#qi-hardware IRC log for Monday, 2016-03-14

sb0rjeffries, oh, hi01:03
DocScrutinizer05wpwrak: the SPAM scene?05:39
DocScrutinizer05the scene that gave SPAM a new meaning05:39
DocScrutinizer05https://www.youtube.com/watch?v=M_eYSuPKP3Y  -  hmm, seems it's not from "meaning of life"05:43
DocScrutinizer05aah Mr. Creosote05:49
shevekHi.  I'm having some trouble with an electronics board and I was hoping someone here (such as wpwrak) could help me.  I have a MOSFET to switch 24V, 4A through a nichrome wire (used as a heater).  I have an avr microcontroller connected to the gate, set it to output and deliver 5V with it.  Everything worked fine and the MOSFET did not heat up much (I could touch it and it didn't feel very warm).  The next day, changing nothing, when I 19:52
shevekswitch it on the MOSFET starts smoking after a few seconds.  I tried several other MOSFETs and they also get very hot.  What can be the cause of this?19:52
shevekBy the way, the other MOSFETs are on a board that insulates the MOSFET from the logic, so it is not connected directly to the controller; I measured the gate of the MOSFET with a scope and it gives me a very flat 24V.19:55
eintopfwhat the hell is a MOSFET20:02
eintopfah, okay I google it20:02
shevekAn electronic switch.20:04
rohshevek: esd issues? is it a logic level fet?20:08
rohalso... what kind of load are you driving? a heater coil can be quite an inductance ;).. so maybe you need some snubbers/spike eating diodes20:09
shevekThe first one is, the datasheet says it should have 0.045© resistance when driving it with 5V (and slightly less when driving it with 10V); the other one isn't so it drives it with the 24V supply.20:11
rohi see. do you have any resistors in the gate line?20:11
shevekIt's a 6© wire which doesn't have too many windings, so I don't think there's much inductance.  I also tried it with no windings at all (well, half a winding strictly speaking, and no core), with the same result.20:12
shevekOn the first board there is nothing on the gate line; avr directly connected to it.  The other board has some logic.20:12
shevekI suppose it's possible that the inductance destroyed the MOSFET originally, so during the second test without windings it was already broken, but I wouldn't expect there to be much inductance anyway.  The scope didn't show large spikes on switching either.20:16
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