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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Cap sees 50 volts max. I guess your problem is way too much inductance on primary. You need to lower it to limit initial spike (and I guess you should have some better impedance match that way).
I have 50/16 = 3,125Vin peak on mosfet and it closely matches richie burnett's 3.3Vin approximatin.
Later i'm considering putting a small ZVS based power supply into the coil to produce some higher voltages for even scarier sparks. (I want it to completely run from some 12 - 15V supply).
4046 IC is a bit pain there as he wants a stable supply, maybe I'l need a low-dropout regulator there.
Single UCC I have there is even more power hungry. Gate resistor is 2 ohms and waveform is pretty sharp and nice at 1,5Mhz.
It draws more than half an amp of current and can easily burn a 7812 even on a big heatsink. If increasing gate resistor fails I'l have to either power it directly from supply or use an switching regulator there...
PS. omg, are you really running that mosfet without any heatsink? Mine would get stinking hot that way after few seconds...
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Kinda going way back but Joe said:
Nice! You won the contest, the price for the first working Class E TC on 4HV is yours!
I think the most i got was about 6" sparks. It was kinda cool i guess because it could make the sword like streamers, but its not quite a fun as full-bridge drivers :P. If you build them right, they dont explode . I sold the coil to some teacher and hes been using it ever since. Heard back to him several months after he bought it and it was still pumping out little sparks like it should, so its pretty reliable. But, it will never handle very high powers like an H-bridge. Each topology has its own place, and class E is perfect for small, high frequency (and efficiency) converters.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I stuck an 7805-based charger into my camera and it works now. I had to drill the connector to make it fit :p Pics of whole mess:
The arc drawn is 33mm long. Looks a bit fuzzy in CW, probably I need much shorter exposure. Coil is running at 16V, with maybe a little more than 1 amp. (circle some 20 watts).
Spark looks pretty good for given input power.
I had to overcouple coil and detune a bit for this, so mosfet could get pretty hot after >10 minutes (but I never managed to kill it yet :/).
I also took a pic of my waveform, when best tuned. Sinewavy thing is DS voltage, and this garbled looking waveform is gate voltage :p (I couldn't help it much).
In best tune and lower coupling spark is few mm smaller but mosfet gets that heatsink up to maybe 50-60 degrees and could run forever like that. Anyway i'm still not sure if I really have maximum efficiency there.
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Class E Circuit
or use an switching regulator there... 
. I sold the coil to some teacher and hes been using it ever since. Heard back to him several months after he bought it and it was still pumping out little sparks like it should, so its pretty reliable. But, it will never handle very high powers like an H-bridge. Each topology has its own place, and class E is perfect for small, high frequency (and efficiency) converters.
