20-60A adjustable ~200vdc current mode buck design

hehehe not suprising -- now if I could get the reference design from the datasheet to model -- I'd be in hog heaven :)

our 220v is really a pair of 120v lines 180 out of phase, when you plug into a 120 socket, the "nuetral" side is pretty much power company ground

so sticking a full wave bridge on it directly gets you half wave pulses :) -- you need both sides to get full wave rectified output

I dont REALLY need earth ground referenced, but it would make some other issues I have to deal with one HECK of a lot easier

Trying to avoid iron as much as possible, and I see what you mean about pain :)

I've been trying off and on for 24+ hours now to get a pos->pos boost to work side by side with a neg->pos boost with a shared ground tied to power company ground (modeled as 2 120v sources, 180 phased, with neg sides tied to ground, pos sides feeding a full bridge and splitting the pos and neg to the 2 boost modules.

I'm getting close -- not using full PFC yet -- just a fixed gate pulse to see where things are going.. and I'm getting fairly stable output, but have one major weird thing going on.... HV spikes showing up on the rectified input to the positive boost that need to go away ... they start on the falling edge of the input voltage pulse, continue through zero and into the begining of the next pulse, with a particularly hard spike as the input voltage bottoms out and starts back up. its got to be the inductor causing it somehow since it is being switched on the other side by the mosfet to ground, so maybe the PFC will make it go away. If you dont think that will help, I'd love to hear what it might be -- Spice simalation available on request :)

Other than that -- its behaving as well as can be expected since I havent fine tuned any of the component values yet, and am still using a spice switch instead of a FET or IGBT.... once all that is done, I'll pack it up in a subckt and start on the PFC controller and stuffing enough of these in parallel to handle my load requirements :)

Reply to
John Barrett
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That's what I meant..

That's sort of what I thought would happen if you wanted to maintain a ground/neutral connection.

May as well do it so you can.

Embrace the 'iron'. You can use the full/half bridge directly to control output current and provide your isolation. There is no need to generate an intermediary DC supply and then add a buck converter you can do it all in one go.

I've had a fiddle with a half bridge using average current mode control and it's looking funky.

It might get messy. I haven't got my brane screwed in yet so I can't draw what you've got.... However boosting neg to pos is going to place extra voltage stress on that part of your converter and its control electronics are going to be referenced to a different point which may well be going up and down.

Spikes are common in simulation. Sometimes it's because you've done something stupid. Sometimes it's because there are two answers, the one you want and the one that has a big spike. Some series and or parallel resistance in inductors can help. However, in this case, it is likely that......

Yes, the node you mention can and will cause stress. Try adding a capacitor from that end of the boost inductor to circuit ground. You'll need one in real life as well. By all means, send me a copy of what you have got. There is an e-mail icon on the front page of my webshite....

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Ideal switches are nice..... (ideal everything) stick with them until it's working the way you expect. Then you might start adding 'real' stuff.

Later

DNA

Reply to
Genome

----- Original Message ----- From: "Genome"

Voltage stress ?? try CURRENT stress -- the neg boost is drawing twice the current for the same voltage out :)

probably because of the non optimal component values I'm testing with -- gonna have to plug all the math into a spreadsheet and work out what SHOULD be there :)

There wont be any point in the control that will be referenced to anything but earth ground except the gate drivers.. using those hall effect current sensors gets me COMPLETELY isolated no matter if I'm sensing high side or low side.. very important since with ground shared between 2 boosts, I cant get in the low side at all, nor do I want to !! (I'm using low side with a bit of a difference from common usage in SMPS design -- to me -- low side is always ground, high side is anything that is away from ground, no matter the polarity. )

and sometimes because its really going to generate spikes :)

Dropped in the cap and spikes go BYE BYE !! :)

Thats the point I'm at -- getting it all "real" so I can subckt this and start the control electronics.

welp, everything is real except the switches now --

ASC file available if anyone else wants to look -- just ask :)

let me know what you think :)

Reply to
John Barrett

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