New family of low power AC-DC flyback converters announced

20th March 2019

UnitedSiC

Lanna Deamer

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UnitedSiC has announced that it has released a range of SiC JFET die suitable for co-packaging with a controller IC with built in low voltage MOSFET to fabricate an extremely fast, cascode-based, 20-100W Flyback product. Ranging from 650-1,700V, these normally-on SiC JFETs enable simplified start-up implementation with zero standby dissipation.

They are suitable for the large Flyback AC-DC applications market, including consumer adapters and auxiliary power supplies.

Controller IC manufacturers can benefit from the small die sizes with very low RDS(ON) and capacitances. The normally-on JFET helps meet light and no-load dissipation regulations when coupled with a low Qg low voltage MOSFET integrated in the controller IC.

SiC cascodes are extremely robust, due the inherent capability of SiC JFETs when it comes to handling repeated avalanche and short circuits.

Since the SiC JFET is in series with the LV MOSFET in the control IC, the source of the normally-on JFET rises to 12V before JFET turns off and the IC begins switching.

This current path through the JFET can be used as a start-up supply for the controller IC. An auxiliary supply from the converter transformer is then gated-in when the converter starts running, with no further dissipation.

Typical low power Flyback applications include consumer electronics chargers such as laptop and mobile device chargers (from 20 to 65W).

Other applications range from wide-input (up to 1,400V) Flyback auxiliary supplies for industrial applications such as motor drives to high power lighting applications such as long LED chains.

“With the addition of these new SiC JFETs, UnitedSiC now has one of the largest SiC power portfolios in the industry,” said UnitedSiC CEO, Chris Dries. “We now have high performance JFET functionality in both die and discrete package form.”