Resistors in gate drive circuit getting HOT

RickR, Fri May 26 2006, 03:19PM

Is it normal for 10 ohm or so resistors in the gate drive circuit for a half bridge to get extremely hot?

I've tried a single 10-ohm (or so) 2 watt carbon film resistor in series with a .68uf PP DC blocking capacitor in the GDT primary, and I've tried using the capacitor alone, with the resistors on the gates of the MOSFETs (IXFN48N50s). I've tried other values of resistors, but if their values are too high, the waveform on the MOSFET gates is too rounded, and if the values are too low, ringing ruins the waveform. I've used a 10-turn 100 Helipot to tune the resistance values while observing the gate waveforms on an o-scope. The best values for me seem to be around 8 ohms. But when I apply power, the resistors get too hot to touch in about 5 seconds.

I'm using a TL494 (single ended mode) and UCC37321/2s (these get only slightly warm) to drive the GDT at +/- 15volts. I guess I could do some series/parallel configurations of resistors to bump the wattage while keeping the optimal resistance value, but before I do this, I want to be sure this is normal behavior. I guess a lot of current is getting passed through these resistors, so maybe everything's good - I just want to be sure.

Thanks,

Rick