Hi all, I'm designing a camera flash unit that will use an IGBT to control the pulse-width of the flash. I came across a part from Toshiba (GT8G151, data sheet at http://www.semicon.toshiba.co.jp/info/docget.jsp?type=datasheet&lang=en&pid=GT8G151) that appears to be specifically designed for the task, and I'm currently trying to make sense of the example gate drive circuit they provide (see attached). I'm new to IGBTs and FETs, and so I'm hoping someone here might be willing to shed some light. First off, I'd like to control the IGBT with an AVR (probably an AT90PWM3B), which isn't able to source more than 20mA from any one of its outputs. The gate resistor that the GT8G151 data sheet seems to like is 62ohms, which would source close to 50mA at 3V -- it seems the AVR really shouldn't be used to drive the IGBT's gate directly. Given the large amount of current the IGBT is handling (pulses of 50A or more), there's probably a lot that can go wrong, so I have a feeling this is not the only reason. And so we have the example gate driver circuit, which has two FETs and a BJT. I think I understand the basic operation: A high signal activates the BJT (with the 1.2k resistor causing just a small amount of current to be sourced from the signal provider, i.e. AVR) which in turn deactivates the N-ch FET and activates the P-ch FET, allowing the 3.3V supply to reach the IGBT (through an unnamed resistor that I assume is the gate resistor and should be 62ohms); A low signal does the opposite, deactivating the BJT and subsequently activating the N-ch FET, deactivating the P-ch FET, causing the IGBT to see ground at the gate and break the xenon lamp circuit. There are several things I don't understand, including the function of both the 20k resistor and the 470ohm resistor... why are they there, some sort of protection?. I also don't get the choice for 910ohm and 91ohm resistors... some kind of voltage divider? And finally, I can't figure out why the FETs are even there in the first place, instead of just connecting the BJT collector to 3.3V, and the emitter to the IGBT, through the gate resistor... perhaps the FETs are also added protection? Any help would be appreciated, as I want to understand the circuit fully before I incorporate it into my design!