I Love GDT’s!
I now hate floating gate drives and love Gate Drive Transformers (GDT). Quite the change of love! After hatcoil worked better on GDT’s and was easily transformed (more on hatcoil later), I figured why not increase the reliability of big-coil with GDT’s. I threw together a quick P-N totem pole pair board capable of driving a GDT in bipolar with no blocking capacitor (assuming 0v DC from an even duty cycle). The results are quite beautiful. I did not realize it was this easy to make a gate drive transformer work great.
Adjusting the voltage put out by the first LM317 allows for adjustment of the gate drive voltage (since this will power the P-N half bridges), and the second LM317 powers the UCC37321 drivers, which allows for adjustment of the intermediary gate drive signal level for minimal shoot through. If this gets too high, certain pairs of FET’s will severely shoot-through and over heat. The FET’s I’m using right now don’t really have an issue but I have used other models that are useless with 15V drive in this particular capacitively coupled P-Fet drive scheme.
The board was carefully routed to have basically no ground loops between output and power supply, and to have bypass caps as local to the output stage as physically possible. The results are incredible, it’s just like having a discrete driver on the brick, but there are no reliability concerns!