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Driving (AC) mosfet switch directly from MPU using GDT
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T3sl4co1l:
The heat spreading length for wire of that size is about an order of magnitude lower than you imagine.  The wires contribute negligible dissipation area.  The transistor assembly is dominant, and can dissipate a couple watts in free air.

Evidently you aren't dissipating much power, so it doesn't matter much.


--- Quote ---BTW: I use maxima software under Linux  instead of Window$ calculator, so probably that is why no smoke so far in many projects  :popcorn:

--- End quote ---

As the saying goes, it is a poor craftsman who blames his tools, or who trusts them blindly.

Tim
Simon:

--- Quote from: beduino on October 26, 2019, 11:11:44 pm ---
--- Quote from: Simon on October 26, 2019, 09:04:46 pm ---Yes of course your rihgt, copper offers no resistance to heat and all of that plastic insulation is as conductive to heat as copper.
--- End quote ---
Plastic insulation doesn't have to be as conductive to heat as copper, since quick estimation of area around 4m long 0.5mm2 copper wire is A: 0.010 [m^2] which is equivalent to 10cm x 10cm sheet of thin insulation, so now imagine what can happen when we heat this quite big area with lets say 0.5W from one side having 25*C room air on other side?   :palm:

Problem is you didn't provide any calculations to proove your claims  :-DMM

--- End quote ---

Oh you want me to do your job for you? personally I am thinking if you die in a fire that involves you alone now that will be better as at the rate you are going clearly at some point you will do something really stupid and injure or kill other people!


--- Quote ---I listen to people like T3sl4co1l , who provided very usefull estimation of gate current needed, so big letters with warning not needed in your posts.

--- End quote ---

I too deeply value Tim's contrimutions when he answers because he is very knowledgeable but you are expecting other people to do your design for you or at least come up with complete and utter proof as to why you are wrong. But I won't bother. If you kill yourself by being stupid and not taking the hint so be it.


--- Quote ---
BTW: I use maxima software under Linux  instead of Window$ calculator, so probably that is why no smoke so far in many projects  :popcorn:


--- End quote ---

So you admit being a troll, good, good, I will feel less bad when i ban you.


--- Quote ---Attached detailed calculation of estimation area around a few meter copper wire. Show us your calculations to proove your claims  :o

--- End quote ---

And what have you proved? that you can calculate geometry, well done you. Do you know what thermal resistance is? If the thermal resistance in 10mm of wire is already too high to let the heat flow to the rest of the wire all of that wire was wasted. I was astounded when I discovered what a "poor" conductor an aluminium heasink was and that putting a power resistor at one end did not really heat up the other end. If you are intelligent you would understand what I am saying.

i could of course set up a test with my thermal imaging camera and show you but why should i waste my time helping you? You will just ignore anything i say that does not resonate with you. So you go ahead and do as you please. i just hope you don't injur anyone else. This project may not hurt you but with your attitude clearly in the future you are likely to do something really stupid and possibly hurt other people.

beduino:

--- Quote from: Simon on October 27, 2019, 07:38:37 am ---i could of course set up a test with my thermal imaging camera and show you but why should i waste my time helping you?

--- End quote ---
So do something to proove your claims  :palm: 

I've working circuit in reality not simulator and it performs as expected  :popcorn:
Simon:
I never said you circuit would not work. I was trying to explain to you that you are not using the wire as a heatsink, not that much anyway. Obviously there is so little heat that your setup works but you have no idea about what is happening, it's pure luck. This one may not kill you, the next could.

I'm done here.
beduino:

--- Quote from: Simon on October 27, 2019, 08:00:33 am ---Obviously there is so little heat that your setup works but you have no idea about what is happening, it's pure luck.

--- End quote ---
There is no luck, when you turn on/off mosfet using GDT :o
Everything depends on application - in this case it doesn't matter when something goes wrong and for example mosfet will be shorted and conduct 100% instead of in a controled way, because of it works as a smart switch, but even when we provide full light bulb power not such a big deal - slightly uncomfortable temperature rise inside sleeping capsule, but it can be easy detected and for example fan forced to higher RPM or turn on alarm.

Yes, I've in my sleeping room alarm clock, but instead of clock it has light sensor, so it will be integrated with sleeping capsule in a way, that you wake up when it is daylight outside-no need to set alarm clock time anymore  :-+
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