On 21.05.13 22:04, Gene Heskett wrote: > FWIW, resistors in the gate to slow the rise & fall times will raise the > switching losses, in some cases enough to destroy the device long before > your finger says its even getting warm.
Coming in late here, after a week out on the farm, but 10 to 20 Ohm gate resistors tend to be found in almost all published designs, because the resistors are intended to minimise destructive oscillation which tends to occur when there's inductance in the FET's source circuit. If you're switching fast, e.g. with one of Jon's IR2113s, and a pile of current is being switched, then microhenries are probably more than enough to give trouble. I've always added the gate resistors, preferring defensive design to blowing up FETs, so didn't have evidence that it was essential. But then, a couple of years ago, the local Aussie electronics mag published a design without them. A month or two later, their "Errata" section included diagrams of how to cut tracks on the PCB, and add the resistors ... to avoid destruction of the FETs. The gate charge required to turn on e.g. an IRF3205 is around 90 nC. Even with adequate drive voltage, 18 or 22 ohms of gate resistor can add a couple of hundred nanoseconds to switching time, so reduce the value if cranking up the switching rate, I figure. Erik -- Leibowitz's Rule: When hammering a nail, you will never hit your finger if you hold the hammer with both hands. ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
