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small multilead HV transformers

J

Jamie Morken

Jan 1, 1970
0
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
 
F

Frithiof Andreas Jensen

Jan 1, 1970
0
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.
 
L

legg

Jan 1, 1970
0
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.
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
 
J

John Larkin

Jan 1, 1970
0
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

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

John
 
J

Joerg

Jan 1, 1970
0
Jamie 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.

How about two of these?

http://www.tamuracorp.com/clientuploads/pdfs/engineeringdocs/G504.pdf

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).
 
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