I had difficulty choosing keywords to narrow the search enough to give me any solid hits for this, and I hope this question isn't too advanced for the basics group.
I'm looking at a full-bridge IGBT switching amplifier circuit (eg., from Eastern Voltage Research's DRSSTC-2 schematic, drawing number SC2045, page 1), and I'm trying to understand the use for putting a diode (Schottky) and a resistor in parallel (eg., CR1 and R1 in the cited document). I've seen this sub-circuit in other places, but I haven't found an explanation for it.
I tried breaking down the problem, but it didn't get me very far. When the [conventional] current flows toward the gate, the current flows through both the resistor and the diode. When the current flows away from the gate, the current only flows through the resistor. The resistor limits the current, with an associated voltage drop, and the diode has a small voltage drop (and I would assume an associated current drop, though I haven't found it mentioned in any reference) when current flows through it. Unless I have missed something, this sub-circuit does nothing more than drop the voltage (and probably the current) more in one direction than the other.
Is that all there is to it, or did I miss something? If that is all there is to it, then what use is it, when the voltage drop across the Schottky is almost neglible? I can see the possibility of protecting the IGBT gate from over- or under-voltage or -current... of .14V to .
46 volts (according to wikipedia)? If you need more voltage or current protection in one direction than the other, it might make sense from an efficiency standpoint. But why do I feel that I'm missing something?.