In the push-pull topology, the switching devices on the primary side will see a voltage that is equal to twice that of the input when the devices are off. As such, the GaN FETs selected should have a voltage rating that 3 times higher than the input voltage. The voltage rating for the GaN FETs was conservatively chosen for the primary side as 170 V for this application based on maximum input voltage of 36 V. This was to account for any transient spikes that were seen during operation. Also ensure that the GaN FETs are properly sized based on the primary current calculations in Section 9.2.2.6.