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Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
I'm trying to build this coil.After I finished my PCB I want to know if it works or not.I remember that someone on this forum says that a DRSSTC circuit without a resonant capacitor is just a conventional SSTC.So I didn't solder a capacitor and solder a wire instead.
But when I power it up,I cannot see any spark and my variac makes a weird sound.and the insulation of that wire melt.It can light up fluorescent lamp.I tried to change phasing by swap two gate driver chips because everything else is soldered on the PCB.But the fluorescent lamp seems to get darker. What's wrong?
I use 47N60C3 MOSFET (datasheet:
secondary resonant frequency is 617KHz(I know this might be too high but I don't like big secondaries)
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
primary feedback doesn't work very well with sstc's. you need high current in the primary circuit to get the ct's to give decent feedback. if you want to run it as a sstc, then find a way to use antenna feedback or secondary base feeback. you can brobably hook it into the input where the ct goes. but if you want it to run as a drsstc, then put in a resonant capacitor, and swap those fets for igbts.
edit: also, dr. dark currents point bellow- in a sstc, you have a primary circuit that is switched to match the ~fres of the secondary. in a drsstc, you have a primary circuit that self resonantes, and you have to match the ~fres of the primary and secondary to the same frequency +- detuning
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
hsieh wrote ...
I'm trying to build this coil.After I finished my PCB I want to know if it works or not.I remember that someone on this forum says that a DRSSTC circuit without a resonant capacitor is just a conventional SSTC.So I didn't solder a capacitor and solder a wire instead.
But when I power it up,I cannot see any spark and my variac makes a weird sound.and the insulation of that wire melt.It can light up fluorescent lamp.I tried to change phasing by swap two gate driver chips because everything else is soldered on the PCB.But the fluorescent lamp seems to get darker. What's wrong?
I use 47N60C3 MOSFET (datasheet:
secondary resonant frequency is 617KHz(I know this might be too high but I don't like big secondaries)
thanks
While in theory that feedback circuit should work down to small primary currents (it uses an unloaded CT clamped to the rails by diodes) in reality it probably won't work on an SSTC due to parasitics - scope the primary current and you'll find its probably some garbage triangular waveform. Also keep in mind the only public schematic I posted is an old one with copper interrupter...the opto driver is still being tweaked (actually, its done tweaking, I just need to update the post).
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
You should invest the $5 or so that the digikey current transformer costs - looks to me like you've got 30 or so turns on a powered iron core, which wouldn't work even if this were set up as a DRSSTC.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
hsieh wrote ...
So I if install a resonant capacitor,it will work?
I know that the core I use is a high u core(5000 or 10000).I get it from a school lab and someone told me that.Will this work?
Test the GDT with a signal generator and see! oneTesla requires a high turns-ratio GDT to minimize current the feedback circuit draws. I had 50:1 in the first version and was experiencing all kinds of horrible effects (feedback resistor catching fire, arcover).
Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
bwang wrote ...
hsieh wrote ...
So I if install a resonant capacitor,it will work?
I know that the core I use is a high u core(5000 or 10000).I get it from a school lab and someone told me that.Will this work?
Test the GDT with a signal generator and see! oneTesla requires a high turns-ratio GDT to minimize current the feedback circuit draws. I had 50:1 in the first version and was experiencing all kinds of horrible effects (feedback resistor catching fire, arcover).
You mean GDT or primary feedback CT?The turns ratio of my primary feedback CT is 1:130.
And what should I use? MOSEFT or IGBT?I worried that 617KHz is too fast for IGBT so I currently use MOSFET.I have some 40N60 IGBT,will they work?
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
hsieh wrote ...
bwang wrote ...
hsieh wrote ...
So I if install a resonant capacitor,it will work?
I know that the core I use is a high u core(5000 or 10000).I get it from a school lab and someone told me that.Will this work?
Test the GDT with a signal generator and see! oneTesla requires a high turns-ratio GDT to minimize current the feedback circuit draws. I had 50:1 in the first version and was experiencing all kinds of horrible effects (feedback resistor catching fire, arcover).
You mean GDT or primary feedback CT?The turns ratio of my primary feedback CT is 1:130.
And what should I use? MOSEFT or IGBT?I worried that 617KHz is too fast for IGBT so I currently use MOSFET.I have some 40N60 IGBT,will they work?
You'll need a new secondary - the fastest IGBT's on the market (Fairchild's field-stop IGBT's) get pretty sad over 400 KHz. The feedback CT needs a higher turns ratio. You'll definitely need IGBT's.
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DRSSTC circuit without resonant capacitor
