> The one on my newly built kit gets pretty warm. Normal? I'm not an ee so go > easy on me :)
The MOSFET is used as a switch. When it's off, it shouldn't have any dissipation, when it's on, its dissipation depends on its on resistance. If your on resistance is low enough, the problem is probably the "in between" part while it's in the process of switching on or off. These high voltage, low on resistance MOSFETs necessarily have large gates, which have a fair amount of capacitance. Charging and discharging that capacitance in a hurry is they key to high efficiency, which translates to low wasted heat. Many of the circuits out there don't do a good job of gate driving, keeping the MOSFET fully on and fully off most of the time, minimizing the in-between times. These days, I tend to recommend using a dedicated gate driver chip, which is optimized for the task. Many of them can source and sink over two amperes, resulting in very fast switching times. In short, check the on resistance of your MOSFET. There may be other parts out there with lower on resistance. The most likely problem is your gate drive circuitry: you need to SLAM that gate on and off as fast as possible, or the MOSFET will dissipate a lot of energy. One last thing is that you need to have sufficient voltage to turn the MOSFET on all the way. If it has a high gate threshold, you may need 12V to fully turn it on. There are parts out there with low gate thresholds that are easier to turn on and off. However, when you want high voltage, low gate threshold, and low on resistance, you're getting into exotic expensive parts. Sometimes it's easier and cheaper to use the aforementioned dedicated gate driver chip to provide the high voltage and high current to get good performance out of a cheaper, more common MOSFET. - John -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/3076B7BC-3D91-4FBB-A535-BA29A5BC3CA3%40mac.com. For more options, visit https://groups.google.com/d/optout.
