small multilead HV transformers

"Jamie Morken" skrev i en meddelelse news:yhTpj.44736$4w.28966@pd7urf2no...

Life will become *much* easier if you use four separate 1:1 pulse transformers - they are easy to get, the layout is simpler because now you got space for the correct creepage distances (and maybe cutouts) and more robust. I have done many field repairs of 1:1:1 pulse transformers for inverters where the breakdown was precisely between the two secondaries!

Anyway, In the past I have sucessfully used a primary winding of coax threaded though a string of ring-cores with multi-turn secondaries for that kind of application. The first of those are probably still running somewhere - i.e 24/7 for 8 years (3.5 kV RADAR modulator).

The secondaries are wired as current-transformers with a (low-value!!) resistive load yielding the proper gate voltage, the primary used 28V DC to get enough drive. That was with a string of 20 MOSFET's so yours will be different.

It is important to connect the coax shield to something "stable" to reduce capacitive losses and corona/arcing. I used a resistive divider made from the bleeder resistor to set the shield at 6 Kv. (The switch was running at 8 Kv). Ring cores "sit" really well in a board if one makes cutouts so that about 1/4-1/3 of the completed core fits into the cutout, fit the cores, then dab each with some hotmelt glue and thread the coax.

It's important to identify and differentiate safety and functional isolation reqirements. Safety isolation requires spacings and insulation layer/thickness redundancy that exceed functional requirements and may not be physically achievable in smaller parts using conventional assembly materials an methods.

UL does not consider pin spacings for functional isolation to be a certification issue, In the application it becomes one of single-fault abnormal performance. Small 1:1:1 pulse transformers can be constructed for functional 500V isolation to one of the windings, but this winding needs to be identified and terminated characteristically. This is not a jellybean telecom pulse application.

RL

IDSN telecom line transformers are great. Small, cheap, fast, 1500 volt rated.

John

How about two of these?

Triad would be a good place, too, but their web site has been screwed up so badly that it's now inaccessible (at least for me).