Electronics > Projects, Designs, and Technical Stuff
Driving (AC) mosfet switch directly from MPU using GDT
beduino:
--- Quote from: T3sl4co1l on October 24, 2019, 01:44:42 am ---This in turn suggests that Fsw should be about as many times slower as the gate drive is. So, if we can't do 4A but we can do 14mA, we should run at a frequency 4/(0.014) times lower, or about 21kHz. And again, lower would be preferable, to save on switching losses.
--- End quote ---
Now changed software and I've nice ~20kHz input to GDT, however bloody cheap YATO multimeter maybe is not capable notice those short pulses ? :wtf:
I think I'll try connect this AC mosfet switch do Saleae Logic analyzer with 470 Ohm pull up resistor and try to catch turn on/off :-/O
Simon:
a cheap meter will do 1kHz at best.
beduino:
--- Quote from: Simon on October 24, 2019, 07:35:38 pm ---light flickering at 100Hz disturbs your dreams?
--- End quote ---
Who knows how our brain works and what it does during sleep?
Even with eyes closed probably everyone is capable notice longer light pulses, but maybe we simply do not notice higher frequencies, but it might somehow affect neurons activity ::)
beduino:
--- Quote from: Simon on October 22, 2019, 08:43:00 pm ---I'm not an expert in pulse transformers but the idea of a zener sounds like a good one.
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It is strange, but when I've disconncted zener diode (I belive in) connected to AC mosfet switch gate (I had only one zener so far and it worked with 4VDC Vgs ) now it works fine with 1k load @ 4Vcc :o
Even with 100k resistor on mosfets gate we have nice ~20kHz output on AC mosfet switch, but this is not supprise, since we have a few mA gate current for sure.
It is strange why this zener diode, which I'll remove from this PCB to examine, makes GDT not working at all as gate driver?
Maybe we need two as suggested in antiparallel, to provide the same GDT secondary load in full period? :-//
Anyway, now we drive AC mosfet switch directly from MPU using GDT, however it will be interesting to see what happends with this 80W 230VAC infrared light bulb, since at 4Vcc and 1k load resitor we had 2V on AC mosfet drains shown by this YATO multimeter, so probbaly it was fine, but this blood zener diode tried ruin my night today >:D
Any ideas, why this zener diode sucks in this AC mosfet switch when we use GDT as gate driver @ eg. 20kHz? :-\
Simon:
--- Quote from: beduino on October 24, 2019, 08:16:27 pm ---
--- Quote from: Simon on October 24, 2019, 07:35:38 pm ---light flickering at 100Hz disturbs your dreams?
--- End quote ---
Who knows how our brain works and what it does during sleep?
Even with eyes closed probably everyone is capable notice longer light pulses, but maybe we simply do not notice higher frequencies, but it might somehow affect neurons activity ::)
--- End quote ---
So your eyes can see the 100Hz but when you chop the still remaining 100Hz up at a higher frequency it sudenly dissaperes? I already explained, this is a fillament bulb. the time it take the filament to cool down and stop glowing is longor than 1 cycle at 100Hz. It is a pysical low pass filter.
As I already said this is all a waste of time. just rectify the mains and if you are hell bent on getting rid of the non existent flicker you are chasing around then you must use a smothing capacitor. Then chop the DC with whatever frequency you like. 1kHz is ample. more than that is plain stupid! Put an inductor in series with your bridge rectifier to try and do something towards restoring power factor.
Also remember that you plan to sleep in this thing. Given you obvious lack of experience I would suggest being extremely cautious about falling asleep with your contraption running. Unless you were having plans for an early death and automatic cremation.
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