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Registered Member #61905
Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23
I've been looking for a simple way to clean up the gate signal of a royer/zvs circuit and I came across this paper:
It describes a way to switch the gates without the complexity and problems of a PLL approach. The self oscillating switching naturally and quickly follows the resonant frequency and handles changes to that frequency well. The gate signal is also pretty clean, compared to what I've seen with the "marko zvs" circuit. So for induction heaters where the frequency changes with load/temperature/time or with a tesla coil where streamers change the frequency, this approach seems to have some advantages. Has anyone here made similar refinements to the marko topology?
Registered Member #61905
Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23
The reason I've been looking into this is I'd like to improve the royer/ZVS self oscillating circuit. Has anyone come up with a better way to drive the gates? I get a pretty messy signal:
You can see the voltage rise via the resistor input until it gets capped by the zener, then a lot of ringing. A faster diode seems to make it worse.
Registered Member #61905
Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23
I've been searching a lot on this subject, and there are a variety of names for what amounts to almost the same thing, like royer, mazilli, marko, ZVS, current fed parallel resonant, etc. I finally found a good paper on this subject that talks about improving the gate drive and lock-up behavior. Interestingly, 4hv.org is in his bibliography:
This is the "active gate" layout that Jonathan David Paolucci published:
He doesn't go into great detail on his component selection, and the picture in his paper doesn't match the part numbers he calls out, but it's a nice paper. Is Jonathan a "regular" around here? I'd be interested in asking him a few questions and hearing how he developed this gate drive. The more advanced ebay boards may be using something similar.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Oops, for some reason my browser failed to load the first two posts. Thought it was a different thread, which would explain why I couldn't find it.
To make a suggestion in response to your second post, have you tried a gate driver IC? they are pretty good, and you can get ones that drive at 10 A peak, which should switch your MOSFETs on pretty fast. (about 10 ns to go through the linear region according to my quick calculation for an IRFP460)
Registered Member #61905
Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23
I saw this ZVS board on ebay:
It looks like the usual self resonant setup, but with something more interesting for the gate drive. It has what looks like 3 transistors per side, so it may be doing something similar to the circuit I posted above.
...it is disappointing that pictures of chineze circuit boards on ebay seem to be the best source of info on this subject.
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Self oscillating gate control vs PLL for resonant frequency: marko, royer, ZVS, mazzilli, etc.
