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[FAQ] PMP21479: What are the trade-offs between using Gallium Nitride (GaN) versus Silicon (Si) FETs in an active clamp flyback?

Intellectual 1475 points

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Part Number: PMP21479

What are the trade-offs between using Gallium Nitride (GaN) versus Silicon (Si) FETs in an active clamp flyback?

  • In the active clamp flyback, the Coss of the primary FET is a major factor limiting the maximum switching frequency. GaN FETs have a much lower Coss than Si FETs for the same die size and on-resistance. As a result, higher switching frequencies can be achieved with GaN FETs vs. Si FETs. A higher switching frequency can result in a smaller transformer and thus overall smaller design and higher power density. However, in the present state of the market, GaN FETs are more expensive than Si FETs and there are not nearly as many available to choose from. The choice basically comes down to cost versus size. The UCC28780 active clamp controller can be easily configured for either GaN or Si FETs by pulling the “SET” pin either high or low. In addition, the LMG3411R150 is a 150 milli-ohm GaN FET which can be used in active clamp flyback applications.

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