Choke Design Using Iron Powder Toroidal Cores

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Choke Design Using Iron Powder Toroidal Cores

• Presented by
• Gurveer Singh
• (Student, EE136 Power Electronics)

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Introduction Choke Design Using Iron Powder
Toroidal Cores

• Iron powder toroids can be very suitable for
  chokes in output filters of power converters.
• The term choke is used to describe an inductor
  which carries
• A large DC bias current.
• Small ac ripple current.

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Design Approach

• Graphical design method based on the nomogram is
  emphasized.
• Nomogram is a plot or graphical representation of
  parameter relations obtained from equations.

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Example of nomogram

• Gives turns as a function of choke current for
  different cores.
• Required parameters
• Inductance
• Core size

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Design Example

• Step1 Calculate the inductance required at full
  load.
• Step2 Obtain
• Core Size
• Turns
• From nomogram

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Design Example (contd)

• Enter the nomogram at the bottom scale.
• With the required maximum load current of 10A.
• Project upward to the required inductance,
  14.8uH. (use heavy line marked 15uH).
• Nearest diagonal (thin line) gives the required
  core size (T90 in this case).
• Horizontal left projection from the core and
  inductance intersect indicates the required turns
  (21 in this example).

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Design Example (contd)
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Select toroidal choke winding depending on the
required performance

• Option A Minimum Loss Winding (Full Winding)
• Lowest copper loss, difficult and expensive to
  manufacture.
• Option B Single-Layer Winding
• Higher copper loss, higher temperature rise,
  simple to manufacture.
• Option C Winding for a Specified Temperature
  Rise
• More difficult to design.

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Design Example (contd) Using Option A

• Already selected Inductance, turns, and core
  size.
• Now select wire size using another nomogram
• Use a nomogram showing the gauge of wire and
  number of turns.
• Enter the graph from the left with the required
  number of turns (21). The intersection of the
  number of turns with the solid diagonal core
  line for the selected core indicates the
  required wire gauge on the lower scale (13 AWG).
• If intersect is above slope discontinuity
  Multiple-layer winding.

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Design Example (contd) Using Option A
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Design Example (contd) Using Option A

• To find temperature rise
• Using previous information find ampere-turns for
  T90 core.
• 10A 21turns 210 ampere-turns
• Now enter the nomogram from left, with 210
  ampere-turns.
• Intersect with the T90 core indicates a
  temperature rise (15degree Celsius) on the lower
  scale.

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Design Example (contd) Using Option A
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Design Example (contd) Using Option A

• Results obtained from this graphical method
• Turns 21
• Core Size T90
• Wire gauge 13AWG (or 3 wires of 18AWG)
• Winding multiple-layer
• Temperature rise 15 degree Celsius
• Inductance, L 14.8uH
• Duty Cycle 0.48
• Total DC Resistance 5mOhm

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Design Example (contd) Using Option A

• Design using PExpert.
• Results obtained from PExpert
• Turns 21
• Core Size T90
• Wire gauge 13AWG
• Temperature rise 16 degree Celsius
• Inductance, L 14.8uH
• Duty Cycle 0.48
• Total Dc Resistance 5.654mOhm

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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Design Example (contd) Using Option A
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Conclusion

• Verified Results for design
• Nomogram (graphical method the book approach)
  results with PExpert results.
• Graphical method is a easy and quick approach to
  designing, but provides approximate values. On
  the other hand, PExpert provides accurate and
  exact values and several other design options. To
  conclude, both approaches yield correct results
  and either one could be used depending upon the
  required accuracy, available time-line, and
  application.