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Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
If you turn both of the fets on at the same time it won't work very well... And even if you got around that you would need to tune the 555 to the resonant frequency of the mess (which will changing depending on loading, etc)
A better solution would be to use something like a 4046 pll circuit that can lock the output, or the self resonant design like the one that you started with.
Registered Member #580
Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410
you have just connected the 2 halves of the primary coil in parallel, with the polarities causing magnetic cancelation. by the way, pin 3 is the output for a 555 IC.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
I think that if it were in that configuration then you wound't need the second MOSFET. You also want the snubber to be directly across the source and drain of the MOSFET that is switching the current.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I agree with myke. That circuit would just be paralleling mosfets and that would cause one mosfet to heat more that the other, as Rds on is different in most mosfets to some degree. It might help with the current carrying capability some, but not as much as the ratings would suggest. Also, that capacitor and diode(i guess the snubber) would keep the upper mosfet from doing much of anything. The snubber would be right across the primary, because it is there to reduce or eliminate any kickbacks from the primary.
Also, that capacitor across the primary is not needed i dont think, it will just use current and reduce efficiency and cause heating.
If everything i said above is in fact correct, you are just left with a regular 555 flyback driver :P.
But, you can use the regular flyback driver and place a capacitor of about .22uf across the drain and source for resonant capacitor. Thanks to Jan Martis for that idea. The resonant cap will improve efficiency and the voltage/current output will be higher. Or at least voltage, as i have no way of measuring the current.
Registered Member #1749
Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497
like this I just want to experiment and find new things when I get my parts from eBay I can try all these and see how many of the 50 mosfets I ordered can blow up just kidding.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
crazy4 wrote ...
like this i just want to experiment and find new things when i get my parts from eBay i can try all these and see how many of the 50 mosfets i ordered can blow up just kidding.
Yup, that schematic is what you should go for with a 555 driver :P. That is what i used for sparks igniting at about 4 inches. I used 35 volts into the driver with the cap, and 4 inch sparks. Be very careful though and make sure you use a chicken stick, the voltage is high enough to either go through the insulation or surface track.
The capacitor should be around .22uf and high enough quality.
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Fly back driver modifacations using different parts and diagrams than original out of curiosity.
