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Very-High-Frequency Magnetic Integration into a Power Module for Current Balancing

Image of die-sized coupled inductors.
Fig. 1. Die-sized coupled inductors.
Threshold-voltage mismatch exists within a module of paralleled SiC MOSFET dies. This leads to unbalanced peak currents during switching transient, and degrades the reliability of the module. The state-of-the-art solution to balance the currents without additional current sensors or control circuits adds coupled inductors at the power source of the paralleled dies. Verification of the method by using discrete SiC MOSFETs in a TO-247 package and air-core coupled inductors was given. However, the limited space between the paralleled dies and the unconfined flux which may interfere with the driving or power circuits makes the air-core inductors not suitable to be included in the power module.

A design of the negatively coupled inductors that is comparable to the size of a SiC MOSFET die, compatible with the existing packaging techniques, and has high coupling coefficient with the ability to handle high dc current working at tens of MHz range is given in this work. The fabricated coupled inductors at the footprint of 5.3 mm × 5 mm × 0.95 mm integrated in the power module were demonstrated to successfully balance the transient currents for paralleled SiC MOSFETs, with threshold voltage mismatch operating at 400 V and 40 A.

Image of fabricated magnetics-integrated SiC module.
Fig. 2. Fabricated magnetics-integrated SiC module.
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