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Registered Member #567
Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147
Yep, another one, with more or less the same problem.
I'm going to build Steve Ward's mini SSTC, since that's where almost everyone starts. Like many people, I can't get the UCC's, and I can only get TC4420's. Not even TC4429's. As to why, that's because I'm ordering from RSSingapore (I live there).
So, I came up with a solution, and I'm not entirely sure if it'll work, and hence I'm submitting it for everyone's inspection.
Does it work, or have I made some horrible error which will oblige me to hide under a rock somewhere in shame? Should I use JFETs or MOSFETs? Bit puzzled what the difference in function is. Also, can someone recommend a suitable pair of FETs to use? I'm not to clear on that... Moreover, do I need pulldown resistors?
EDIT: Forgot something. If I want to run it on the mains earth, what kind of filter should I use?
Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
Well you only need one fet. Feed the input signal into the source pin and the interrupter into the gate and a pullup on the drain. Ive done this before but using a 2n3904.
Registered Member #567
Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147
Whoops, seems like I've solidly forgotten the KISS principle! (Keep it simple, stupid!) Thanks for pointing that out!
By the way... I see you dabble in BEAM too. That was where I got my start in electronics!
Could someone suggest a pair of common N and P channel FETs with as closely matched rise/fall times as possible? (I know it shouldn't matter all that much, but I'd still like to be sure.)
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
why not use a 4007 ic for this? 4 complementary n and p channel fets just great for this job.
but i dont know how well it will perform. you can use a 4000 or 7400 instead, use one nand to invert the signal for the other 4420 driver, then feed the signals to 2 another nand gates (2 input nand) connect 2 inputs from both nand gates together and use it as your interrupter input. the output of the nands to the driver ics. that will be much simpler and i used it before in my drsstcs and it works just fine and is really fast.
Registered Member #567
Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147
The 4007 IC looks perfect for the job, thanks for the suggestion!
Also, Reaching, I had considered a similar scheme, but in the end I decided that there were too many delays and I didn't like it much. (Yes, I know it shouldn't make that much difference, but I'm slightly paranoid.)
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
yep, delay is a problem with this circuit, but its in the range of 5 to 20nS. okay for a low frequency drsstc with around 80khz or so, but for sstc work with frequencys above 200khz not the best solution.
Registered Member #567
Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147
Hm, new question-
Is there any reason I can't use primary current feedback to run the tesla coil? Just a torroid with 100 or so turns on it, then a loop of the wire going to the primary into it?
Also, can I use a relaxation oscillator (say, 1 resistor, 1 cap, 1 diac run at 12v, then diode clamped output to 5v to get a near square wave?)
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