CM Choke Gate Transients

Trying to simulate the back EMF created during the off cycle of a boost converter and an interesting way to block it using a common mode choke. The common mode choke (as well as some of the other components) can be switched in and out to show the effect it has which is to prevent any transients on the FET’s gate from being fed back to the “gate driver”. Said transients are caused by the sudden rise in the drain as the inductor (not present) attempts to generate its own current as the mag field collapses; this happens because the gate and source are capacitively coupled, so when the drain rises, the source and gate rise as well. The FET has built in capacitance in the sim which can be adjusted by the channel width/length but it’s easier to just throw on a small cap to simulate instead which in this case is about 5 nF. The logic signal isn’t connected because when it goes low it “overpowers” the transient and then it doesn’t matter, so it’s there for reference only (as the gate signal from the “FET driver”). The common mode choke is essentially protecting said “driver” from said transients. The 12 V rail is simulating the power rail sourcing the FET driver. The clamping diodes are there to clamp any transients a diode drop above the source and ground. The diode on the gate of the FET adds yet more protection for the “driver output”.

published 4 years ago