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the mini sstc relies on the interrupter pulse to start oscillation. if there is no interrupter, you must include a "start" button. of course an SSTC can run cw, but the coils and transistors must be dimensioned adequately, use more turns on the primary and larger coils.
Well you're sort of right; there needs to be some kind of ping to start the oscillation. A simple change in operating procedure can solve the issue though; simply power the DC bus before powering the UCC chips. When the UCC chips start up (same as when they received an Enable HIGH from interrupter) they will ping the circuit, starting oscillation. I started this procedure because my UCC chips oscillate at around 8MHz (and subsequently overheat!) when there is no feedback to their Inputs but there is a HIGH or float on their Enables. So, I only power the driver boards when I am ready to run the coil, and as a result, it starts up oscillating every time.
On Steve Ward's page, he said that due to the way the chips work they will send a pulse without doing anything special.
On an unrelated note, what should my bridge rectifier be rated for? Currently I have an 800V, 8A one.
Depends on your power source. 1.618 x Vrms is a good value for direct-from-mains. (Note that 1.414 x Vrms = Vpk, and that is the minimum rating. I like to include some overhead so I use Phi (1.618)).
So you're saying 340Vdc rating for 120V mains service? The capacitors and diodes in UL listed USA products are only rated for 200V! I don't disagree that more headroom is always better, but I've never seen such a large margin used and I've never heard of US mains spiking higher than 140Vac (which is still 197Vpk).
Anyway, to the OP's question about trace widths; which traces? On the driver PCB standard widths should be fine for most parts but you'll want thicker traces for the power lines to the UCC chips and the lines going to the GDT primary, for low inductance. The bridge shouldn't be made on a PCB, at least not without using super wide traces which are exposed and then wave soldered for extra conductor cross section. If you're using protoboard you can manually lay out thick (three-dimensionally) traces with solder, but either way there is a large current demand for the bridge AND you need to keep inductances low.
Anyway, to the OP's question about trace widths; which traces? On the driver PCB standard widths should be fine for most parts but you'll want thicker traces for the power lines to the UCC chips and the lines going to the GDT primary, for low inductance. The bridge shouldn't be made on a PCB, at least not without using super wide traces which are exposed and then wave soldered for extra conductor cross section. If you're using protoboard you can manually lay out thick (three-dimensionally) traces with solder, but either way there is a large current demand for the bridge AND you need to keep inductances low.
I misunderstood more things :(
I did my driver on this PCB. So that will be a problem?
And for the bridge, is a protoboard with solder traces the way to go?
I never liked those "IC friendly" protoboards, they're not doing anyone any favors. Pad-per-Hole style protoboard is the way to go, you choose where to put every trace and don't have to cut any. The copper pad gaps are close enough to make it easy to solder-bridge traces but far enough for good protection from unintentional bridges. I use for my general electronics prototyping (there's smaller ones available too, but notice how every hole has its own pad, none shared).
For the (half) bridge, certainly not! Ideal construction is point-to-point "wiring" using flat and wide bus bars. You can get by just fine with using heavy gauge (at least 14ga or higher) wire directly on a large heatsink if you don't have access to a shop to mill and fabricate the planar bus connections (most of us don't).
If you want an example of good but easy wiring based half bridge layout I invite you to my website where on the Products page under the "USSTCC" section I have suggested construction files for my board. The half-bridge data there will work fine with Steve Ward's driver. I've tested this layout and design to over 3kW in SSTC use. I can probably whip up a photo of one of my bridges if you need too.
I never liked those "IC friendly" protoboards, they're not doing anyone any favors. Pad-per-Hole style protoboard is the way to go, you choose where to put every trace and don't have to cut any. The copper pad gaps are close enough to make it easy to solder-bridge traces but far enough for good protection from unintentional bridges. I use for my general electronics prototyping (there's smaller ones available too, but notice how every hole has its own pad, none shared).
For the (half) bridge, certainly not! Ideal construction is point-to-point "wiring" using flat and wide bus bars. You can get by just fine with using heavy gauge (at least 14ga or higher) wire directly on a large heatsink if you don't have access to a shop to mill and fabricate the planar bus connections (most of us don't).
If you want an example of good but easy wiring based half bridge layout I invite you to my website where on the Products page under the "USSTCC" section I have suggested construction files for my board. The half-bridge data there will work fine with Steve Ward's driver. I've tested this layout and design to over 3kW in SSTC use. I can probably whip up a photo of one of my bridges if you need too.
So should I rebuild my current driver board?
I will definitely rebuild my bridge using your layout. Nice site, definitely bookmarking it.
EDIT: I'm getting a new GDT toroid too, will this work? AL = 4.62uH
If you driver checks out fine then there's no reason to rebuild it really.
That is a N30 core, I've used worse, but there are certainly better. I recommend T38 cores as most applicable core sizes are >10,000AL. This is the core I use and recommend: it is good up past 1MHz.
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Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Matt, The rating of diodes and electrolytic capacitors are two different things. An electrolytic cap will absorb a voltage spike, as well as it will handle temporary overvoltage. A diode will explode within 1us of overvoltage. Plus the rectifier is a much cheaper component than electrolytic capacitor, so overrating it is a good practice in quality electronics (not china).
The standard here is to use 600-800 volt rectifiers and 500-600 volt switching transistors for 230 VAC mains, and 1200 volt components for three phase (560 VDC). I have even seen 1700 volt three-phase rectifiers used even in smaller motor controllers.
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Can I run Steve Ward's Mini SSTC without an interrupter?
