DirectFET®; MOSFET: Select the Correct Heat Sink

Selecting the Correct Heat Sink Type
  • In general
    • Rounded geometries outperform similar sharp-edged fin shapes
    • Staggered fins outperform in-line fins
    • Interrupted, or pin based fins outperformed parallel plate fins
    • Pin based, or omni-directional are best in “unknown” conditions
  • Low pressure drop systems
    • Elliptical fins work best
  • High pressure drop systems
    • Round pin fins offer the highest performance (Masud-Behnia)

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VRM/VRD Heat Sinks – Optimized?
  • Typically, VRM/VRD heat sinks are not optimized for performance
  • Someone picks a “standard” extrusion profile and cuts it to fit
  • VRM/VRD heat sinks are more “custom” therefore requiring more engineering at the system level
    • Fin cost is heavily dependent on material volume


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Heat Sink Optimization
  • Depending upon the air flow conditions, modifying the fin geometry can make significant improvements in performance
  • If the fin efficiency is already 80% or better, minimal improvements can be made In essence, if the base of the fin is near the same temperature of the fin tips, you are “convection limited” and the only ways to improve performance are to 1) increase the airflow 2) enlarge the sink
Heat Sink Manufacturing
  • The manufacturing process determines not just the cost, but also the vendor’s ability to optimize the heat sink to the users specifications.
  • Predominant manufacturing methods/types:
    • Stamping
    • Extrusion
    • Bonded/Brazed/Crimped Fins
    • Castings
    • Folded Fins
    • Forgings
    • Injection Molding
    • Tower or Cylindrical Fins
    • Heat pipes
  • International Rectifier recommends the following heat sink manufacturers:
IR’s proprietary DirectFET®; technology is covered by US Patent 6,624,522 and other US and foreign pending patent applications.