On Monday, 13 October 2014 13:34:05 UTC+1, joenixie wrote: > > Now for my two cents. I have not looked at the schematic due to time > issues, but I know I ran into issues driving a standard mosfet with a logic > level gate signal. It got hotter than blue blazes! If the gate signal only > goes to 5 volts, you must use a mosfet that will turn on fully at this > level otherwise, it acts like a power resister. >
Not the problem in this case - there is a 12V driver for the FET - generally, a FET may be considered as a voltage controlled resistor - if its fully on, then is DS resistance is RSDon, which in this case is about 800milli-ohms - this is the lowest DC resistance the FET will exhibit. If the FET is not fully on, then its DC resistance will be greater, leading to far greater thermal losses, i.e. it'll get hotter... In an SMPS, its vital that the switching device is either fully on or fully off, and not ever somewhere in its linear region - its being used as a switch, and should be driven in a way that ensures that's exactly what happens... Logic-level FETs are available which, as their name suggest, switch at lower gate voltages, but they also tend to have a low Vds and so are not suitable for simple HV boost converters (there are other, more appropriate, topologies should use wish to use these sorts of devices). However, that's not what's going on here (if, indeed, anything at all untoward is happening...) Nick -- 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 [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/3ed1cd0b-c644-407a-a285-effb512cbbe2%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
