Hi Kyle,
The energy required to achieve ZVS in the active-clamp-flyback is described by the equation below:
E = 1/2Lm * Im ^2 > 1/2Cp * Vds^2
Where Lm is the magnetizing inductance of the transformer, Im is the negative magnetizing current built up when the high-side FET is on, Cp is the total switch node capacitance, and Vds is the drain-source blocking voltage of the low-side FET.
The immediate benefit of GaN is that the value of Cp in the equation above is significantly lower compared to a similarly sized Silicon FET. In other words, Silicon devices require more energy for ZVS.This large energy requirement requires a longer on-time of the high-side FET, which reduces the switching frequency and increases the primary peak current.
The combination of higher peak current and longer on-time leads to an increase in the RMS currents that show up as conduction losses in the high-side/low-side FETs, as well as the transformer windings. In many cases, these incurred conduction losses can completely negate the other benefits of the ACF, such as zero-clamp-loss and ZVS. As a result, the ACF can switch at high frequency while providing valuable power loss savings, but only under the condition that the RMS currents are managed.
The LMG2610 device provides a good balance between conduction loss and cost for the high-side and low-side devices, while providing the benefits of GaN, and additional integration.
