Cooler with EMI-Limiting Inductor


A power switch is mounted on a cooler via isolating dielectric ( such as alumina or aluminum-nitride) that forms a "parasitic" capacitor (referred to herein as C dielectric) measuring tens to hundreds of pico-Farads. As the switch's terminal(s) transitions from one voltage level to another, noise current commonly known as EMI (Electro-Magnetic Interference) is injected from the switch into the cooler via C dielectric. It propagates to earth ground and is coupled to the other electrical systems sharing the earth ground. An inductor in series with C dielectric is expected to be helpful in limiting the di/dt of the noise current to attenuate the higher band of the EMI spectrum. The invention provides a means to integrate such inductor with minimal impact on thermal management and the operation of electrical circuit served by the switch. A circumferential ring of the cooler material (usually copper or aluminum) is removed from the top portion of the cooler, and is replaced by a ring of magnetic material that becomes the core of the inductor. The cooler, C dielectric, the switch, and the conductive path between the switch and earth ground forms the winding. The core could be constructed from magnetic alloy with relative initial permeability of 100,000.  A footprint of 2cm squared and cross-section of 4mm squared would yield initial inductance about 10 micro-henry. The EMI current through a C dielectric of 100 pF is expected to be attenuated from 5 dB to 20 dB between 10 MHz and 100 MHz

Patent Information:
For Information, Contact:
Li Chen
Licensing Associate
Virginia Tech Intellectual Properties, Inc.
(540) 443-9217
Khai Ngo
Han Cui
Chi Ming Wang
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