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Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
I discovered that my SSTC gives much better sparks if I pulse a big 300V electrolytic through it than if I drive it from a 50V DC supply. So I am in the process of putting together a kind of "high side modulator" which basically is a 555 wired to a MOSFET to dump a 4000uF 400V cap into the coil every 100ms or so. I am choosing this over a traditional interruptor because the gate driver chips I am using (4422) do not have an "enable" option, so I would have to think of somethink clever to prevent the inverting driver from going high during the pauses, which I cant. Are there any obvious drawbacks for this kind of modulation? I dont really see any, the only extra expense over the conventional interruptor being one FET.
Registered Member #229
Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
Joe, it is an old idea since my first internet days (1999?). The SSTC it is just a combination of one Mazzilli Vladimiro design with the new DR-DRSSTC of Terry Fritz. Practically you charge a big cap, and then start a half/full bridge with a triggering pulse.The bridge will drain all the cap charge and stop oscillating after that. What is more important, this design does not use chip drivers (as the royer), but can work at higher frequencies.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I'd still try to do it low side. Its going to take a lot more components to do this than you think and its very easy to implement the modulator on the gate drive using a few logic gates - very simple.
with the high side, you have to add a big power FET, an isolated drive as well, possibly another floating source, especially if you use a n-type device as p-type of devices aren't available in super low Rds packages, etc...
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Dan, you are right on that one. Since the MOSFET gate is floating on mains, so is the whole driver circuit. I was planning to drive the logic off a battery so I can just have it all floating, but this is just a kludge. If this gives me too much trouble, I will order a few logic gates.
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High side interruptor any good?
