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Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
Here's my going-to-be HF low power Mazzilli SSTC. I built it yesterday, but I accidentally reverse powered it (d'oh!) and the IRFZ44 MOSFETs died instantly. Hopefully it'll get running when I get new MOSFETs. The capacitor is 470pF. This coil is going to run at about 4 MHz.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Dr. 2N3055 wrote ...
Here's my going-to-be HF low power Mazzilli SSTC. I built it yesterday, but I accidentally reverse powered it (d'oh!) and the IRFZ44 MOSFETs died instantly. Hopefully it'll get running when I get new MOSFETs. The capacitor is 470pF. This coil is going to run at about 4 MHz.
I think the pullup resistors will really have a tough time pulling up those gates.
The gate is 1.3nF, 4MHz= 250ns period, 50% dutycycle. Assuming 470R gate resistors, the gate will charge to 18% supply voltage during the time the MOSFET should be on. I think that's just not doable.
Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
Dr. Kilovolt wrote ...
Dr. 2N3055 wrote ...
Here's my going-to-be HF low power Mazzilli SSTC. I built it yesterday, but I accidentally reverse powered it (d'oh!) and the IRFZ44 MOSFETs died instantly. Hopefully it'll get running when I get new MOSFETs. The capacitor is 470pF. This coil is going to run at about 4 MHz.
I think the pullup resistors will really have a tough time pulling up those gates.
The gate is 1.3nF, 4MHz= 250ns period, 50% dutycycle. Assuming 470R gate resistors, the gate will charge to 18% supply voltage during the time the MOSFET should be on. I think that's just not doable.
So would it help if I used smaller value pullup resistors?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Dr. 2N3055 wrote ...
Dr. Kilovolt wrote ...
Dr. 2N3055 wrote ...
Here's my going-to-be HF low power Mazzilli SSTC. I built it yesterday, but I accidentally reverse powered it (d'oh!) and the IRFZ44 MOSFETs died instantly. Hopefully it'll get running when I get new MOSFETs. The capacitor is 470pF. This coil is going to run at about 4 MHz.
I think the pullup resistors will really have a tough time pulling up those gates.
The gate is 1.3nF, 4MHz= 250ns period, 50% dutycycle. Assuming 470R gate resistors, the gate will charge to 18% supply voltage during the time the MOSFET should be on. I think that's just not doable.
So would it help if I used smaller value pullup resistors?
Yes, but I think the power dissipated in them would be impractical. It turns out that even 22 ohms might be to big, maybe it would run with 10 ohms, at this time you will dissipate around 10W in each resistor (assuming 12V supply), which could still be acceptable but I have no idea if 10 ohms is low enough.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Ok, so I think I've officially gone overboard and spent too much money on the cap bank :S
Casters and hardware
Total 3800uF at 450V -> 3.8kJ. The 8 big caps and 4 smaller caps give 3.8kJ, and the tiny caps (simply aren't designed for pulse discharges imo) would theoretically bring it to about 4.5-5kJ, although they'd probably explode.
A sketch diode (leaky?) next to my biggest stud SCR. I got it for free, and I have been struggling to find a nut to go with my SCR.
A plastic moulded tray from the box of caps on the shelf.
Registered Member #122
Joined: Fri Feb 10 2006, 12:55PM
Location: Milano Italy
Posts: 148
very nice! One thing i would suggest though, is make a scr triggering circuit because triggering it with a 9v battery alone may ruin it. Especially at those powers the battery doesn't supply inough pulsed current to trigger the gates properly. Trust me, i have lost several scr's that way.
thank you for the advice, but unfortunately i learned the lesson in the hard way i'm also lost many SCR before finding the last configuration, now i have 2 SCR in a really strange configuration and no more relays, i never lost any more components after this modification
Fabio, that's some SERIOUS gear!
This was the inside of a very old abandoned locomotive (i think that it was build in 1930)
Ok, so I think I've officially gone overboard and spent too much money on the cap bank :S
nice gears, but actualy yours SCR is really small and it surely cannot withstand the tremendous power of the capacitor bank i suggest a bigger one (aka hockey puck)
i also suggest you to build the coils only with big cables, as you can clearly see, a 4 square millimeters wire cannot withstand the power
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