TCA785 problems

hello again
i have been working on the attatched image using a modified circuit lifted from the data sheet "(here)":http://www.call-n-deal.de/uwe/projekte/stagelightning/pp785/tca785.pdf
the shown examples are designed around a mains supply L and N.
should i ground the negative rail in my circuit to fix it to zero volts ?
as i cannot get the shown waveforms, or is there something else ive overlooked ?
Thanks in advance

I used a circuit similar a number of years ago as an active inrush limiter, it may even be the same part. Although in my circuit there were no isolation transformers which is ok, it not needed. When you say grounding there is of course no rectification, 1/2 wave isolated rectification and full wave isolation so please identify what nodes you thing should be connected. Hopefully your scope is isolated or the AC input is, otherwise that could get interesting.

Are the SCRs even triggering?

hello sarah, hello earl. according to the schizmo on the data sheet, the ground pin (8) is not shown connected. if this is what you are referring two, then i would connect it to the N line thru a rectifying diode since the ic is powered by the mains line thru quarter rectifier circuit. all you need is the remainder of the halfwave rectier. Ground pin to anode, cathode to N line. if this is not the case, then please disregard this comment.

It appears that from the block diagram that the Reference (8) is actually an output, just in case an external circuit would need a semi regulated voltage, common on PWM controllers.

Going to need some wave forms, threshholds of voltages on pins, or additional info to help much more.

thanks for that clarification earl. it appears i need new glasses. my mistake.
good luck sarah. i am of no use to you.

Yes but my glasses are always dirty, so4 eyes better than two.

I have a other one. What are you designing it looks like a 48 V battery charger whitout current limit!!!

this will be my sixth attempt to post a reply, theres something wrong with the forum and it keeps booting me out !!
ive altered the circuit to match the data sheet , so its directly off the mains and it appears to be working. i have only built upto the trigger coils, so i am scoping the output of these and i get a spike a channel 1/2 a phase out which is what i expected. its just if i scope on the chip o/p i get a mess of a signal.
My original question related to grounding the transformer to make 1 side as "neutral" at 0v instead of going to -18v. is this not correct ? the data sheet is also confusing as one schemo shows the ic ground pin (1) not connected, another shows a different timing capacitor.
but hey, getting there
the purpose of this is for my high current power supply (there was a previous post that died ) one last ditch attempt before my husband convinces me to go down the linear route.
so a simple design at the moment to test for the quality and see how ripple etc effects the outcome. then its onto how to control it all LOL.
Thanks for your help, any suggestions greatly appreciated.

OK so the 18V isolated DC supply, as shown is floating, which probably not a good idea for several reasons not to get into. Also your drives are isolated as well.

There are several ways to ground this, i.e., reference it.

It can be referenced to the AC input or the secondary DC output. Now since you indicate you wish to add control to this, oh by the way, good idea, this could be referenced to the DC.

To do this you can simply take the signal termed, "??," and connect that to the node TH1/TH2 anode.

Another point, I'm looking at the diagram and I see Pin 1 of TCA 785 is connected to a reference, with the signal name ??, which I suppose you could call Gnd B, or what ever. In any event connecting node ?? to the anodes of TH1/TH2 would give you a ground and also when you want to do control, you can do so more directly vs isolated.

Your controller is ,"Grounded," otherwise it wouldn't work.

I'm thinking the signal ?? is as it is, so that you have options on how you would want that referenced.