ZHCU578 October 2018
The main switching FET (Q2) needs to be able to stand off the input voltage plus the output voltage, even during output OVP events. This FET must also have a sufficient current rating for this application. The minimum transistor voltage and current rating can be calculated using the following equations:
A 80-V, D2PAK Q-grade FET is chosen for the switching FET (Q3). This FET is chosen for low gate charge along with good thermal dissipation package.