26 nH and 32 nH with intervals of 2 nH.
Acknowledgments United States Office of Naval
Research