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Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
Hi all,
I have built Kaizers SSTCII, but can not get it to work. The input voltage on the mosfet drivers drops to about 2V for some reason and won't work. Here is the pcb if you can spot why it might be doing this.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
Hi Coronafix,
Do you have a UCC37321 in one socket and a UCC37322 in the other?
Suggestions: * connect the unused inputs of U2 to something, * check the voltage before the UCCs' regulator, what do you see? * are any of the electrolytic capacitors in backwards? * does disconnecting the GDT primary affect the UCCs' voltage?
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
Hi Matt, If you mean pin 2 on the ucc's, then that is correct. I found that my second pair of ucc's were toast and it now works...sort of. At 60V half wave rectified to the bridge I am getting 2-3mm sparks to earth. Interupter is working but antenna doesn't seem to be picking up much, could too long an antenna be a problem? It is about 400mm long. Thanks for the help.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
How close is your antenna to the secondary? I have mine no more than 10 cm from it, varying in height by having it stand in a plastic tube, with higher bus voltage you need to lower the antenna coupling to avoid too much corona on it.
Try to change phasing of your primary coil for the small spark output problem.
The only beef there really is with this coil is it will begin to run unstable at high bus voltages, the antenna feedback is just not good enough for em fields of that magnitude.
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
Hi Mads, Tried the phase change on the primary but no output. You do mean the primary coil of the TC yes? I have the primary and outputs of the GDT as your schematic. Is it necessary to have the unused pins on the 74HC14 grounded? Or is it ok to leave them unconnected?
I am getting 10mm sparks to ground now at ~60V input. The high side of the bridge is heating up a fair bit as both fets are on one heatsink. Low side still cool, drivers cool also. Antenna less than 100mm from secondary.
The secondary I am using only has 600 turns on it as I haven't got around to getting the proper guage wire yet for this project so I just used an old secondary I had. I imagined that I wouldn't get really good sparks off of it, but not this small.
Any other tests anyone can suggest to ascertain the problem?
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
I notice you have separate bridge rectifiers and regulators for two parts of the circuit. Are they connected to the same transformer winding? What about the supply for the H-bridge?
If they're connected together, an unrelated short on once circuit will pull down the other. Similarly, if the coil is running badly tuned, is it drawing so much current to load down some shared supply voltage?
Are the smoothing capacitors on the bridge rectifiers big enough?
wrote ... Tried the phase change on the primary but no output. You do mean the primary coil of the TC yes?
Yes, or you can invert the GDT primary if it is more convenient.
wrote ... Is it necessary to have the unused pins on the 74HC14 grounded? Or is it ok to leave them unconnected?
Yes, as the high-impedance gates will go batshit, possibly increasing current draw (though not enough to drag the rail down to 2V), or radiating noise into the adjacent gates then into the UCCs. Connect the unused inputs to GND or VDD, or series the unused gates into a chain and GND the first input. Whichever is convenient on your PCB.
wrote ... Any other tests anyone can suggest to ascertain the problem?
Tie those ENBL pins firmly to V+ on the UCCs, then cut off the antenna, connect a signal generator and sweep.
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