Jamie Morken said:
Hi,
I have an application that needs 4 isolated secondaries all with about
1kV isolation, for supplying floating fet gatedrivers. Does anyone have
a transformer part that would be small and still UL certified for
500Volt pin spacing, like 0.1" or more.
cheers,
Jamie
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.
