[Al (astral highway)]

Pic shows what should be a square wave, with obvious defects.

My gate drive transformer, on type 77 material, is into a load of 18nF on one of its windings. I can't accurately test the inductance of the GDT but it appears to be about 2.76mH

The pulse should be a perfect square wave, frequency is about 200KHz.

I can see there's an initial very fast rise time, then a slight overshoot, then the core is biased in the opposite direction, but problems have begun from the start and this is far from being a square wave.

Overshoot in itself is not a problem as currently no gate resistor is in place. It's the overall shape that needs to be tight and a conventional square wave.

I note the parasitic oscillation addition at the end of the waveform, as it decays to zero.

Only I can't think of probable causes of this. The gate drive circuit is very capable indeed and not underpowered. The windings on the core are tight and leakage inductance is minimal.

I'd appreciate any technical reasons for this waveform and its saturation behaviour if relevant.


Thank you!