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Driving (AC) mosfet switch directly from MPU using GDT
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beduino:

--- Quote from: T3sl4co1l on October 24, 2019, 01:44:42 am ---I'm not sure what numbers you used here.  Qg(tot) * Fsw does equal supply current for a gate driver IC.  The peak current is circa T2/t times higher though.

--- End quote ---
Thank you very much for so detailed calculations, which I've already tested previous night sleeping in capsule with heat coming from 80W 230VAC driven by gate transformer in a way where I use software pseudo-random generator with additional xor of AVR time counter for even better randomness to create gate drive pulses with avg ~20kHz frequency in average in a range something like 10kHz-30kHz  8)



So, It looks like those IRF840 mosfets in AC switch opens (turn on) very well at predicted switching frequency in this case, since after a few hours test during the night, no any significant temperature rise on mosfets- maybe slightly warm.

BTW: I have no idea why peak current might be circa T2/t times higher - I'll study also another manuals howto estimate this current needed to drive mosfets at given frequencies, but for the moment it looks like logic analyzer output from AC mosfet test and real experiments with ~100W 230VAC light bulb shows that your calculations were really helpfull to make this thing working as expected  :-+

WARNING: Off course I didn't touched those mosfets on  230VAC circuit side by hand while  connected to mains power grid  contact !!! I never do this even of datasheets claims sometimes some triacks and other stuff heatsink tap is insulated !!!

beduino:

--- Quote from: Simon on October 25, 2019, 07:19:43 am ---As I already said this is all a waste of time.

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Nope, it works as expected now, thanks to very helpfull detailed analysis of gate current requirements at given frequency  made by T3sl4co1l  :-+

I will try debunk this flickering free at 100Hz pure mains claims, while powering infrared light bulb later - I need setup this experiment with phototransistor  :-/O
beduino:

--- Quote from: Simon on October 25, 2019, 07:19:43 am ---Also remember that you plan to sleep in this thing.

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Nope, this thing I mean sleep capsule covers bed, but 230VAC 80W-100W is outside at least 0.5m and infrared light comes inside by using aluminium 110mm pipe which reflects light inside, so 230VAC light bulb is outside sleeping place and is not more danger than  table night lamp not far away from bed  8)



AC mosfet switch with control electronics is a few meters away in another room right now.

I've made photo right now how this infrared light pump looks like in the dark, but it might be patent pending, so sorry no image in daylight  >:D

Now, since we have AC mosfet switch working @ 20kHz +/-10kHz and powered light bulb from mains 230VAC 50Hz for the moment It could be interesing to see if there are any disturbances in output infrared light other than 100Hz coming from mains AC power, since I've implemented random switching frequency of AC mosfest switch and sample waveform below - already posted above earlier:



Simon:
oh now it's a random frequency that is above the frequency that is already above the low pass frequency of the bulb :palm: I'm sure your patent will be wonderful.
beduino:

--- Quote from: Simon on October 25, 2019, 07:19:43 am ---Given you obvious lack of experience I would suggest being extremely cautious about falling asleep with your contraption running.
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This thing below was running previous night for about 8 hours sleep and I can confirm amazing dreams comes   >:D

Patent for good sleep  :D



Anyway, what do you think about the way I disipate heat in this AC mosfets switch from mosfets drain taps directly to wires using 3mm hole connectors in a way shown above.
It is at least 0.5mm2 copper wire and at least 2m long from this pcb to mains contact and more than 3m to infrared light bulb ~100W?
This means, that at 230VAC mains 50Hz we have I~0.434A  with IRF840 max RDSON R~1 \$\Omega\$, but ~@ 20kHz PWM we have 50% on/off so, it looks like we can expect power loses something like: 2*(I^2*R)*50% ~0.2W total while two mosfets in series, but only ~0.1W per mosfet?  :o

After this 8 hours test today those mosfets were maybe only slightly warmer than room teperature, so do we need any heatsinks, while it looks like in this case, copper wires via those soldered 3mm connectors mounted directly under mosfet drain taps shouldn't quite well disipate any heat into >0.5mm2 copper wires >5m long on both sides of this AC mosfet switch?  ::)

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